Originally Posted by mistersmith2017
Noelex...I haven't read anywhere about requiring MPPT for larger panels...just that I should make sure I have a controller that can handle the amps. In this case, a ProStar 30a should handle 300w just fine. Could you explains what you mean?
PWM controllers will only work (with a 12v battery) with panels that have 36 cells. These panels have a Vmp of around 18v.
There are lots of panels like this. Most (not all) panels below about 130w conform to these specs and have 36cells.
However larger panels are more commonly (not always) higher voltage panels, with more than 36 cells and Vmp in the 30v+ range.
(For the technically minded this is because large solar cells are difficult to make, therefore to increase the wattage in large panels, more, smaller cells are added to the panel. This increases the voltage not the current)
For these panels to work in a 12v system the voltage needs to be converted to lower voltage.
Only MPPT controllers do this.
With 36 cell panels you can use a PWM controller, or a MPPT controller. Higher voltage panels can only use a MPPT controller otherwise the output is very poor(and sometimes the controller is damaged).