mppt vs pwm

jrnymn7 wrote:
Grizzzman,

I was thinking more in terms of the controller protecting itself, like current limiting on a power supply unit or converter-charger. But now that I think about it, it's probably not a protection found on pwm controllers; although I've read here that some controllers do "clip" amps, but not sure if that only applies to upper end mppt controllers?

My PWM 30 amp solar charge controller clips amps "safely" at 31 amps so I would have to say nope ??

red31 wrote:
My shunt controller had a frequency of ~ 1 day. It stopped at 14.2v and came back on at 13.0v. If it stopped early enough in the day, it might come back on but with a small panel, it likely never reach 14.2v by sunset.

Yes there is enormous confusion about On/Off as the definition of "shunt" vs "series" where amps taper with a constant voltage.

My ASC did do on/off. But it had that varying "duration" of the "pulses" so they called it Low Frequency PWM" not "Shunt"

With that running after it started "controlling" in the afternoon once the batts had reached the set Vabs, you could see on the Trimetric that when it went "off" both voltage and amps fell, then came back up when it turned back "on" At first this was very rapid and made you dizzy. Later it was not so rapid and the amps reached when on were lower.

Let's call that my new term, "Modified Shunt"

Next I got an EP Solar LandStar "Series" type PWM controller. On the Trimetric, this one did not make you dizzy on the voltage reading, which stayed constant, but the amps went up and down a lot becoming less and less each time. That was the "tapering" Not a steady decline really like a tapering converter in Absprption, but that was the idea instead of varying the duration of on and off.

I think the suggestion is that by turning right off each time, the battery might like the little kick start with the total on and off each time better than the smoother Series method?

It is all very obscure and terminology variance is no help. Some of it may even be ( my favourite!) "proprietorial" so we'll never know among Brands. :(

I was just as happy with my ASC and with the LandStar as to how they got the batteries done up each day each with its own version of "tapering amps" during Absorption.

I sure would not have been happy with a strict Shunt type that got to the "high set-point" and then let go till Vbatt got down to the
"low set-point" and then got going again.

jrnymn7 wrote:
Grizzzman,

I was thinking more in terms of the controller protecting itself, like current limiting on a power supply unit or converter-charger. But now that I think about it, it's probably not a protection found on pwm controllers; although I've read here that some controllers do "clip" amps, but not sure if that only applies to upper end mppt controllers?

It sure applies to the MS MPPT60 which clips at 60A

My shunt controller had a frequency of ~ 1 day. It stopped at 14.2v and came back on at 13.0v. If it stopped early enough in the day, it might come back on but with a small panel, it likely never reach 14.2v by sunset.

jrnymn7 wrote:
Grizzzman,

I was thinking more in terms of the controller protecting itself, like current limiting on a power supply unit or converter-charger. But now that I think about it, it's probably not a protection found on pwm controllers; although I've read here that some controllers do "clip" amps, but not sure if that only applies to upper end mppt controllers?

Most(all?) 12v PWM controllers do not clip the amps and "let through" whatever the panel is doing. The panel can exceed its ratings at times. The "rule" is to pick the "amps size" of your controller to have at least a 20% margin over the panel's rated Isc at STC. IE, for a total 25 amps of Isc you want a 30 amp controller.

The reason is at near max controller rated amps they get warm. Go over and they get hot. So there is a time factor how long over before they fry. ( A brief (5 or 10 minutes usually is max time for that) overage from "edge of cloud effect" is not enough time for it to fry. It would have to be a case of too much array.

So it is up to the PWM controller buyer to get a big enough controller for the array.

MPPT controllers (all or some, don't know) seem to clip their amps at the controller amps rating. From what I gathered during my buck converter gizmo education on here, that is probably due to the buck converter output limit? Vague on that. :( (PWM controllers have no buck converter)

Anyway, it seems an MPPT can run at max (even if clipped) amps without getting so hot it fries. This allows you to run a bigger amps array (watts/Vbatt) than the controller size so you get more amps most of the day and only miss out on some amps mid-day.

It just means if you have more array you get more amps (gee!)
But it allows you to do that with a mere $300 controller instead of getting a bigger $500 one that also will handle mid-day without clipping any. Somebody figured you got almost as many AH with the smaller size clipper and saved $200 or whatever on controller cost.

Grizzzman,

I was thinking more in terms of the controller protecting itself, like current limiting on a power supply unit or converter-charger. But now that I think about it, it's probably not a protection found on pwm controllers; although I've read here that some controllers do "clip" amps, but not sure if that only applies to upper end mppt controllers?

"As far as pwm controllers doing nothing in bulk, I'm not sure I'd agree. No, they are not regulating voltage, as such, but I would think they are always monitoring, and perhaps maintaining a steady pulse width, if only to limit current?"

Why waste the amps? Why increase the heating in the controller? There is no point. No advantage. Ok why limit current durring bulk?

BFL,

That sure looks like an "on/off" controller; the type later referred to as "low frequency pwm", in order to distinguish them from the newer technology, dubbed as "high frequency pwm". But it's not a shunt type on/off, this much seems true.

Specialty Concepts even makes reference to these controllers being the industry standard for over 30 years, whereas PWM made its way into wide use only 15-20 years ago.

Like I've said, there are those who still swear by the older technology, and I can't help but wonder if they were given a fair shake. I remember watching a 4 hour documentary many years back, where it was shown how Nintendo muscled their way into the game station market. And a similar thing happened with beta vs. vcr, as far as I can tell.

As far as pwm controllers doing nothing in bulk, I'm not sure I'd agree. No, they are not regulating voltage, as such, but I would think they are always monitoring, and perhaps maintaining a steady pulse width, if only to limit current?

Salvo wrote:

...
Yes, mppt and pwm controllers use different architecture to get to the same result.
...

Ok, let's just leave it at that.

The "PWM" controller does nothing in Bulk, but the MPPT controller does.

I will try to find that ASC explanation again for "low frequency PWM"

It is very confusing to separate the different actions. It does switch the panel on and off. It somehow is able to time the periods (durations) of on and off to reduce the time on and increase the time off as battery SOC rises, while the Vabs is maintained.

These "durations" are here called "pulses" and since they change duration that can be seen as a form of "pulse width (or "length") modification"

The rapidity of the pulses is called "pulse repetition rate" but that is not the "frequency" which is the cycles in the actual pulse if it were radar, say.

But here with "low frequency PWM" they seem to be talking about the pulse repetition rate, as the "frequency" not the frequency (hertz) of the "pulse".

"CHARGING METHOD: Low Frequency Pulse Width Modulation : - The ASC
provides pulses of charging current at varying durations to maintain the batteries at
a full state of charge and insure the long-term health on the batteries. The “on” and
“off” cycle time is wide enough to eliminate electronic noise and short enough to
insure the batteries are always topped off. This method allows the batteries to
reach a higher voltage with the “on” cycle and protect the batteries from gassing in
the “off” cycle. This will provide the benefits of the higher voltage (reduced
sulfation and stirred up electrolyte) and prevent excessive gassing and excessive
water loss."

Scroll down to page 12 of 24 "Operation"

http://www.specialtyconcepts.com/SPECIALTY_CONCEPTS_PDF_FILES/ASC_INSTRUC_MANUAL.PDF