# question

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## Correct MPPT controller size

We have installed 5 x 390w sun power solar panels. We have one MPPT controller per panel. Our victron dealer has used 75/15 controllers - is this correct?

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4 Answers
Kristof G. answered ·

Hoi,

We need ISC and VOC values of the panels to know that ...

Kristof

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Hi Kristof the ISC value is 6.55amps and the VOC is 75.3volts

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Murray van Graan answered ·

I assume it’s like that because of the high open circuit voltage (75.3v) and the fact that it’s 5 panels. If it was even quantities, you could have put them on one, bigger 250V MPPT provides they are all facing the same direction. Point of concern, you might exceed the input voltage on those 75V MPPT’s if the panels cools down a bit - and that will damage them. I’m assuming these are the panels you have https://zerohomebills.com/wp-content/uploads/sunpower-maxeon-3-residential-solar-panels-400-390-370-DataSheet.pdf

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wkirby answered ·

It depends where you live.
The Voc of those panels is 75.3V. In colder climates this Voltage will be higher and will damage these controllers. The 75V limit of these controllers is an absolute limit and should not be exceeded.
The datasheet stated Voc is already higher than the limit of the controller, so I think your dealer should have specified 100V controllers.
The panel Voltage will be lower than 75.3V when loaded, but a designer should always specify a controller with a maximum Voltage well above Voc.

You did not state what your battery Voltage is.
Assuming 24V, then a 100/15 would be the most suitable. Plenty of Voltage headroom for the panel and full PV power harvest with a battery Voltage over 26V.

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again answered ·

Yes they are our panels, the 390w ones. One thing I should have mentioned earlier is that we are on a boat so running a 12v system

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Oh well, then those controllers are completely wrong.
On a 12V battery system you will need 5x 100/30 controllers. Each controller will make 30A @ 13V (390W) in good conditions.

Those controllers specified by your dealer will only make ~220W MAX! With a 390W panel that is not very good.

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