A charge controller is basically a voltage and/or current regulator from the solar panels to keep batteries from overcharging. Most “12 volt” panels put out about 16 to 20 volts, so if there is no regulation the batteries will be damaged from overcharging. Batteries need voltage ranging from about 10.5 to 14.6 volts, depending on the state of charge of the battery, the type of battery, and temperature.
What is the difference between MPPT vs. PWM Charge Controller?
First off, according to multiple manufacturers, MPPT (Maximum Power Point Tracking) charge controllers “provide an additional 10‐15% of charging capability” compared to a standard PWM (Pulse Width Modulation) controller. This efficiency is particularly evident under cold conditions, a low battery charge, or with long wire runs. Our recommended Renogy DCC50S is an MPPT controller.
An MPPT controller must be used if your solar panels are at a different voltage than the battery. This would be the case when two 12V panels are wired in series, which adds up each panels’ output voltage to at total of at least 24V (or closer to 38V if producing peak power). A PWM controller could not down regulate this voltage to charge a 12V battery.
An exception to this is actually our recommended DCC50S MPPT controller, which cannot be used with solar panel voltage greater than 25V, so multiple panels would need to be wired in parallel so as to not increase their voltage.
If you want to know the ‘why’ and ‘how’ behind this MPPT efficiency like we did, read on! If not, we won’t hold it against you (but you may regret skipping this info if you ever run into system issues 🙂 ).
For example, let’s use the specifications from our preferred solar panel, the Renogy Flexible 160 watt panel, and battery, the 125 Amp-hour AGM battery by VMAX (yes, we’d choose a flexible instead of rigid panel. We explain it in our Guide to Choosing Solar Panels).
This 160 watt panel has an operating voltage of 19.1 volts and current of 8.4 amps (19.1V x 8.4A = 160W).
The current (amps) is what matters to your batteries, which receive 8.4 amps.
The battery is sitting at 12.5 volts, because it’s at about 60% state of charge (per VMAX’s chart). Those 8.4 amps are effectively charging only 105 watts (12.5V x 8.4A = 105W), a loss of 55 watts from what your panel was generating! That lost power just gets converted into heat.
An MPPT controller adjusts incoming voltage and amperage in real-time to minimize this lost current.