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Ask Dave: Will solar panels overcharge my batteries?

Answers to questions about RV Repair and Maintenance from RV expert Dave Solberg, author of the “RV Handbook” and the managing editor of the RV Repair Club. This column appears Monday through Saturday in the RV Travel and RV Daily Tips newsletters. (Sign up for an email reminder for each new issue if you do not already receive one.) Today Dave discusses solar panels.

Solar panels and batteries

Dear Dave,
With solar, can your battery overcharge? I have a battery disconnect. Should I use that rather than continuously charging when in storage in between trips? Thank you! —Thomas

Dear Thomas,
It depends on the size of the solar panel and if it has a charge controller. Many manufacturers are installing a small solar panel on the roof to maintain the batteries when the rig sits at the dealership. For years, units sat at RV manufacturers or dealerships without being plugged in. The batteries would drain down and the LP leak detectors would start “chirping.” It was quite a spectacle at a dealership as it sounded like crickets in a field at times.

These were just small 30- to 40-watt units that only produced a slight 13.2-volt maintenance charge. A lead-acid battery will not accept a charge below 13.6 volts if it is charged to 12.6 volts. So, as the coach battery voltage is drawn down by the LP leak detector, or just naturally, it would get “maintained” by the 13.2 volts from the solar panel. In this case, I would not disconnect the battery with the disconnect switch. These can also be used for AGM batteries.

If you have a large 100-watt or higher solar panel, it will produce a 13.6-volt or even higher 14.6 bulk charge to the battery. That can overcharge the battery and boil out the lead-acid if it does not have a charge controller.

Don’t go the cheap route on solar panels

Oftentimes, RV owners go the cheap route and purchase panels from discount tool and home improvement companies. Those can just throw a charge and will cause premature battery failure. You can use these IF you monitor the battery charge and disconnect when it hits 12.6 volts. This is not a solar panel you would want to use during storage.

The best scenario is to have a larger solar panel and a charge controller that provides a multi-stage charge. That is 14.6 volts in the bulk stage, to break up sulfation that coats the plates during discharge, then goes into a float and equalizing stage. This will extend the life of your batteries significantly. In this situation, I would let the solar panel do its job and leave the switch on. As with the trickle charge, these can be used with AGM batteries if the controller has an AGM mode.

Read more from Dave here

Dave Solberg worked at Winnebago for 15 years developing the dealer training program, as marketing manager, and conducting shows. As the owner of Passport Media Creations, Dave has developed several RV dealer training programs, the RV Safety Training program for The Recreation Vehicle Safety and Education Foundation, and the accredited RV Driving Safety program being conducted at rallies and shows around the country. Dave is a leading expert in the RV industry and author of the “RV Handbook” as well as the Managing Editor of the RV Repair Club.

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