wgrygus avatar image
wgrygus asked

BMV712 Voltage Drop

I hooked up the 712 and the soc says 100% but as soon as I put a slide out the voltage plummeted to 12v but still said 100% soc

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2 Answers
geomz avatar image
geomz answered ·

A bit more information is needed,

What kind of battery?


How full/charged?

I'm going to assume lead-acid based on how you describe the issue.

Keep in mind that SOC is not at all dependent on voltage (like those old brick-led push button things). The SOC measures the actual current flowing into and out of your battery.

Thus, to work correctly it has to have a known state of charge. Meaning, the battery has to be fully and completely charged and then the SOC will be 100% and accurate.

The BMV has to also be configured correctly for the chemistry of your batteries (lead-flooded, lead agm, lithium) and configured for the correct capacity and voltages, tail-current, Peukert factor, charge efficiency, etc.

Even with that, lead acid batteries suffer what is known as current voltage sag. Meaning, under a heavy load the voltage will tank (as will capacity). But, depending on charge, the voltage should recover when the load is reduced.


Double check your BMV settings and match them to your battery.

Fully charge the battery (including a full absorption cycle).

Then watch the BMV do its magic, despite voltage swings :)

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wgrygus avatar image
wgrygus answered ·

Geomz I did the set up as per the manual and have brand new batteries. Is there any calibration or reset for the soc? The new batteries still show 100%

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geomz avatar image geomz commented ·

A BMV has no real knowledge of the charge of a battery until it has gone through a full recharge cycle and seen the tail current/ voltage dropoff configured -as appropriate for that chemistry.

Are these lead or lithium batteries?

You can manually force it to 100%. And it "assumes" 100% the very first time it's turned on. And can be configured to "assume" 100% on reset (not advisable).

But a full charge cycle is the only way to make sure they match.

As you turn on loads, I assume you're seeing Amps - and as you're charging I assume you're seeing Amps +?

So, I'd just let it charge from your charger until it's really full. Then the bmv will match (pretty darn closely) to real charge. It will, over some time, drift, as any battery monitor will, and will require an occasional full-charge cycle to get things back in order.

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geomz avatar image geomz commented ·

Also, if you don't already have it, download the VictronConnect app for your appropriate mobile device (Andriod or iOS). Since you have a 712, with Bluetooth, that's a MUCH easier interface than that pixely looking goofy "text" on the device itself.

It's fine for numbers, but with text and all the scrolling... well, that's not so much :)

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