SmartShunt Installation - Marine - Emergency Parallel

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rudders asked Nov 30, '23

SmartShunt Installation - Marine - Emergency Parallel

Hi folks,

I have a twin diesel 40ft Cruiser with the following 12V system.

a house battery bank - 2 * 270AH AGM in parallel
a starter battery bank - 2 * 185AH in parallel
2 Volvo Deisels ~ 500HP each.
relatively low load on the house bank - 10A typically (fridge, lighting etc) - 200A peak if the inverter is on and we're boiling the kettle ;)

I want to install a SmartShunt on the house batteries and monitor the starter bank with the Aux which all seems pretty simple and instructions for this are clear. But I have a couple of related questions. The house and starter bank can be (emergency) paralleled in the event that the starter bank is flat or otherwise insufficient to start the motors. This would obviously put the starting load onto the house bank essentially.

Do I need a Shunt that is sized to cope with this sort of starting load in the event we need to parallel?
Any thoughts on whether 500A SmartShunt is enough or should we upgrade to 1000A or 2000A?
Could the emergency parallel circuit be left direct to the battery and avoid the Shunt meaning the 500A would probably be sufficient..

Cheers and Thanks in Advance

Rudders

SmartShunt marine

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Answer 1 · 2023-11-30T09:54:00Z

pwfarnell answered · Nov 30, 2023 at 09:54 AM

If you connect the start battery negative direct to the house bank negative bypassing the shunt it would need to be switched because if it was permanently connected it could be a route for current flows to bypass the shunt and not get counted depending on how the boat is wired.

If it is a permanently wired connection without a switch the proper place to connect is on the load side of the shunt to avoid bypass routes. There have been questions about this before and the consensus was that a 500A shunt is fine, it will give a bit extra voltage drop but will not measure the peak current. If you put a larger shunt in you will loose accuracy for counting low loads.

See for example

https://community.victronenergy.com/questions/121755/bmv-702-shunt-max-short-time-current.html

and other threads can be found using search.

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rudders commented · Dec 01, 2023 at 03:09 AM

Thanks for the info - much appreciated.

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