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Old 07-07-2020, 07:53 PM   #1
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Question Converting Factory PWM to Aftermarket MPPT?

I just purchased a 2021 Winnebago 29STT which came with 200W of solar on the roof and this Go Power! PWM-10-SQ controller.

Any ideas/pointers on how easy it would be to "upgrade" it to an MPPT controller? Any suggestions on which to use if so? I was sort of hoping I could just pop this one off and reconnect the factory-plumbed wiring...



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Old 07-07-2020, 08:39 PM   #2
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You can just replace one with the other.
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Old 07-07-2020, 09:47 PM   #3
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It may not be worth the trouble and expense. How is it working now? If you go to MPPT, you should wire the two panels in series.
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Old 07-07-2020, 09:58 PM   #4
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So an MPPT controller would be maximized if the panels were wired in series, but still work in parallel?

Right now the system seems to work fine, but I wonder if battery life and charging would be "better" with mppt...
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Old 07-07-2020, 10:02 PM   #5
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200 watts and only a 10 amp controller? You're not getting the full potential of your panels. Should be at least 15 amps. If you upgrade go with a 30 or 40 amp controller or larger to allow room for additional panels.
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Old 07-07-2020, 11:59 PM   #6
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The controller is right at the max the panels will put out. Depending on your battery bank it may be enough and PWM will keep the batteries in good shape. I have an older system with 605 watts and a Morningstar PWM controller and it does fairly well.

Do you have two 100 watt panels or one 200 watt panel? How many and what type batteries?
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Old 07-08-2020, 05:46 AM   #7
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Sounds like I'm ok then. I have two "100W" panels up on the roof. The dealer is installing a second lead acid battery. Probably group 24s or something. I'm not going for anything exotic, just figured MPPT would extend the life of batteries and charge a bit quicker.

So far I've been ok with just one battery overnight, running the furnace. Daytime I really don't have to run the generator at all unless I want 110V...
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Old 07-08-2020, 09:07 AM   #8
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Quote:
Originally Posted by John Hilley View Post
The controller is right at the max the panels will put out. Depending on your battery bank it may be enough and PWM will keep the batteries in good shape. I have an older system with 605 watts and a Morningstar PWM controller and it does fairly well.

Do you have two 100 watt panels or one 200 watt panel? How many and what type batteries?
Yup. Right at the max. The Go Power specs show a maximum of 190 watts for this controller but that would probably never be seen except with an occasional cloud edge effect. Assuming the PPV of the 100 watt panel is 18.0 volts then 200/18=11.1 amps.
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Old 07-08-2020, 10:11 PM   #9
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Quote:
Originally Posted by swavescatter View Post
So an MPPT controller would be maximized if the panels were wired in series, but still work in parallel?

Right now the system seems to work fine, but I wonder if battery life and charging would be "better" with mppt...

As I pointed out and did the math in other threads... at 200w it's a toss up. MPPT may lose 3-5% efficiency at series voltages and low ~ 50W output. On those cloudy days when you need it the most.

Decision depends on your wire gauge, wire length, and it's power loss. If they used cheap 14 Gauge, go series. If 12G or better, why not leave well enough alone?

In AZ on nice sunny days my MPPT does ~ 20% better than PWM.
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Old 07-10-2020, 05:29 AM   #10
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Thanks for all the input guys. Given I use it only to keep batteries topped up and we generally have plenty of sun it sounds like leaving it as is works. I have too many unfinished projects as is...
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