# NiCD Charging with Solar Panel

Discussion in 'General Electronics Chat' started by BillM, Feb 9, 2009.

1. ### BillM Thread Starter New Member

Feb 9, 2009
6
0
Hello,

I'm seeing some odd results while attempting to charge 3xAA NiCD batteries with a solar panel (4.5V, 90MA) (realistically 4.3V, 40mA)

The short circuit current is measured around 40mA. This is about the trickle charge rate I was hoping for. When I connect it to my batteries, the current going to the batteries is only like 8mA and it decreases with time.

I'm assuming as the batteries gain charge their voltage is increasing. So if my panel is 4.0V and my batteries are 3.6V, the small .4V differential will reduce the current.

Should I increase my solar panels to 8V 40mA to make sure I always have a good voltage differential between my panels and my batteries to ensure a healthy charge (40mA)?

Thanks!

Bill

2. ### Audioguru New Member

Dec 20, 2007
9,411
896
Ni-Cad cells are obsolete and have been replaced by Ni-MH cells with 5 times more capacity.

A Ni-Cad or Ni-MH cell charges to 1.4V to 1.5V when fully charged so you are not fully charging yours.

Use a solar panel with a higher voltage, then you can add a series diode to stop the battery from discharging into the solar panel at night.

Last edited by a moderator: Feb 9, 2009
3. ### mik3 Senior Member

Feb 4, 2008
4,846
63
That is a quite large amount of current!!!!

90MA means 90 Mega Amps

It should be 90 mA.

4. ### BillM Thread Starter New Member

Feb 9, 2009
6
0
Hey, I got the realistically part correct I swear the box says 90MA

Ideally what constant voltage should a battery be charged at? 2.0v per cell? Or should I just be measuring the battery resistance and calculating my voltage based off my desired charge current?

I don't want to over charge my cells, but I'd like them to stay in the sun all day for a healthy daily charge. So maybe 2x(4.3v 30mA) panels?

Bill

5. ### HarveyH42 Active Member

Jul 22, 2007
425
5
Depends on where you live, and how you define a full sunny day... In Canada, you might need a couple of days to obtain a full charge (with some prayers...). Here in Florida, mine do fine pretty much year round, 'cept maybe during the hurricane season.

Solar yard lights seldom get a full charge in one day, and are discharged every night. You didn't mention your load or application, so if you aren't using the batteries, they'll continue to charge, and over charge (except in Canada).

6. ### italo New Member

Nov 20, 2005
205
1
You eventually will get the idea that is not the way to go solar panels and battery works fine for a while when brand new out of the box. Next year big expense again to replace the batteries. Consider this buy a phone wall transformer for \$5-10 and wire them LEDS in series parallel for as many LEDS that you desire . Never worry about the sun or needs for batteries. They just stay on and on. And since the wattage is very low run them forever and forget about them.

7. ### HarveyH42 Active Member

Jul 22, 2007
425
5
Not exactly true. I've got six yard lights more than 5 years old, never had to change a battery. Got a couple of spotlights, never really worked well (bad placement, cheap design), which I need to work on. Got 10 real cheap ones 2 years ago, plastic over the solar cell is cloudy, but they still work. Rechargeable batteries aren't that expensive anymore, under a \$1