AC vs DC power in data center

There has been a debate going on for some years if the traditional AC or new DC power distribution is best approach to power a data center. The DC power side has been pushing their technology with claims of quite considerable power savings. In many published articles, expected improvements of 10% to 30% in efficiency have been claimed for DC over AC. I have had my doubts of the numbers on their promises. Now there is some new data on AC vs DC issue available.

White paper compares AC vs. DC power distribution for data centers article tells that a new white paper from APC by Schneider Electric provides a quantitative comparison of high efficiency AC vs. DC power distribution platforms for data centers. The latest high efficiency AC and DC power distribution architectures are shown by the analysis to have virtually the same efficiency, suggesting that a move to a DC-based architecture is unwarranted on the basis of efficiency

A Quantitative Comparison of High Efficiency AC vs. DC Power Distribution for Data Centers paper demonstrates that the best AC power distribution systems today already achieve essentially the same efficiency as hypothetical future DC systems. It also tells that most of the quoted efficiency gains in the popular press are misleading, inaccurate, or false (like I have suspected to be for some time). And unlike virtually all other articles and papers on this subject, this paper includes citations and references for all of the quantitative data (which is very good).

The paper first describes that there are five methods of power distribution that can be realistically used in data centers: two basic types of alternating current (AC) power distribution and three basic types of direct current (DC) power distribution. These five types are explained and analyzed.

One AC and one DC, offer superior electrical efficiency. The paper focuses on comparing only those two highest efficiency distribution methods, which are very likely to become the preferred method for distributing power in future data centers. The data in this paper demonstrates that the best AC power distribution systems today already achieve essentially the same efficiency as hypothetical future DC systems.

The best AC system is based on the existing predominant 400/230 V AC distribution system currently used in virtually all data centers outside of North America and Japan. Increasing Data Center Efficiency by Using Improved High Density Power Distribution white paper gives details how it could be used in USA. It says that the use of the international 230/400 V distribution system instead of the USA standard 120/208 system can save 56% in the lifetime cost of the distribution system, and save floor space and weight loading.

The preferred DC system is based on a conceptual 380 V DC distribution system (consensus in the literature as a preferred standard) supplying IT equipment that has been modified to accept DC power. In the proposed international ETSI standard for DC distribution for data centers, the 380V DC system is actually created with the midpoint at ground potential to keep the maximum system voltage to ground to within +/- 190 V.

Based on the data I think the 400/230 V AC distribution system is the best way to go in data centers around the world.


  1. Tomi Engdahl says:

    48V direct-conversion dramatically improves data-center energy efficiency

    It’s easy to summarize the power needs and costs of data centers and servers in a single word: enormous. Of course, there’s much more to the story than this. These critical network hubs – which are now woven deeply into society’s infrastructure – require megawatts to function, resulting in very high power-related direct-operating costs. Those costs are further extended by the costs associated with dissipating all the associated heat the equipment generates.

    Consider a representative 5000 ft2 (1500 m2) server/data center. It uses about 1 MW, with a power usage efficiency (PUE) rating between 1.2 and 2

    These PUE numbers means that non-core losses range from about 20% to 100% above the basic operating requirements. The higher the PUE, the higher the total cost of ownership (TCO), and depending how it is defined, PUE may not even directly account for the costs of getting rid of all the power that is wasted and transformed into heat, and somehow must be removed. A lower PUE also directly affects associated CO2 emissions and carbon footprint, and so has regulatory implications.

    The challenge in reducing PUE is that there is no dominant source of loss in the server or data center. Instead, the losses are spread along the entire power-distribution chain, starting with the primary power source AC supply, down to the low-voltage DC which is supplied to individual ICs

    cumulative sources of inefficiency as power passes from line mains through 48VDC/12VDC converters and multiple 12V DC/single-digit rail supplies.

    Losses add up quickly

    Simple math shows the impact of cumulative losses along the power path. Assume there are four stages between the 480 VAC/DC mains and the ultimate low-voltage rails, each with efficiency of 90% (actual numbers will vary for each stage, of course). The end-to-end efficiency is the product of these individual efficiencies, and drops down to just 65.6% – a substantial loss.

    What can be done? The “obvious” answer is to improve the efficiency of each stage, and that has been the dominant strategy. If each of those five 90% ratings can be boosted to 92%, the overall efficiency will increase to about 71.6%.

    A system which is 90% efficient is clearly 10% inefficient. Even a 1% improvement is a huge gain:

    From AC mains/400VDC → 48VDC → 12VDC PoL → single-volt rails

    Historically, the power path has used an intermediate voltage of 48VDC, which then feeds numerous 12V point of load (PoL) DC/DC converters that produce the specific end-use rail voltages, such a 12V, 5V, 3.3V, 1.2V, and even sub-1V. This topology worked well, and improvements in efficiency in the intermediate converter stages and the PoL units made it a successful approach which has lasted for many years.

    Direct conversion offers better approach

    Fortunately, a new approach called direct conversion offers a path out of the dilemma. If you completely eliminate one of the power-conversion stages, such as the 48V/12V intermediate stage, and instead go directly from 48V DC to the low-voltage rails, the impact would be both significant. Looking at the four-stage 90% example again, going to just three 90% stages improves efficient from 65.6% to 72.9%

    There’s another very good reason to skip the 12V intermediate stage: the bus bar behind the rack brings hundreds of amperes to the server boards at 12V. The associated losses, which are already high, are becoming even more significant as these current levels continue to increase. Increasing the distribution voltage to 48V greatly reduces these bus-bar distribution losses. Using 48V as the distribution voltage is a reasonable compromise between the need to decrease the losses and the safety regulations which begin at 60V. Also, 48V distribution is compatible with distributed uninterruptible power supplies (UPS) where the energy storage unit (typically a 42-to-48V battery) is located close to the rack, rather than at a centralized UPS sited far from the equipment.

    Of course, it is easy to propose direct conversion; it is actually hard to execute. Several manufacturers have devised “partial” solutions.

    ST’s three-IC solution embodies advanced concepts

    To allow power-system architects to realize the benefits of direct conversion, ST developed a multi-IC solution with what is called Isolated Resonant Direct Conversion technology, along with the critical infrastructure which supports it.

    There’s no question that the existing multistage power-conversion chain has worked well, but its time has come to a close. It’s no longer sufficient for the task of meeting the efficiency needs and growing server/data center power demands. Further, it cannot meet the VR13 specification, lacks scalability and flexibility, and is not highly efficient across all load ranges.

    That’s why the multichip direct-conversion solution developed by STMicroelectronics, featuring power conversion from 48VDC directly down to the individual IC rail voltages, is a better solution.

  2. Tomi Engdahl says:

    Analyst: Data center rack densities remain below 5 kW

    In its most recent analysis of the rack PDU market, IHS Markit found that the uptake of higher-power rack PDUs strongly outpaces the actual power density within racks in the data center. Sarah McElroy, senior research analyst for data centers and cloud with IHS Markit, pointed out, “Rack PDUs with higher power ratings, in the 5-10 kW range, accounted for 41 percent of global rack PDU revenue in 2015 compared to 38 percent in 2013, proving that a shift is occurring. While 5-10 kW rack PDUs are growing in popularity over those 10 kW, accounted for 18 percent of global rack PDU revenue in 2013 and grew to account for 22 percent by 2015.”

    “Despite the growth in rack PDUs with higher power ratings, IHS finds that average rack power densities are not as high as the rack PDU power rating data might suggest. IHS estimates that average rack power density globally is approaching but remains below 5 kW per rack.”

    Advances in the energy efficiency of power supplies and IT equipment has increased the achievable compute per watt.

    Server virtualization allows users to run servers at higher capacity, for example 80 percent instead of 20 percent capacity. Instead of adding additional servers, users are now running current servers closer to full capacity, which generally results in less power draw than adding new servers to perform the same amount of computing.

    “While average rack densities still remain below 5 kW worldwide, densities of up to almost 50 kW have been implemented in applications such as supercomputing. It’s no longer uncommon to see rack densities of 20 to 30 kW in some applications”

  3. Tomi Engdahl says:

    Alternation current vs Direct current
    Which one is more dangerous AC or DC and why?

    AC VS DC – Pain Test (Experiment)

    This has been argued about for over a century.
    I would refer you to this link,
    and this one,
    Both links have useful information, but in the end it’s still up to you to draw your own conclusions.

    I think both presents a danger to the human body. Basically, the voltage factor differs for DC and AC.

  4. Tomi Engdahl says:

    Which is more dangerous: AC or DC power?

    Alternating current (AC) and Direct current (DC) have slightly different effects on the human body, but both are dangerous above a certain voltage. The effect on a particular person is very difficult to predict as it depends upon a large number of factors – amount of current, duration of flow, pathway of current, voltage applied and impedance of the human body.

    Having said that, I would rate AC as more dangerous owing to the following reasons,

    1. To produce the same excitatory effects, the magnitude of DC flow of constant strength shall be two to four times greater than that of the AC. i.e more DC current is required to induce the same harmful effects as AC current.

    2. Accidents with DC are much less frequent than would be expected from the number of DC applications, and fatal accidents occur only under very unfavorable conditions, for example in mines. This fact is highlighted in the IEC publication 60479 – Effects of current on human beings and livestock. This reveals that DC is only an ‘occasional culprit’ compared to the ‘serial killer’ AC.

    3. Ventricular Fibrillation is considered to be the main cause of death by electric shock. The probability of a human suffering from Ventricular Fibrillation is much higher in the case of AC than DC.

    4. The total impedance of the human body is higher for DC and decreases when the frequency increases. Since the impedance for DC is higher, the severity of electric shock would be comparatively lesser than AC.

    5. It’s comparatively easier to let go of the gripped ‘live’ parts in the case of DC than AC. This is in contrary to popular belief.

    Given the above reasons, we can safely conclude that AC is more dangerous than DC. Nevertheless, you should always avoid contact with high-voltage electrical conductors, regardless of the type of electrical current.

  5. Tomi Engdahl says:

    Which is more dangerous to the human body: AC or DC current and voltage?
    The effects of both on the human body differ, but one is more hazardous than the other

    All of that being said, if it comes down to one or the other, AC can generally be viewed as the more dangerous of the two currents — here’s why:

    1) To start off, in order for both currents to have the same effect on the human body, the magnitude of DC flow of constant strength needs to be two to four times great than AC; that is, more DC current is needed to induce the same amount of physical damage as AC current.

    2) When death by electric shock occurs, it’s typically due to ventricular fibrillation, and the likelihood of a human suffering this sort of life-ending injury is much higher when coming in contact with an AC than a DC due to the fact that the human body’s threshold of DC-caused ventricular fibrillation is several times higher than for AC.

    3) Generally speaking, the human body’s impedance is higher for DC, and it only decreases when the frequency increase. As such, the severity of electric shock is less when in contact with DC than it is with AC.

    4) It’s easier to let go / remove contact with “live” parts in the case of DC than AC.

  6. Tomi Engdahl says:

    Putting power forward

    Designers of advanced computing systems are no longer able to consider the power supply as a “black box” that can be plugged in at the end of the project. Giving due consideration to power design at an early stage is essential given the growing complexity of server boards, demands for greater power and efficiency, and the need to plan for multiple product generations. On the other hand, engineers also need flexible power solutions in order to respond to system design changes and adopt a platform approach to the power design, which can help streamline future development. The ability to easily configure, control and monitor power delivery functions is a valuable characteristic enabled by digitally configurable power modules.

    Designers of advanced computing systems are no longer able to consider the power supply as a “black box” that can be plugged in at the end of the project. Giving due consideration to power design at an early stage is essential given the growing complexity of server boards, demands for greater power and efficiency, and the need to plan for multiple product generations. On the other hand, engineers also need flexible power solutions in order to respond to system design changes and adopt a platform approach to the power design, which can help streamline future development. The ability to easily configure, control and monitor power delivery functions is a valuable characteristic enabled by digitally configurable power modules.

    Pressure on power design

    High-performance computer boards such as data-center servers present increasingly complex routing and component-placement challenges as designers seek to maximize data-processing and storage capabilities in the minimum possible area to comply with the standard rack dimensions. With a mix of advanced processors, ASICs and FPGAs that feature large numbers of I/Os and multiple power domains, the PCB can incorporate 20 layers or more for timing-critical high-speed signal traces and power distribution.

    Up to 40 or 50 power rails can be needed, which call for a large number of point-of-load (POL) converters that are powered by intermediate bus converters (IBCs) fed by an AC/DC front-end power supply

    The design of the power-delivery infrastructure is becoming increasingly exacting.

    While it makes sense to establish the power distribution architecture early in the project, designers also need flexibility to be able to modify aspects such as POL output power, rail voltages or power-up and power-down sequencing as the system design evolves.

    A common reason this situation occurs is that the load current increases beyond the original specifications and thus the need for electrically larger components to supply the additional load current. One advantage of using power modules is the impact of the design upgrade to the complex and expensive host PCB can be minimized.

    Moreover, digital power supports an efficient “platform” approach, recognizing that system power demands will become more complicated in the future

    Paying attention to power supply design early helps optimize thermal management. In addition, digital modules simplify monitoring of power performance in real-time, which permits on-the-fly adjustment to optimize energy efficiency.

    The PMBus specification provides a common language for configuring, controlling and monitoring digital power modules in a power system. The AMP Group (Architects of Modern Power) consortium has simplified the design-in and interchangeability of digital power modules by standardizing the behavior of digital power modules in response to PMBus commands.


    As the power requirements of high-performance computing and data equipment become increasingly stringent, engineers must engage with the power supply design at an earlier stage of system development. Today’s systems require increasing numbers of power rails, and impose exacting demands in terms of sequencing, regulation and transient performance. Maximizing energy efficiency is also increasingly important.

  7. Tomi Engdahl says:

    High-performance GaN-based 48-V to 1-V conversion for PoL applications

    48V to point-of-load (PoL) conversion is common in numerous markets, including telecommunications, industrial, aerospace, and increasingly, server environments. The prevalent system solution is a two-stage conversion from 48V to an intermediate bus (9V to 12V) and then to PoL, typically 0.8V to 3.3V.

    Data center operators are particularly interested in single-stage 48-V to low-voltage DC/DC conversion and its associated efficiency gains, because data centers may consume as much as 140 TWh of power usage in the U.S. yearly by 2020 [1], or about 3.5 percent [2] of overall U.S. usage. The PoL in the application discussed in this article includes general-purpose and application-specific processors, field-programmable gate arrays (FPGAs) and application-specific integrated circuits (ASICs).

    While the limitations of silicon-based converters force a two-stage solution, new gallium nitride (GaN) devices enable single-stage conversion. Two key design requirements are efficient power conversion and ultra-fast load transient response of the ASIC/processor core rails.

    GaN’s advantages are strongly evident during single-stage conversion, with higher efficiency and smaller size than traditional solutions, while simultaneously reducing bill of materials (BOM) count and systems cost. In this article, I will discuss the design of a 48-V to 1.0-V PoL 50-A converter using a GaN half-bridge module and a high-performance controller for the single-stage topology, achieving efficiency exceeding 90 percent.

    One of the strongest application areas for GaN is in the 48-V input converter space, targeting telecom and industrial customers as well as aerospace and server applications.

    In 48-V telecommunications and server applications, there is strong demand for conversion down to PoL in order to power processing-intensive cores like microprocessors, FPGAs and ASICs. Traditionally, the conversion from 48V down to PoL uses a two-stage approach. This entails a brick-type bus converter performing an isolated conversion between 48V and an intermediate voltage such as 12V or 9V using a hard-switched half-bridge or full-bridge topology, or a resonant topology such as inductor-inductor-capacitor (LLC). Next, a multiphase buck converter converts down to PoL at up to 200A, while handling the transient response requirements of a highly dynamic digital load.

    The traditional solution’s beginning-to-end efficiency is a product of the two individual stages.
    With the first stage peak efficiency of 96 percent and the multiphase buck stage peak efficiency close to 92 percent, the total efficiency is only 88 percent

  8. Tomi Engdahl says:

    Utilizing GaN transistors in 48V communications DC-DC converter design

    As the world’s demand for data increases seemingly out of control, a real problem occurs in the data communications systems that have to handle this traffic. Datacenters and base stations, filled with communications processing and storage handling, have already stretched their power infrastructure, cooling, and energy storage to their limits. However, as the data traffic continues to grow, higher density communications and data processing boards are installed, drawing even more power. In 2012, communications power consumptions of networks and datacenters added up to 35% of the overall electricity use in the ICT sector (Figure 1). By 2017, networks and datacenters will use 50% of the electricity, and it will continue to grow.

    One solution to this problem is to re-architect datacenter systems from distributing 12V power along the backplane to distributing 48V on the backplane. Just recently, in March 2016, in the USA, Google announced that it will join the Open Compute Project, and contribute its knowledge and experience (since 2012) of utilizing a 48V distributed power system. Though this helps to solve one problem, it creates another: How do the power designers of the communications and data processing cards increase the efficiency, decrease the size and increase the power levels of their DC-DC converters, provided from 48V?

    In today’s architectures, using 12V backplanes, the industry is able to use 40V MOSFETs

    Using a 48V backplane forces DC-DC designers to use 100V MOSFETs, which have significantly higher FOM values and therefore are inherently less efficient. 100V enhancement mode GaN devices, however, are able to meet the challenges of DC-DC designers by delivering a very high efficiency, high frequency solution

    One of the most critical design considerations to make for a 48V DC-DC converter using GaN transistors is to minimize the dead time between one transistor turning off, and the other turning on. This is because in a GaN E-HEMT transistor there is no intrinsic, parasitic diode, nor is there a need for one.

    The final analysis

    48V datacenters and communications systems will require DC-DC converter designers to learn how to maximize efficiency using 100V transistors. GaN E-HEMT transistors, when compared to Silicon MOSFETs at 100V and even at 40V, offer a significant improvement in FOM and gate drive performance, allowing designers to achieve high frequency, high power density designs at very high efficiency levels.

  9. Tomi Engdahl says:

    Industrial supply accepts three-phase input

    Delivering up to 3200 W from a 2U-high package, TDK-Lambda’s TPS300-24 power supply operates from a three-phase delta or wye input ranging from 350 VAC to 528 VAC. The ability to handle high-voltage three-phase input eliminates the requirement for step-down transformers and assists phase-load current balancing.

    The TPS300-24’s regulated output voltage is adjustable from 19.2 V to 28.5 V. Rated current is 125 A

  10. Tomi Engdahl says:

    Bi-directional DC/DC power supplies: Which way do we go?–Which-way-do-we-go-?_mc=NL_EDN_EDT_EDN_today_20161213&cid=NL_EDN_EDT_EDN_today_20161213&elqTrackId=57bea209b61e44f781dfb7533361c55f&elq=ebad62c42ca141668eadcc8c35861e14&elqaid=35145&elqat=1&elqCampaignId=30702

    This article is part of EDN and EE Times’ Hot Technologies: Looking ahead to 2017 feature, where our editors examine some of the hot trends and technologies in 2016 that promise to shape technology news in 2017 and beyond.

    The bi-directional DC/DC converter has been around for a while, but new applications are quickly emerging which necessitate the use of this architecture in so many more systems. Applications today require better energy efficiency and such systems as green power with solar or wind generation, need storage so that when there is no wind or sun available the electricity flow is not interrupted.

    Battery back-up systems need bi-directional DC/DC converters since the batteries are charging during the time when there is an available power source, but in the event of loss of power, the battery now becomes the source of stand-by power. Vicor has a great solution for that area with their new bi-directional DC/DC topology.

  11. Tomi Engdahl says:

    So Where’s My Low Voltage DC Wall Socket?

    That phenolic smell has gone from our modern electronics, not only because modern enclosures are made from ABS and other more modern plastics, but because the electronics they contain no longer get so hot.

    Before the 1970s you would not find many household appliances that used less than 100 watts, but if you take stock of modern electrical appliances, few use more than that.

    There are many small technological advancements that have contributed to this change over the decades. Switch-mode power supplies, LCD displays, large-scale integration, class D audio and of course the demise of the thermionic tube, to name but a few.

    Mains electricity first appeared in the homes of the very rich at some point near the end of the nineteenth century. Over time it evolved from a multitude of different voltages supplied as AC or DC, to the AC standards we know today. Broadly, near to 120 V at 60 Hz AC in the Americas, near to 230 V at 50 Hz AC in most other places. There are several reasons why high-voltage AC has become the electrical distribution medium of choice, but chief among them are ease of generation and resistance to losses in transmission.

    The original use for this high-voltage mains power was in providing bright electric lighting

    So here we are, over a hundred years later, with both 21st century power conversion technology, and low power, low voltage appliances, yet we’re still using what are essentially 19th-century power outlets.

    There will be some among you who will rush to point out that the last thing we need is Yet Another Connector System. And you’d be right

    The IEC60309 standard, so-called CEE-form connectors, for example has a variant for 24 V or below. Or there are connectors based on the familiar XLR series that could be pressed into service in this application. You might even be positioning USB C for the role.

    Sadly there are no candidates that fit the bill perfectly. Those low-voltage CEE-forms for example are bulky, expensive, and difficult to source. And the many variants of XLR already have plenty of uses which shouldn’t be confused with one delivering power, so that’s a non-starter. USB C meanwhile requires active cables, sockets, and devices, sacrificing any pretence of simplicity. Clearly something else is required.

    Oddly enough, we do have a couple of established standards for low voltage power sockets. Or maybe I should say de facto standards

    The USB A socket is our first existing standard. It’s a data port rather than a power supply, but it can supply 10W of power as 5V at 2A, so it has evolved a separate existence as a power connector.

    Our other existing standard is the car accessory socket. 120 W of power from 12 V at 10 A is a more useful prospect, but the connector itself is something of a disaster. It evolved from the cigarette lighter that used to be standard equipment in cars, so it was never designed as a general purpose connector.

    Where this is being written the wiring regulations do not apply to voltages under 50 V, so that sets our upper voltage limit. And while it’s tempting to pick a voltage near the top of that limit it also makes sense to stay with one more likely to be useful without further conversion. So while part of me would go straight for 48 V I’d instead remain with the familiar 12 V.

  12. Tomi Engdahl says:

    The evolution of high voltage digital power system management

    A new step-down controller takes inputs up to 60V and produces two 0.5V-to-13.8V outputs—enabling it to easily drop into industrial, server and automotive environments as an intermediate or point-of-load (POL) supply. Other controllers with similarly impressive input/output ranges cannot match the LTC3886’s digital management capabilities. Its I2C-based PMBus-compliant serial interface allows power supply designers to configure, monitor, control and expand capabilities via PC-based, graphical LTpowerPlay and then store optimal production settings in the LTC3886’s onboard EEPROM.

  13. Tomi Engdahl says:

    One component for switching high voltage DC:

    G7L-X PCB Power Relays
    Compact Power Relay Capable of Switching 1,000 VDC Loads

    Compact design that achieves high-capacity DC breaking and switching. (52.5 × 35.5 × 41.0 mm (L×W×H))
    Two poles wired in series to break or switch 600 to 1,000 VDC.
    Complies with solar inverter safety standards (UL and EN).
    Designed for safety with 6.0-mm contact gap (two-pole series wiring).

    G7L-2A-X: 25 A at 600 VDC / 25 A at 1,000 VDC
    G7L-2A-X-L: 20 A at 600 VDC / 20 A at 1,000 VDC

    The relay contacts are polarized. Incorrect wiring may cause a failure to break the circuit. Wire the Relay with care

    The Relay is designed and manufactured under the assumption that it will be used with 2-pole series wiring. Do not use just one pole only.

    The Relay weighs approx. 100 g.

    These Power Relays are suitable for switching and breaking high-capacity DC. Do not use them for switching minute loads, such as signals.

    These Relays must be used for high DC voltages. The final
    failure mode is failure to break the circuit. In a worst-case
    scenario, burning may extend to surrounding components. Do
    not use these Relays outside of the specified ratings and
    service life, or for any application other than high DC voltages.

    The electrical durability of these Relays is specified as the
    number of load switching operations under a resistive load

    The coil drive circuit, ambient environment, switching
    frequency, or load conditions (e.g., inductive load or capacitor
    load) may reduce the service life and possibly lead to failure to

  14. Tomi Engdahl says:

    Schneider Electric DC Rated Circuit Breakers

    from 30 to 1200 A

    Dual Rated AC/DC Circuit Breakers

    Standard dual-rated ac/dc circuit breakers may be used in dc system applications and will provide thermal (overload) protection as shown on the ac time-current characteristics curve. These circuit breakers are UL Listed for application in dc systems using the instantaneous trip multiplier for the ac time-current characteristic curve. Standard ac/dc circuit breakers may be used on grounded or ungrounded dc systems.

    QO/QOB – Available with dc voltage ratings from 48 Vdc to 125 Vdc.
    QOU – Available with dc voltage ratings from 48 Vdc to 125 Vdc
    Multi 9 – Available with dc voltage ratings from 60 Vdc to 125 Vdc
    FA and LA – Available with dc voltage ratings from 125 Vdc to 250 Vdc
    PowerPact® H-frame and J-frame – UL/CSA labeled for applications up to 250 Vdc

    EATON Direct Current (DC) Circuit Breakers

    UL489 listed Direct Current Molded Case Circuit Breakers are designed for use in general DC circuits such as ungrounded battery supply circuits, transportation applications, and solar photovoltaic systems. Breakers are available from 15A to 2500A at 600 Vdc and up to 150A at 750 Vdc for transportation applications.

    DC Molded Case Circuit Breakers are ideal for energy storage, transportation, and industrial DC circuits. They are also used in ungrounded battery supply circuits for emergency back-up and standby power. Available up to 150A, 750 VDC and up to 2000A, 600 VDC. For DC breakers used in grounded photovoltaic systems in solar installations, application engineering and review ensures protection requirements are met.

  15. Tomi Engdahl says:

    ABB circuit-breakers for direct current applications$file/vol.5.pdf

    Direct current, which was once the main means of
    distributing electric power, is still widespread today in
    the electrical plants supplying particular industrial ap-
    The advantages
    in terms of settings, offered by the em-
    ploy of
    d.c. motors and by supply through a single line,
    make direct current supply a good solution for railway
    and underground systems, trams, lifts and other trans-
    port means.
    addition, direct current is used in conversion plants (in-
    e different types of energy are converted
    into electrical direct energy, e.g. photovoltaic plants)
    and, above all, in those emergency applications where
    an auxiliary energy source is required to supply essential
    services, such as protection systems, emergency lighting,
    wards and factories, alarm systems, computer centers,
    etc.. Accumulators – for example – constitute the most
    reliable energy source for these services, both directly
    in direct current as well as by means of uninterruptible
    power supply units (UPS), when loads are supplied in
    alternating current.

    Knowing the electrical characteristics of direct current
    and its differences in comparison with alternating current
    is fundamental to understand how to employ direct

    Network insulated from earth
    This type of network represents the easiest connection
    to carry out, since no connection between the battery
    polarities and earth are provided.
    These types of systems are widely used in those installations
    where earthing results to be difficult, but above
    all where service continuity is required after a first earth fault

    On the
    other hand, since no polarities are earthed, this
    connection presents the inconvenience that dangerous
    overvoltages could occur between an exposed conductive
    part and earth due to static electricity

    Network with one polarity earthed
    This typology of network is obtained by connecting to
    earth one polarity (either the negative or the positive
    This connection type allows the overvoltages due to static
    electricity to be discharged to earth.

    Network with the middle point of the supply source connected to earth
    This typology of network is obtained by connecting the middle point of the battery to earth.

  16. Tomi Engdahl says:

    AC versus DC load breaking comparison with a knife switch

    Difference in electrical contact by alternating current to direct current.

    “Despite the voltage discrepancy, I think this is a great quick video to showcase AC having a lower tendency to arc. Regardless of voltage, AC crossing zero potential each half cycle is something that can be used to explain why it is used in a home over DC.”

  17. Tomi Engdahl says:

    AC vs DC Breakers

    Most of us are familiar with AC breakers found in the typical residential service panel.

    The function of a breaker (AC or DC) is to detect when too much current (amps) is flowing through the circuit, then disconnect the circuit from the main power source to protect the wiring from overheating. During the act of disconnecting, the internal contacts separate. As they pull apart from each other, an arc will form as the current jumps across the air gap.

    This arc must be extinguished. The AC and DC breakers extinguish this arc differently. This design difference is why AC and DC breakers are not interchangeable.

    AC Breakers

    The voltage alternates between +V and –V, 60 times a second. That means there is a point at which the voltage is 0v, 60 times a second. It is at this 0v point that the AC breaker will “break” the connection, extinguish the arc, and protect the wiring from too much current.

    DC Breakers

    In contrast, a DC circuit does NOT alternate. It stays at a constant voltage. Since there is no 0v point, the AC breaker design will NOT work in a DC circuit. The DC breaker uses a magnet to attract the arc, pulling it from the air gap, and extinguishes it. The AC breaker is NOT equiped with a magnet, and cannot extinguish a DC arc.

    Moral of the strory, use AC-rated breakers for AC circuits, and DC-rated breakers for DC circuits.

    Only breakers that are labeled as DC-rated should be used for DC applications. NEVER attempt to use an AC-rated breaker in a DC circuit! Why? It will fail to extinguish the arc, the wires will overheat and cause a fire.

    If a breaker is DC rated, it will state so. NEVER assume an AC breaker is DC rated just because the amps and volts match what you need. Conversely, don’t use a DC rated breaker in an AC circuit. NOTE: It is OK to use a breaker that has a dual AC and DC rating (stated on the manufacture’s label)

  18. Tomi Engdahl says:

    Differences between DC Circuit Breaker and AC Circuit Breaker

    A very important difference when interrupting alternating current and direct current is that the arc extinguishing point is higher for a DC circuit breaker. In direct current where voltage is continuous, the electric arc is constant and more resistant to interruption. For this reason, DC circuit breakers must include additional arc extinguishing measures: they typically have a mechanism to elongate and dissipate the electric arc in order to simplify interruption. In AC circuit breakers, arc interruption is simpler because the current is alternating and has values of zero in every cycle where it is easier to interrupt.

    Since the protection mechanism is virtually the same for AC and DC, some models of circuit breakers are designed to work with either type of current. However, it is always very important to verify that the current type of the electric supply and the circuit breaker are the same. If a circuit breaker of the wrong type is installed, it will not be able to protect the installation effectively and electric accidents might occur!

    Just like AC circuit breakers, DC circuit breakers are also available in miniature version and molded case version

    photovoltaic solar panels and electric vehicles, work with direct current and use DC circuit breakers for electric protection.

    DC circuit breakers are typically used to protect direct current electric motors, which have plenty of industrial applications.

    LED lamps work with a light emitting diode, which can only operate with direct current. Therefore, it is common for entire circuits to work with direct current if only LED lamps will be connected. For circuits of this type, a DC circuit breaker will be required for protection.

    DC circuit breakers are less common than AC circuit breakers, but equally important since they have plenty of applications in both homes and businesses. For home owners, DC circuit breakers can be a relatively new technology since most home devices work with alternating current.

  19. Tomi Engdahl says:

    Unlock Data-Center Power Capacity with “Software Defined Power”

    The booming demand for cloud computing and data services will only accelerate as the number of conventional computer-based users is rapidly dwarfed by the multitude of connected “things” that the veritable Internet of Things (IoT) threatens to bring about. Challenges will emerge in trying to scale up the capacity of networks and data centers to support the 50 billion sensors, controls, and other “things” that Cisco forecasts will require access to the internet by 2020. Perhaps more challenging will be addressing the constraints of data-center power capacity.

    The solution to this problem isn’t just providing more power capacity, as this is expensive and time-consuming. Plus, just adding more power supplies assumes the local utility can support the additional load, which for a typical data center is forecast to grow from 2015 levels of around 48 GW to 96 GW by 2021.

    So what’s the answer? Well, firstly, two key factors limit how much of the installed capacity of a traditional power architecture is actually available to use. Historically, data centers have had to ensure high availability to cope with mission-critical processing workloads. This need has been met through supply redundancy, which often leaves power supplies idle. Then there’s the way power is partitioned between server racks, which may result in supplies operating well below their load capacity.

    Power provisioning also needs to allow for fluctuations in the highly dynamic processing loads experienced by data-center servers.

    What’s needed here is a method to even out power-supply loads, perhaps by redistributing processing tasks to other servers or by pausing non-time-critical tasks or rescheduling them to quieter times of day.

    Intelligence Quotient

    What characterizes all these potential solutions is the need for greater intelligence, not just in the management of the data center’s processing operations, but in the way power is managed. One potential solution is the Software Defined Power (SDP) that might unlock the underutilized power capacity available within existing systems.

    Implementing Software Defined Power in data centers and similar IT systems doesn’t need to be difficult. At its simplest, SDP uses feedback to control the distributed power architecture found in data server racks, dynamically responding to changing loads and adjusting intermediate and point-of-load voltages to maximize the efficiency of every supply in the chain. On a broader front, SDP becomes part of a higher-level hardware and software solution that embraces techniques such as peak-shaving and dynamic power sourcing.

  20. Tomi Engdahl says:

    Design, maintain, test batteries in mission critical facilities
    Engineering design, maintenance, and testing of batteries in mission critical facilities is imperative for proper operation and safety.

    When designing electrical distribution systems for mission critical facilities, the overriding factor is reliability. These systems are called mission critical for that very reason: It is critical that power remains uninterrupted. But this mission critical label does not apply to every single part of the facility. Some processes are more important to the business than others, and that is where the focus of the design lies. Certainly, designing for a mission critical facility can be challenging. There are many considerations in play. The system has to be very robust with no single point of failure.

    When designing electrical systems, maintenance is an important factor, specifically in deciding what battery to implement. Maintenance includes not only the cost of replacement of a battery cell, but also the accessibility of the battery system, the ease of disassembly and reinstallation, the frequency of service, and the conditions needed in the space (temperature, humidity, etc.).

    The goal of maintenance is to prolong the life of the batteries and to make sure the batteries perform as designed.

  21. Tomi Engdahl says:

    Tesla Vs. Edison

    The phrase “Tesla vs. Edison” conjures up images of battling titans, mad scientists, from a bygone age. We can easily picture the two of them facing off, backed by glowing corona with lightning bolts emitting from their hands. The reality is a little different though. Their main point of contention was Tesla’s passion for AC vs. Edison’s drive to create DC power systems to power his lights. Their personalities also differed in many ways, the most relevant one here being their vastly different approaches to research. Here, then, is the story of their rivalry.

    Edison’s DC System

    Once he’d come up with a commercially viable light bulb, he needed some way for his customers to power them. In 1880 he formed the Edison Illuminating Company to build electrical generating stations, starting in New York City. In 1882 he switched on the Pearl Street Station’s electrical distribution system, the first of many, supplying 110 volts DC to 59 customers.

    But at the same time, AC systems for arc lighting were popping up. AC systems had the advantage of being able to transmit over a longer distance with thinner wire. Using transformers, the electricity could be stepped up to high voltage but low current

    No such good voltage conversion technology existed for DC at the time and so Edison had to keep the voltage reasonably low along the full route.

    But for reasons we can only speculate about today, Edison refused to switch to using AC

    War of Currents

    The War of Currents refers to a period from the late 1880s to the early 1900s when the battle between distributing electricity via AC or DC was at its fiercest. The battle was fought primarily between the Edison Electric Light Company and George Westinghouse’s Westinghouse Electric Company.

    Westinghouse began his foray into AC electricity distribution in 1886 by forming the Westinghouse Electric Company.

    Work began on the Niagara Falls generating station in 1893 and started powering Buffalo, NY in 1896. As to whether AC or DC won the War of Currents, you need only look at our electrical distribution system today to see.

    However, we can’t fault either for their different approaches, either to problem-solving or in choosing AC or DC, given the positive effects their respective accomplishments had, and still have today.

  22. Tomi Engdahl says:

    380V DC Power: Shaping the Future of Data Center Energy Efficiency

    Traditional distribution practices employed to power data centers and their IT equipment have become antiquated as new standards emerge, driven by our need for new solutions that provide a higher level of efficiency without sacrificing reliability.

    In the traditional electrical distribution scheme utilized by the majority of today’s data centers, energy must go through multiple conversions from Alternating Current (AC) voltage to Direct Current (DC) voltage, from the utility power grid, through the Uninterruptible Power Supply (UPS) and Power Distribution Units (PDU), out to the servers on the data center floor. The server power supplies then convert the voltage one last time from AC to DC, because the electronics inside the servers are resident DC devices. This process results in wasted energy, rejected in the form of heat, which then must be cooled, wasting even more energy and increasing operational cost. Deploying DC power distribution in the data center instead of using the traditional AC design is one way to reduce power loss, eliminate unnecessary conversions and, ultimately, lower energy costs.

    Electric Power Research Institute (EPRI) teamed with the EMerge Alliance, an industry association that is creating standards for commercial implementation of DC power distribution, to advance the adoption of the 380-volt DC UPS solution. However, while 380V DC has been installed in many data centers around the world and acceptance of the technology has gained momentum over the last decade, its path to becoming the principle power standard within the data center industry still faces the challenge of the availability of 380V DC server power supplies.

    By incorporating a 380V DC solution, only a single conversion from 480V grid-supplied AC to 380V DC is required to power the native DC data processing equipment.

    reducing energy usage by 10 to 20 percent.

    he benefits of 380V DC power don’t stop there. Additional attractive features of this innovative solution include:

    Up to 15 percent energy efficiency improvement due to reduced heat loss from conversions.
    Elimination of harmonics, phase load balancing and other issues associated with AC power.
    Lower CAPEX and maintenance costs due to the elimination of conversion equipment.
    Enhanced reliability through simplified design.
    More marketable data center space thanks to DC power’s capability to be plugged directly into equipment.
    Additional OPEX reductions through integration of renewable energy sources such as solar panels.

  23. Tomi Engdahl says:

    DC distribution is not just for the giants

    Kraus suggests the following additional advantages of using DC power:

    There are fewer components in a DC system, meaning less space is taken up, initial equipment and installation costs are reduced, and the system is more reliable.
    Using DC eliminates the need for phase load balancing (more on this later).

    Facebook has been one of the early adopters, employing both AC and DC power technology in its Prineville, Oregon data center.

    The big name data center operators are not the only ones considering or implementing DC power. It’s being tested in various pilot projects

    John Meinecke, president and CEO of EDCS Power explains: “We take a 208V AC drop just like any normal AC-PDU (Power Distribution Unit), and convert the 208V AC to 12V DC at a power shelf in the rack.”

    To make use of the 12V DC at the rack, EDCS Power modifies 1U servers incorporating a 12V DC power supply and backup battery within the 1U confines.

    If the rack contains networking gear (normally 12 VDC ready), Meinecke says the power draw is low enough that EDCS Power includes a single battery backup for all the networking devices in the rack.

    “EDCS power systems are approaching an efficiency of 92 percent.”

    Besides the gain in efficiency, John Unger, president of Vaultas, expects to eliminate the following equipment from the Milwaukee data center:

    Static transfer switch
    UPS systems and all supporting equipment
    In Row PDUs that provide the breakers for each of the two whips going to each rack

    Unger also sees several big-picture benefits from using the hybrid approach:

    The cooling load should be reduced
    Removing unneeded electrical components will gain valuable floor space
    Quarterly maintenance of the UPS will no longer be required

    both Meinecke and Unger is deploying a hybrid AC-DC power system

    Not everyone is convinced that DC power is the answer. It seems that the return on investment (ROI) is not all that some data center operators want them to be.

  24. Tomi Engdahl says:

    400-V DC Distribution in the Data Center Gets Real
    Switching regulators for dc power buses are common in smaller-scale systems, so why not data centers?

    Since at least 2007, data-center engineers have been talking about distributing 400 V dc (sometimes 380 V). Data centers are bigger and use a lot more power than telco central offices. At a minimum, higher voltage distribution would mean lower I2R losses and/or thinner power-distribution cables.

    As data centers have grown in size and as cloud computing looks more and more economically viable, the use of 400 V has started to gain traction. In addition, one semiconductor company has released the missing silicon link in the chain. There is now a 400- to 12-V switching buck regulator device with efficiencies in the high 90s.

    The generally accepted solution was the Intermediate Bus Architecture (IBA). An IBA implementation has three stages:

    • A front-end supply in the equipment rack steps down and rectifies the ac mains volt- age from the power company to semi-regulated 48 V dc. It isolates the boards and circuits downstream from the lethal characteristics of the ac mains.

    • Each board in the system has its own step-down supply, or bus converter, that changes the front end’s 48 V to 12-, 8-, or 5-V bus voltages. The actual voltage is a tradeoff between the efficiency of the buck regulator at the point of load (POL) and the bus IR drop and I2R losses.

    • The bus voltage is stepped down and regulated by non-isolated buck converters termed point-of-load (POL) converters located at each load.

    Many engineers, including Electronic Design’s emeritus editor in chief Joe Desposito, argued that swapping 48 V dc, a separated or safety extra-low voltage (SELV) according to international standards bodies, for 400 V dc, capable of pushing a lot of current, was never going to be popular. Actually, it’s coming faster than you think.

    According to Intel, 255 to 375 W is required at the input to the data center to deliver 100 W to the electronic loads. Anywhere from 50 to 150 W is used for cooling. About 50% of the power that’s left is lost in front ends, power distribution units and cabling, power supply units, voltage regulators, and the server fans used inside the cabinets that hold the blade servers. Better efficiency is possible with 400-V dc power delivery because it eliminates three power conversion steps and enables single end-to-end voltage throughout the data center.

    Why 400 V In Particular?

    Previous studies also have identified 400-V dc power distribution as the most efficient. According to the 2007 IEEE paper, 15 different nominal voltages have been proposed, and Intel recognizes the need for flexibility. Nevertheless, having said that, 400 V dc does offer some particular advantages.

    No phase balancing is required, which reduces the complexity of power strips and wiring. No synchronization is required to parallel multiple sources. There are no harmonic currents to worry about, eliminating the need for power factor correction (PFC) circuits. It can use fewer breakers (up to 50 percent for this case study) because of fewer power conversion stages. And, it simplifies wiring since only two conductors are required.

    Also, a link voltage of approximately 400 V dc already exists in today’s ac power supplies, as well as in the bus in light ballasts and adjustable speed drives (ASDs) that often are used to power fans and pumps in the data center.

    Uninterruptible power supply (UPS) systems typically use a higher voltage dc bus of 540 V dc, which can easily be re-designed to support 400 V dc. Additionally, the spacing requirements per the IEC 60905-1 standard for power supplies are the same for universal input (90 to 264 V ac) power supplies and for dc power supplies with a working voltage below 420 V dc.

    Furthermore, 400 V is well within an existing 600-V safety limit. It operates over standard 600-V rated wiring and busing systems.

    When the two alternatives were modeled, the researchers obtained the results noted above. Specifically, the dc approach produced a 7.7% energy savings with a 50% load and 6.6% savings at an 80% load.

    In terms of reliability, calculations showed a twofold improvement in availability over five years, with a calculated probability of failure of 6.72% for the dc distribution versus 13.63% for ac distribution.


    Whether it’s ac or dc, 400 V will hurt. Placing yourself across 400 V pushing hundreds of amps won’t leave a whole lot to bury. Yet ac or dc, 400 V is what we already have in data centers.

    “Operation and maintenance personnel are presently familiar with voltages at these levels, and the use of a 400-V dc system is not more hazardous than what is presently used. It is known that the use of higher ac or dc voltages inside of the data-center racks and cabinets may expose data center personnel to voltages with which they are not normally familiar,”

    “In the U.S., however, any nominal voltage above 50 V is considered hazardous to personnel, and when one is using or working with a higher voltage than this, the same precautions and personal protective equipment are mandatory,”

    Found: The Missing Link

    In January, Vicor announced the first 400-V dc to 48-V dc (nominal) bus converter module to use its CHiP (“Converter Housed in Package”) module technology. The BCM380y475x1K2A30’s dc input range is 262 to 410 V dc. Its nominal output voltage is 47.5 V dc, but it can be set for any output footage from 32.5 to 51.25 V.

    Rated for 1200 W, the module can handle up to 1500 W peak.

  25. Tomi Engdahl says:

    Direct Current (DC) Data Center

    Presentation by Reino Buchmüller, Head of Low Voltage Systems
    Helsinki, August 31 2011

  26. Tomi Engdahl says:

    The Move to DC Power in the Datacenter

    Relying on alternating current (AC) instead of switching back and forth between it and direct current (DC) can save money in equipment costs and enable a datacenter to operate far more efficiently.

    While the industry is not there yet, DC power is a hot topic. Utilities deliver AC to its customers, including datacenters. End user equipment in these facilities – PCs, servers and other gear – run in DC. Several transitions often are necessary in the distribution of electricity through the building and its ultimate use by the equipment. This wastes electricity.

    Sartor, who helped put the course together, said that finding ways to reduce datacenter energy consumption by minimizing AC/DC transitions is a hot topic. One organization that is working in this area is The Open Compute Project.

    There is a parallel driver of the research into use of DC in datacenters. Datacenters are among the biggest consumers of solar energy, which generate DC electricity. Limiting the number of DC/AC/DC conversions – from the solar platform (CD) to the building distribution system (AC) and back to data center equipment (various DC voltages) – saves money and drives efficiency.

  27. Tomi Engdahl says:

    Now there’s a better alternative to alternating current.

    Starline DC Solutions enables data centers and other DC centric applications to adapt to current and future power generation systems (solar, wind, fuel cells, etc.) in the form of reliable 380V Direct Current.

    Starline DC Solutions has developed the unique power support system technology that makes 380V DC power a reality now.

    rack Busway can accommodate most installation requirements for power delivery and offers customization of plug-in units with DC rated components, including circuit breakers, fusing and connectors. Metering options are also available

    Utilizing DC power for lighting applications is a definite benefit, especially for LED installations.

    Our proven Track Busway product can be leveraged as a collector and distribution bus, enabling you to directly connect your DC centric renewable devices such as solar, wind and fuel cells directly to the busway. With battery storage and rectification also included in the implementation, all of the necessary components to install a fully-functional renewable system are available to you.

  28. Tomi Engdahl says:

    High input voltage (450V to 800Vdc) industrial DC-AC sine wave inverters

    The compact sine wave inverters are cooled by conduction and natural convection – no fans required

    ABSOPULSE has recently released the CSH-300-F6 and CSH-400-F6 series of high input voltage DC-AC sine wave inverters. The units use microprocessor controlled, high frequency PWM technology to deliver 300VA and 400VA pure sinewave output voltage respectively. The inverters convert 600Vdc industrial input voltage (450V to 800Vdc range) to an isolated sine wave output of 115Vac continuous at 60Hz or 400Hz, or 230Vac continuous at 50Hz. The design topology allows for higher input voltages of up to 1200Vdc.

    The high input voltage DC-AC sine wave inverters are designed for industrial applications that require clean sine wave AC-output voltage. They are suitable for operation in industrial automation and control, transportation, power plants and electrical utilities.

    The input meets EN55022 Class A with wide margins. Class B available on request.

  29. Tomi Engdahl says:

    5kVrms isolated switch controller with telemetry has diverse applications

    Designers sometimes have high voltage designs they are crafting or maybe need a good high voltage DC Hot Swap controller for their system. Other times a designer may want to break a ground loop, or monitor power, or maybe isolate a distributed power system.

    Applications abound for high voltage DC power supplies; such as, industrial motor drives, F-22 and F-35 fighter aircraft, electric vehicles, and data centers to name only a select few growing areas.

    Let’s look at a few fast-growing examples starting with industrial motor drives. This power architecture rectifies the incoming 120VAC, 240VAC, or 480VAC and converts to DC voltages ranging from 170V to 680V. Modern jet fighter aircraft, like the F-22 Raptor and the F-35 Lightning II, are primarily powered from 270V DC to enhance performance. In electric vehicles such as the Nissan Leaf and Tesla Model S, the Li-ion battery stack’s has voltage peaks around 400V.

    And now we have data centers becoming increasingly aware to improving power efficiency with the onset of cloud data centers’ growth. Power system designs are moving to converting AC to high voltage DC (380V or ±190V), eliminating power conversion steps, facility footprint, and operational costs while easing integration with renewable energy like solar. Circuitry controlling such supplies needs to be galvanically isolated for operator safety and to protect the low voltage electronics from the dangerously high voltage.

    Well, there is a new component from Linear Technology that can do all of these and more. The LTM9100 is a μModule deemed an ‘anyside high voltage isolated switch controller with I2C command and telemetry.’

    Most hot swap controllers on the market today are designed for systems of 48V or less

    Enter the LTM9100 μModule, an alternative solution that provides a complete, galvanically isolated MOSFET/IGBT controller with I2C interface. It can be used as a load switch or hot swap controller.

    Due to the isolated, floating character of the switch, it can be configured for use in high side, low side and floating applications (hence the term anyside).

    Isolated measurements of load current and two voltage inputs are made by a 10-bit ADC and accessed via the I2C interface. The logic and I2C interface is separated from the switch controller by a 5kVRMS isolation barrier which is perfect for systems where the switch operates on busses up to 1000VDC. Galvanic isolation provides critical control circuit protection, operator safety, and breaking ground paths.

    The device can be used to control inrush current in hot-swappable cards, AC transformers, motor drives, and inductive loads. Adjustable undervoltage and overvoltage lockout thresholds will ensure that the load operates only when the input supply is in its valid range.

  30. Tomi Engdahl says:

    LTM9100 – Anyside™ High Voltage Isolated Switch Controller with I²C Command and Telemetry

    UL-CSA Recognition Pending: 5kVRMS for One Minute
    Reinforced Insulation
    Integrated Isolated Power Supply
    Adjustable Turn-On Ramp Rate and Current Limit
    I2C/SMBus Interface
    10-Bit ADC Monitors Current and Two Uncommitted Channels

    The LTM®9100 μModule® (micromodule) controller is a complete, galvanically isolated switch controller with I2C interface, for use as a load switch or hot swap controller. The load is soft started and controlled by an external N-channel MOSFET switch. Overcurrent protection minimizes MOSFET stress during start-up, input step and output short-circuit conditions. Owing to the isolated, floating character of the switch, it is easily configured for use in high side, low side and floating applications.

  31. Tomi Engdahl says:

    560V Input, No-Opto Isolated Flyback Converter

    a flyback converter with a wide input range from 20V to 450V

    The LT®8315 is a high voltage flyback converter with an integrated 630V/300mA switch. The LT8315 eliminates the need for an opto-coupler, complicated secondary-side reference circuitry, additional start-up components, and an external high voltage MOSFET.

    In standby mode, the LT8315’s preload is usually less than 0.1% of full output power, the quiescent current is lower than 100μA—important for applications requiring high efficiency in always-on systems.

    The LT8315’s high voltage input capability is easily applied in nonisolated solutions. Nonisolated converters do not require the transformer of an isolated converter, instead adopting a relatively inexpensive off-the-shelf inductor as the magnetizing component.

    The LT8315 operates at a wide input voltage range of 18V to 560V, delivering up to 15W of isolated output power. It requires no opto-coupler, and includes rich features such as low ripple Burst Mode® operation, soft-start, programmable current limit, undervoltage lockout, temperature compensation, and low quiescent current.

  32. Tomi Engdahl says:

    SCTE to Present 380 V Powering Case Study

    According to an SCTE/ISBE case study that will be presented at an Energy 2020 meeting this month, cable operators can address power density and cost issues associated with delivery of new services by shifting from 48 VDC to 380 VDC powering. The meeting and plenary will be conducted on April 18-19, at Comcast’s (NASDAQ:CMCSA) Chesterbrook, PA, facility.

    The case study will discuss the current situation facing service providers: the need to address anticipated 10X or more increases in power requirements for server racks in coming years; the inability of traditional 48 V systems to meet that demand because of cable congestion that restricts power delivery into server areas; and the cost barriers to relocating data centers to new facilities that could be served by 48 V power.

    At the meeting, Energy 2020 members will learn how implementation of a 380V system enabled a service provider to extend the useful life of its facilities and to raise facility average power density from 100 W per square foot. In this case, the cost of the 380V approach was 27% less than the 48V alternative.

  33. Tomi Engdahl says:

    Power Integrations highlights importance of power factor correction at APEC 2017–at-APEC-2017

    Power factor correction is the process of improving a low power factor in a facility by increasing the ratio of real (working) power to apparent (total) power.

    Here is what HP says about power factor correction, especially regarding data center needs1:

    Before computing and storage devices can use electrical power, the AC provided from the source must be transformed to direct current (DC) by a power supply. The term “power” is the rate at which the electricity does work, such as running a central processing unit (CPU) or turning a cooling fan. The power that the electricity provides (apparent power) is simply the voltage times the current, measured in volt-amperes (VA). There is a difference between the power supplied to a device and the power actually used by the device because of the capacitive nature at the input of the device to delay current flow.

    A power supply that has a PF of 1.0 indicates that the voltage and current peak together, which results in the most efficient loading of the device. Power supplies for servers usually contain circuitry to “correct” the power factor (that is, to bring input current and voltage into phase).

    Power-factor correction allows the input current to continuously flow, reduces the peak input current, and reduces the energy loss in the power supply, thus improving its operation efficiency. Power-factor-corrected (PFC) power supplies have a power factor near unity (~1), and thus are highly efficient. The use of energy-efficient PFC devices, including uninterruptible power supplies (UPSs), can lead to significant cost savings.

    Many designers may try a low-cost approach to correct low power factor; that is, installing capacitors within a facility’s power distribution system. Capacitors will behave like a temporary storage bank for reactive (magnetizing) power (kVAR).

    Capacitors have been used to improve poor power factors since 1917; this is 2017 and designs are “not your father’s” PFC architectures.

  34. Tomi Engdahl says:

    Schurter showcases 400 VDC couplers per IEC standard 62735-1 at Data Center World 2017

    Schurter, a manufacturer of circuit protection, connection, switching and EMC products for the information and communication technology (ICT) industry, will feature its latest connectors at Data Center World 2017 (April 3-7) at the Los Angeles Convention Center.

    This year the company is showcasing its newest coupler for 400 VDC applications, according to the latest IEC standard 62735-1. Designed specifically for enabling pluggable power in DC systems, this new interconnect device is first to comply with the new IEC standard, asserts Schurter. “Manufacturers of power distribution units (PDUs) and other equipment for data centers have long waited for a standardized solution for safe and reliable interconnection, to support the ever-increasing trend toward increased efficiency and reduced costs,” adds the company. The new IEC standard is slated for official introduction at the end of 2017.

    IEC TS 62735-1:2015
    Direct current (DC) plugs and socket-outlets for information and communication technology (ICT) equipment installed in data centres and telecom central offices – Part 1: Plug and socket-outlet system for 2,6 kW
    IEC TS 62735-1:2015(E) applies to plugs and fixed socket-outlets for class I equipment with two active contacts plus an earthing contact, a rated power of 2,6 kW and a rated voltage range from 294 V to 400 V d.c. They are intended to power d.c. information and communication technology equipment only, products according to IEC 60950.

  35. Tomi Engdahl says:

    Schurter Showcases New 400 VDC Couplers at Data Center World 2017

    SCHURTER, an innovative and progressive manufacturer of circuit protection, connection, switching and EMC products for the information and communication technology (ICT) industry will feature its newest connectors at Data Center World 2017, which takes place April 3-7 at the Los Angeles Convention Center. This year SCHURTER is showcasing its newest coupler for 400 VDC applications, according to the latest IEC standard 62735-1. Designed specifically for pluggable power in DC systems, this new interconnect device is first to comply with the new IEC standard. It is slated for official introduction ending 2017. Manufacturers of PDUs and other equipment for data centers have long waited for a standardized solution for safe and reliable interconnection, to support the ever increasing trend toward increased efficiency and reduced costs.

    Im Gleichschritt – 400 VDC fürs Data Center

  36. Tomi Engdahl says:

    Industrial and multiphase power plugs and sockets

    Industrial and multiphase plugs and sockets provide a connection to the electrical mains rated at higher voltages and currents than household plugs and sockets. They are generally used in polyphase systems, with high currents, or when protection from environmental hazards is required. Industrial outlets may have weatherproof covers, waterproofing sleeves, or may be interlocked with a switch to prevent accidental disconnection of an energized plug.

    While some forms of power plugs and sockets are set by international standards, countries may have their own different standards and regulations.

    Three phase sockets provide three line contacts, they may also include either or both of a neutral and protective earth contact. The designations of the three contacts may vary. The IEC standards use the Line designations L1, L2 and L3.[15] NEMA standards use the Phase designations X, Y and Z.[16]

    Europe-wide IEC 60309 system

    In Europe, the most common range of heavy commercial and industrial plugs are made to IEC 60309 (formerly IEC 309) and various standards based on it (including BS 4343 and BS EN 60309-2). These are often referred to in the UK as CEE industrial, CEEform or simply CEE plugs, or as “Commando connectors” (after the MK Commando brand name for these connectors).

    Plugs are available in P+N+E (unbalanced single phase with neutral), 2P+E (balanced single phase), 3P+E (3 phase without neutral), and 3P+N+E (three phase with neutral). Current ratings available are 16 A, 32 A, 63 A, 125 A and 200 A.

    Voltage and other characteristics are represented by a colour code (in three-phase plugs the stated voltage is the phase-phase voltage, not the phase-neutral voltage).

    NEMA connectors

    “Industrial-grade” connectors are constructed to meet or exceed the requirements of more stringent industry testing standards, and are more heavily built to withstand damage than residential and light commercial connectors of the same type.[21] Industrial devices may also be constructed to be dust or water-tight. NEMA wiring devices are made in current ratings from 15–60 A, and voltage ratings from 125–600 V.

    There are two basic configurations of NEMA plug and socket: straight-blade and locking. Numbers prefixed by L are twist-lock, others are straight blade.

  37. Tomi Engdahl says:

    How to Calculate Current on a 3-phase, 208V Rack PDU (Power Strip)

    In recent years, extending 3-phase power distribution all the way to server cabinets and racks has become extremely popular in new data center builds—for many good reasons. Principally, for cabinet power capacities above 5kVA, utilizing 3-phase rack power strips can significantly reduce the copper required to supply such dense loads.

    But unfortunately, many users (rightly) find it cumbersome to provision and calculate current (amperage) for 3-phase power in the rack

    In North America, where 3-phase, 208V power distribution is wired “line-to-line”, the answer to this question is particularly counter-intuitive.

    Why 3-Phase (208V) Power Strip Loading Is Difficult

    With single-phase power strips, loading and provisioning is straightforward: if you add a device to the rack that draws 10 amps—in turn, 10 amps of additional load is drawn from the input line of the power strip.

    But with 3-phase power strips, when you add the same 10 amp device to a server cabinet, it is unclear what results. From which of the three lines will additional current flow? How much of the 10 amps flows from which of the three lines? etc.

    As we shall see, the answer is not always obvious.

    1. In North America, a 208v, 3-phase power strip is divided, well, into 3 sections:

    L1/L2: outlets that are wired to draw current from lines L1 and L2 (aka, XY);
    L2/L3: outlets that are wired to draw current from lines L2 and L3 (aka, YZ);
    L3/L1: outlets that are wired to draw current from lines L1 and L3 (aka, XZ);

    2. One would intuitively expect the following to occur when a load is applied:

    Start with a completely empty rack / power strip;
    Add a 10A load onto an outlet that is supplied from L1/L2;
    In turn, 10A of current flows from L1; and 10A of current flows from L2.

    n all seriousness, the essential truth illustrated by the diagram is that the amount of current on a given line (L1, L2, and L3) depends on the amount of current on the other two lines. Calculating each line value requires vector addition (a.k.a. “complex” arithmetic),

    Generally-speaking, 3-phase rack power strips can be purchased most commonly in the following 208V electrical configurations:

    30A (24A derated) : NEMA L21-30P or NEMA L15-30P input plugs;
    50A (35A derated) : Hubbell CS8365C “California-style” input plug, but with only three branch circuit breakers [or, less desirably, fuses] on the unit.
    50A (40A derated) : Hubbell CS8365C “California-style” input plug, but with six branch circuit breakers [or, less desirably, fuses] on the unit.
    60A (45A derated) : IEC 60309 60A, 3-pole / 4-wire, “pin-and-sleeve” input plug, but with smaller, 6# AWG gauge input conductors. Check your manufacturer’s spec sheet closely. If it states that: (a) the rated current is 45A; or (b) the rated power capacity is 16.2kVA [not 17.3kVA], then you have this type of power strip.
    60A (48A derated) : IEC 60309 60A, 3-pole / 4-wire, “pin-and-sleeve” input plug, but with larger, 4# AWG gauge input conductors. Check your manufacturer’s spec sheet closely. If you have this type of power strip, the spec sheet will explicitly state either: (a) the rated current is 48A; or (b) the rated power capacity is 17.3kVA [not 16.2kVA].

    3-phase, 208V Power Strips (Rack PDUs) Demystified, Part II : Understanding Capacity

    Despite the growing ubiquity of 3-phase power distribution (at 208V) in North American data centers, data center operators are still not sufficiently fluent with the real-world capacity implications of 3-phase power in their cabinets.

    The principal reason is because—at 208V—the math required to understand 3-phase power distribution at the cabinet is completely counter-intuitive.

    THE SHORT VERSION: 2 Primary Tips

    1. If you don’t totally, 100% understand 3-phase power distribution, it is best if you do NOT think or speak in terms of amps. In all likelihood, you will say something incorrect that confuses your electrician.

    Instead, think about how many watts your equipment consumes, and how many watts your 3-phase power strip can provide. Watts are universally comparable, regardless of the supplied electrical configuration available at your rack: both your power strip manufacturer and your IT equipment vendor will tell you how many watts can be supplied. No matter what voltage you use; the rated current (amps); or whether you have 1-phase power or 3-phase power; etc… you can always compare watts.

  38. Tomi Engdahl says:

    3-Phase Voltage: Uncovering Hidden Agility in Your Data Center

    In the world of data centers, there’s a lot of talk about voltage and power delivery: the best options, the most efficient choices, the latest and greatest voltages, etc. Oftentimes, 3-phase voltage is the power delivery method of choice.

    As a combination of three single-phase circuits that deliver power so the load is the same at any point, 3-phase voltage allows utilities to deliver more power over smaller, less expensive wires. If 3-phase voltage is what you have to work with in your data center, there are ways to make the most of it.

    Although other voltage options exist, the most common 3-phase voltage is 208V power as a feed to the rack. A 3-phase voltage is 120V phase to neutral, and phase to phase voltage of 208V

    Using a power distribution system that supplies all three phases, neutral, and ground to the rack with, for example, an L21-20 or another type of amperage and plug style, offers several options to help ensure quick and easy upgrades down the road.

    3-phase voltage also allows you to have 120V or 208V outlets; you can mix and match types in a single PDU (power distribution unit) or have one voltage cover the entire strip.

    Implications of 3-Phase Voltage

    So what does this all mean for you?

    If you’re a co-lo data center, offering equipment, space and bandwidth for rental, 3-phase voltage delivers the ability to support a wide range of customers.

    If your co-lo data center is attempting to standardize parts, you may not need 120V or 208V (or both) in a rack. If you choose three PDUs and select an outlet with an L21-20 receptacle for the PDU to plug into, the only thing that needs to be done if the voltage changes is to change the PDU – not rewire. This translates to no scheduled downtime, and the elimination of hazardous hot or live electrical work by electricians.

    If you want to futureproof your data center, 3-phase voltage allows you to be all 120V today – but, by using a 3-phase outlet and a L21-20P, you can upgrade or add 208V with a simple PDU change. Because this switch can be made quickly, you’ll increase your speed to redeploy, upgrade and MAC work.

  39. Tomi Engdahl says:

    Know your Data Center Power, Part 3 – Single phase vs. three phase

    With a 3-phase supply you have two ways of connecting a traditional, 2-wire load, such as a light bulb or a server. In a Y system you can connect it between any phase (X, Y or Z) and neutral (N). In a both Y and delta systems you can also connect it between any two phases (X-Y, Y-Z or Z-X). In a 3-phase system the voltage between any two phases is 3 times higher that the voltage of an individual phase by a factor of 1.73 (square root of 3 to be exact). If your X-N (and Y-N and Z-N) voltage is 120V (common in the US), the X-Y (and Y-Z and Z-X) voltages (a.k.a. “cross-phase” voltages) will be 120V * 1.73 = 208V. The 208V (sometimes confused with the European 220V) comes from cross-phase connections to a 120V three-phase system. A 220V system with three 220V phases has a 220 * 1.73 = 380V cross-phase voltage.

    Single Phase vs. Three Phase Power: What You Need to Know?

    Many of the residences in the North American and European regions use single-phase alternating current electric power supply, which is typically used for powering up lights and household appliances. However, a single-phase system may not be the best choice when it comes to industrial or business usage as it involves heavy load and power requirements. As today’s data centers are growing power hungry with a need to provide more computing and storage capability to keep up with the explosion in demand, power supply has become a major consideration. Traditional single-phase systems can no longer keep up with the power requirements for these data centers without going through a rewiring process as the number of units that can be mounted in a rack has gone up way high because of miniaturization. Fortunately, three phase power distribution systems can come to the rescue with their superior power carrying capability at a reduced cost. Here are some of the key differences between single phase and three phase systems that you need to know.

    What are the benefits of three-phase systems over single-phase?

    The cost to install and maintain three-phase systems is substantially lower than that of single-phase systems. Three-phase systems use substantially less conductor material than that of single-phase systems – about 25 percent less for the same amount of power delivered. For the same amount of time, three-phase power lines can carry more power than that of single-phase power lines at a reduced cost. In addition to reduction in copper, a three-phase system requires fewer circuit breaker pole positions for 208 Volt loads.

    There are different ways to draw power from three-phase system. In delta configuration, power is drawn by combining any two of the phases to form a circuit, while wye configuration includes a phase and a neutral. The first combination results in 208 Volts while the second one results in 120 Volts. This kind of setup provides maximum flexibility in terms of voltage and power, helping to balance power across all the equipments. Three-phase systems are also safer to work, and require a lower labor and equipment to handle.

  40. Tomi Engdahl says:

    The Next Opportunity for Utility PV Cost Reductions: 1,500 Volts DC

    The average cost for a 20-megawatt fixed-tilt utility PV project in the U.S. in 2015 is just above $1.50 per watt — relatively cheap in historical terms. However, with record-low PPAs being signed at these levels, even subtle changes in component costs can kill projects.

    The most immediate opportunity that we see for utility-scale PV system cost reduction is the installation of 1,500 Vdc systems. Higher-voltage systems enable longer strings, which allow for fewer combiner boxes, less wiring and trenching, and therefore less labor. According to our research, installing 1,500 Vdc systems in place of now-standard 1,000 Vdc can lower costs by as much as $0.05 per watt.

    Déjà vu: The history of higher-voltage PV

    If this conversation seems familiar, it’s because we’ve had it before. Prior to 2013, most systems in the United States were installed at 600 Vdc, while systems in Europe were installed at 1,000 Vdc. This enabled lower system costs in Europe, while installers in the U.S. were kept at low voltages by UL testing limitations and the National Electric Code, which limited voltage to 600 Vdc due to a broadly interpreted revision added in 1999.

    In 2013, however, many authorities began allowing 1,000 Vdc systems for commercial and projects, and UL standards evolved to enable this.

    From an installation perspective, the shift to 1,500 Vdc has similar benefits and regulatory barriers to the 1,000 Vdc transition.

    The beginnings of 1,500 Vdc

    When 1,000 Vdc systems became prevalent in the United States, there was already widespread availability of products from Europe, and thus the testing standards were the main barrier. Testing standards are also a barrier to 1,500 Vdc, but 1,000 Vdc is still the standard voltage in Europe, and so there is also exceptionally limited availability of 1,500 Vdc products.

    This doesn’t mean Europe didn’t lead the U.S. again with 1,500 Vdc. Europe’s electrical standards body, the International Electrotechnical Commission (IEC), considers 1,500 Vdc the low-voltage limit and enables certification to that voltage.

    As a result of these industry efforts, 1,500 Vdc parts are now commercially available for every system component. But module manufacturers are limited by the existing standards landscape.

    Product availability has been the primary barrier to 1,500 Vdc in Europe, but product introductions have been hampered by standards in the United States. Nobody wants to introduce a product that is unable to be used in the U.S. market. UL 1703, the gold standard for PV modules, currently only enables module testing to 1,000 Vdc.

    We expect all standards issues for 1,500 Vdc to be resolved in the next two years.

    As these regulatory barriers dissolve, manufacturers will begin to introduce 1,500 Vdc products in volume. We expect this to begin in mid-2015 and continue into 2016.

    1500 VDC Collection Systems

  41. Tomi Engdahl says:

    Loss of Battery-Cable Isolation Prompts EV/HEVs to Protect Against Potential Hazards

    Deployment of high-voltage battery systems in traction drives employed in EV/HEVs has raised concerns for human safety. Exposure to hazardous high voltages may occur due to deterioration of cable insulation materials or by accidental events. Therefore, it is important to monitor such potential faults and when necessary issue timely warnings.

    The main function of an isolation monitor is to warn the EV/HEV operator that there is a potential (latent) hazardous condition. In the case of a single fault, this monitor is intended to protect the service/maintenance personnel and first responders, rather than the regular operators.

    when there is no proper isolation between battery cable and the chassis, the isolation monitor notifies the vehicle’s host computer to take corrective action.

    In a typical topology of the modern electric vehicles and of the so-called IT (“Isolated Terra”) power systems, the whole Energy Storage System (ESS) or Rechargeable Energy Storage System (RESS) floats with respect to chassis (or ground). There are two main reasons for it:

    1. Even a hard short (single-fault) from anywhere within the system to ground will not immediately produce a catastrophic event, or even a malfunction with respect to the continuous usability of the system.

    2. A floating system actually enables the detection and measurement of leakages in the system.

    In operation, EV/HEV battery cable insulation may deteriorate either gradually or suddenly, shorting the battery voltage to the chassis. In addition, capacitances from the power system to the chassis may inadvertently change, accumulating hazardous charges. If either condition is detected, the operator should be notified to immediately service the vehicle. Another possibility is that the isolation of the car battery may be compromised during an accident

    For protection purposes, today’s state-of-the-art technology only detects resistive leakages and only when the system voltage does not vary significantly. For industrial and commercial systems that would have to be in operation most of the time, that limitation can be dangerous. In contrast, Sendyne’s SIM100 is an automotive-rated isolation monitoring IC that detects potential electrical hazards during the dynamic operation of high voltage ungrounded systems, such as EVs and HEVs

    The SIM100MOD continuously monitors the isolation resistance between a vehicle’s power system and chassis for deterioration of insulation and potentially dangerous leakage current. The module detects not only resistive leakages, but also capacitively stored energy that could be harmful to human operators. The SIM100MOD can detect these potential hazards while the system is operating and voltages are fluctuating as much as 100 V.

  42. Tomi Engdahl says:

    Is the Electrical Grid Keeping Up with Smart Solar Inverters?

    Today’s solar inverter technologies do more than convert the variable dc output of a photovoltaic solar panel into utility frequency ac suitable for a commercial grid or to a local, off-grid electrical network.

    Within the fast-growing solar-energy market, solar-inverter suppliers must keep pace with electronic technology advances in order to deliver more efficient and reliable parts at a lower cost. Inverter efficiency indicates the percentage of the available solar power that’s actually converted by the inverter and fed into the utility grid; some smart inverters reach a total efficiency of 98%. To achieve high efficiency, it’s important to design the inverters using the most reliable components from power semiconductors (MOSFETs and/or IGBTs), capacitors (electrolytic capacitors, high-capacity film capacitors), transformers, cooling systems, etc.


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