An RV solar charge controller is necessary to regulate the voltage produced by solar panels in order to properly charge your batteries. The controller also prevents current from flowing back out of the batteries and into the solar panels at night.
In this article I'll go over the specifications and features you should look for when choosing a solar charge controller.
The amp rating is the maximum amperage output to the batteries. If the RV solar charge controller is rated at 10 amps and you have two 100 watt solar panels with a peak power of 6 amps each, the controller would not be a good match. Your panels would produce 12 amps total, however the controller would only output 10 amps to your batteries. 2 amps would be wasted.
Choose a solar charge controller with a rating 25% higher than the total peak power (in amps) of your solar panel array. There are times when your solar panels will actually produce more than their rated output and having 25% more charging capability will take advantage of those situations. You will also want to take into account any additional RV solar panels you plan to add later.
An RV solar charge controller with multistage charging and pulse width modulation (PWM) is recommended. Avoid a shunt controller, single-stage controller, or dual-stage controller. With these current is tapered off as the battery becomes charged.
PWM does not taper off the current, but provides your batteries the full amount of current in pulses. The benefits of this type of charge controller are:
This is a must-have feature as it prevents your batteries from being overcharged or undercharged. It automatically adjusts the charging set point depending on the battery temperature in order to prevent excess water loss and plate sulfation. Both of which are bad for your batteries.
MPPT can increase the power output of your RV solar panels and boost the charging current to your batteries. You will see the biggest boost when your solar panels are cool and the battery voltage is very low. This feature can improve charging performance and shorten the time needed to recharge your batteries.
With this feature you can adjust the charging voltage set point to suit the battery type you have, whether it be flooded lead-acid, gel, or AGM. Consult the battery manufacturer for the proper charging voltage.
Having an on/off switch is handy as it enables you to shut down the RV solar charge controller and stop charging without having to remove the fuse at the battery.
This switch allows you to change the battery charge set point from maximum power, which is best for RV boondocking, to stand-by mode, which is best when plugged into shore power. Switching to shore power mode is also a good way to maintain your batteries while your RV is in storage.
Learn all about RV solar panels, tilting your solar panels for maximum power output, and portable solar panels so small they fit in a backpack. It's all here...