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USB Charger TechEval
on July 7, 2010
Any time I purchase an item this inexpensive, I'm always apprehensive about connecting it to a considerably more expensive device and risk damaging the connected device.
Therefore I decided to evaluate this charger with a dummy-load. I measured the charging current draw of my old Sansa MP3 player, which was nominally 180ma. For USB, the charger should maintain nominal output voltage of 5VDC, under various loads. Here are the results of the evaluation.
Open-circuit (no load) output voltage: 5.15VDC
Output voltage with 10 ohm (10 watt) resistor: 4.83VDC (ripple less then 200mv, sawtooth waveform, 30KHz, nominal current draw 480ma).
I burned-in the device under continuous load for 24 hours; the re-measured output voltage showed no substantial change. Also, after the burn-in period, the 2.4 watt load draw did not result in a significant temperature rise felt in the charger itself.
Disclaimer: These results are for the single unit I evaluated, I make no claims that all, or any other chargers of this type will produce the same results. It's clear that I did not stress to unit to it's maximum stated capacity of 1000ma. Users should not assume that their USB devices will not exceed the current draw rating of the device, particularly when charging more then one device. I have done this evaluation for my own purposes; I have no connection with any of the sellers, or the manufacturer of this device.
UPDATE: I used the charger to successfully recharge the Sansa MP3 player without issue. Of course, at this point I can not speak to reliability over time, as I just started using the device. As a side point, the power pins of the unit I have appear to be very firmly attached; again this is the only unit I have at this point (three more on order), so I can not speak to quality-control as regards this USB charge in general. Reminder, care should be taken not to exceed the current ratings of the device, as this could result in over-heating the charger, which could in turn result in loosening of the power pins.