mppt vs pwm

JiminDenver wrote:
BFL

You still have PPT and MPPT confused. PPT is always on, MPPT is in bulk only because it is not linked to the battery voltage and acceptance rate.

Well that is certainly confusing! Maybe one of our experts can say if it is correct.

Even so, things are much clearer. I used to believe that when in PWM you could only get Isc as your max amps even with 24v panels. Now I see that "PWM" has a different actual meaning and that it is the lack of any buck converter in a "PWM Controller" that limits you to panel Isc.

There is still some trickery I don't get how the tracking gizmo in the MPPT controller might have two roles but I can live with the "black box" version and not know what goes on inside it.

I did want to know what to expect when I am measuring my set-up when it is operating like panel voltage in Float, so that is solved--thanks all! I do still need to get my actual intake amps to go with my intake panel voltage so I can derive intake watts to compare with the output watts the controller displays. Then I can get controller efficiency.

I can derive input amps right now from the other measuremnts I got, but only by assuming a controller efficiency number. I can say that the efficiency is pretty good to get that output power, so it is not like the controller is not working right. I am interested in whether it has a lower sort of efficiency from being nearly maxed out

12thgenusa wrote:

BFL13 wrote:
If voltage is lower than Vmp you get less power but go up in Isc on the IV curve, so to get lower power but also lower amps, you have to raise the panel voltage?

Yes.
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In Float I will see 2 amps or so going into the batteries. This equates to less than 1 amp on the panel side. If you look at a typical IV curve the only place you will find 1 amp output is near Voc. I have verified this as panel voltage is 41 to 42 volts in float with little to no loads.
...

That's pretty clearcut.

Perhaps the advantage of using the high V, low I side of the power curve to reduce power would be lower line losses from the panels to the controller?

Not sure what PPT is?

Vmp and MPPT only applies when demand is equal to or greater than what the PV array can supply. It is during this time that the MPPT algorithm is functional and the controller is attempting to supply all that it can.

At demands less than full output, the controller is no longer looking for Vmp, but for a voltage that will cause the array to supply the necessary not maximum power.

On most controllers there are adjustments for the transition points between MPPT, Abs and Float on the output side using battery voltage and current.

BFL

You still have PPT and MPPT confused. PPT is always on, MPPT is in bulk only because it is not linked to the battery voltage and acceptance rate.

Thanks! Ok so the MPPT is "not functional" but the "controller" still picks panel voltages as demand requires.

The MorningStar one has the MPPT "on" all the time playing with voltages to do this.

Is this just wording? As in--- the MPPT is "on" in Abs and Float but its "Tracking" is "not functional" and it is using its voltage fiddling circuitry it can do while tracking to find Vmp to get MPP for a different task now--ie keep the power "enough" to meet demand?

Somewhere off to the side is that if battery voltage drops to some set-point like 13.2, the MPPT tracking part comes back on and the controller is now in Bulk (even if the battery is not in Bulk I guess)

Not sure if that is the same thing as saying the controller goes back into Bulk if the power demand goes up to a certain amount at the output end of the buck converter. ("Power" is such a wishy-washy thing! :( )

I doubt at this point it is necessary with the explanation given BUT if you want more test...it's below freezing and sunny here. I planned on testing my little solar oven anyways and can drop a panel on the driveway while I'm at it. Voc, Vmp, battery voltage I can do but please no Isc. At these temps all I'll be able to tell you is that they are over 10a as I hear the pop and my meter dies. lol

BFL13 wrote:
If voltage is lower than Vmp you get less power but go up in Isc on the IV curve, so to get lower power but also lower amps, you have to raise the panel voltage?

Yes.

Think of it this way. The controller has a supply side (PV array) and a demand side (battery and other loads). The supply side will only produce what the demand side requires.

During low SOC and/or high load demand the MPPT controller will look for the highest power output to supply the demand. The PV array should be at Vmp at this time.

At higher SOC and/or lower load demand (Abs and Float) the PV array can supply the demand at less than full panel power. The controller will switch from MPPT to Abs or Float (Rogue MPPT is not functional in Abs or Float as max power is not needed). Panel voltage is adjusted to supply the power that is needed. It will be somewhere between Vmp and Voc. The lighter the demand the closer panel voltage will approach Voc.

In Float I will see 2 amps or so going into the batteries. This equates to less than 1 amp on the panel side. If you look at a typical IV curve the only place you will find 1 amp output is near Voc. I have verified this as panel voltage is 41 to 42 volts in float with little to no loads.

I have done as JiminDenver described earlier and 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.

So here is a wrench to toss in to the works.

I keep seeing how the controller stops charging to check the panels voltage or cuts the power on and off in PWM. When I first started using the solar i reported that once in float I was able to turn on anything in the trailer and have the panel run it while the battery stayed in float. I was told that was impossible, that the battery was discharging and recharging so fast that you couldn't see it on the controller or even with a meter. So to prove my point I set up a panel, controller, battery, inverter and light bulb, got it all running and pulled the battery off of the system. The light stayed on, it wasn't pulsing. The inverter would have shut down at any drop in voltage so the power was constant as long as the sun shined.

I don't see how it would be possible with the power cutting in and out.

If voltage is lower than Vmp you get less power but go up in Isc on the IV curve, so to get lower power but also lower amps, you have to raise the panel voltage?

But if still buck converting, you get the output amps from the output power, not from the panel. So panel amps don't matter if they go up or down? Which means panel voltage could be more or less than Vmp in Absorb?

So the MPPT when not "in MPPT" (so it is in "PWM" but this means "now in PWM only" since it is also in PWM with the MPPT "on" ---if I got that right! :( )

So if PWM is always on too, then "panel voltage" is always on/off and is some sort of average amount- even the Vmp during Bulk?

I don't know how the massively over priced, over hyped, out dated or buggy expensive controllers do it but we had someone here take apart a Eco-w and showed how it's tracking function worked. It may be less expensive but sans the extra features, it is just as functional.