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
CA Traveler wrote:
BTW I've never understood or perhaps appreciated how a PWM controller can charge at Isc.
I've connected panel wires together to measure Isc. Great but guess what? Yup the voltage is 0V, so how does the battery get charged? Capacitance or inductive energy in the controller?
Semantics. The panel's IV curve they show on the panel's specs for 1000 thingies is at its Isc for the I at the lower voltage end. Sort of a coincidence.
So when you are at STC and Vbatt is under about 13.3v, you get the same I to the batts as the rated Isc of the panel. With less sunlight directly on the panel, when you measure the Isc with panel disconnected, and get an I less than rated Isc that is still the same I you get to the batteries at the lower voltage end. So it happens that you get the same I as Isc, but not that you can get the Isc ,as defined, with the panel connected.
The I on the IV curve does not taper much to the left of the knee at 15v, so you still get good amps all the way up.
So I have been saying Isc when I mean I, but I was wrong. It is all the fault of those people who draw the IV curves, with the top curve being for rated Isc, see?
So I want to get the same I as the 24v panel's Isc as my I to the battery, when keeping an eye on it.
