DC to AC inverter and UPS Page

    DC to AC converter and UPS circuits

    Have you ever wanted to run a TV, stereo or other appliance while on the road or camping? Well, a power inverter should solve that problem. An inverter is an electrical device that converts 12-volt power into mains power (120V 60Hz AC or 230V 50 Hz AC typically). Typically you run an inverter off of your car's battery or off of a deep-cycle battery that you buy specifically to power the inverter. An inverter is usually a very easy and inexpensive solution to get mains power where it is not normally available if you can keep your power demands in the 200-watt range. With around 300 watts of continuous power inverter you can run items like desktop computers, monitors, full size fax machines, battery chargers and AC adapters for notebook computers, cellular phones, camcorders,small power tools, drills, mid-sized TVs, soldering guns, and a variety of rechargeable equipment on the road. If you have a higher power inverter, you can run more devices or more powerful devices. With a lower power converter you can use only devices which use less power. Power inverters are also very useful in solar power system which generally use low voltage batteries (usually 12V DC) to be ableto run mains powered devices in them.

    There are different kind of inverters. Besides the input voltage, output votlage and power rating there are inerters that output the power at different waveforms. The three most common outputs for inverters are square wave, modified sinewave (sometimes called a quasi sinewave), and sinewave outputs.

    Square wave is the simplest method that is widely used in the cheap low power devices. Many years ago this was the only waveform available at cheap inverters. Square wave waveform inverters generally consist of an oscillator driving switching transistors, that swich the incoming power to different sides of the center tapped transformer primary. The square wave mains voltage is outputted from the transformer secondary. The converter transformer can be pretty similar to normal 12V-120V or 12V-230V mains power transformer rated to inverter power rating. The square wave power is quie far from the waveform available from normal mains outlet, and this can cause problems on equipment originally designed for the sinewave power in mind. Most devices with variable speeds such as electric drills, or devices with chargers such as cordless drills or screwdrivers, can behave irrationally when operating with modified sine or square wave inverters. Sqare wave power might not be nice for some sentive electronics devices.

    The next step for power that is more near to mains sineware is system called "modified sinewave". The "modified sinewave" waveform is became nowadays popular on many even inexpensive inverters because it is quite easy to make with modern electronics. This type of inverters generally use a switch mode power supply that generates 150-300V DC that is then switched to the output at right way using few high voltage power transistors/FETs controlled by output control timign electronics. "Modified sine wave" would be more accurately called "modified square wave" because it's made from two square waves out of phase. The phase is adjusted with load so that the RMS voltage remains correct when the peak voltage sags. As long as the load is normal, the peak voltage is close to what you'd have in a sine wave. The waveform is compatible with electronics but it may induce loud mechanical buzzing. Here is an example what "modified sine wave" power waveform looks like:

        __          __          __     
    | | | | | |
    | | | | | |
    | | | | | |
    -- -- -- -- -- --
    | | | |
    | | | |
    |__| |__|

    Some small wall based chargers (called wall warts) can have overheating problems with modified sine or square wave inputs. Some computers and stereo equipment use switching power supplies that utilize SCRs and Triacs as well. These pieces of equipment may experience the same troubles with non-sinewave power.

    True sine wave output allows connected loads and equipment to operate the same as they would from utility supplied power. Unfortunately the true sine wave output inverters are more expensive than the ones which use square wave or modified sinewave.

    Generally you can buy a small 150- or 300-watt quasi-sine-wave inverter for about $50. Higher power or true sinewave models cost generally more.Sinewave is the type of voltage wave form one normally receives from grid connected power. The reason of this preferred wave form is the improved performance of equipment such as AC motors. An Uninterruptible Power Supply (UPS) is a device that sits between a power supply (e.g. a wall outlet) and a device (e.g. a computer) to prevent undesired features of the power source (outages, sags, surges, bad harmonics, etc.) from the supply from adversely affecting the performance of the device. UPS devices generally consist of some form of internal battery, inverter and intelligent switching electronics. When normal mains power is available, it is supplied to the devices connected to UPS. When mains power is not available, the devices connected to UPS output are powered by the inverter circuit inside the UPS. UPS devices aren't designed to let you keep working for a long period of time after power outage; they're designed to give you enough time to shut your system down in the normal manner.

    NOTE: Most of the circuits below have square wave output and are not suitable for driving sensitive electronics equipments. The AC from those inverters can damage some equipments connected to them.

      General articles

      • How Emergency Power Systems Work - A wide variety of natural disasters can cause long-term power outages. An UPS or battery and inverter can provide emergency power for some time, but there are also other alternatives for this.    Rate this link
      • TAMU Fuel Cell Inverter 10 kW Design & Cost Analysis - The report outlines the technical approach and the cost analysis to achieve the objectives proposed by the 2001 Future Energy Challenge organizing committee. The Texas A&M team believes it has developed an efficient and cost-effective inverter system. The team has developed a low cost analog control solution for the DC-DC converter, an efficient 3-terminal DC-DC push pull topology, a unique DSP control for DC-AC inverter control, and a rigorous cost reduction approach for the 2001 Fuel Cell inverter project. The 3-terminal push-pull DC-DC converter topology provides isolation for safety, suitable boosting of the fuel cell voltage to 400 volts, reduced cost and reduced size of the energy storage elements in the converter.    Rate this link


      • Basic 200 W power inverter - This is a 12V DC to 110V 60 Hz AC inverter circuit with up to 200W continunous square wave output. This circuit was reverse engineered from a Tripp-Lite "Power-Verter" Model PV200 DC to AC Inverter - typical of those used for camping or boating applications where the only source of power is an auto or marine battery.    Rate this link
      • Building a dc to ac converter - Otherwise known as a dual axis drive corrector, this unit is intended to provide 240 volts/50 Hz (or 120 volts/60 Hz with minor modifications) for a right ascension (ra) drive and a reversible declination motor. The supply requirement is from 11 to 16 volts d.c. at 500 mA. The overall output frequency is adjustable from 47.5 Hz to 52.5 Hz or from 40 Hz to 60 Hz on the remote unit. This frequency is stabilised against voltage or temperature change.    Rate this link
      • Inverter offers design flexibility - works from a 12V car battery and produces mains voltage with closed-loop voltage regulation    Rate this link
      • SCR Inverter - outputs 300V 400Hz, waveform is vaguely sinusoidal, 5W output power    Rate this link
      • The I2K Power Inverter: A 2kVA 12VDC to 120VAC inverter for power backup - This circuit is a 2kVA 12VDC to 120VAC inverter for power backup. This description of the inverter is preliminary and incomplete.    Rate this link
      • Circuit makes simple high-voltage inverter - A simple high-voltage MOSFET inverter solves the problem of driving a high-side MOSFET, using a low-voltage transistor. You can drive the circuit with a single CMOS gate. This circuit is probably the simplest high-voltage inverter you can design. It has served in thousands of three-phase motor drives from 0.37 to 0.75 kW.    Rate this link

      UPS techology

      An uninterruptable power supply (UPS) system provides backup power supply for an application in the event of an electrical outage. Although the UPS has traditionally been designed as analog circuitry, digital UPSs are now preferred. These devices use low-cost MCUs or DSPs and offer sophisticated control algorithms with highly flexible software, the ability to add user interfaces, reduce components, introduce testing procedures, and increase reliability. Several basic UPS topologies exist,differentiated by function during a power outage. The online UPS offers the greatest reliability and continuity of power supply. During normal operation, the load is connected to an inverter powered by a battery and/or another inverter. If a power outage occurs, the inverter is supplied by the battery with no switching or switching delay.

      • APC UPS Haemon - Apcupsd can be used for power mangement and controlling most of APC's UPS models on Unix and Windows machines. Apcupsd works with most of APC's Smart-UPS models as well as most simple signalling models such a Back-UPS, and BackUPS-Office. You will need a serial port cable between the APC UPS and your computer running apcupsd. You can use either the cable that came with your UPS (the easiest if we support it) or you can make your own cable,    Rate this link
      • Uninterruptible Power Supply (UPS) FAQ - This is a FAQ document on Uninterruptible Power Supplies. It is intended to provide a starting point for those people that want to find out what they are, what they do, and what's available. Most of this document is very US-centric. The power numbers, companies and services all emphasize US consumer needs.    Rate this link
      • Uninterruptable Power Supply with DSP - An uninterruptable power supply (UPS) system provides backup power supply for an application in the event of an electrical outage. Combining a microcontroller unit (MCU) and digital signal processor (DSP) in a single chip allows creation of a digital UPS offering higher performance at lower cost.    Rate this link
      • Uninterruptible Power Supply Types - Most people know that UPSes exist, but many seem to think that there is just one kind of device that goes by that name. In fact, there are several different major designs in use for UPS models. Those who sell these devices share much of the blame for this situation, because too often, the different kinds of UPS are all called the same, generic name.    Rate this link
      • UPS signaling cables plans - Here you can find plans for APC Simple Signalling Cable (Dumb) and Smart Signalling Cable. This document describes also APC PowerChute Pro and APC Smart UPS DB9 interface connector pinouts (relay outputs). Also many other UPS cable plans are shown.    Rate this link
      • Wiring for apc ups cables smart ups uninterruptible power supply    Rate this link

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