Hello, I recently ran a test charging a 35aH AGM battery with two 12 watt solar panels connected in parallel. While the panels put out 750 - 800 mA at 20V open circuit (each) I only got about 700 mA charge current at about 12.8V on the battery (with both connected). Also the battery did not seem to charge very well. After two days (one very cloudy, the other very sunny) the battery only ran for about 20 minutes (at a 1.3 Amp load) before voltage dropped below 12V.
So my question: is the resistance of the large battery too much for the small panels to overcome and charge sufficiently? Would I be better off with a smaller battery?
Also, I assume that when the battery drops below 12V under load I should disconnect? (even though the voltage pops back to 12.8 once the load is disconnected).
This is going to run some security lights that I want to run for 5 hours every night, then for 5 minutes at a time after triggered by a motion sensor. I've read the articles at Battery University http://batteryuniversity.com/ but did not find info about battery size and resistance.
So my question: is the resistance of the large battery too much for the small panels to overcome and charge sufficiently? Would I be better off with a smaller battery?
Also, I assume that when the battery drops below 12V under load I should disconnect? (even though the voltage pops back to 12.8 once the load is disconnected).
This is going to run some security lights that I want to run for 5 hours every night, then for 5 minutes at a time after triggered by a motion sensor. I've read the articles at Battery University http://batteryuniversity.com/ but did not find info about battery size and resistance.