mppt vs pwm

BFL13 wrote:
So when in "PWM mode" is it just that the MPPT gizmo circuit thingy is still working, but now instead of trying to keep at a moving target MPP, it now just fiddles with panel voltage to get "enough" power, which can also be a moving target if loads are applied on and off?

That's my understanding.

BFL13 wrote:

Since MPP is at the knee of the IV curve with Vmp being lower than Voc, it seems the panel voltage would go down the steep slope to the right to get the reduced power which means panel voltage is higher than Vmp during Absorption as stated by 12thgenusa above?

Rather than looking at the panel Iv versus Vp curve, look at the panel power versus Vp curve (fig 6.1, righ panel in the Rogue 3048 manual). Roque *could* run the Vp higher than Vmp to reduce power, but if it runs the Vp lower than Vmp, it has a more linear and less steep slope to work with. That's what I would do, but I don't know which way Rogue goes.

Let me first say I know nothing about how the Cheap Chinese MPPT controllers function or don't.

For the MPPT-60 it ALWAYS (depends on the operational mode configured, Solar charger, Wind charge controller, etc..) uses a PWM mode for the battery charging needs. Yes it might be fully switched on or even fully switched off but always uses a PWM charging mode. Ahead of the PWM charging function is the Buck Conversion stage which can easily be bypassed via a simple FET if need be. The Tracking function is ahead of the Buck Conversion stage - All functions are interconnected and communicate with each other via the on board micro processors.

What is this MPPT gizmo?

The tracking algorithm is where the magic comes into play and truly differentiates the higher quality controllers. Blue Sky on the 2000e simply has a user adjustable pot to set and forget - I have no idea how or even if the lower end cheapo units even try to scan for Vmp.

BFL13 wrote:

Since MPP is at the knee of the IV curve with Vmp being lower than Voc, it seems the panel voltage would go down the steep slope to the right to get the reduced power which means panel voltage is higher than Vmp during Absorption as stated by 12thgenusa above?

PWM is on/off, on near Vbatt off near Voc (no power), average of Vbatt and Voc is greater than Vbatt, as the duty cycle decreases (longer in Voc) the circuit stays open longer, longer at Voc.

So when in "PWM mode" is it just that the MPPT gizmo circuit thingy is still working, but now instead of trying to keep at a moving target MPP, it now just fiddles with panel voltage to get "enough" power, which can also be a moving target if loads are applied on and off?

Since MPP is at the knee of the IV curve with Vmp being lower than Voc, it seems the panel voltage would go down the steep slope to the right to get the reduced power which means panel voltage is higher than Vmp during Absorption as stated by 12thgenusa above?

brulaz wrote:

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.
...

In that situation, the Rogue controller will not be able to maintain the absorb/float voltage at the batteries and will switch to MPPT mode.

To clarify: To maintain the battery absorb/float voltage the controller has to put out the same power being absorbed in or removed from the battery. It does that by adjusting the array voltage. Figure 6.1 of the Rogue manual shows a nice linear increase in power as a function of array voltage up to the Max power point.

If the amount of power needed to maintain the battery setpoint voltage exceeds the Max power point, the controller drops into MPPT mode.

I'm not sure what the load current (at the battery voltage) exceeding the panel Isc has to do with it, as potentially the panel voltages can be much higher than the battery voltage (Voc=44v for mine) so power can be maintained. As long as the power required does not exceed the Max power point, the battery voltage can be maintained.

All this has been gone over and over and over ..................
Many folks have tried to explain it several times

I do not remember the load / light conditions since it's been a few years - but look at the voltages. Vmp changes all the time temp/light conditions etc..... The buck conversion stage can easily be bypassed (a simple fet switch) if the panel voltage is low enough to cause the bypass - it will NEVER bypass in this setup. "Tracking" if that is what you folks are calling the MPPT mode is always active.

The picture shows "Battery" Current which is NOT true it should be labeled LOAD Current

Hi,

Another strategy for me is to deliberately trigger an equalize session. That forces the Blue Sky to a maximum of 15.4 volts. I caused to have a switch added in parallel with the dip switches inside the unit. Why they did not spend another ten cents to have a switch on the panel is beyond me. Unless it is because they wish to promote sales on their (outrageously expensive) remote control.

BFL13 wrote:
So what panel voltage is in effect during Absorb and Float instead of Vmp?

Wouldn't it be whatever panel voltage is needed to maintain Vabs (bucked down to Vbatt/Vabs), and as the current tapers the panel voltage will decline following the IV and or power curve?

PWM would kick in at ~Isc or Vpanel = Vabs?

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.
...

In that situation, the Rogue controller will not be able to maintain the absorb/float voltage at the batteries and will switch to MPPT mode.

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

The higher the SOC, the closer the panel voltage will approach Voc. The power pulses become shorter with longer time between. Panel voltage rises to Voc.

It's probably not correct to think of your Vmp as a set number such as 30v. That might be the published voltage at STC, but it varies with irradiance and panel temp. My panels have an STC Vmp of 36 yet I see voltages from 31 to 36 when charging in MPPT. That is the point of an MPPT controller. It you see 30 volts all the time I would have to doubt that it is truly MPPT.