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.