Solar Question: PWM vs MPPT

Isaacs · 09-15-2018, 10:50 AM

Scenario 1: I'm parked in the shade and my single rooftop solar panel is only putting out, say, 11 volts into my PWM charge controller. Can I assume this is doing absolutely nothing to charge my batteries? If I add another panel, wired in parallel, will it still do nothing because of the low voltage?

Scenario 2: I'm parked in the same shade with two rooftop panels wired in series. I now have 22 volts and I'm using an MPPT charger. Are my batteries charging? Is this a good way to go?

PlayersZ28 · 09-15-2018, 12:23 PM

Either PWM or MPPT will produce a charge current @ 13.8-14.x volts to charge the battery. MPPT will let you series panels to increase the voltage. Shade takes down all the panels in a series string AFAIK. The way I see it for a small install (1-200w) use PWM, larger go to MPPT for more flexibility in wiring. I have 640w into MPPT.

bdreinv · 09-15-2018, 12:39 PM

Huge difference in MPPT controllers,lots of info on the web!

**Mustang65** · 09-15-2018, 07:27 PM

This video goes into detail regarding the difference between PWM and MPPT SOLAR Charge Controllers. At the very end of the video he explains why RV's should use MPPT.

Don

My Registry

RVing with SOLAR

https://www.youtube.com/watch?v=wmyuxKmlBCk

Seann45 · 09-16-2018, 01:22 PM

Quote:

Originally Posted by Isaacs

Scenario 1: I'm parked in the shade and my single rooftop solar panel is only putting out, say, 11 volts into my PWM charge controller. Can I assume this is doing absolutely nothing to charge my batteries? If I add another panel, wired in parallel, will it still do nothing because of the low voltage?

Scenario 2: I'm parked in the same shade with two rooftop panels wired in series. I now have 22 volts and I'm using an MPPT charger. Are my batteries charging? Is this a good way to go?

Volts or amps?????

**Mustang65** · 09-16-2018, 02:32 PM

If there is ANY chance of shading, PARALLEL is the way you need to go. See the attached picture for how a few leaf's can affect the output of SOLAR panels.

Don

Isaacs · 09-18-2018, 08:30 AM

Quote:

Originally Posted by Mustang65

If there is ANY chance of shading, PARALLEL is the way you need to go. See the attached picture for how a few leaf's can affect the output of SOLAR panels.

Don

I guess I just don't understand how a panel that is putting out only 11 volts could do any charging at all.

Bullitt6283 · 09-18-2018, 05:59 PM

Quote:

Originally Posted by Isaacs

I guess I just don't understand how a panel that is putting out only 11 volts could do any charging at all.

^^^ x2 ^^^

.

**Mustang65** · 09-18-2018, 07:31 PM

How much shade are we talking about. If both panels are putting out 11 volts each, then I would say that there is a LOT of shade. Do you have any high output lights that you could shine on the panels, and check the output voltage? Can you remove a panel and put it in direct sunlight, and check the voltage?

What is the mfr of the panels? SOLAR charge controller? Specifications?

Don
My Registry

RVing with SOLAR

PlayersZ28 · 09-19-2018, 05:53 AM

Is the 11v a theoretical number or something you observed on your panel?

Looking at mine right now I show 30.8v & .32A out of 640w of panels (2x2) and the controller is charging 12.5v @ .81A, basically nothing. Sun is just coming up here.

Isaacs · 09-19-2018, 06:51 AM

Quote:

Originally Posted by Mustang65

How much shade are we talking about. If both panels are putting out 11 volts each, then I would say that there is a LOT of shade. Do you have any high output lights that you could shine on the panels, and check the output voltage? Can you remove a panel and put it in direct sunlight, and check the voltage?

What is the mfr of the panels? SOLAR charge controller? Specifications?

Don
My Registry

RVing with SOLAR

Quote:

Originally Posted by PlayersZ28

Is the 11v a theoretical number or something you observed on your panel?

Looking at mine right now I show 30.8v & .32A out of 640w of panels (2x2) and the controller is charging 12.5v @ .81A, basically nothing. Sun is just coming up here.

The 11 volts is theoretical, just trying to figure out how multiple panels should be wired.

At the moment I have only one 130W panel which is wired into a cheap PWM charger. I really haven't had any problems but since I went to 2 - 6V batteries, I can't get the "overvoltage" light on the charger to flash which I assume means things are fully charged. This is at my favorite campsite which I visit every year. I guess the trees have grown and I don't get full sun on the panel 'till about 2 PM. And I suppose these batteries are a bit harder to get to full charge than my old 12V.

In my driveway I have full sun and the light flashes happily all afternoon long. As I said, I don't really have any problems--just looking for some!

I'm thinking adding another panel and updating the charger might be the way to go. I think my current panel is a Renogy mono crystalline.

PlayersZ28 · 09-19-2018, 07:08 AM

If you series the panels then you have a higher input voltage and want the MPPT. However shade will knock out the series string. The way I see it, once you get past a small single panel system then the MPPT provides benefits that outweigh the small addt'l cost.

I would say if you see 11v from the panels then it's dark

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