# question

## PWM controller

How to you do to size correctly a PWM controller nominal current ?

Thanks

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Panel Isc (short circuit current) must not exceed PWM controllers rated current.

To be safe, give 20% margin.

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

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but if Impp excide the rated current what will happen?

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djibi ·

Panel Impp should be lower than Panel Isc. If you exceed the Amps, it will likely damage your PWM.

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markus ♦♦ ·

and exemple I have a solar panel with Immp=8.29A and Isc=8.89A

Can I use a PWM of 10A?

for me no because : Icontroller = 1.25*8.29=10,69A is more than the 10A of rated current.

Am I right or can I accept? Or my formule of calculation is wrong?

THANKS

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djibi ·

If you want to be safe, no. You have a 25% Margin in your calculation...

Don't use Impp for calculations, use Isc.

Nothing to be sorry for, I can understand you perfectly.

Regards,

Markus

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markus ♦♦ ·

So if I use Icontroller=1.25*Isc=1.25*8.89=11,11A

So the good controller to choose is the PWM 20A.

Right or false?

Another question the 25% is save or what is the save one?

Thanks

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djibi ·

Yes, you got it right.

You can even add more panels in future with the 20A, if you want.

The common practice is to use 25%, to be safe under all circumstances.

If you are not sure, on what this safety depends on, just use 25%.

Regards,

Markus

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markus ♦♦ ·

to add: consider temperature derating too.

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markus ♦♦ ·

Thanks Markus if I add another pv of 150W the current will be now 22,22A which is more than the controller rated current ( 20A).

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djibi ·

Then not... :o) As long as the panels have the same voltages, you can add a lower rated panel in parallel.

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markus ♦♦ ·

Don't Know how to thanks you.

Thanks you very much

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