USB Power Current Voltage Tester

How could I measure the normal power consumption of my USB gadgets? How can I measure how much current a smart phone charging takes from USB port? A special built USB measurement adapter for multimeter or USB current/voltage meter can answer to to those questions (and sometimes you get some information from device manager USB hub information). There are DIY plans for this, but this time I chose to get a cheap (around $6) ready made product for this: USB-AV USB Power Current Voltage Tester – Translucent Blue + Silver

USB-AV USB Power Current Voltage Tester – Translucent Blue + Silver is an easy tool to measure USB voltage and current. You just plug it between your power source (USB charger or PC) and the device to be measured. The device passes all current and data signals through, and at the same time shows current and voltage reading. The device has one display, so it alternates between different displays automatically (shows each measurement around 4-5 seconds and switches to other display). The device is easy to use and does what it promises to do pretty well. Very easy to use. Just plug-in and use. The product does not affect USB operation, so I can measure current from any USB device.

The measurement ranges measure well normal USB voltages and currents, and also quite well outside normal operation. The voltage measurement range is 3~7.5V and current range is 0~2.5A. So this device can show which USB power supplies that are out of spec and which power supplies will deliver their rated current still keeping voltage stable.

The USB 1.x and 2.0 specifications provide a 5 V supply on a single wire to power connected USB devices. The specification provides for no more than 5.25 V and no less than 4.75 V (5 V±5%) between the positive and negative bus power lines. For USB 3.0, the voltage supplied by low-powered hub ports is 4.45–5.25 V.

In the USB 1.0 and 2.0 specs, a standard downstream port is capable of delivering up to 500mA (0.5A); in USB 3.0, it moves up to 900mA (0.9A). The charging downstream and dedicated charging ports provide up to 1500mA (1.5A). Car chargers can output anything from 1A to 2.1A.

I tested the measurement accuracy. The voltage readings matched very well with the readings I got with multimeter. I actually measured the voltage with two multimeters, and the reading I got with this USB meter were between the numbers I got with them. So I could believe that promised +/- 1% accuracy. The typical voltages I got were around 5.06-5.08V on my computer USB ports, and around 4.8-4.9V on the ports on the USB hub I had.

The current seemed to do pretty well at higher current levels, but the current measurements does not seem to be very accurate at low current levels. The current display constantly shows 10-15 mA less than the real current that flows through. This means that I get no reading on the display until the current to device reaches around 20 mA, which somewhat limits measuring the low power devices. The current measuring error seems to be pretty much same 10-15mA on higher currents, so when measuring current it does not matter there that much. I can’t get that less than 2% error that manufacturer claims in any other than at maximum current the device can measure.

The device seems to be using shunt resistance to measure current. That shunt resistor should be pretty small in resistance, because I could not accurately measure it with multimeter though the connectors. When looking at the circuit board the biggest resistor seems to be marked with code R050. Discussion on this product notes the internal current shunt resistance is 0.05 ohm, and thus the voltage drop at 2.5A is 0.125V.

Other con is related to shape of the device, especially how the connectors are located. You can’t use that everywhere because plug is located on the edge. Fortunately a short USB extension cable it can solve that when it becomes problem.

With this device I can easily see the charging current to the tablet, phone or any USB device. Simple, cheap and functional.


  1. Tomi Engdahl says:

    On thing on this product that later annoyed me in lab testing was that the product all the time alternated between voltage and current display.

    DX seems to have a newer model with LCD display and switch to control what the display shows (current or voltage). I have no tested but could be worth to check out:

    USB Terminal Power Adapter Voltage Current Tester – Grey + Black

  2. Tomi Engdahl says:

    A little meter that shows the big differences in charging plugs and cables
    The Practical Meter shows you the nerdy truth about which USB thing charges which USB thing faster.

    The brilliant thing about the Age of Almost-Universal USB Power (AAUUP) is you can get power from almost anywhere: a laptop, a wall plug, a portable battery backup, your car, maybe your bike—anywhere there’s a little rectangular slot and a cable.

    The tough thing about the AAUUP is that you are not aware of just exactly how much power is passing through to your phone or other device. Would you be better off charging through your laptop, right in front of you, or is it worth plugging directly into an AC plug?

    Power nerds (and I am certainly one of them), take heart: the Practical Meter has arrived, fresh off a successful Kickstarter campaign (“successful” as in 16 times their goal). It works, and it will surprise you with just how different your myriad charging options can be.

    Why isn’t one USB just like another? The short version is that different device makers stick to different standards, and that gadgets sometimes ship with the cheapest cord or wall charger that will work for that particular device.

  3. Tom Henry says:

    I found this much better quality for USB Power Meter – AboveTEK’s low cost LED based USB voltage and current meter from amazon website:–Multimeter-showing/dp/B00HTAH3KY/ie=UTF8?m=A37ZOD60SUJEE6&keywords=usb+power+meter

    Same function and feature but less than 10 bucks!

  4. Tomi Engdahl says:

    It seems that has pretty similar looking USB meter (same or slightly different?) on sale now

  5. Tomi Engdahl says:

    Legion Meter nearly doubles smartphone, tablet charge rate

    The Legion Meter is their latest gadget to hit Kickstarter, and it has already smashed all the company’s previous records for success.

    The Legion Meter features USB connectivity and a built-in OLED display to provide instantaneous information. Since this device is a miniature multimeter, users can view the current delivery of watts, volts, amps, and milliwatt-hours. Not all cables, USB ports, and wall adapters are created equally. Although a product may list an input of 5V/1A, it rarely (if ever) draws that maximum amount. The Legion Meter helps you separate the wheat from the chaff.

    On top of that, the Legion Meter has a charge accelerator, which is good for Apple and Android devices. Selecting this mode allows the USB port to safely draw the maximum amount of power.

  6. Tomi Engdahl says:

    Legion Meter – Charge your smartphone 92% faster

    A USB multimeter with integrated OLED display designed to accelerate your smartphone or tablet’s charge speed up to 92% faster.

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  8. Tomi Engdahl says:

    USB Charger Doctor Review

    The USB Charger Doctor is a small device that goes in series with your usb cable to measure the devices voltage and current consumption. It can be purchased for around $3 overseas on eBay or $4-5 on eBay from a retailer that has already imported the unit.

  9. Tomi Engdahl says:

    Hackaday Prize Entry: Smart USB Hub And IoT Power Meter

    [Aleksejs Mirnijs] needed a tool to accurately measure the power consumption of his Raspberry Pi and Arduino projects, which is an important parameter for dimensioning adequate power supplies and battery packs. Since most SBC projects require a USB hub anyway, he designed a smart, WiFi-enabled 4-port USB hub that is also a power meter – his entry for this year’s Hackaday Prize.

    Smart USB/4 port hub/Power meter with LCD
    Need power up your’s USB devices and monitor consumption? Yes!

    6 port USB power meter with 2.2″ LCD display will monitor every USB port and show real time used current (A) and power (W) maesuring up to 3AMPS and batterys charging (mAh).

    With added 4xUSB 2.0 hub to it you can use it with your’s Raspberry Pi or PC for connecting external USB flash or HDD, Wi-Fi or Bluetooth dongles and others devices, like USB port extension and USB PSU/charger. It will help you to project any USB device and control it’s consumption.


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