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sailallday avatar image
sailallday asked

BMV-712 what info is accurate

my 712 monitor will show battery voltage of 12.1 volts, yet the battery % shows 71% and my AH's show -158 out of a 440 AH battery bank. this does not make sense to me. 12.1V should show a battery down 50%, not 71%. 158 AH out of 440 AH should show 36% for the battery %.

my question is, what is a reliable source of info on the state of the battery? should i use the voltage, the battery % or the AH's? Are any of those measures actually accurate? if there is any charging or a draw on the battery, i would think the V is not an accurate measure.

Also, why would my monitor show 71% on the battery but show 12.1 V? is that just because there was a drain on the battery at the time so the V is not accurate? i would think those 2 numbers are tied together.


thank you


monitoring
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Stefanie (Victron Energy Staff) avatar image Stefanie (Victron Energy Staff) ♦♦ commented ·

Hi @sailallday,

in order to help there is more info required.

What type of batteries. Parallel or in series configuration. BMV settings.

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sailallday answered ·

Sorry for lack of detail. I have 2 sets of 6 volt lifeline AGM batteries. Each pair is wired in series and then paralleled to the other two for a total of 12 volts and 440 amps. I am not sure of my settings in the 712 outside of I use a 20 hour capacity. I can check that later and post. thank you

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wkirby answered ·

Did you set the AH capacity of your battery bank in the BMV settings?
The BMV calculates % and Ah by measuring the amount of energy flowing out of or into the battery bank. It does not use the Voltage to calculate the % or Ah used as this is a really vague way of estimating the SOC of a battery.
If set up correctly, a 158Ah drawn out should show a SOC of around 64% for your 440Ah bank.

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sailallday answered ·

Yes, I did set up the BMV for 440AH but I will double check that. Agree, based on -158AH and a 440AH battery bank, I should show an SOC 64% and I show 71%. Not sure why that is calculating that way based on what you said unless my AH capacity is not set up correctly?

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