Charge Controllers

Solar charge controllers sit between your panels and your battery. The controller takes whatever the panels are making, turns it into the right charging voltage, and stops when the battery is full.

Two kinds, and the choice is mostly about how much panel you have. PWM connects the array almost directly to the battery, so the panel gets pulled down to battery voltage and everything above that is lost. It is cheap, it is reliable, and on a small array the loss does not amount to much. MPPT converts rather than connects, so it takes the panel’s full voltage and turns the surplus into extra current. On a large array, and in cold or overcast weather, that difference is real money. We stock PWM from 10A to 45A and MPPT from 20A to 100A.

You size a controller on two numbers and most people only check one. The first is charge current, which is the array wattage divided by the battery voltage. 1000W of panel on a 24V bank is about 42A, so a 40A controller is already too small. The second is the array’s open circuit voltage, and that is the one that kills controllers. Panels put out more voltage when they are cold, so an array that measures comfortably under 100V on a warm afternoon can go over it on a frosty morning, and a controller rated at 100V is then dead. Our MPPTs run from 100V on the PROSTARs up to 250V on the Midnite Classic 250, and the Midnites carry HyperVOC headroom for exactly this.

The more array voltage a controller takes, the less current it puts out. That is the trade-off across the three Midnite Classics: the 150 gives 96A at 12V, the 250 gives 61A. Pick the one that fits the array you actually have rather than the biggest number on the page.

Wind and hydro need a different controller. A turbine cannot simply be disconnected when the battery is full, so the surplus has to go somewhere. The hybrid wind controllers here take a turbine and solar at the same time and come with a dump load. The Midnite Classics and the TriStar have wind and hydro modes as well.

If you are not sure, tell us the panel wattage, the panel open circuit voltage and the battery voltage, and we will tell you which one fits.