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cottersay avatar image

Victron BMV 712 Smart battery monitor -- WTH??

I have the Victron BMV 712 Smart battery monitor (with two 100Ah BattleBorn 12V Lithiums), and while the monitor works great when boondocking, it does not work great on shore power; the readouts then make no sense: State of Charge (after a week on shore power): 13% (and dropping); Voltage: 14.44V; Current: -2.52A; Power: -36W; Consumed Ah: -186.9Ah.


Any idea what's up here?


Thank you!


-Cotter

BMV Battery Monitorvictron
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4 Answers
Mike Dorsett avatar image
Mike Dorsett answered ·

Please can you indicate your schematic? From an initial guess it would look like the shore power charger is wired to the wrong side of the shunt...so the charge current isn't being monitored, but the discharge is.

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Matthias Lange - DE avatar image
Matthias Lange - DE answered ·

There is a ton of other questions about this topic. In most cases it's a wrong wiring of the shunt.

In your case I guess the charger is connected directly to the battery and not to the shunt.

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Thanks guys, but this is exactly how I have my own system wired up (The converter's positive output goes to the battery's positive side and the converter's negative is grounded to the chassis, as is the shunt):

582-bmv-20181221133007.png

Oh, and I should add that when I was charging the batteries with a generator (which has a floating ground), the readouts of the BMV made perfect sense, but on (bonded ground) shore power, they make no sense whatsoever.

Please make some pictures of your installation (battery and shunt wiring).

cottersay avatar image cottersay Matthias Lange - DE ♦ ·

Here is some more info on the issue:
When I unplug from shore power the batteries are fully charged, even though SOC may read 13% or less.

When I charge the batteries while boondocking with my portable gas generator (floating ground), the 712 monitor has all of the correct readings. I have to charge the batts every day with the generator (at 10,000 feet the genny huffs and puffs inefficiently along). I manually reset the SOC to 100% after a full charge while boondocking. I also charge from my RAM’s alternator at that altitude, because the genny can give out and refuse to start. The RAM method is rather ineffective, but when you absolutely need to pull the awning and slide back in with dead batts, well…

I also tried to clear the History on the app, but there is no longer a “clear history” selection under Miscellaneous.

Photo of my battery setup. Shunt is water sealed and hard to get to, but it has no other wires or loads attached to the terminals.


batts.jpg

batts.jpg (1.3 MiB)
The cable coming off your battery negative should go directly to the shunt battery connection, your earth, all loads and charge sources should go to the load side of the shunt.

From your picture it appears that your battery is ‘earthed’ prior to the shunt.

Thanks Vance, but the ground-looking connection is actually a floating SPST battery switch.


The wiring is this: From the negative batt terminal to the SPST lug 1, from SPST lug 2 to the Victron Shunt input, from the Victron shunt output directly to chassis ground.
Mike Dorsett avatar image
Mike Dorsett answered ·

It looks like the battery negative is grounded, rather than floating. The connection from the battery negative to the shunt should be regarded as a 'live' connection, and the non-battery end of the shunt regarded as the true ground. This is what's allowing the charge current to bypass the shunt - as you say the charger negative is also grounded.

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Thanks miked, but the ground-looking connection is actually a floating SPST battery switch. The wiring is this: From the negative batt terminal to the SPST lug 1, from SPST lug 2 to the Victron Shunt input, from the Victron shunt output directly to chassis ground.

cottersay avatar image
cottersay answered ·

Guys, just to put the solution here for folks who may have the same problem as I. All I had to do was perform a full BMV reset back to factory (long press Setup and Select at the same time), then re-enter the Lithium battery's parameters, and all is now well so far!

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