Shadowmite.com Blog

So in continuing my new line of robotics hobby work I believe I’ve chosen a power source and charging method etc for the HWBY robot. At first I started looking at http://talkingelectronics.com/projects/SolarCharger/SolarCharger.html
which goes into detail about a pretty decent method of charging a battery with solar cells that don’t output at the same voltage level by using a pulsed high voltage spike at very low current. However this method is horridly ineffective and looses a lot of the power. Dealing with a already low power source we want as much effectiveness as possible.

Since I want to use a Li-ion battery for weight as well as size and have choosen to use 7.2v motors I will need 2 cells in series at least. Since Li-ion is a little on the dangerous side I also need to make sure I have some kind of regulation and cut-off safegaurds. As such I have decided on a 4400mah pack at http://www.batteryjunction.com/tenergy-74-4400-pcb.html which also happens to include these safeguards built in! This means we can safely just pump in 10% of the mah of the battery which would be a solar panel at about 440ma output in bright light. This brings me to this solar panel at eBay (link will expire after a while, sorry, I’ll describe the panel) which gives:

Monocrystalline Silicon  convert efficiency: > 15%

Size:  165 x 152 mm  ( 6.5 x 5.98 inch )

DC output:  7.5V   450mA    3.4 W

7.5V solar cell joined with a 1N5817 Schottky diode (Voltage drops 0.2-0.3 V), the voltage will hit 7.1-7.3V.

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