29-11-2019, 01:26 AM
(This post was last modified: 29-11-2019, 02:02 AM by Stuart Giles.)
Ultimately, IMO WRT to cable size, it depends on which end of the telescope you're looking through, if you set up your car from the perspective of the CCA figure of a typical large 6V battery - like the MGB one which is the biggest 6V battery I've managed to squeeze into a non-special A7 floorpan -the CCA (Cold Cranking Amperage) figure on one of these is about 600A. So, if you designed your setup from the cable requirement for 600A, because that is the maximum current, that would require 70mm sq cable (i.e.) 17mm+ Outer Diameter. Counsel of perfection on this would say we need to minimise voltage drop, so why use 70 sq mm. 95 sq mm would be the thing to have for 600A load - the resulting cable would be the best part of an inch diameter of course. The reality is that the battery's 600A CCA figure is deliverable for moments at best; the MGB 65 ampere Hour battery in this example won't deliver that 600A (3600W) for long, Certainly not long enough to overheat a reasonable sized battery cable.
I have set up several 6V cars with 25 sq mm cable -the exact same stuff that has been good for extended use @ 180A+ on one of my welders without any undue heating- in an A7 they've all cranked the motor at a reasonable (6V) speed and started the car OK; if the battery happens to be right at the rear of the car, it may be worth going up to 35 sq mm cable, to be sure.
I have set up several 6V cars with 25 sq mm cable -the exact same stuff that has been good for extended use @ 180A+ on one of my welders without any undue heating- in an A7 they've all cranked the motor at a reasonable (6V) speed and started the car OK; if the battery happens to be right at the rear of the car, it may be worth going up to 35 sq mm cable, to be sure.