Battery wiring

[jointventureII]

Hi there,
Have just added a second battery with a changeover switch, on a 23ft outboard engined vessel. However, the second battery struggles to turn the engine over, and the wires get extremely hot. Thus, I shut it off. The original battery still worked fine, no excess heat in the wires. The 2 batteries are exactly the same, 12v 678 batteries. Could this be due to the thickness of the wires? The new wires did seem a tad thin, and the original battery works fine.
The engine ran fine on the original battery

Many thanks

 

[VicS]

You know the answer. The wires are too thin. If you use the same thickness of wire for the new battery as the old you should be Ok.

 

[aztec]

yep, too thin..

however is it set up to start the engine on the aux battery, or is the aux just that?

the changeover switch used just to recharge the aux.

 

[pappaecho]

Best source of double insulated "battery wires" is the thick flexible wires sold for "meter tails", that is the connection of the consumer unit in the house to the main fuse from the incoming main. The inner insulation layer is either red or black(blue) and both are covered witha grey outer sheath. Good for 100 amps or so, and a fraction of the cost of !2 volt "battery wire" usually sold by the meter - I have a 8 metre run from my 200 amp service batteries and when used to crank the 4108 they dont even get warm.

 

[markdj]

The thick wires which are double insulated is for 3-phase AC house installations. The cable may as well be solid core as there are only about 16 strands for the thick cable. This is totally not the cable to use as the vibrations in a boat will eventually work harden the copper and snap it in two causing a fire hazard due to arcing which can happen in the middle of the cable. Go for grade 2 or preferably grade 3 flexibility which is very fine stranded stuff that you can wrap round your wrist. It is preferable to sheath the cable in flexible conduit too and support it every 18 inches.

 

[andy_wilson]

Provided that....

... the length of the cable run is comparable. Longer run thicker cable (of course your existing gauge may be thick enogh for a longer run, but you get the picture).

 

[VicS]

Re: Provided that....

The length of the cable run is not relevant to the heating problem but it will affect the volts drop and hence the ability to turn the engine quickly.

 

[brianrunyard]

I use Welding cable, sourced from local welding suppliers, much more flexible and not prone to fracture with vibration.
It's also tinned, so doesn't go black with corrosion.