trfarmerjr avatar image
trfarmerjr asked

BMV 712 wiring

I installed the BMV 712 to my motorhome

Set up is 4 - 6v agm batteries 2@ in series and then parallel for a total of 12v 448 AH for house batteries.

My starter batteries are a bank of 2 12v paralleled

The BMV shows 13.4 - 13.7 V, +14 - 15 AMPS when plugged into shore power and charging, when unplugged and drawing from the batteries the BMV still show a +14 AMPS.

I am not getting a reading from the starter batteries.

I am ok with reading the total of the 4 connected house batteries. Mid point not needed?

Wiring drawing is attached. Where did I go wrong?

BMV Battery Monitorinstallation
bmv712-wiring.jpeg (187.2 KiB)
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1 Answer
Mark avatar image
Mark answered ·

It's not a good idea to monitor current flow in/out and SOC% of multiple DIFFERENT battery banks - particularly if one bank will be disconnected at different times. You wont get much 'sensible' data out of the BMV.

I would only fully monitor current and SOC% for the house bank and use the B2 auxiliary input to only measure the voltage of the starter battery bank.

BUT if you really want to measure current flow in/out of the starter battery together with the house battery bank then you need to move the starter battery negative cable to the 'BATTERY' side of the shunt if you want it to be considered by the BMV.

Also be careful as the supplied shunt is rated to 500A and the cranking current of a big engine stater motor could potentially be higher.

If you see a current reading with your current wiring (even though you don't expect it) then there really is some current flow in/out of the house battery bank - either from one battery bank to another battery bank or from a charge source or to a load.

A + (positive) current reading means charging and a - (negative) current reading means discharging.

It's also best to run a dedicated negative cable for all loads and charge sources direct to the shunt 'LOAD/CHARGER' side, rather than using the the chassis as the return path.

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trfarmerjr avatar image trfarmerjr commented ·

Voltage from the starter battery is all that I expect. I have the small fused wire running from starter positive to B2 and get no reading.

I do not understand why the large +14 amp reading on the house bank while discharging. Basically I have a $200 volt meter at this point. Do you see anything wrong with the wiring?

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Mark avatar image Mark ♦♦ trfarmerjr commented ·

Its good to know what you expect and that will work when setup correctly.

Is the RELAY that you have on the positive side (linking the 2 batteries together) open or closed when the BMV displays +14A? Check this.

If closed then there will be some current flow between the 2 batteries - whichever battery is at a higher voltage will transfer charge to the other until they equalize. This will happen even if 'discharging' from the two banks combined - the battery bank at a higher SOC could be powering the load and transferring charge to the other battery bank simultaneously.

If you want to use the auxiliary input B2 to monitor the starter battery you should also check the BMV settings are also setup accordingly using Victron Connect. Go to Settings > Misc > Aux input > ensure it is set to 'Starter battery'.

Then check that the BMV its set to display the starter battery voltage under Settings > Display > ensure that 'Starter voltage display' is active/on.

Also check that the fuses in both positive supply cables are not blown.

In terms or wiring it should 'work' as you have it but this is the wiring diagram from the quick installation guide;

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1564109819296.png (73.6 KiB)
trfarmerjr avatar image trfarmerjr trfarmerjr commented ·

The starter battery is open. I will be back to the RV Wed. I'll check the B2 or starter set up again. I still have no idea why the positive amperage reading.

Thanks for your help.

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