Battery inter-connect cable

[JusDreaming]

I know this has been hashed out before, but just want to confirm. I am adding two grp. 31 AGMs but don't have room to put them adjacent to the bank. So the new batteries will be approx. 12 ft. from existing bank. So in your opinions what size cables will I need? The existing bank has two batteries and will be charged by solar or genset/battery charger

[Andina Marie]

The + and - cables paralleling the batteries should be at least as heavy as your existing starter motor cables so you don't lose power or burn them out when drawing starting currents.

[djmarchand]

Do you have a separate engine starting battery? Do you have an inverter hooked up to the house batteries?

These are the only really high amp loads on a boat. If you have a separate starting battery and no inverter, then your highest load/supply device will be your alternator which is typically 80-100 amps.

#6 wire can safely carry 120 amps and will work as there is no supply or load that will exceed that. You will need a 100 amp fuse at each end of the 12' run to be safe.

[noelex 77]

Originally Posted by djmarchand

Do you have a separate engine starting battery? Do you have an inverter hooked up to the house batteries?

These are the only really high amp loads on a boat. If you have a separate starting battery and no inverter, then your highest load/supply device will be your alternator which is typically 80-100 amps.

#6 wire can safely carry 120 amps and will work as there is no supply or load that will exceed that. You will need a 100 amp fuse at each end of the 12' run to be safe.

Voltage drop is usually the deciding factor in boat systems.
Aswg 6 or 16mm squared is much too small for this application. The voltage drop at 100 A is 1.6 v. The current will not be 100A, but that voltage drop is way too high.

50 mm squared would be my choice, but you could get away with 35mm with some compromises.

[Viking Sailor]

With that length of run you would be better off setting the new batteries up as a second bank. You will need two switches. One to switch loads from one bank to the other and the other to switch the charging sources between the two banks.

[goboatingnow]

Originally Posted by noelex 77

Voltage drop is usually the deciding factor in boat systems.
Aswg 6 or 16mm squared is much too small for this application. The voltage drop at 100 A is 1.6 v. The current will not be 100A, but that voltage drop is way too high.

50 mm squared would be my choice, but you could get away with 35mm with some compromises.

I agree 50 sqmm at the minimum, thats a 8-10mm diameter cable

[JusDreaming]

I currently have two banks, one bank has the refridge on it and the other does have an inverter. No designated start batteries, basically I isolate the banks to maintain one bank as starting bank for both engines by combining the two. And I do have solar wired into the system which charges both banks by combining them. Then when the sun goes down I isolate the two. The easiest would be to add one battery to each side or use two perko switches like the drawing #3 attached shows

[Viking Sailor]

Configuration #3 looks good!

[barnakiel]

Maybe size for max apms you expect and the run. Then add 50% and you should be fine.

b.