Solar Panel "Battery Maintainer" Project Ideas

[G7PSK]

That black device is the reverse protection diode the led is totally parasitic and is just there to look pretty, it is across the output and just uses up half the power the unit produces in most conditions, to produce full rated power I would think that the cell needs to be under the noon sun on the equator.

[Kevin.D]

These crappy  amorphous? panels are on sale for a very good reason .They are totally
inadequate for keeping a car battery topped up  .I bought exactly the same one about 5 years ago .
They only provide about 30 mA in full sun at my latitude (I am in Uk ,  are you in Canada. ? You will get prolly get about 25 mA full summer sun there ).
The self discharge rate of a 50 Ah lead acid car battery  is prolly about 25 mA
then on top of that theres the cars standby current consumption of things like  clock and car alarm which for my car was about 30 ma .
So you can see just to keep a car battery the same will need  50 mA constant charge .
I bought one of these 5W monocrystalline ones http://www.ebay.co.uk/itm/5-W-Monocrystalline-Solar-Panel-5-Watts-12V-PV-/200753595685?pt=UK_Gadgets&hash=item2ebdd8c525
They are about the same area and produce about 3-4 times the output .I get 90 -120 mA in full sun, and about 70 mA on cloudy day.

Treat manufacturer's power output rating's on solar panel only as a very very rough guidance ,as they are quoted at  very high sun incidence (midday at the equator with cooled panels) .You never get anywhere near these outputs in real life .

[edy]

Hey folks... An update!

I disconnected the LED/diode and connected 1 panel directly to my 12 V car-USB-charger (pictured in a previous post on this thread) in FULL SUNLIGHT, and this time the GREEN LED on the 12V car-USB-charger actually LIT UP! Progress! So I plugged in an iPod Nano. The display on the iPod Nano showed the little "battery icon lightning" symbol showing it was charging!

As soon as a I covered up some of the panel in shadow, the iPod battery indicator "lightning bolt" disappeared. When I took my hand away and full sunlight on it again, the lightning symbol came back!

Now I don't know if the panel is putting out enough juice, but the iPod seems to think so and it is not complaining (by saying "source insufficient to charge this device") or whatever. I have to try it with my Blackberry phone next to see, as it requires about 700mA charger. The iPod nano (version 1) 2gb is really old, maybe it requires very little mA charging. Not sure. Either that or it doesn't detect a minimal mA and doesn't display any warning.

I plan on hooking up my other panel in parallel to hopefully increase the current. I returned the other 2 panels (I bought 4 originally) because I thought it was a lost cause... But maybe there is still some hope!? Still, at $11.99 a pop I don't think I want to invest any more money in this fun little project.... Rather put it into a real panel that does the job.

Looking forward on reporting my results once I solder everything up and test the charging capability.

[edy]

I finally tore apart the panels and got rid of the blinking LED circuit. I hooked up one of my panels and read about 10V coming off. The other panel, in the exact same position from the light (an overhead incadescent 60 watt) was reading 2 Volts !  Why such a huge difference?

One panel was showing 10 V reading while the other 2 V, same distance from the light. When I brought the 10V panel closer to the light the voltage went up to close to 20V. When I brought the 2V panel closer to the light the voltage also went up, maybe to about 9 or 10 V. I am sure in direct sunlight they will both be up close to 20V, however I am surprised by the difference at the lower light levels.

Also one of the wires attached to the back of the panel fell off, I noticed it was soldered with a "blob" to the back of the panel. Didn't look like it was connected to anything, just splatted against the back of the glass on the panel. Perhaps I am not bridging to the proper layer or the solar panel it is shorting itself somewhere.

Anyone have any ideas?

The back of the panel has a black film which looks to be glued down. When I peel it off, and then rub away the glue layer, I see a silvery finish. If I rub this with sandpaper or scratch it nicely it will go right through to the glass and I can see right through. So I assume the silver finish is the amorphous silicon layer on the glass which is what I need to solder to.

I don't think it is my solder job, since I tried the voltmeter probe directly without solder to many other places on the back of the panel and got the same readings. If it was my connection or the layer I was connecting to, I assume it would have changed the voltage reading as I moved my probe around on the back. It was always the same.

So could there be a "short" in my panel causing this?

One more question, what are the lines visible when looking at the solar panel? There are no obvious wires there, it looks like it is just a gap in the silvery part... because when I peeled back the black backing layer from my panel and looked through, the lines correspond to the areas I could see through the glass clearly, whereas the other part of the panels still looked dark (I assume due to the silvery film and silicon layer stuck on the back of the glass).