This is a quick way to build a cell phone battery booster while inside a Radio Shack or similar store. You may want to have one of these ready if you want to livestream or record an event, and don't have time to order a proper battery booster because the event starts in an hour or so. Build time is about five minutes.

The schematic is extremely simple: this is just a 1N400x diode in series with the batteries.

Cheapie wall-wart phone chargers output 5V nominal, but the actual voltage varies wildly, going as far high as six volts and usually stabilizing between 5 and 5.5 volts while under load. Cell phone manufacturers know this and design some tolerance into the phones.

A silicon diode drops around 0.7 volts (it's actually a curve: look up any datasheet) from the roughly 6V from the batteries, which brings us nicely where we want to be -- the little bit of extra voltage is handy in that it allows partially depleted batteries to still work with this circuit.

If you want to make a lot of these, here are suggested Digikey part numbers -- buy fifty and the cost of these chargers will end up being roughly $2.50 per. USB connector (watch your polarity!) this should let people use their existing phone cable Diode Battery holder for AA batteries Battery holder for D batteries Battery holder for C batteries

Page last modified on April 15, 2014, at 12:40 AM
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