Charge controller for RV?

Hello, I've recently inherited a Class A RV with a pair of small PV panels mounted towards the front of the roof. I can't find any literature on the panels nor any specs printed on the panels themselves so I have no idea of their output. I do know they were installed well after the RV was purchased.

The RV sat in outside storage for several years before I got a hold of it and I've replaced the standard 2 - 6v battery bank with flooded deep cycle golf cart batts. Since replacing, I've kept an eye on their water level and it's needed to be topped up every few weeks. Question is, should there be a charge controller added to the system? If so, which is recommended? The RV is very rarely used and my small inverter plugged into a 12v outlet shows a max. voltage of 15.2 volts at the peak of a sunny day.

Thanks for your help!


  • BB.
    BB. Super Moderators, Administrators Posts: 33,479 admin
    Re: Charge controller for RV?

    If you have a reasonably accurate VOM/DVM--First disconnect the solar panels (or disconnect at least one lead).

    Measure the open circuit voltage--no load (and give us the cell or ambient temperature). Hopefully the voltage will be round 21 volts or above. Vmp~=0.8*Voc...

    Next, measure the short circuit current (set the meter to 10 amp scale and short one panel at a time). The Imp~=0.9*Isc for the panels.

    You probably want to get a small controller for these panels... You are essentially equalizing the batteries every sunny day instead of usually recommended once or twice per month. Mostly you are just boiling out excess water (more maintenance and some loss of acid).

    Also, not all solar panels have a blocking diode and can leak current from the battery when it is dark out (charge controller will block leakage current too).

    Once you have the ratings of the panels, you can get an appropriate sized controller--and you want a multi-stage controller that has a separate "float" charge setting (lower voltage setting that does not charge the battery--but keeps it at 100% charge for long term storage).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset