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The boat I have has 2 Volvo D4 260 engines. There are 4 batteries. 1 is dedicated for starting the Port engine and the other 3 are for starting the Starboard engine and supplying the 12v power to the boat, therefore the starting amps will be going through the shunt. I cannot find out how many amps starting takes. What is the maximum intermittant power I can put through the shunt?
I wonder about the same thing, i have 2 x Volvo Penta TAMD 74P. The starter takes 3600 watt, that means 3600/12 volt = 300 amps. So i think starter on mye engine will be okay?
I don't believe the issue is what the shunt can take. The starting amps won't be there for long enough to really heat the shunt up.
The issue I think is with the electronics. It measures the voltage across the shunt. If you exceed the shunt rating, you also exceed the maximum voltage the BMV was expecting. I suspect at this point the BMV would clamp the voltage in some manner and you would effectively inject (small) errors into the BMV's calculations because the voltage-current relationship is no longer linear. I don't know how safe it is for the electronics either. The exact behaviour and impact only the Victron designers can tell you.
The fix (to my mind, others may have differing opinions) is to have a dedicated return for the starter so it bypasses the shunt.
You could also use a high current shunt (kilo amps are possible) but you lose resolution at the low end for smaller currents. Except in fringe cases I'd guess you lose more than you gain with a high current shunt.
