mfred68 avatar image
mfred68 asked

Mppt rs450/100 spec's

I have lots of roof space and am planning to fit 30 x 415w solar panels (but not all on the same roof) I'm wondering if a 450/100 mppt can handle the following configuration:

Panels are Voc 50v, Isc 10.55A

3 parallel strings of 5 panels in series on one mppt

Making Voc 250V , Isc 31.55A

3 parallel strings of 4 panels in series on the other mppt

Making Voc 200v, Isc 31.55A

Can a 450/100 handle this configuration?

mppt rsmppt calculator
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2 Answers
Alexandra avatar image
Alexandra answered ·


Since you have asked a few solar config related questions, my suggestion to your is use the excel spreadsheet for all your different scenarios.

It is important you use the temp coefficient of your panels for I and V.

But off the top of my head if you have one string per tracker you will be fine. No parallel strings on the RS mppts.

FYI you can have uneven strings as well lets you be more flexible for roof set up

VOC is 8 x battery float. See the manual.

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mfred68 avatar image mfred68 commented ·

Where do I find the temperature coefficient data?

Here is the label on the back of the panels 1000037750.jpg

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nickdb avatar image nickdb ♦♦ mfred68 commented ·
Download the panel spec sheet would be the place to start.
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mfred68 avatar image mfred68 nickdb ♦♦ commented ·

Ok I did find the spec sheet for my panels and put them in the mppt calculator, but the results seem unexpected.

Apparently, the calculator selected the mppt 450/100, but only allows 7 panels per string, that's only Voc 350v @Isc 10.55A. That mppt can handle 450v

I was hoping to use 8 panels per string but the mppt calcuator turns up with "no suitable mppt found" yet 8 panels at 50v each is still under the float voltage of the batteries. Thoughts?

Oh, and it states its 35% undersized.


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Alex Pescaru avatar image Alex Pescaru mfred68 commented ·

Hi @mfred68

Because 8 * 50V = 400V and with 8.75% correction for -10*C, as you've entered, is about 435V.

Above the 432V maximum defined in the application (see above) for MPPT RS450/100.


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mfred68 avatar image
mfred68 answered ·

Do you think -10 degrees is a bit over the top, considering the uk rarely gets that cold and if it did, solar production that time of year would be minimal with much lower panel output

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sean avatar image sean commented ·
You are right, but there will be some very cold very bright days (albeit not many in the UK) when the unloaded panel voltage will rise very close to the specified limit, usually early morning in one of my systems - mine simply faults and produces no output untill I reset it, providing ambient has risen slightly the output returns to normal.

Some here will tell you that the world will end if you exceed the controllers max input voltage, but a few volts over the hard limit certainly doesn't harm mine.

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