question

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BMV-700 slowly returns to 100% without there being a charger attached.

Hi. I have a BMV-700 monitoring my amptron 100ah lithium battery which is charged from a redarc bcdc1225d with vehicle input whilst the vehicle is running, and solar input usually. For the purposes of testing the accuracy of the SOC I disconnected the solar and haven’t turned the vehicle on. If I run a load such as 6 amps until the SOC on the BMV is around 90% and I then leave it, it slowly trickles up to 100% even though the voltage stays within 0.1 of a volt. I end up with the SOC being 100% but the voltage being 13.25, for example.

My settings on the BMV are:
Battery capacity: 100ah
Charged Voltage: 14.1V
Tail Current: 3%
Charged Detection Time: 5 minutes
Peukert Exponent: 1.05
Charge Efficiency Factor: 98%
Current Threshold: 0.02A

When I recharge the battery I’ve tried synchronising manually but it doesn’t change anything.

I have a fridge which draws approx 4A when the compressor is running, but other than that there is no other load or input into the system at the moment, but the SOC still gradually returns to 100% over the course of a few hours or so.

Any clues as to why the SOC might be slowly trickling back to 100%? Thanks very much.

BMV Battery MonitorNMEA 2000 - N2K
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1 Answer
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T Cooper answered ·

I have an interesting development; there is a fake current which comes in when the display is asleep, and goes away when you wake up the display. I’ve video evidence of it now. Anyone had a problem like this before with the BMV700???

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How large is this current, to bring the SOC back up by 10Ah over a few hours means it is around 5Ah, much larger than the current flow through the backlight if a zero current calibration had been done with the backlight on.

I have done the zero current calibration when all the fuses were pulled and I know there is nothing being consumed. Here’s the video I took of it. I’m thinking it must be a problem with the gauge and I might need to return it or something.