USB Power measurement

USB Power Meter – 5.12 v

It is really strange that a data-connector would manage to become a standard power plug, but USB achieved just that: most devices which can work or charge using 5 volts nowadays come with a USB connector. I think this is generally a good thing, one standards means less redundant incompatible hardware, and people don’t need to have N power adapters around. Of course there are compatibility issues, and we already have reached the point where determining the power draw of a device connected over USB is black magic: this can be determined by software nobody implements (original spec), or by putting some magic resistors between pins, with each manufacturer using his own secret sequences.

This leads to the second interesting question: how much power do these various devices use? I just bought a small device that is pretty useful to answer that question: a short USB plug that measures both the voltage and the power consumption on a USB connector. This device only gives you half of the story, how much power goes into the device, not how much was consumed by the power supply (which might be a computer, a printer, or a TV), it still gives some insights into the electrical power consumption of various gizmos – as a good charger typically has 75% efficiency.

For instance, a Qi wireless charger uses 0.04 Amperes when empty, that is 0.2 Watts for doing basically nothing. Charging my Fitbit Charge draws 0.03 Amperes out of my laptop (0.15 Watts). When docked and charged, my iPhone 5 consumes 0.3- 0.4 Amperes (1.5 – 2 Watts).

I’ll need to try more devices around the house. I also would like to measure how efficient the various chargers in the house are.

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