question

jonathanr avatar image
jonathanr asked

MPPTs overcharging battery

I have a 14s4p battery made up of Nissan Leaf G2 modules and managed with a JK BMS. I also have a Pi running VenusOS and 4 Victron MPPT charge controllers. The battery doesn't have a Victron shunt or BMV; the JK BMS sends the battery voltage, SOC etc. to VenusOS.

The max cell voltage alarm on the BMS is set to 4.15v, and both the absorption and float voltages in each MPPT controller are set to 57.4v (average of 4.1v per cell). On the VenusOS, DVCC is enabled, but BMS control is disabled, so while the BMS provides shared voltage, the individual MPPT controllers control charging.

For the last couple of weeks, my battery has been basically full with only the small system loads (around 10w steady). My issue is that the MPPT controllers are charging the battery to above 58v until the BMS alarms and shuts off charging. At that point, the max cell voltage is at 4.15v while the lowest cell is at 4.14v.

I guess I can drop down the float and absorption voltages to 57.2v, but I'm confused why the MPPT controllers are charging above the set voltages?


MPPT SmartSolarmppt overvoltage
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1 Answer
nickdb avatar image
nickdb answered ·

Is temperature compensation enabled?

Moving to modifications section given the Pi and BMS etc.

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jonathanr avatar image jonathanr commented ·

It seems to be set at -64.80mV/degreeC (I assume this is the default since I haven't changed it). Daytime temperatures have been around 9 degrees C for the last few weeks.

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jonathanr avatar image jonathanr jonathanr commented ·
I wasn't familiar with temperate compensation, but the internet consensus seems to be that it should be turned off for Lithium batteries. So I'll try that.
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nickdb avatar image nickdb ♦♦ jonathanr commented ·
Yip. That is what the bms is for. Usually only enabled on an mppt that doesn’t have a lithium profile set.
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jonathanr avatar image jonathanr commented ·
Confirming that making this change solved the issue.
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