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jabdy asked

Different V showing on BMV 712 Smarts

I have 2 identical battery banks. Each lifeline AGMs 900Ah.

They each have their own BMV 712 Smart. They both show the same readings, though the SOC % slowly drifts apart a little until I equalize.

I also have a 'Master BMV' this always shows a different V usually around 0.1 lower.

So at the moment the BMVs are showing 12.66 for each bank and the master is showing 12.58. The voltage at the bars where all the large wires come into with the fuses is 12.62.

From this I am assuming that the individual BMVs are showing the correct V.

And charging the batteries on this reading.

Is that correct?


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kevgermany answered ·

SOC shouldn't drift if you fully charge the batteries, the BMVs resynch to 100% on each full charge.

BMV does not control charge, it reports it. If the BMV is connected to a GX, then some chargers can be controlled by the GX based on BMV readings.

The lower master voltage indicates high resistance in its connections. Could be the fuse.

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jabdy answered ·

Sorry, I didn't mention that I am on a boat and sailing in the S Pacific without shore power available. Been without it now for over 3 months.

I equalize every 2 weeks and set SOC to 100% on completion.

The BMVs are connected to a colour control. The master BMV is consistent in its V difference.

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kevgermany answered ·

Your charge controllers are charging to this point, yes. The lower readings will be due to resistance, possibly minor differences between the individual BMVs and the master BMV. Could be corrosion. Might be worth charging to a higher voltage if you can

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jabdy answered ·

Ok. Thank you. I think I'm probably being a little anal. The batteries are now working very well since I have been equalizing regularly. Prior to that it was a bit of a disaster.

But it does take around 14 hours.



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kevgermany answered ·

Might be worth sharing the charger battery settings. Looks to be too low. Also the BMV battery settings.

Unless recommended by battery maker, not a good idea to equalise AGM batteries.

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pwfarnell avatar image pwfarnell commented ·
Lifeline do recommend equalising their AGMs, one of the few that do.
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