Gary Anderson

True Wally, but consider what you've seen melt. It's always the end connector or terminal. I suspect the voltage drop at those points is much more than the cable.
I agree, it never hurts to go bigger, but the factory cable is probably bigger than necessary. And you can always use a load tester on the cable ends to confirm.
Gary

Wally

Thats true Gary.....most times its the connectors that do go first. The thing people dont understand about current is that the more surface area there is the more current it can flow......thats why stranded wire works much better then solids. Electrons flow on the surface of the wire not through the solid part of it......best analogy i heard in school was to take a soild pipe and glue marbles around the outside of it....those would be your electrons.......now take a whole bunch of small individual tubes with marbles glued on the outside of them and put together as many as you can to make the same size as the big single one.....you will see that you have way more marbles covering the smallers tubes then the big one. Same goes with the stranded and solid wires when it comes to current capacity.....

Stormrider

TJ309,

I'm in the wire and cable business.
I can get you large sizes of rubber or pvc cable.
1/0 or 2/0, let me know and I'll see if I can help you.
West Marine is muy $$$$.

Also, this is all I could find so quickly.
Let me know if you want me to find out more on Monday.

Rob

offthefront

if you just add a 3rd battery forward to run stereo and accessories ... seems you could size the cable just for Alternator size ? prob less than 100 amps .....

Stormrider

But that won't solve the CG problem... thats why he wants to move the batteries.

rush

Whats the CG problem?

Stormrider

CG purposes, problem... whats the diff?

Probably would be alot easier to add some lead upfront.

tj309

Yes I could add lead up front but why haul excess weight when I have two batteries that weigh enough? I am an aero engineer and also an electrician on the side so I do understand all the technical stuff. As an electrician I work with AC and was not sure if the DC worked the same with voltage drop and all. Sounds like it does. That makes it easy for me.

As far as the CG problem - My 24' cat with 2 x 300 outboards with 17" of setback....I want the bow lower for cruising and during initial acceleration. The bow is almost 15' and I want to see over it. I am also a pilot and understand CG extremely well and just putting a couple of batteries in the bow will really move the CG forward; thus lowering the bow significantly. Thanks for all the help....TJ

BadDog

OK, you have established that the batteries need to go forward and that the wire size will need to increase and wire is expensive. Up the positive to whatever size you are comfortable with. As far as the negative we have also established that the ground needs to be the same size, or does it?

You have two grounds going to the same place, those big hunks of two stroke back there. Why not run a smaller less expensive and lighter ground cable? Just strap your two grounds together at the batteries and tie your engine grounds together? Your ground is essentially using both cables at the same time. Not quite as convenient with an OB setup as an I/O. I run a 1 size larger from the common post on my battery switch as it will see current from both batteries when set to all. The negative is slightly undersized when in the all position but you only need enough capacity as what the started will draw. For an OB I am assuming it is a lot less than an 8 cyl Gm with high compression.