mppt vs pwm

Your confusion stems from the fact that solar panels are not voltage sources but current sources. In bulk mode, the panel is directly connected to the battery. The panel voltage is equal to battery voltage. As battery voltage rises, so does the panel voltage. When the battery voltage reaches the absorption set point, pwm action begins.

When using a pwm charge controller, panel voltage is never at 17V. Panel voltage has two states, either Vbat or Voc (panel open circuit voltage).

MrWizard wrote:
you seem to be under the assumption that panel output is 14v instead of 17v ?
and doesn't get altered and processed to become 14+ charging volts
try measuring the panel voltage at the input of the controller

So far, I've stayed small in my solar panel application, stayed 12V, and stayed PWM. Observing and learning from others more experienced than me has proved helpful.

All this stuff will change again for charging needs when LiFePo gets more cost effective and mainstream in RV battery applications. What will we debate to death and fanboi over then???

BFL13 wrote:

MrWizard wrote:
Well I give in and will drop the debate
The proffered explanations, do not match the true definition of PWM
So mfg have borrowed and corrupted the terminology

Yes, salesmen vs engineers again. ISTR the usual sort of bulk converter also has some variety of PWM to hold its output voltage constant. It can get very frustrating tying to follow all this!

I know my head is swimming but wada thread. :)

MrWizard wrote:
you seem to be under the assumption that panel output is 14v instead of 17v ?
and doesn't get altered and processed to become 14+ charging volts
try measuring the panel voltage at the input of the controller

a shunt controller goes on off

a PWM controller "modulates" the voltage

i know you don't believe me , you think i'm wrong
test equipment will tell the truth either way

When battery is say around 12 volts in the morning a PWM controller will
go into bulk. Durring this phase the panels are just plain connected to the battery untel absorbsion voltage setpoint is met. At this point it goes into PWM. Remember solar panels are current devices. It is only after the battery resists the amps (as decided by the voltage setpoint)
That voltage will rise to the setpoint. The big consern with what you are stating is misinformation.

The poor "lurker" who is trying to get a handle on solar may choose to believe you.

MrWizard wrote:
Well I give in and will drop the debate
The proffered explanations, do not match the true definition of PWM
So mfg have borrowed and corrupted the terminology

Yes, salesmen vs engineers again. ISTR the usual sort of buck converter also has some variety of PWM to hold its output voltage constant. It can get very frustrating tying to follow all this!

Well I give in and will drop the debate
The proffered explanations, do not match the true definition of PWM
So mfg have borrowed and corrupted the terminology

We've been thru that with the fake mppt controller that pulses in bulk to make one believe the input voltage is higher since off is 21v and on is Vbatt, the ave is higher than Vbatt. I see in/out the same till Vabs then my meter goes nuts on the input occasionally reading 21v then back to 14.8 then 21 then ... as the duty cycle is less than 100%

https://www.youtube.com/watch?v=la-gvy0DfJs about 6:30

you seem to be under the assumption that panel output is 14v instead of 17v ?
and doesn't get altered and processed to become 14+ charging volts
try measuring the panel voltage at the input of the controller

a shunt controller goes on off

a PWM controller "modulates" the voltage

i know you don't believe me , you think i'm wrong
test equipment will tell the truth either way

ewarnerusa wrote:
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.

The on/off method is called "Shunt-interrupting" which goes between two voltage set points.

The newer method where voltage is held while amps taper is called "Series-interrupting" (this short circuits the panel to interrupt current) The Series method is also called "PWM"

In retaliation, when that came out, the Shunt people at the time like Specialty Concepts with their Shunt controllers (Automatic Sequencing Controller or ASC) started to call their controllers " Low Frequency PWM"

In fact the newer Shunt ASC types did not go between an low and high set-point. They did do on and off, but also there was pulse width
so as the battery rose in SOC the length of the time it was on got less and the length of the time it was off got more when it was on or off. Both voltage and amps went up and down to make you dizzy.

In response to that, AM Solar (Greg somebody ISTR) about 10 years ago came out with a sneering report that this old style Shunt method (ignoring the latest pulse width thing) was not really "PWM" and was just marketing language. Meantime AM Solar was pushing for everybody to get the "newest thing" which was their new MPPT controller :) And so it goes.

Shunt types were eg, SCI mark 15, ICP Solar PRO. Series PWMs were Heliotrope RV-30SE eg, and the latest thing to replace all those was the MPPT HPV-22.

My first controller was an ASC shunt type with the pulse length trick. That worked great. Next was an EP Solar Series type that tapered the amps during Absorption but I would not be able to say they were any different really. Worked great too. Perhaps the Series is a bit smoother than the Shunt with pulse length during Absorption if that matters to anybody. I doubt the batteries care.

I now see that the MPPT Tracer by EP Solar has the same charging profile as their Series PWM LandStar controllers. (and the same diagram of that and the exact same word for word blurb on that is in the MorningStar manuals

Do you understand what happens in bulk mode? There is no voltage regulation. If there's no voltage regulation then there's no pwm action.

Why would you want to throttle back current during bulk? :h

MrWizard wrote:
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