Connecting different sized panels

[matthew6]

Hi all,

Over the last year I have collected several different smallish solar panels of varying types.  I have a 30 watt solar concentrator panel which I bought very cheaply on ebay (hopefully it won't overheat in the NM sun...), a 10 watt panel, a 7 watt panel a 3 watt panel a couple of ~1 watts, and three glass panels, two rated at 2 watts I think, and I forget the other (but it's 12" square).  If I wanted to put all of these together in a hodge-podge array for 12 volt charging, could I?  What might I want to take into consideration in doing this?

I also have a side question, mostly out of curiosity:  How high can the voltage be above the battery voltage before it can harm the battery (assuming you weren't using a controller, but just checking it occasionally, as with a AA charger)?  Is it only the current that matters, or does the voltage need to be a within a certain range of the battery voltage?

Thanks.

[AbyssUnderground]

If you connect those panels in parallel you will be fine.

I believe there is no limit on the voltage into a battery until it comes up to almost fully charged where the voltage rises quickly, and if left in that state it would boil itself to death. However you don't get any extra power from using a higher voltage. For example if you series your panels you wont get any extra power, just more voltage (and you would also limit the current to that of the smallest panel). You'd need MPPT to get the extra power out of them in series (and they would need to be of the same wattage or again the smallest would limit them all).

19-21v is nominal for a 12v panel so stick with that and you'll be fine.

[fungus]

They should all work in parallel ok, just make sure there is a diode on each of them, otherwise on panels with different voltages, currents can flow into the others, lowering the output.