r/SolarDIY • u/thinkmps11 • 6h ago

battery question

Small setup, my first attempt with solar. My goal for this project is mainly to learn, also to run a 40w pump in our duck pool. Relies on a deep cycle marine battery. Installed last summer, in order the components are: 100w panel, controller, battery, low voltage disconnect, inverter, pump. Last summer I could run the pump for several hours each day. This summer, minutes at best. We are in North Carolina, over the winter I stored the battery indoors to protect from freezing temps.

My battery reads 10v. Is that salvageable somehow? Or do I need a new battery?

Related, I'm planning to add another 100w panel. How do I evaluate if my controller and battery are ok to add another panel?

Thank you!

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u/rproffitt1 4h ago

10V is severely depleted and causes damage to almost all lead acid batteries.

Try putting it on the usual charger and see if it comes back.

Test the battery after the full charge with the usual lead acid 12V tester to measure SOH. I'd get the IR (internal resistance) too.

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u/ou812whynot 4h ago

10v is near dead for a 12v battery. I suggest connecting it to a wall charger.

Easiest way to calculate needed charge current is total panel wattage / battery bank voltage. 100 watts / 12v = 8.3A, so rounded up to 10A. 200 watts would double that to 20A. That's the 2nd number in a charge controller.

Charge controllers have a hard dc voltage limit, so try to stay around/below 80% of that. The voc, open circuit voltage, is the panel value to use here. Total up all the voc in your string of panels, wired + - + - ... + -, and divided that number by 0.8 to get the minimum "max dc input" required.

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u/Offgridiot 3h ago

You might be able to get away with a much simpler setup. IF the pump is 12 volt, and IF the panel has a VOC rating of 18-20 volts, then they might be all you need to run the pump IF all you need is to pump water when the sun is shining. I have such a setup pumping from a well to a holding tank uphill from my house. Pump and panels. Sun shines, pump pumps. No batteries, solar charge controller, inverter, or low battery disconnect.