Another max voltage question


Quick question for you all. I have 3 x 325W fixed panels connected to the AC200MAX. Works very well and I often get 900W+ in the afternoons.

VoC is 45.5V x 3 = 136.5V. So this is under the 145V max input. I’ve also only ever seen about 120V in full sunlight.

I live in Canada and it’s going to go cold here in winter. I could see (once in a while) -20C.

I’ve been told that as the panels get colder the max voltage will increase.

I guess I’m wondering if this configuration is safe or if I should reduce to 2 panels before the cold weather arrives.

Or - can I go 2 series, 1 parallel?

Any suggestions?


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You want your panel strings to have the same voltage, so 2s1p is not advised as one string will have an open circuit voltage of 91V and the other 45.5V which creates a system imbalance. I don’t actually know if this will merely cause the MPPT controller to not be able to do its job properly or if it might damage the panels. Hopefully someone else can chime in here.

During winter you could run on just two panels (wired in series) if you want to be safe but you do have the option of buying the Bluetti D050S charging enhancer and run the third panel through it and wire the 2 other panels in series to the AC200Max via the solar charge port.

A simple test is keep monitoring max voltage and when start temperatures to drop just connect two panels to give an idea if three would be over max voltage.

@bxm6306 I think the charging enhancer would have been ideal. Unfortunately I just finished running conduit for the panels and, at least for this year, I’m not looking to drill another hole in the side of my house :slight_smile:

I think I will go with @Chorlton approach for now. I’ll see how 2 panels go and monitor the voltage and multiply by 1/3 to see if it is going to go over.

I had heard that the worst time was a cold morning when the sun comes out. You get high voltage but no current and that can burn out the MPTT controller if it goes over the design voltage. But I don’t know for certain.

Thankfully it’s quite easy to disconnect one of the panels outside.

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That’s a good safe approach, except you’ll want to multiply the open circuit voltage by 1/2, not 1/3 when you have two panels to estimate the voltage of one additional panel.

Obviously it’s too early for Math this morning!

Thanks :slight_smile:

I have overvolted my other bluetti ac50 and EB150 accidentally because I’m an idiot and all I got was an error. I didn’t blow out the MPPT.

I’m not making any recommendations but if you look at the manual I think you’ll see that the unit has overvoltage protection and an overvoltage error, check first, but I think you are probably ok to try leave it as it is. You can also try running some cold water over the panels to see if the voltage increases.

62V on an EB3A (Max 28V) will fry the input circuit. I would be curious (for science) what the limit is for other models where the input circuit gets permanent damaged and the over-voltage protection stops working.

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TL:DR Yea, you could go over 145V in the winter with that set up. Also, I’m not an EE, so I may have the math off a bit here.

The math involved here isn’t all that hard if you want to run it. There is a missing piece of info though and that is the TVoc rating on your panels. Generally they are -.26~-.28 though.

Assuming a -.28TVoc

Adjusted voltage = 45.5v x 100% of (-20 (coldest air temp) - 25(STC temp)) x -.28

-45 x -.28 = 12.6. AKA 126%.

So your 45.5v panels could actually have an open circuit value in the early AM of (45.5 x 1.126) 50.6V. Three of them in series would be over 150V.

The link below has a far better explanation of how to run the math.