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Paulio avatar image

BMV Charge status still 100%. Voltage down to 12.3V

I have a BMV connected to GX. There is a steady draw from the batteries which is dropping the voltage slowly but not registering on the state of charge. The state of charge works when under heavy load. Is there a reason for this please as at 12.3V I would expect less than 100%. The full charge settings are correct and I have performed a factory reset.

BMV Battery Monitor
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Having checked the connections I can confirm that all the negative connections and chassis are connected through the shunt. Is there any other possible explanations please?

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Ross avatar image
Ross answered ·

I now have my SOC showing the correct reading. My issue was setup. The setting "Charged voltage" was set to zero volts. This may be the default from new or it may have occurred after the firmware update.

Check the setup for that parameter. It may fix a number of issues on this thread.


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Hi @Ross, what do you mean by "The SOC reset was set to zero volts?"? Are you referring to the value of the charged voltage setting?

Yes in the manual there is a setup for soc reset. There are 3 factors, battery fully charged voltage, a current less then set vatue, a period of time set value dependent on the battery. You can opt to have auto reset on or off. Mine was on with zero volts.

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MrDias answered ·

i am having the same problem, with a LifePo at 13v the BMV is giving me 100% battery. This last night for example i went to bed with 75% and woke up after 2h of cloudy day at 100%... thats impossible with the amount of solar i have. Yes the shunts is the first thing coming out of the battery negative.

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What settings are you using? both in the BMV as in the charger(s)?

i followed Ross advise, the SOC reset setting in the bmv (setting number 3) was set at 13.4v, changed it to 14v, seems good now.

Forgive me if this is a stupid question. But I was having the same problem, of SOC = 100%, despite battery at 12.5v. So I changed the "charged voltage" setting from default 13.2 to 14.1, since I'm usually solar charging. But the SOC still reads 100%. Further, since I'm now concerned about my battery health, I tried to recharge with a generator. However, it seems that the system thinks it's at 100%, so float stage, and only draws 15 amps (it would usually draw 50+ amps off this Honda 2000W). My battery bank is two 8D batteries, so 15 amps will take forever. Or is something else wrong? Many, many thanks in advance

Ross avatar image
Ross answered ·

I have the same problem that under very small loads and when the load is almost equal to the solar input my 712 did not pick up that the battery was going flat. It seems that the monitor is not picking up the small incremental loads. The first sign of trouble was when the battery monitor alarm came on. I can confirm there are no loads on the battery side of the monitor shunt. The shunt is reading the correct current. . The unit is reading the correct voltage. I was also asked to do a firmware upgrade recently. I am suspecting that this is a sampling issue with the monitor. The battery is new and accepts charge. Any ideas??.

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Luit-Jan answered ·

Gents, my (old) battery has according to the specifications lots of Ah. And also this battery keeps on saying that it was at 100% even with voltages lower than 23,9 V

I decreased the capacity in the settings and now the charge status is more according to the voltage. Some tuning with the capacity in the settings results in a reliable number.

And so I found out that my battery has lost lots of it’s original capacity. :-(

So my message is: tune your battery capacity. Hope it helps . . .

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Paulio avatar image
Paulio answered ·

I found the issue to be the zero calibration. Also a defective battery was not performing to expected Ah.

With zero calibration carried out the system is working better.

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JohnC avatar image
JohnC answered ·

You could try 'tuning' your BMV via Peukert factor, Round-Trip-Efficiency, etc. Inappropriate settings will accumulate the error.

https://www.victronenergy.com/blog/2017/04/13/instructional-video-how-to-optimise-the-bmv-700-series-sync-parameters/


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Thanks, will give it a go.

Did you find a solution? I'm having the same problem....

Hi, no unfortunately not. Under very low load the BMV rails to register the current. Higher loads are fine. Ive tried everything now and am out of ideas.

Mine does register current but the SOC still doesn't match up with the level of charge as indicated by the voltage reading. Having issues with my charge controller now as well.


Extremely frustrated

Paulio avatar image
Paulio answered ·

I have checked and tested all wiring and it was good. I have found that my Venus GX & Router are taking a combined 300ma. I put the system onto a single battery and connected the - for these two directly through shunt to battery -. The BMV still doesn't show any current or charge drop but the voltage drops steady over time. The BMV functions correctly under higher load (fridge/lights etc). Could it be a faulty shunt? Not sure what else it can be now.

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Graham avatar image
Graham answered ·

Maybe this might help regarding where the shunt goes and how


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WKirby answered ·

That makes me think that your battery wiring is incorrect. Are you certain that you have wired the shunt correctly?
Remember, you are not to connect any loads at all to the negative terminal of the battery, the shunt must be the only thing connected to the negative terminal of the battery and the negative of the loads connect to the other side of the shunt.

https://www.victronenergy.com/upload/documents/Quickinstallsheet_BMV70x_part1_2.pdf


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Thats what i though too. Here is a video; somewhere half way they explain it perfectly:


https://youtu.be/tV055vmZgvY

Thank you both for your reply. Is far as I'm aware its all wired correctly. I have recently rewired the system and I wonder if there is somehow a 'Stray load'. Ill double check that. Thanks once again.