mppt vs pwm

with need somebody with a freq meter and an O-scope to look at the output of a good brand PWM solar controller

and post pix

Thanks Salvo. I've read through the manual many times. And while I think I understand it, I read forum threads like this one and I second guess what I think I know. But the manual says it tapers the current down while holding the voltage constant when in absorption mode. This is unlike how I'm understanding on/off shunt controllers which just toggle the full panel current on and off.

Your charge controller would act not differently. During bulk, it will be full on, no pwm action. pwm begins with absorption. Read your manual, Section 4.1.1! Float is also pwm, but they don't mention it.

ewarnerusa wrote:
I thought the same thing that MrWizard pointed out regarding the OP video comparing MPPT to an on/off type of controller. I am no expert at all, but I remember when I was researching my PWM controller I read reviews of small cheap ones claiming, "Not truly PWM but just on/off toggling." So how would my Morningstar TS45 PWM behave differently in this sort of bench test?
Product manual Morningstar TS45 PWM

BFL13 wrote:

Once the MPPT controller gets the batts to the high voltage set point, the MPPT stops and now you are in "PWM Mode"

My pwm controller's input voltage 'bounces' from Vabs setpt to panel Voc while 'pulsing' in Vabs, cv. The MPPT in Vabs or "PWM mode", does the input 'pulse' for Voc and Vmp or some other V.

The efficiency of the buck converter is important for the MPPT controller.

As is the programming that tells the controller what to do. Case in point is that the Eco-Ws have a very different interpretation of what absorb should be and something tells it that if the battery starts charging at 12.4v to be gentler than if it starts out lower or I run the coffee pot. Without doing those things, I'd never see max amps out.

The "PWM" controller has no buck converter. Panel voltage = battery voltage plus a bit for line loss at the amps of the moment. The amps you get to the battery is on the panel's IV curve at that panel voltage. Same whether the controller is Shunt or Series.

With MPPT it is different. Now you have a buck converter so you have panel voltage and amps input making input watts, which comes out as watts and now you introduce battery voltage and get your amps to the battery.

Once the MPPT controller gets the batts to the high voltage set point, the MPPT stops and now you are in "PWM Mode" but the buck converter is still working, so it is not like the "regular" PWM controller where panel voltage = battery voltage.

The efficiency of the buck converter is important for the MPPT controller.

A pwm controller has a set point which is perhaps at 14.2V. If the battery is below that voltage the pwm will be full on. There's no regulation (in other words pwm action) until the battery reaches 14.2V.

It makes sense to me that pwm does basically nothing, voltage wise, while in bulk. It seems correct to suggest pwm simply sits back, while Vbatt and Rcircuit determine the voltage necessary for charging. Once the setpoint is reached, and cc changes to cv, then the pwm does its thing.

For example, if I set a converter/charger to 14.8v, and the battery is at 12.2v, the voltage will start out in the high 12 to low 13v range, not 14.8v. So it is the battery and circuit that determine the necessary voltage, not the charger. Likewise, although 17 volts may be available from the panel, they will not go into the bank during bulk stage.

Salvo wrote:
I don't believe that's the case. When in bulk mode, there's no pwm action. The panel should be shorted to the battery.

MrWizard wrote:
Don
Pulse width modulated, means the power is modulated all the time
It's a a high frequency pulse in the dc current, used to stimulate the plates to accept charge and remove sulfation
Doesn't matter wether it's in bulk or float

if that was the case
the output to the battery would be the same voltage as the input to the controller, NOT a desirable situation at peak summer voltage

do you know where PWM originated or Why
it originated with machinery controls for motor speed
to precisely control motors , i was working with this technology 40 years go to precisely control the speed of huge motors with 3 phase windings in industrial milling machinery making aerospace and ordinance parts
( it probably originated with controlling the speed of the motors driving, nuclear submarines )

it has been adapted to voltage control of solar chargers

"My point is that if one wants to point to wiring panels in series as a reason for poor performance he had better look elsewhere."

12thgenusa,

If you're referring to looking elsewhere, rather than at the efficiency graph, I agree. It compares efficiencies at various voltages, in and out, apparently at a given ambient (not panel) temperature, and at a particular irradiance; perhaps artificially produced?

But either way, what I see is mppt working slightly more efficiently at 17v input, than at 34v input. But there's much more to the issue than simply comparing minor differences in efficiencies. In fact, minor differences in efficiency may be the least important factor, here. What really matters (to me at least) is the overall performance of a system, measured in Ah's harvested. Do minor differences in efficiency play a part? I'm sure they do; but probably not a major one. What I am becoming more and more convinced of, though, is the issue of series vs. parallel may be more a matter of panel performance rather than controller performance.