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piperfly avatar image
piperfly asked

MPPT 15 75 with a 535W solar panel

Hello,

  • I bought a 535W and was installed on my campervan conversion. Initial intention it was to install a 250W panel but this is what I found at good price and I was suposed that a bigger panel will give much more current on cloudy days.
  • My panel specs are: P Max=535W; Voltage at Pmax=41.5 V; current at Pmax=12.9A; open circuit voltage=49.35V; short circuit current=13.78A

So my question is: is my small victron 15/75 suitable for this system? The max current and voltage are still below mppt limit and I understand that I can get a maximum 50% of potential energy but with advantage of higher efficiency in low sun.

Is working or I'll burn the mppt unit?

Thank you

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gazza avatar image
gazza answered ·

It is within the limits on the input side, just (the Isc is close to the max input current of 15A, it is not unheard of for panels to exceed their spec in certain conditions, so I would consider fusing it?), but you will just be limiting what you get out of it... For a 12V system the 75/15 will give you 220W (at max), it will just clip the usual power/time curve over the day. Yes, it will give you better response at the tail ends, or on cloudy days, compared with the recommended 220W panel for a 12V system.

Taking the long view... over time you will obviously not be making the most of your panel on sunny days.
The Victron MPPT calculator suggests the 100/50 as the best match to get the full power. (Then you would of course be undersized in terms of PV.)

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Alexandra avatar image Alexandra ♦ commented ·

Or 100/30. It's a nice middling size if you don't mind a bit of over panel and power loss.

The 75/15 will get ultra hot as well so in terms of long life the 100/30.

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