12v MPPT and 24v MPPT vs 24v PWM Test
Got a chance to try out comparing amps to the battery using MPPT vs PWM on a 24v battery bank and comparing those with the usual MPPT on 12v with my 230w panel. The bank is four 6s, so it was easy ...
Forum Discussion
jrnymn7 wrote:
As I understand it,
1) Voc is always > Vmp. I can see low light conditions causing Vmp to approach Voc. However, at no time can an mppt controller charge, using Voc; as that would reduce current down to zero amps.
2) PWM controllers use Voc; which is maximum panel voltage at that moment, in those particular conditions. And provided it meets Kirchoff's voltage law, charging will commence.
PWM controllers let the battery voltage to the panel so panel voltage is battery voltage (and line loss). The IV curve for that panel at that insolation then determines the amps you get at that battery voltage. (The V in the IV is battery voltage)
With PWM it is no use thinking of a spread between panel and battery voltages for figuring how many amps you can get. (It is there, but not seen, so just use the IV curve which takes care of that)
With MPPT in MPPT mode, the controller sets the panel voltage at Vmp so you get whatever watts the panel is at divided by Vmp and that is the Imp, which is a fairly useless number, because it is not the amps to the battery, just the amps to the controller.
Amps to the battery with MPPT is whatever it comes out to be when you divide the output watts from the controller by battery voltage. Lower Vbatt, more amps. Higher Vbatt, fewer amps.
