Smartshunt on twin outboard 3 battery with common ground?

DIY
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1

Hello
I installed two 500A SmartShunt yesterday on my boat but doubts creeped in my mind. Main reason is that the port engine SmartShunt always show negative A values , even with the engine running and i am sure that i wired it correctly the right way.

1 SmartShunt for Port outboard = Port engine Battery
1 SmartShunt for Stbd outboard = Stbd engine battery and house battery both in parallel

I have two outboards on my Motorboat who charge 3 12V 95 Ah AGM Batteries as follows
Port engine starter battery is single battery and charged by port outboard
Stbd engine starter and house batteries are two batteries in parallel and charged by Stbd outboard
All three -12V posts are interconnected with jumper cables for having a common ground

Port engine starter battery +12V goes only to port outboard
Stbd + House battery bank 12V goes to Stbd engine and all other load as
navigation electronics, lights, bilge pumps, anchor winch, etc, etc

My question is regarding my setup as above:

  1. will the SmartShunt work as supposed if all -12V are interconnected?
  2. All -12V cables on each of the batteries shall be mounted to the Load Post on the respective Smartshunt, including the parallel jumper cable?
  3. The jumper cables go also on the Load Post on the SmartShunt?
  4. The jumper cables stay on the respective battery post to connect all -12V posts for a common ground, only the cable coming from the outboard and the other load cables are on the Load Post on the SmartShunt?

I understand that having the battery setup as i described above (1 starter battery and twin starter and house battery in parallel) is not very common, but that is how Grady White wire and install the batteries. I am not happy about that, but the boat is new to me and in winter i will change that to 2 x starter battery (one for each outboard) and 1 x House battery (most likely 100Ah LiFePo)

I hope my description is understandable, if not i may make a design of my setup.

Chris

2

I am not totally.understanding you descriptions and think you may have some problems.
The battery -12V go to the battery side of the shunt. This is the only connection to the battery -ve and shunt battery side. Every other connection goes to the system/load side of the shunt including your jumper cables for common ground. Do not common the port and starboard batteries themselves, common the load side of the shunts.

See the FAQ

https://community.victronenergy.com/t/shunt-battery-monitor-not-reading-the-correct-soc-amps-missing-solar-decreasing-daily-or-other-misreading-problems/87

3

Thanks pwfarnell!

Yes, both shunts are as described -12V battery pole to Battery 12V on the Shunt.

I will make a design to be clear how is my setup, that should avoid misunderstandings.
However, i went back to the bat and run into another issue, there is only one -12 Cable coming from both engines what let me believe that there is somewhere a -12V busbar where both -12 cables coming from the two outboards are connected together and then only one -12V cable goes to the batteries.
I always rigged my and clients boats by my self and i always had one starter battery for each engine and 1 or 2 batteries for house so i am a bit lost in how this boat was rigged and it seems to me it was rigged by the manufacturer as it is now.
I am investigating where the second -12V battery cable is, meanwhile i will make a design of the actual setup i have now.

Thanks again

Chris