Engineering Question if you please.

MovieMaker

OK, if I have six 1.2 volt DC batteries that are alkaline rechargebles and they are 350mha batteries and I wish to charge them with two 4.5 volt solar cells.

Can i place a simple diode making the current go in only one direction and allow the voltage to be hooked in parallel ? I have done a google search for how to build a rechargeble battery charger from solar cells. But, I have found nothing useful.

Any real engineers or amateurs want to tackle this?

Mike Green

If they are true alkaline rechargables, you may need a special charger. I don't believe they're designed for use with simple chargers.

If you're using standard NiCd or NiMH batteries, these are designed to be charged indefinitely at a 10% rate. If they're 350 mAh cells, you can charge them at 35mA without any special care. Two 4.5V solar cells is probably not enough. Your battery's rating is 1.2V, and 6 in series would require 7.2V. Add a diode drop (0.7V) and you get 7.9V. The batteries probably have a terminal voltage higher than 1.2V near full charge, say 1.5V. Your solar panels would probably reach 4.5V only near full mid-day light levels in direct sunlight. I suspect you'll need 3 x 4.5V solar panels with some kind of current regulator like an LM7805 as described in most LM78xx datasheets.

MovieMaker

Thanks Again Mike. You are always so helpful. This gets me started in the right direction. I actually have four 4.5 volt cells. I figured two for each boebot.


I was wrong. They are NiMH batteries.

Post Edited (MovieMaker) : 12/27/2008 4:14:27 PM GMT