Originally Posted by Chris1573
I am in the process of fitting a dual battery system using the Merlin VSR charging relay and isolating switch block. This allows you to parallel the batteries if the crank battery goes flat.
Merlin suggest that fusing both the batteries is a good idea. Is this the case?and if so what size fuse would I need to ensure it does not blow when cranking a cold 90HP engine.
Of course all the instruments and switch panel are fused seperately anyway they are actually talking about fusing the two positive terminals on the batteries.
Hi Chris, there is no need to fuse batteries for a 90 Hp engine.
Perhaps for an old Diesel with high compression but not a 90 hp petrol.
There is little that the second battery can assist in torquing a 90 Hp petrol engine to start. Furthermore based on little old Kirchoffs law (split currents) and internal resistance of the batteries, You would need both batteries to be in equally good condition.
For what you want, I suggest a Bosch or Lucas Hot start system. These can be charged to near perfect whilst carring on board as back up.
If these cannot start your engine given that any young man can hand start a warm 90 in reasonable condition, then you should not put to sea with such a crock.
You will seriously mess up the batteries by fusing...