davidread avatar image
davidread asked

BMV712 discrepancy between SoC and Ah remaining

My customer has a BMV712 with 2x 12V 200Ah Gel Batteries in parallel and there is a discrepancy between the SoC reading and the Ah Consumed. His load is a DC fridge that draws 7A when the compressor is running.

For example, SoC = 91.6% with 19.9Ah Consumed.

This means that there is 380.1Ah remaining. Total capacity divided by Ah remaining should equal SoC. 400/380.1 = 95.0%.

The batteries can get cool overnight, say 10deg C. But the temperature coefficient is is set to 0.

Peukerts exponent should make the SoC read higher as the current draw when the fridge is running is low compared to the battery capacity.

Any help on this would be very much appreciated.

Thank you.

BMV Battery MonitorSOC
2 |3000

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1 Answer
JohnC avatar image
JohnC answered ·

Hi David, and welcome to the Community. Just some thoughts:

The BMV's reported Ah figure will be an 'absolute', as measured at the shunt. Peukert will be applied at calculation time, indeed increasing the 'effective' Ah used to calculate SOC.

I have no idea what algorithm Victron use to do that, but I suspect that's what your client is seeing.

There's also an 'Efficiency' figure in there too, which I always assumed was largely applied to the charge side, but *maybe* there's a portion of that applied to the discharge side to allow for batt self-discharge too?

For commercial reasons I wouldn't expect Victron to provide details of exactly how they do it, but these things could be experimented with, given patience..

Pb's can be frightfully inefficient too, and out-vs-in figures can often show <75%. Such is the real world..

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