NiCd solar charger

[HarveyH42]

I want to charge 6 AA Nicd batteries in series (9 volts more or less...), and have a 12volt 80 mA solar panel. Do I need to do much more than add a diode to prevent discharge through the panel at night? Will the batteries tolerate the extra voltage?

 

[Nigel Goodwin]

NiCd's are charged by current, NOT voltage, as long as it's more than 9V, and suitably current limited, then it's fine. A solar panel has only very low current capacity and will be no problem.

 

[HarveyH42]

Cool, just what I was hoping for. What about over charging? This is in Florida, and it's wildfire season (for a couple more months anyway, then huricane season begins...). Plenty of sun, little cloud cover...

Nicads don't really explode, in the sense of a violent fireball, right? More like when the guts come flying out of a capacitor? I would want to touch off a fire here in town, it's been very dry this year.

 

[Nigel Goodwin]

Cool, just what I was hoping for. What about over charging? This is in Florida, and it's wildfire season (for a couple more months anyway, then huricane season begins...). Plenty of sun, little cloud cover...

I suggest you try measuring the current the panel provides to the NiCd's, I can't see as it's a problem at all - the spec on the panel is only 80mA, and even Florida probably isn't sunny enough to provide that very often?, or for many minutes?.

AA NiCd's are usually 800mAH or higher, and you can trickle charge them at 1/10th (that is 80mA) permanently - considering half the time it's going to be dark, there's no chance of over charging.

However, I would be very interested to hear what readings you get when charging in bright sunlight - just stick a multimeter on current range between the panel and batteries.

 

[HarveyH42]

well, found the 9 volt battery pack wouldn't hold a charge overnight. Removed the plastic wrap, found a bad cell (leaked), some of the others looked bad, so trashed it all. Hooked up a different one, but only charges to 8 volts. I've had it flashing 4 red LEDs for a few hours. Haven't done anything more with it (too much overtime last week) . Guess I'll go buy a 9.6 battery pack for an R/C car someplace.
Wonder how hard it would be to simulate a flame with LEDs? The red LEDs I was playing with really put off some light, thought it would make a nice effect using some pulsating yellow and amber LEDs, just no idea how to pulse them slowly. Anyway got enough going on, maybe something to play with another time.