mppt vs pwm

jrnymn7 wrote:
What about the test on the LFP batteries? How were the 12v panels wired?

If in series, wouldn't that be completely biased in favour of mppt? And if in parallel, wouldn't it be biased in favour of pwm?

It was a single panel wired to each controller.

BFL13 wrote:
Well somebody please nip out there and measure panel voltage during Absorb/Float while running a load that puts amps above array total Isc.

It is easy to do. Just put the meter across the pos and neg controller input terminals or do it out at the panel. Nothing disconnected of course.

My Vmp is 30v so when I check for that when MPPT is on I get 29.3 at panel and 29 at controller. So I have a 1% line loss there. YMMV. Trouble is I never took the voltage later on after it dropped out of MPPT. Can't check again till after mid-April.

So somebody here must be on MPPT solar now that can help out! :)

D

Someone down in Quartzsite, AZ.

Well somebody please nip out there and measure panel voltage during Absorb/Float while running a load that puts amps above array total Isc.

It is easy to do. Just put the meter across the pos and neg controller input terminals or do it out at the panel. Nothing disconnected of course.

My Vmp is 30v so when I check for that when MPPT is on I get 29.3 at panel and 29 at controller. So I have a 1% line loss there. YMMV. Trouble is I never took the voltage later on after it dropped out of MPPT. Can't check again till after mid-April.

So somebody here must be on MPPT solar now that can help out! :)

D

BFL13 wrote:

...
The MPPT, which is not "on" in Absorb and Float, ensures that the best panel voltage is chosen as buck converter input, but only during Bulk. So what panel voltage is in effect during Absorb and Float instead of Vmp?

It can't be just battery voltage as with 12v PWM controllers, because you get more than Isc when running loads in Absorb and Float.

If you download the Rogue 3048 manual and look at figure 5.2.1, the top line shows the PV array voltage as the controller goes through MPPT to ABSORB to FLOAT.

There are annotations like "PV voltage rises, PV power drops to maintain absorb voltage" and "PV voltage drops, PV power rises to maintain float voltage". IOW, it maintains the float and absorb setpoint battery voltages by adjusting the PV voltage. Whereas in MPPT mode it adjusts the PV voltage for max power.

All I know is when I crank up the loads I can see close to the same amps in float as I do in bulk. Not a shock load like the micro that will instantly pull down the battery but rather slowly adding loads. Even if I add one too many I can see the amps climb until the voltage starts to fall. Right before that point I see 16a+ with each panel. Then again I run 2-1 watts to Ah and float is a very early thing for us. I usually pull the extra panel off the inverter bank once it hits float unless we are going to do a long run of the microwave or air conditioner.

"... That's why I can pull the same amps in float as I do in MPPT. "

Not so sure about that! Yes you do get more amps than panel Isc which shows that the buck converter is working. But do you get as many as if panel voltage were at Vmp?

The MPPT, which is not "on" in Absorb and Float, ensures that the best panel voltage is chosen as buck converter input, but only during Bulk. So what panel voltage is in effect during Absorb and Float instead of Vmp?

It can't be just battery voltage as with 12v PWM controllers, because you get more than Isc when running loads in Absorb and Float.

Salvo wrote:
On the contrary, there's no need for his behavior. Is he so desperate that he has to put a 34Vmp panel to a 12V pwm system to show substantial mppt gains?

You never think you just might be bit out of line sometimes?

There is always power point tracking, it's only maximized in bulk when as said the batteries can take it. What controls the buck converters output after bulk is the same as in PWM, the voltage and acceptance rate of the battery. Should a load bring the battery below float, it will return to bulk/MPPT. Should a load keep it from achieving the absorb set point, it will stay in MPPT at what ever level you balance it at.

It's not like there is some hidden power that is only there in bulk/MPPT. The power is just tweaked to bring up the battery the fastest. That's why I can pull the same amps in float as I do in MPPT.

What about the test on the LFP batteries? How were the 12v panels wired?

If in series, wouldn't that be completely biased in favour of mppt? And if in parallel, wouldn't it be biased in favour of pwm?

On the contrary, there's no need for his behavior. Is he so desperate that he has to put a 34Vmp panel to a 12V pwm system to show substantial mppt gains?