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Problem Report - Smart Solar MPPT sometimes sets Optimum Operating Point near Zero

Here is, I believe, a unique problem with the MPPT algorithm. (We don't have many cloudy days here in Phoenix (Arizona). So we never had opportunity to see this problem before.)

Hopefully my short video shows (and explains) the problem.

https://jmp.sh/ijkBgeh

Briefly, I was helping a buddy with his camper van conversion on an overcast day. He has a Smart Solar MPPT (latest firmware) and one 370 W solar panel on his roof. This day it was making about 60 W at best.

We were doing some load testing on his system, and so we were operating his Dometic brand Air Conditioner, which draws 2000+ Watts. (He has a Multiplus 12/3000.)

We had depleted his battery bank down to about 50% SOC during testing. (Battery Voltage at about 12.5 V when loaded.)

While we were testing, he decided to see how much power his MPPT was delivering. I was surprised when he showed me it was showing near Zero Watts.

I noticed that the battery voltage was dithering a lot. And so I hypothesized that the MPPT couldn't find an optimal operating point with one of the parameters moving around too much.

To test my hypothesis, I turned off the Air Conditioner. The output of the MPPT jumped almost immediately to 60 W.

Then to make sure this was consistent, I turned the Air Conditioner back on. And the output of the MPPT returned to near zero.

Now, I don't know if the root problem is that the voltage was dithering, or if the battery voltage was too low for the algorithm.

It's sunny outside today and his batteries have been recharged to 100% SOC. So I suppose that I should go to his house and perform another test to see if this "failure" mode only happens when the batteries are low.

I will plan to do that test tomorrow and report back here.

MPPT Controllers
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pmikep avatar image pmikep commented ·
More data: I went back to the camper van in the late afternoon. Sunny, the Solar Panel/MPPT was making 120 W. Batteries at 100% SOC. I turned on the Air Conditioner and the MPPT Output stayed at 120 W. The battery voltage, when loaded, was about 13 volts, but it was fluctuating as before.


Then I covered half of the panel, which lowered the output of the MPPT to 60 W. When I turned the Air Conditioner on, I observed the same result in my video: the Output lowered to zero.


So I have to change my hypothesis. It's not the dithering voltage that is confusing the MPPT. (Nor is it the batteries being at 50% SOC.) My new hypothesis is that if the available power from the solar panel is too low, then the MPPT cannot find a solution in this particular case of high current draw (170 Amps) from the batteries. (Something to do with impedance of the batteries when delivering high current?)

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kevgermany answered ·

What voltage is the panel generating in lower light/covered? Victron MPPT starts charging at battery actual voltage +5V and stops when panel voltage is less than 1V higher than battery. First guess is that panel voltage is dropping too low.

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