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Hello,
I have a BMV712 Smart battery monitor and I am trying to connect it to a dual battery setup on my boat. I have the temp sensor version. I am having difficulty interpreting where I should hook the sensor up. Should I have two because I have two batteries? Or prioritize a single battery (which one?) I've attached my schematic for your review. I appreciate any assistance you may be able to provide.
If you want to fully monitor both batteries, including state of charge then you will need 2 BMVs, one connected to each battery. You can not monitor both batteries with one BMV because it needs to measure current in and out of the battery (bank). Most people only monitor voltage on the starter/crank battery.
As mentioned previously, the shunt of the BMV needs to connect directly to the battery negative with NOTHING else connected to that side of the shunt. In fact, your diagram shows BOTH sides of the shunt connected to the house battery negative and the negative busbar.
Here's a diagram that might help:
https://www.victronenergy.com/upload/documents/DS-Lucians-Victron-Van-Automotive-Alternator.pdf
As I understand it, your question is starter or house battery.
Most starter batteries get used for little except starting the engine, then the alternator takes over and handles the loads. Also they're charged direct from alternator which has no temperature compensation. So little need for it on the starter side.
The BMV is designed to monitor a single battery bank fully, and voltage only on a second battery.
Looking at your schematic, it looks as if you're not wiring the BMV properly.
It should be connected directly to the negative pole of the house battery. Nothing else should be connected there. All the negative connections, including battery grounding, should be to the load side of the shunt. No exceptions.
There must also be a good connection between the house and starter battery, looks like that's in. If they're separate systems, voltage on the starter will be wrong.
So temp sensor to house battery, look at shunt wiring.
Ok, so if I understand you correctly:
The two batteries will be connected via negative terminals, then, 1 neg wire to the shunt. Then, 1 neg wire from load side of shunt to the neg bus. All other neg connections attached to the neg bus? I do believe I have it that way in the schematic. The only other wires going direct to one of the neg terminals is a small ACR wire (which I have been advised must be connected directly to the neg terminal of one battery, I had assumed crank battery so that it can ensure the crank battery is always good to go? But I now see my schematic has the ACR neg wire going to the house battery, I can change that so that it is connected to the crank battery) and my dual bank battery charger (which I was also advised must be connected to the neg and of course pos terminal on each battery). Looking at it closely though, I do also see the engine Neg wire is hooked direct to the neg terminals. Should I relocate that to the neg bus? Or is that a no-no? I figured it was best connected direct to the neg battery terminals.
With respect to the temp sensor wire, thank you so much. I will ensure it goes to the house battery :-)
Starter battery neg to load side of shunt/neg Bus. You must wire so this only keeps voltage the same. This makes sure no current that should be measured for the house battery can bypass the shunt.
Ok, so starter battery neg to the load side of the shunt. Then, load side of shunt to the negative bus? Does this mean the battery only side of the shunt goes to the house battery?
Also, I see that the "load" and "charger" are referenced as the same side on the
instructions but I had no plan to connect the NOCO charger to the shunt, only to both batteries + and - terminals as per the charger instructions. Is this correct?
No. The ONLY thing that connects to the house battery negative is the battery side of the shunt. Most instructions for devices like the noco charger don't consider things like the BMV's shunt.
Again: the house battery negative connects ONLY to the shunt's battery terminal. Nothing on the shunt battery terminal either besides the battery. ALL negative connections to ALL other devices connect to the load side of the shunt.
If you still have doubts, I suggest you find a local installer.
Ok. Thank you for this answer. So, how do I connect the two batteries (house and starter)? Currently, they have a neg wire connecting the two. I'm assuming this is incorrect based on your answer?
It seems like I should instead make the only connection that they have in common be the neg bus? My only other thought is what I do with the ACR which requires connection to one of the grounds (starter battery as I understand). Otherwise, they are just connected to the + terminals of each battery.
I'm attaching a revised schematic based on your feedback for review.
The negative connection between the batteries goes from the load side of the shunt to the negative side of the starter battery.
Your updated schematic is still not going to work.
Should be:
House battery neg - shunt battery
Shunt load - neg Bus.
Starter battery neg - shunt load.
All other negatives to neg Bus.
Note: nothing except shunt battery to house negative.
There's another problem. Your charger connects the positives of the starter and house battery. I don't know the charger, but unless it's built to charge both types of battery at the same time and without allowing a cross current between them, Don't do it.
Thank you so much for helping me out with this. I truly appreciate it. I am going to have to contact NOCO to confirm that my dual bank charger to inquire about cross currents as I am not aware.
I updated my schematic again and believe it reflects what you last explained. 
You still have connections to the negative pole of the house battery bypassing the shunt.
There's a good diagram in the quick start guide. Number 11 is your starting point.
