mppt vs pwm

jrnymn7 wrote:
RE; Panel Wiring and MPPT:

Correct me if I'm wrong,
(snip)
Assuming ideal conditions, and using two 140w panels with specs of 7.9a Imp, 17.7v Vmp, and 8.2 Isc, and using a Vabs Setpoint of 14.8v:
(snip)
If wired in series:

While in mppt mode, bulk charging at an average of say 14v, average current would be 20a (280w / 14v)... Same as with parallel wiring.

Just before switching to pwm mode, bulk charging current would be at 18.9a (280w/14.8v)... Same as with parallel wiring.

However, as it switches into pwm mode, current would drop to only 8.2a (1x Isc), and amps would taper from there. So if abs charging continued for any significant length of time, there would be significant losses.

Couple of things incorrect here.

Wired in series, the current from the panels would be 7.9A (Imp) but at 35.4 volts (Vmp*2) for a total power of 280 watts. When the Vabs setpoint is reached nothing dramatic happens. Assuming the battery acceptance rate has been intersected, the output voltage will be held at Vabs and the current will begin to taper as battery acceptance declines. If additional loads are added such that the output voltage sags below Vabs, the controller should revert to MPPT to attempt to satisfy the demand.

JiminDenver wrote:
A MPPT controller switches to PWM mode after float for two reasons. There is no longer the loss with the battery being at a higher voltage and the battery could not accept the additional current anyways. The extra current is still there, just not being used to charge with.

Not technically correct. Current only flows when something is creating a demand. It does not "lurk" in waiting. There is however more potential power available from the panel. (Not to be confused with potential meaning voltage difference).