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The panel puts out 7.8v in direct sun with the sun very low in the sky. I need to check at noon, but I won't be home again until next weekend.
The panel fed directly into the batteries in series. No circuitry at all. The nicad batteries are 1.2v each. I think they terminate around 1.33v. 5.32v.
I have no idea the miliamps the panel can put out. Do I measure in series with a battery charging?
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Batman, all you need to do is look at the shorted loading current with your DC milliammeter set to say 1 amp.
That will give you a very good IDEA what the panel can output.
Once you have that number, you can take a pilot lamp or go to Radio Shack and get an asst of 1/2 watt resistors. And some cheap test clip leads...
Use a value of about 200 ohms across the panel and measure the current into the resistors and the voltage across them, in two steps, to make juggling all the wires a bit easier.
What you want to do is load the panel until the open [no load] voltage gets dropped about say, 20%.
For examp, if the open ckt is 7.8 vdc, then keep loading it in steps with sufficient resistance to bring it to 6 vdc or thereabouts.
Next put your ammeter in series with the resistance and panel and measure the current.
Multiply them together and you will have the wattage. Easy!
I like to use different panel lamps for the load, like say a number 47 lamp.
They're cheap at R-S and make a nice resistance to load some panels to. The voltage and current are usually on the lamp packaging/card.
If you try to measure the power output of the panel with batteries, etc, in the circuit, all you do is make the measurement more complicated and introduce possible -likely- error.
ETA A #47 pilot lamp is rated at 150 ma [.15 amps] at 6.3 volts.
It might make a perfect load for your panel.