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petajoule asked

MPPT 75/15 shows wrong battery voltage, results in detrimental behavior

MPPT75/15 conected to a 8 x 90Ah LiFePO4 battery bank and 2 x 260Wp Winaico PV panels.
There is a 230W microinverter connected to the battery bank, BMS system with overvoltage and undervoltage protection makes sure microinverter is turned off when battery voltage becomes too low, PV panels are disconnected when voltage becomes too high.

So far so good, has been working for almost 4 years with no problems. 3 days ago I noticed 0W microinverter generation amidst brightest sunshine. One battery dead - like 0.5V, one blown.

The VEDirect smart protocol shows an abnormal of 4 hours float before the whole system failed.

Changed the batteries LVP circuit closed and the microinverter started working. MPPT shows only float AND like 29V battery voltage, while voltmeter shows 23V.

Moreover, MPPT seems not to work if connected only to battery, it is only when I connect it to the PV that it starts working (Bluetooth connection that is). I would assume FW is newest as the VE:Direct Smart software would suggest an update (as it has done from time to time).

Naturally, as the MPPT detects a voltage far too high, it keeps the battery in "float" mode, while the BMS has already opened the low voltage protection circuit because two cells are below 2.7V.

Anyone experienced this, what could be the reason - is my MPPT toast?


If I completely detach the battery from the MPPT and keep just the PV connected, the MPPT still signals a constant battery voltage of 29.2V :-P

MPPT Controllers
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1 Answer
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petajoule answered ·

More observations:

VictronConnect (5.1 something) via USB from PC doesn't work, doesn't find the device. Bluetooth connection works.

When I disable the charger of the MPPT, the shown battery voltage starts dropping even below the 23.x V that the voltmeter(s - checked with two) show. Voltage returns immediately to fantasy levels as soon as the charger is enabled.

I guess I simply get a new MPPT and see how that works out. What I am quite uncomfortable with is that there is no error the MPPT is showing. Neither any LED code, nor internally and this specific type of errorneous behavior actually can and did kill my cells.

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Hi @PetaJoule

What I'm missing in your observations: did you measure at the MPPT's battery connection terminals?

What you describe sounds like a loose battery connection / open fuse / etc.

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petajoule avatar image petajoule Daniël Boekel (Victron Energy Staff) ♦♦ commented ·

Open (burnt) fuse it was! Why - not sure yet.

Can you confirm that with an open fuse VE.Direct via Bluetooth works while via USB doesn't?

Replaced the fuse and VE.Direct via USB started working. It's quite intriguing.

Also, FW was 1.39 the PC did update it to 1.42. Equally intriguing, as the Android/iOS VictronConnects didn't offer any FW update.

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