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vocoder asked

SOC 6%, Voltage 14.2 - Normal?

New to the game and just had my RV fitted with lithium batteries (400Ah), additional solar panels (600W total) and a BMV-712. The BMV-712 shows a 2.8A load with the battery cut-off switch enabled. After 6 days, the SOC was showing 6% (no use, RV sitting outside in the California sun, battery disconnect set to off) and the voltage showed 14.2.

I discovered the "Zero Current Calibration" procedure in the manual, and have yet to perform it as the trailer is still in storage. But that made me wonder:

- Is the SOC reading affected by the potentially inaccurate 3A draw reading, and the batteries themselves are (near) fully charged?

- If SOC really is 6%, wouldn't the batteries show something less that 14.2V?

I enjoy learning about these things, but admittedly, am just starting out with Lithium/Solar/Victron. Thanks in advance for any advice.

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2 Answers
wkirby avatar image
wkirby answered ·

If the BMV is showing 2.8A discharge and there is actually no current flowing, then the zero current calibration procedure must be performed. Easy to do on the app, just ensure that absolutely zero current is actually flowing when you do this.

If the BMV was wrongly measuring 2.8A discharge then it will calculate the SOC based on that information and so the SOC will decrease as it has done.
The SOC calculations are based on current flow into or out of the battery, the battery Voltage is not considered. Besides, lithium batteries' discharge curve is too flat and so Voltage to one of the most useless parameters for estimating SOC with these type of batteries. Only the top and bottom of the discharge curve are of any use to prevent cell damage.

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vocoder avatar image vocoder commented ·
Calibration done - and everything looks better. Will now wait a few days and check the SOC. Thanks!
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Nev avatar image
Nev answered ·

At 14.2V I would reset our monitors to 100%. In fact both would automagically do that within a few minutes.

Assuming that the battery is indeed isolated from all loads the BMV-712 is likely either faulty or requires calibration

Check the inline fuse. Our Victron SmartShunt gave strange readings once apparently caused by a poor fuse to end cap connection. A simple unscrew and rescrew fixed it.

Although battery voltage is a usually a poor indication of SOC what I can tell you is that for our now 8 year old 4 cell 300Ah LiFePO4 battery it is ALWAYS at 100% SOC when the voltage reaches 14.1V at the battery terminals whether we are charging at 1A or 140A from solar and alternator.



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