Maker Pro
Maker Pro

Useful Power from A Single Solar Cell


Steve Cothran

Jan 1, 1970
"Electronic Design" magazine publishes some gems sometimes. Here is a
boost circuit that will start up at about .25 volt and supply 8-10V
(open circuit) from a single solar cell. It cost about 5 bucks to

It's also useful for sucking about every last ounce of energy from a
standard battery. Most multivibrators quit at ~.8V and this one just
keeps on goin' down to about .25-.27V.

I built the circuit and tested it. I didn't have the exact inductors
in stock here, so I used some 44uh units. Some observations:

It seems to charge two nicads in series, although slowly. Don't exceed
2.0V input, this destroys the transistors. For a light load circuit
this thing is neat. The solar cell I had is about .6V @50mA.

After I'm done fiddling with it, I'll find out when it complains,
current-wise, short it under power and otherwise stress it and see
what happens. I only have 4 of the germanium tranisistors here so I
have to make them count.


Jan 1, 1970
One of my round tuit projects is to equip my generator with some piles to see if I
can use waste heat to generate some more electricity in enough quantity to make it
worthwhile. One of the tuits I need is a source of cheap piles.

The conversion efficiency of peltier modules is next to hopeless.

But in the homepower world there is no such thing as waste heat.
Either dump it into a hot water tank or, if you have too much hot
water, drive an absorption refrigerator. Running generators, even on
waste oil and not grabbing the last bit of energy from them isn't IMHO
very green.