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lightful-mind-vet avatar image
lightful-mind-vet asked

Exceeding MPPT wattage limit

Yes, I know this is related to other questions/posts, but I need some clarity. I have four 340 watt (Hyundai HiS-S340Ti) panels, and 1120 ah 12 volt DIY battery (LiFePO4) on & in my travel trailer. My inverter/charger is the Victron MultiPlus II 120x2 12 volt, the charge controller is a Victron MPPT 150/100, and pretty much everything (except for the DIY batteries/BMS) is being managed by the Victron Cerbo GX. Yes, I wish I could have gone with a 24 volt system, but the MultiPlus II only comes in 12 volt, at this time - Victron, are you listening? With the four panels in full/direct sunlight in Arizona in mid March, I'm making 7.5 kwh per day, and consuming around 7 kwh/day - yeah, don't judge me :). I have the panels in a 2s/2p configuration. I want to add two additional panels, since it was my original plan and the cables are already up there - two of the six panels were destroyed in shipping. But, I'm concerned about the max wattage limitation of the MPPT (1450 for a 12 v system). I realize I'll only be clipping/exceeding capacity at the peak of the day when the sun is high in the sky provided I'm in a very clear and sunny environment - and that it a real possibility from time to time. Most of the time, it will stay under that - especially on cloudy days (excluding cloud edge effect), and in places where I have some blockage. Currently, at the peak of the day in AZ, I'm generating just over 1000 watts - Vmax around 85 volts. I just want to be able to keep the system breaking even, or providing a net gain, when I'm in the forest and/or experiencing a lot of clouds. At present, like I mentioned, I'm making only slightly more (about .5) kwh more than I'm consuming in an almost ideal solar generation environment. That said, how big of a risk of destroying something would I be taking by adding the two additional panels in a 2s/3p array? I'm considering getting/making a cover for the extra two panels, when I feel there might be a risk of exceeding capacity, but I'm sure I might miss/forget to put it on occasionally. So, again, how much of a risk would I be taking to add the two additional panels? How fragile are these MPPT charge controllers? Do they frequently burn out when input exceeds the max wattage?

MPPT Controllerssolar sizing
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lightful-mind-vet avatar image lightful-mind-vet commented ·
One additional note, I'm using the absolute minimum electricity I can. I have the fridge on LP, no AC, and the windows open for circulation. Also, I have no obstructions, but I'm heading to the Pacific Northwest, soon, and I'm certain I'll be in places with moderate to heavy obstructions and/or cloudy/foggy environments very often.
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2 Answers
netrange avatar image
netrange answered ·

Not the maximum power of your modules but the maximum voltage of your configuration endangers your MPPT controller
If you can generate more power BUT stay below the MPPT voltage there is no danger. The MPPT does not convert more line than it CAN ...


I am currently running 3S/3P on a 150/35 and since it can still be quite cool in our area at the moment, there are small peaks above 130V around midday ...but then there is already an overvoltage fault.
But the power it limits all by itself


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lightful-mind-vet avatar image lightful-mind-vet commented ·
I appreciate the info. My panels are claimed to be 38.4v (Vmpp) and 8.9a (Impp) at Pmax. With the 2s/2p configuration I have right now, over the past 5 days, I've seen a just over 80v (81-84v) Pmax. So, with an additional pair of panels, I don't think I would break over that - the current would increase, but I'm cabled to handle the increased amperage.


So, I don't think I'm at risk of going over the 150v or 100a limits, if my math is correct. I was just concerned about the max wattage limit (1450 for 12v) Victron puts in their datasheet for the MPPT. I had another (supposedly reputable) installer tell me that exceeding that from my panels would/could cause damage to the MPPT.

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wkirby avatar image
wkirby answered ·

The MPPT limits its power output to 100A. It does not matter how much more PV there is available, it will only take as much as it can.

There is a 24V version of MultiPlus II 120x2 - https://www.victronenergy.com/upload/documents/Datasheet-MultiPlus-II-3kVA-2x120V-EN.pdf

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lightful-mind-vet avatar image lightful-mind-vet commented ·
I wonder if that's a new/different product, or if my 12 volt unit is capable of 24 volts? The latter option would be great, but I'd pissed that my installer didn't know it. I don't see a different part number for the 24v model, though. If mine is capable of running in 24v mode, all I would have to do is replace my 4s BMSs with two 8s BMSs, rewire the prismatic cells for 24v, switch my MPPT to 24v, get a DC:DC 12v regulator/converter to feed my 12v system, and a few other minor changes. I originally wanted to go 24v, but the installer said that the MultiPlus II only came in 12v - which is why we configured the batteries the way we did for 12v.
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wkirby avatar image wkirby ♦♦ lightful-mind-vet commented ·
Unfortunately, the inverters are not multi Voltage. So a 12V model can't be switched to work on 24V.

I think the 24V model is pretty new, so don't be annoyed with your installer, they were probably right at the time.

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Related Resources

MPPT Product Page

MPPT Error codes

MPPT 150/60 up to 250/70 Manual

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