afinhert avatar image
afinhert asked

Panel voltage oscillates by 20v every 4 seconds.

I have 2x 100w panels in series, connected to a 100/50 MPPT, connected to a single flooded 12v Interstate deep-cycle battery.

The panel voltage and amperage both go greatly up and down inversely every 4 seconds in mildly shaded 12pm sunlight.

The indicator light on the controller shows bulk charging. When I open the app and view trends the voltage goes up to about 33volts for 2seconds, then drops down to 14v for 2seconds. It continued this cycle for hours until the panels were in direct sunlight and then is was better.

Is my MPPT faulty?

Is this because my panels are in series? And it’s simply due to shade?

Would parallel panels correct this issue?

How can I maximize my solar harvesting if I purchase 2 additional panels for my RV?

2 100w panels in series parallel connected to another 2 100w panels in series?

MPPT Controllers
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1 Answer
JohnC avatar image
JohnC answered ·

Hi A. This could be the mppt trying to start, but the required conditions not being met.

Those conditions are a >5V difference between Voc (your 33V) and Vbat (let's say 12.6V, for you to check). That condition met, a start is attempted.

The panel mpp will be tracked, and the Vmp comes into play (your 14V). The difference then applicable becomes 1V between Vmp and Vbat. So you're getting awfully close, and a little wire resistance, a jump in Vbat under charge, and maybe minor V spiking can influence that. I suspect you're stepping within the 1V limit under shade, and the cycle is begun.

Your mppt is likely fine, and yeh, the shade is the culprit. Paralleling the panels will only worsen it.

If adding panels, match their specs. If you added a single one to that string (3S) it would likely lift you out out of the cycle by virtue of the higher V's. 2x more, wire them 2S2P, and maybe just the extra grunt might do (no warranty there).

It *might* even be possible to have 4x panels in 4S config. But come back with your panel specs (Voc mostly). Already guessing here..

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