mppt vs pwm
Hi, A nice little video comparing mppt vs pwm with the batteries in bulk mode. mppt vs pwm
Forum Discussion
Salvo: You seem to be missing the distinction between output/battery voltage and panel voltage.
Apparently a pwm controller applies the battery voltage to the panels during float or absorb. But the MPPT controller does not. It maintains a constant battery voltage (or tries to) by adjusting the panel voltage. Here's quote from earlier in this thread where the panel voltage decreases as needed to the MPP voltage:
The Rogue manual has a graph showing panel voltages during the day, including during Absorb and Float. It shows the same behaviour described above. The panel voltage drops with panel power output rising to maintain the battery at the Float voltage.
It's easier to understand when you have the graphs in front of you.
http://www.roguepowertech.com/documents.htm
Apparently a pwm controller applies the battery voltage to the panels during float or absorb. But the MPPT controller does not. It maintains a constant battery voltage (or tries to) by adjusting the panel voltage. Here's quote from earlier in this thread where the panel voltage decreases as needed to the MPP voltage:
... slowly added loads while in float. As demand increased, PV voltage decreased. At about 17 amps (still only 2 going to the batteries), the controller gave up and switched back to MPPT to supply the demand.
The Rogue manual has a graph showing panel voltages during the day, including during Absorb and Float. It shows the same behaviour described above. The panel voltage drops with panel power output rising to maintain the battery at the Float voltage.
It's easier to understand when you have the graphs in front of you.
http://www.roguepowertech.com/documents.htm
Salvo wrote:
That's the description to search for the maximum power point. In order to do a complete search, the controller needs to do a sweep. There may be several peaks and valleys in the I-V curve. The first peak that the controller finds may not be the larges peak (meaning it's not at the maximum power point). Hence the sweep.
However, this has no relevance when the controller is in absorption mode. The controller doesn't care about the maximum power point. It outputs a constant voltage.brulaz wrote:jrnymn7 wrote:
...
So, is the "mppt-capable" controller still doing something the pwm cannot do? IOW, Can the pwm raise or lower panel voltage to accommodate for variances in lighting, or just for variances in Vbatt?
dunno about pwm controllers.
But JiminDenver's quote about MPPT controllers pretty much agrees with Rogue's manual. Rogue talks about occasionally doing a "sweep" of the panels (guess that means changing the voltage and seeing what happens), especially when changing modes. And it the frequency of "sweeps" can be adjusted.
But it also "dynamically" checks panel output as well without a sweep. Much of this is probably proprietary, but my guess is that in MPPT mode is constantly trying adjacent voltages to see if the current output increases.
