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hartleb avatar image
hartleb asked

Ideal voltage differential for an MPPT controller.

I have an MPPT 100/15. My panel configuration was 3x50 Watts in series giving Vmp 59.4V and Imp 2.92A. So I had a good differential between the Battery voltage and Vmp which I believe is important for the MPPT controller to work efficiently.

I have had a panel failure. The panel spec wrongly claimed that the max system voltage was 1000V it has been found to be only 45V. I now have two 50Watt panels in parallel and the Vmp is 19.8. with a Imp of 5,84A. Will my 100/15 MPPY controller be effective with this configuration? What is the ideal differential be between the Battery voltage and Vmp.

thanks


Brian

MPPT Controllers
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2 Answers
Mark avatar image
Mark answered ·

I don't think that there are any firm rules with regards to the voltage delta, but solar voltage must exceed battery voltage by +5v each morning for the MPPT to start up.

So if your solar Vmp is only 19.8v it's cutting it a bit fine, particularly on overcast days.

I would recommend to wire your remaining 2 panels in series rather than parallel so that Vmp is ~40v.

Voc will obviously be a little higher than Vmp and during MPPT start up there will be no load, so Voc may be a better voltage to reference for this.

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hartleb avatar image hartleb commented ·

Thanks mark. I appreciate your answer but I am concerned that given the dodgy spec on the panels, I would be pushing close to the limit of 45 system volts if they are in series. However, if there is no optimum delta I might just monitor the history regarding start-up.


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Mark avatar image Mark ♦♦ hartleb commented ·

No problem, give it a go and see how you go.

But I am a bit sceptical about this 45v PV string limit - I think this may be an excuse to explain the panel single panel failure you had.

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JohnC avatar image
JohnC answered ·

Hi Brian. I'm not sure where you're getting this 45V limit from, but that 1000V spec is a limit for the 'system' if you had enough panels in series to reach that. In my country it's 600V (household), but that's just a series wiring limit. Nothing relevant there for your mppt - it has a limit of 100/ (100V).

Mark's advice is good, and you could safely follow it.

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hartleb avatar image hartleb commented ·

Thank you John. The advice re 45V max system voltage came from the people who sold me the panels. They have been very helpful. The issue is with the manufacturer wrongly specing the the panel. I appreciate your input.

Brian

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