Battery Monitor Shunt Wiring

[YukonRon]

I'm installing solar on my R25sc and also adding a Victron BMV-712 Smart battery monitor. Instructions say that the shunt goes directly to the negative terminal, and ALL negative connections go to the shunt so that all current flow is measured. Unfortunately, It's not that simple in our boats. We have 3 battery banks (house, engine , and thrusters) with ACRs in between. Various circuits are connected to the negative posts on each battery, as well as the BUS bar. The engine battery has ECU leads directly connected; the thruster battery has thruster leads directly connected, etc.
I'm really only interested in monitoring the house bank, but understand that current flow from all charginging sources will flow through the other banks when the ACRs close. In order to get an accurate measure of all current flow in and out would mean moving ALL negative leads to the BUS bar. Is this acceptable given that the 3 banks operate in isolation when the ACRs are open?
What have others done when installing a battery monitor on these boats?

 

[trailertrawlerkismet]

Ron, I installed the same unit on our R29S. Not sure if what I did for my install will be helpful or not for you but I had a like type gauged negative cable made by a local parts store. I installed this from the shunt to one of the House batteries to complete my connection. May not apply to how your battery banks are set up but it worked for me.

Jim F

 

[fishheadbarandgrill]

You only need to monitor your house bank.

 

[YukonRon]

Ron, I installed the same unit on our R29S. Not sure if what I did for my install will be helpful or not for you but I had a like type gauged negative cable made by a local parts store. I installed this from the shunt to one of the House batteries to complete my connection. May not apply to how your battery banks are set up but it worked for me.

Jim F

Jim:
Yes, I will do that to connect the shunt to the battery, but I'm confused about the LOAD end of the shunt. Did you move every negative cable to the shunt, or do you still have negative cables connected directly onto the Engine and Thruster batteries too? Do these cables need to be left on their respective batteries, because those banks will be isolated by the ACRs, or should they be moved to the shunt so I can measure the current flow when these devices get used?

 

[YukonRon]

You only need to monitor your house bank.

Bob;
I am really only interested in the House bank, but just want to be sure if I can isolate it. When the ACRs detect charging, from any source, they will close and send current in to ALL battery banks. When drawing power from the House bank, the ACRs remain open so the the current flowing out comes only from the House bank. So will this skew the battery monitor's readings, because current flowing out of the house bank will not measure the same as current flowing in?

All charge current will flow through the common positive to all batteries because the ACRs are closed, but the BMS will ignore charge going to the Engine and Thruster banks, if their ground cables are by-passing the shunt. Is that that correct? Maybe I just answered my own question? I believe that is the case but I'd like to confirm it.
I just got confused when all the install documentation insists that absolutely nothing should be connected to any negative battery post without going through the shunt. Nothing seems to address the situation of having multiple banks separated by ACRs.

 

[Red Raven]

Hi Ron,

Only the house battery negative is tied to the negative side of the shunt. All other negative connections including the buss bar and negatives to all other batteries are tied to the other (load or system) side of the shunt. That way only current to and from the house is measured. Charge currents going to the other batteries when the ACRs are closed will be ignored because they bypass the shunt (which is what you want).

Curt

 

[YukonRon]

Thanks guys. Yes, I think I had it right all along, but confused myself thinking about all those other connections.

 

[iggy]

I'm installing solar on my R25sc and also adding a Victron BMV-712 Smart battery monitor. Instructions say that the shunt goes directly to the negative terminal, and ALL negative connections go to the shunt so that all current flow is measured. Unfortunately, It's not that simple in our boats. We have 3 battery banks (house, engine , and thrusters) with ACRs in between. Various circuits are connected to the negative posts on each battery, as well as the BUS bar. The engine battery has ECU leads directly connected; the thruster battery has thruster leads directly connected, etc.
I'm really only interested in monitoring the house bank, but understand that current flow from all charginging sources will flow through the other banks when the ACRs close. In order to get an accurate measure of all current flow in and out would mean moving ALL negative leads to the BUS bar. Is this acceptable given that the 3 banks operate in isolation when the ACRs are open?
What have others done when installing a battery monitor on these boats?

If it was me?? I would tie all the Neg battery post/wires on a bus bar as you mentioned. Basically they are all tied in anyways and this is how your parallel switch works. Anyways, than use your shunt and reattach the Neg side of all the loads. The shunt can handle up to 500 amps and I don't think but and not sure if your starter pulls more than that. They do make bigger shunts.

Now you can use the battery's on and off switches to monitor each bank. Great for trouble shooting if you having a problem with any one bank. So if you want to see the house only, than turn off the starting and thuster batteries. But they should not be pulling a load anyways. If they are, you have a problem!