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jllgd avatar image
jllgd asked

PWM or MPPT controller in older solar system?

I have a small, older solar panel system which is being used at a mountain cabin.

My older PWM solar panel regulator is now partly defective, and I can no longer read input charging amperage or load amperage output values.

System is based on two solar panels:

Solarex MSX60

P NOM 60W

P MIN 58W

P NOCT 54.6

VoC(V) 21.1

I(SC)A 3.8

I NOCT 3.6

V NOCT 15.1


Two batteries: 12 volts each, 110Ah, wired in parallel, 220Ah total.

Solar panel 1 is directed towards ca. 190 degrees south, located on the south wall of the cabin.

Solar panel 2 is directed towards ca. 230 degrees southwest, located on the west wall of the cabin.

This is due to the design of the cabin, and lack of space for having both panels on the same wall.


Panel 2 is thus receiving solar energy some hours later than panel 1 and is therefore in the shadow, until in the afternoon.

I now want to purchase a new solar panel regulator.

Question is if I need/want a PWM or MPPT regulator?

I’ve read a bit about it online but I am not able to make a decision.

Second question is if I should wire the solar panels to the new regulator in parallel or in series, for max performance.

When deciding a new regulator type, I must also plan ahead as I perhaps want to install a third panel on the east wall, or perhaps somewhat bigger panels.

Thanks in advance.

MPPT Controllers
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astrayan avatar image astrayan commented ·

Yes, don't put panels in series, if they are on different walls, but in parallel will be OK.

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5 Answers
astrayan avatar image
astrayan answered ·

PWM is good for instant power, if you need to run a pump and your batteries are dead flat.

Solarex panels of that age have deteriorated to such an extent, they probably need to be in series, to get enough voltage. But I seriously recommend getting a new panel - any panel. I have those panels lurking around in my garden, burned by 30 years of Australian sun. Maybe you want them for nostalgia, but there's not much in them.

There is no need to read a great deal of literature re PWN vs MPPT, because all the technology has gone into MPPT, so you get data logging and nice displays. I have seen some decent PWM chargers, by Morningstar and Victron, but they will overshadow the value of your panels. If I were you, I would get a cheap Epever Tracer AN with a MT50 display, but if you want the Victron equiv, it's a 100/15 or something like that, around $90. The problem with victron is that you get bogged down by Bluetooth interface and internet. You can be stuck with Victron asking you to update your software to you can get your non-working Bluetooth to run.

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kevgermany answered ·

With different orientations/illumination, connecting to a single controller will limit output. Adding a new panel will make things worse.

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jllgd avatar image
jllgd answered ·

Thanks for all your replies so far. Appreciate it.

I’ve read that the Victron MPPT regulator needs 13v+5v = 18v to start charging the batteries.

So, are my solar panels and their VoC(V) = 21.1 volts, perhaps too low for utilizing a MPPT regulator?

(V NOCT = 15.1 volt).

Will the MPPT regulator in fact be able to start charging at all?

And do all MPPT regulators have this 5v threshold above the battery voltage?

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astrayan avatar image astrayan commented ·

The main problem with victron mppt is no display. Their PWM Pro thing is made by Epever, and has an MT50 display. But it's around $110 for a 20A one and display. The Epever Tracer 2206 can be got for around the same price, and also needs the MT50 display to finesse the programming. I chose the MPPT for my vegie patch pump, because I could not be certain from the PWM manual, that I could control the absorption length. PWM can have very primitive options that destroy your battery. My pump system is a car battery and a 20Voc panel. If you pick a random PWM off ebay, there will be something bad about it.


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jllgd avatar image
jllgd answered ·

Thanks for your inputs and comments so far.

But I really like to know if a MPPT regulator will in fact be able to start charging my small/older solar panels at all?

And do all MPPT regulators normally have this 5v threshold above the battery voltage, like the Victron units?

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kevgermany avatar image kevgermany ♦♦ commented ·
The threshold is there because as you draw power from the panels, the panel voltage drops. Once charging starts, PV voltage 1V higher than battery maintains charging.

Your values look ok to start charging. AGMs will settle at about 12.7V without load. They're gSooing to be lower than this if there's load overnight. charging will start once the panels reach 17.7V.


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jllgd avatar image
jllgd answered ·

Thanks for all your replies so far.Appreciate it.

I’ve read that the Victron MPPT regulator needs 13v+5v = 18v to start charging the batteries.

So, are my solar panels and their VoC(V) = 21.1 volts, perhaps too low for utilizing a MPPT regulator?

Will the MPPT regulator in fact be able to start charging at all?

And do all MPPT regulators have this 5v threshold above the battery voltage?



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