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matst asked

MPPT wattage varies greatly when sun strong

I have a MPPT250/100 on my solar panels (correctly sized), with which I go to 24V lead-acid batteries and from there I go to a MultiPlus Compact 24/1600/40-16. Using a Raspery with Venus Software I set ESS so that the batteries always remain charged except in the event of a grid failure.

I have 8x 12V batteries:
-4 parallel
-2 serial (using a Victron balancer)
Each has 65Ah 12V,so it‘s a total of 260 Ah, 24V
I know, using those in parallel isn‘t perfect…

The exceeding power I feed back into the grid via MultiPlus.

Now, when the solar power exceeds the power of the MultiPlus, the charge voltage at the MPPT starts to vary in around 5 seconds cycles strongly, sometimes it goes down towards almost 0 watts and then jumps back up to around 1650W.

I have now tried to limit the maximum charge current at the MPPT, then this no longer happens, but in certain cases, of course, I no longer have the optimum power of my panels.

Does anyone know where the problem could be that the charging power always starts to fluctuate so in the limit range (batteries are of course 100% full)?


ESS
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Alexandra avatar image Alexandra ♦ commented ·
@matst

Heat could be the problem.

Heat on terminals, heat on panels, heat on mc4 connections? Cabling heat both ac or dc?

Heat and resistance are related weird behaviour usually has something to do with the two.

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matst answered ·

Thank you so much for your help, but it looks like there's nothing running hot.
To me it almost looks like the MPPT would react too slow, then overshoot in both ways, but I'm not sure if and why that happens.

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klim8skeptic avatar image klim8skeptic ♦ commented ·
@matst plz confirm battery bank Ah capacity.
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matst answered ·

Oops, sorry. Not really 65Ah.

I have 8x 12V batteries:

-4 parallel

-2 serial (using a Victron balancer)

Each has 65Ah 12V

Actually it‘s a total of 260 Ah, 24V

I know, using those in parallel isn‘t perfect…

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