NIMH solar charging questions

Thread Starter

mbohuntr

Joined Apr 6, 2009
432
Morning, I bought a cheap solar panel (6V, 250mA) from radio shack to expieriment with as well as a lm317 and 25 ohm pot for limiting current. I quickly discovered (duh) that the max output for this panel never exceeds c/10 (250mA for 2500mA batteries) so the LM317 wasn't needed. My question is this, each cell is 1.2V, would putting 4 in series drop the current too much for the panel to be useful for one day charging because of the internal resistance?, and, if I put 2 in series, is the supply voltage harming the cells? should I pop in a couple of diodes to drop the voltage?

Thanks, Mike
 

Dodgydave

Joined Jun 22, 2012
10,095
You can put the batts in series and they will all charge at the same current, so that would give you 6v-4.8=1.2volts, if you charge at 200ma that would be a 6ohm resistor in series with the nicads.Or you can use the lm317 in series set it to 200ma constant current mode.
 
Last edited:

MrChips

Joined Oct 2, 2009
24,645
No need to drop the voltage. The batteries will charge as long as they can receive a surplus voltage. The only concern would be overcharging. You need a way to stop charging when the terminal voltage has been reached. This is where a voltage regulator comes in handy.
 

Thread Starter

mbohuntr

Joined Apr 6, 2009
432
Thanks guys, I tried dropping the voltage using the r1(220ohm) R2 (5k pot) configuration and got around 1.2V-4.7V. Problem was that the output current dropped to 40mA regardless of output voltage?? I was looking to charge a couple of D cells to power the wifes portable fan in the camper. The 12v model we use now burns up the camper batteries in about 4 nights, and these are 2 -27's in parallel! :eek: I was looking to charge a set during the day, and burn another set at night. 2 sets would allow me a day without sun and not hurt too bad.
 
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