Allen,
The strap between the two 6volt batteries should be the same as the
cable on both ends. More is no value(except as a cash reserve?) and
less is probably not much of and issue except as voltage drop. It will
be in -relatively- open air and if it gets hot enough to smoke it should
get your attention before it causes real trouble.

The fact that you are successful with three parallel pairs is quite
remarkable. The stacks (pairs) should not be counted on to share load
equally. It is actually very hard to make batteries do that.

I am surprized that a 250amp fuse will crank a 4-108. It must be a
better starter than the one I measured. Take good care of it.

Fair Wind and Smooth Sea
Matt Colie

bushman wrote:
Thanks Chuck and Matt
I think I am OK with the size wire from the batteries to the boat or engine
but what is the load on the wire that joins the two 6 volt batteries in a
pair in series? I have three pairs joined in parallel so I'm guessing that
each pair would have one third my max load and the wires joining them would
need to be sized for accordingly. I generally like to go a size larger. You
never know when I might get stranded somewhere and can sell the copper off
to get me to the next island. The 250 amp fuse on the starting battery has
never blown. The Perkins generally fires on the first revolution but one
time I lost prime and had to crank for half a minute or more at a time and
the fuse held.
- Allen

"witheld" wrote in message
...

Allen,

Wire must be sized for the expected load.

It should be fused to protect it and the connected equipment form damaging
current in the case of failure.

The cranking current of a 4-108 at shirtsleeve temperature is hard to
measure, but the peaks are around 500-600 ampere for 70-100 miliseconds
then dropping to 300-400 between peaks. If the fuse is in the cranking
circuit, I'm surprised it is still intact.

Stater motors are not very voltage sensitive. Most engines can crank on a
#2AWG wire and not have a problem.

Do not try to set up to crank from the house battery, just be sure that
the only load on the start battery is the engine. It is a waste of time
and effort and will only cause you problems.

This is what I do www.southpointechandler.com, in my area of the world.

If you want to discuss this more, I'm here alot.

Matt Colie


bushman wrote:

I am ready to install new batteries. I have not found a reference for
wire size - between - batteries. I have six T105 six volt batteries. What
size wire should be used to series and parallel them? The boat has 2/0
with a 250amp fuse running to the battery selector switch. I am not sure
how much my started draws (Perkins 4-108) but I would like to size to
start from either the starting or house batteries or both. One more thing
that does not look right is that the Neg wire on the starting battery is
size one or two connected to the house bank Neg only. Shouldn't there be
a jumbo size wire directly to the engine block at the starter?

Thanks as always. I couldn't have come this far without you folks.
- Allen