Battery Cable size

[oakleyb]

I'm going to be adding a second battery to my domestic bank, the problem i have is that i need to situate it about 2 metres away. Is this ok ? what cable size should i use ?

 

[Trundlebug]

Without knowing all sorts of teccy details like the size of the batteries, charging rate etc (yawn yawn) which you'll no doubt be asked for shortly, I would say a safe rule of thumb would be to use 35sq mm multi strand cable and you won't go far wrong.
Be sure to use the same for both +ve and -ve cables.

 

[VicS]

[ QUOTE ]
(yawn yawn)

[/ QUOTE ] You enjoy your sleep zzzzzzzzzzzzzzzzzz.

An important factor will be whether or not the new battery is to be available for engine starting. If it will then it'll need appropriately sized cable. If not then it will need cable capable of carrying the max discharge or recharge current.

This calculator might help http://www.unlimited-power.co.uk/cable_sizing.html

A fuse might be a sensible addition.

 

[philip_stevens]

All the Westerly original installed cable on my boat is 25mm sq. I have added extra batteries and used the same size multi-stranded cable obtained from motor factors.

 

[simonfraser]

the fuse is there to protect the +ve wire, so put two in, one at each end.

 

[FlorealIII]

if the battery is intended for starting you need 50 sq mm
if the battery is intended for service 15 to 25 sq mm will do

 

[William_H]

If you use very heavy cable as in starter cable then the fuses may not be appropriate. The theory may be that the battery can not provide enough current to overheat the cable to the point of fire. If you do fuse however you can fit big fuses ie hundreds of amps.

If you go to smaller wire then it can overheat if shorted. You must decide about the risks of it shorting to the other wire and if a red hot wire can cause a fire. Clearly in older cars there was a lot of heavy wire to the starter which was not fused.

Anyway one tip which has come up recently is regarding balancing the current from the 2 batteries. If you simply extend the wires from the existing battery to the new one with power taken from the original battery, the resistance of the added wire will mean more current comes out of the original battery than the new one. One trick is to use wire to parallel the two batteries as normal but to run the positive wire from one battery terminal and the negative from the other battery terminal so neither battery has less wire to the load than the other. good luck olewill