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Why do my batteries charge well with 1 panel but not with 3?


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I have 2 x 12v batteries connected in Parallel, 1000w inverter, 40amp charge controller and 3 x 150w panels. When the 3 panels connected (in series), the controller reached absorbtion quickly and then goes into float mode (controller shows 0amps coming in). When sun goes down batteries at 12.2v. When i only connect 1 panel. Charges slower, goes into absorbtion mode shows amp trickling in. When sun goes down batteries at 12.8v. Why? 

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Three panels in series is probably way too much voltage for the solar charge controller (the thing that charges the battery). So the charger is probably turning itself off to protect itself from over-voltage for most of the day, and your battery is under charged.

Add the Voc specification for your panels and compare it with the maximum PV voltage that your inverter can handle. You can probably find this information on the back of your panels and the side of your inverter. 

And as gooseberry said, IF your charge controller is the PWM type as opposed to the MPPT type, then you have to wire your panels in parallel, not series. 

Edited by Coulomb
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