question

walter-widmore avatar image

MPPT is giving lower amps than other

Hi,


I've 2 MPPT controllers, one with 8 solar panels and one with 12.

Problem: The one with 8 panels is giving a way higher amperage than the one with the 12 panels.


Both MPPTs are in the BULK stage. I would assume I've connected them wrong but the voltage seems accurate. The panels are all installed next to each other, no shadows.


Any idea what could go wrong?

Thanks

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img-4911.jpegscreenshot-2022-01-20-at-140131.png


MPPT Controllers
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3 Answers
snoobler avatar image
snoobler answered ·

Using ESS?

Are both MPPT set to 100A output?

Is a GX device limiting the total charge current?

Why are both MPPT reading very different battery voltages?

Why are your battery voltages so low?



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Using ESS

Both are set to the max output. One is 85, other 100. The 85 is the one giving more power but is connected to more panels.

If I turn off the 85, the 100 does not provide more power.

Setup is connected to a Cerbo GX, I don't think there is any current limit setting on the Cerbo?

No idea why the voltages differ, now they seem to be equal (22.75 / 22.74).

The battery ranges from 18V to 25.2V so the battery voltages are as expected.


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100.png (372.5 KiB)
85.png (376.0 KiB)
snoobler avatar image
snoobler answered ·

ESS overrides MPPT settings.

Is your ESS config in any way limiting the current?

Ah. I'm guessing these are 6S Tesla NCA modules.

Is your BMS interacting with the GX? If so, does that BMS have a current limit? If so, is the BMS limiting the total charge current?

Since the MPPT are reading notably different voltage, that is likely due to the different current each unit was providing. Are you using a BMV, smartshunt or smart battery sense for voltage sensing? If not, you should.

Given, "turning one off does not increase the other," it's likely an actual array issue - either a panel performance issue or a connection issue. At this point, you should check:

  1. Take each string out of the array and see if the performance respond. Since you should have each string with a fuse or breaker, that should be pretty easy.
  2. Check current in each 4S string with clamp ammeter in the full array and operating independently.
  3. Voc and Isc of each panel as needed.


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Thanks for the quick reply(s). These are indeed Tesla modules. BMS has limitations but it's higher than the MPPTs reach. I'll check the solar array as you said. Thx
JohnC avatar image
JohnC answered ·

Hi @walter_widmore

I'm suspicious of the panel V's. They're very high, and indicate very cold conditions, but why the difference between them (160V vs 169V)? You could check if the mppts are actually tracking. You can usually see this clearly every 10 min on the Trends plots for V and I. Varying insolation can interfere with this too, so may need consideration.

Update the mppt firmware to the latest, if not done already. There's something fishy here, so a process-of-elimination..

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A way to isolate whether it's the MPPT or not is to swap them between the two arrays.