mppt vs pwm

jrnymn7 wrote:
Grizzzman,

I was thinking more in terms of the controller protecting itself, like current limiting on a power supply unit or converter-charger. But now that I think about it, it's probably not a protection found on pwm controllers; although I've read here that some controllers do "clip" amps, but not sure if that only applies to upper end mppt controllers?

Most(all?) 12v PWM controllers do not clip the amps and "let through" whatever the panel is doing. The panel can exceed its ratings at times. The "rule" is to pick the "amps size" of your controller to have at least a 20% margin over the panel's rated Isc at STC. IE, for a total 25 amps of Isc you want a 30 amp controller.

The reason is at near max controller rated amps they get warm. Go over and they get hot. So there is a time factor how long over before they fry. ( A brief (5 or 10 minutes usually is max time for that) overage from "edge of cloud effect" is not enough time for it to fry. It would have to be a case of too much array.

So it is up to the PWM controller buyer to get a big enough controller for the array.

MPPT controllers (all or some, don't know) seem to clip their amps at the controller amps rating. From what I gathered during my buck converter gizmo education on here, that is probably due to the buck converter output limit? Vague on that. :( (PWM controllers have no buck converter)

Anyway, it seems an MPPT can run at max (even if clipped) amps without getting so hot it fries. This allows you to run a bigger amps array (watts/Vbatt) than the controller size so you get more amps most of the day and only miss out on some amps mid-day.

It just means if you have more array you get more amps (gee!)
But it allows you to do that with a mere $300 controller instead of getting a bigger $500 one that also will handle mid-day without clipping any. Somebody figured you got almost as many AH with the smaller size clipper and saved $200 or whatever on controller cost.