What Does a Solar Charge Controller Do?
A solar charge controller regulates the amount of voltage and current that is supplied to your batteries from your solar array. Connected between your solar array and your batteries, the controller ensures that the proper amount of voltage is applied to your batteries during charging. The controller should also reduce the voltage to a trickle charge (float voltage) when batteries are fully charged to prevent overcharging.
If you are using one or more solar panels to charge your batteries, you will need a quality charge controller with multi-stage charging capability. Victron, Renogy, Outback, Morningstar, and Blue Sky are all quality manufacturers of charge controllers.
Types of charge controllers
PWM controllers have been the standard for some time. They are less expensive and work well in situations where the solar panel output voltage matches the battery bank voltage (e.g. 12-18v solar array charging 12v battery bank). A PWM controller can also be used with higher voltage panels (20 volta and higher) as long as the voltage does not exceed the maximum input voltage of the controller. However, only a portion of the power from a high voltage solar array will pass through a PWM controller to your battery bank. So, if you have high voltage panels, an MPPT controller is recommended.
MPPT charge controllers operate more efficiently, can be used with higher voltage panels, and are able to convert unused voltage to higher amperage. MPPT controllers are also much more expensive. If your solar array outputs a higher voltage (20 volts and higher) you will need an MPPT controller to collect all of the power generated by your solar array. MPPT controllers also claim to provide an additional 20-30% boost in current compared to their PWM counterpart.
Do I need an MPPT charge controller?
If you are using high-voltage solar panels, then YES you will need an MPPT charge controller to convert the extra voltage to more current for your batteries. I have higher voltage panels on my RV and, therefore, needed an MPPT controller.
In this video, I demonstrate how my MPPT charge controller converts excess voltage to more charging amps.
If the output voltage of your solar array is closely matched to the circuit voltage of your battery bank (e.g. 12-18v solar array charging 12v battery bank), then you do not need and MPPT charge controller.
The operative word here is “need”. MPPT controllers also advertise an additional 20-30% of boost in charging current, but this comes at a price. While a good PWM controller may cost you $75 – $150, expect to pay $400 and up for a quality MPPT controller. The choice to go the MPPT route is yours to make. You must decide whether the MPPT benefit is worth the added expense.