PV AAA-Battery Charger

System

Hi folks,
I recently obtained a couple of solar panels from friend of mine who works at a PV manufacturing plant.
The panels were discarded because of asthetic reasons (i.e wrinkles on the surface).  I soldered the two together, in series, with bypass diodes, and copper test leads.  I put it front of a 500 watt work lamp and tested it for voltage with my ancient, but trustworthy, Midland Multi-Meter.   I got a reading of 3.5VDC...I think.  I am rather new to electricity.  I was wondering:
1. How do I test for current?  (My brothers keep saying I should have known load in series with the multi-meter, but I don't fully understand why or how to do that)
2. Will knowing the current help me understand the wattage output?
3. Ultimately I'd like to make a AAA-battery charger out of this set up.  What other parts/components should I be looking into and trying to understand before I go any farther?
(I'm going to attempt to attach an image of what I put together so far...)

niel

Re: PV AAA-Battery Charger

i doubt you'll find a lamp even with 500 watts that will be sufficient to test the pvs. put them into the sun and measure the open circuit voltage. it would also be helpful if you ask your friend the working rating for voltage and current so you get a ballpark idea of how the ones you've obtained are doing. to test the short circuit current is to use the meter as the shorting load while measuring high current, but be carefull that the meter will handle the current. most dmms can go to about 10amps. again this is on a bright sunny day with the pvs aimed at the sun.

mike95490

Re: PV AAA-Battery Charger

With small pieces of cells or panels, it's hard to hurt much. You can easily overcharge ni-mh batteries, wihch will cause them to die an early death, and then you have to buy new ones.

For example - look at some solar power lawn / patio lights. The often have 2 or 3 AAA cells in them, and generate enough voltage and milliamps to charge the batteries for several hours of light each night.

With solar cells, each "cell" produces about .5 V Amps are set by the surface area - square inches. Most small cells produce 20-50 mA Large cells, like in solar panels, produce 500mA, and several are arranged in varried series and parallel configurations to get the desired voltage and amperage.

Measurements Say you have 1 amp of current , if you move the decimal place 3 places, you get the next value in mili-amps. 1 amp = 1,000 mA 1/2 amp = 500mA

Here is a chart that may help you some too:

System2

Re: PV AAA-Battery Charger

Thanks Niel and Mike,
I haven't seen that chart since I was a kid! These panels are about 11"x14" and I worried that that lamp would be inufficient due to the fact that it's probably all stacked up in the IR range. So I do want test for current in order to determine wattage. In talking with my brother last night, he mentioned I should test for current with one or more 5-10ohm (hi-watt) resistors in series. Make sense? I'll pick up a solar patio light, but I would really like to know what's going on: I understand simple circuits, but I have a feeling I'm going to come across something foreign in there. Are there any links out here that could show me the basic circuit that I'm looking to build? Inititally, something that would just dump current into a battery, but working towards a smarter circuit that would sense resistance to further charging and shutoff automatically.

mike95490

Re: PV AAA-Battery Charger

Compare the surface area of an 11x14 panel, (154") to the 2x2 panel (4in) in a garden light, and you will find your batteries will charge in half hour or less, you may even let the magic smoke out of them. It would charge them on a cloudy day though.

System2

Re: PV AAA-Battery Charger

Ah yes, i remember over-clocking my old Pentium chip until it emitted the magic smoke...