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MPPT Sizing Help

Hiya, I recently purchased three Victron 175w monocrystaline panels and plan to connect them in series (Southampton UK here) to three Probat Lead Acid Calcium 12V 130ah batteries giving a total of 390ah.

The Victron MPPT calculator suggests the SmartSolar MPPT 150/35 but some of the numbers in the output calculation are shown in red (minimum PV voltage at max temperature) showing as 46.5 volts and other numbers in orange. Should I be worried about these number colours?

Also not sure if I'm using the calculatior correctly as it will let me select three panels in series but always shows additionally one in parallel?!

If someone with considerably more knowledge and confidence could confirm which MPPT controller I should get (and possibly what guage wires I need) I would be very grateful.

MPPT Controllers
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2 Answers
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wkirby answered ·

The red number is nonsense, it is basically saying that the value of 46.5 is less than 13 (the number above it), but it is not. So don't worry about that one, the number of those panels in series of three is perfectly fine.

The orange numbers mean that in absolutely ideal conditions, full sunshine, cool temperatures and panels on axis to the sun, the string of panels would have the capacity to produce more than 35A to the battery. However, the MPPT will automatically limits the charging current to a maximum of 35A, so the additional potential would be wasted. The wasted potential is not very much though in your case and let's be honest, we don't often get those ideal conditions here in the UK ;)

The 1 in parallel is fine, you have a single string of panels which has to be mathematically expressed as a single string. You couldn't have a string of 0 panels otherwise you'd have 0 panels.
It's more of a problem with the English language making the expression seem silly.

The 150/35 would be a good choice. Another option would be the 100/50 which would allow full charge power under those ideal conditions. I don't think there is much difference in price between the two.

I'd recommend 16mm² wires from the MPPT to the battery. The PV to MPPT wires could be 4mm² perhaps 6mm² if the run is long.

I hope that clarifies things.

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seb71 answered ·
Also not sure if I'm using the calculatior correctly as it will let me select three panels in series but always shows additionally one in parallel?!

That "1" means a single string of 3 panels in series.


In the MPPT sizing tool, one number is how many panels you have in a string (so how many in series).

The other number means how many strings you have in parallel.


Maybe the explanations I gave in this thread will be be of some help.

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