Is bigger always better?

[wagoon 2,429]

Is there such a thing as to big a cable for Power and earth cable on a car. I am going to put the battery in the boot and I can get some welding earth leads in pretty good condition. It is 70mm sqaured in size ( around the thickness of a finger), its also gives duty cycle but I didnt think that would matter if using on a car. I also should have enough for all the other earth points in the car. So would using this size cable cause any problems other than adding 20 kilos of weight to the car.

[gerg 10,871]

That sounds like about 300 amp. You can never go too big except if your limitation is cost and weight. At that distance I'd twin it (if you have enough) to allow for voltage drop. A bloody decent set of jumper leads will often mean the difference between working and failing. You'll break your back carrying them though. Same goes for batt cables (and batteries)... Just get the biggest, dumbest meat-axe battery and cables and you're already ahead.

[wagoon 2,429]

Thanks Greg. Yeah duty cycle on the cable says 650Amps@30% 450Amps@60% so would assume around 300Amps@100%.

What do you mean by "twin it", is that just run 2 length from the pos terminal on the battery to a single point in the engine bay? Sorry for such a basic question, just want to get terminology correct.

[gerg 10,871]

Yeah that's it double it up, from batt + all the way to starter, same goes for earth to chassis and to battery -. You can use one big lug at each end with the 2 wires crimped together or a separate lug for each wire and bolt them together at the terminal. Either way you should sweat some solder down into the crimp to eliminate that as a weak spot.

 

Dunno how many times our breakdown truck has given us grief from having the batteries moved right down the back (down next to the crane). Not only was it slow cranking but they never charged properly either. All from voltage drop. As soon as I put a second set of batts in down the front, we've never had to think about that shit any more.

 

Also as a rule of thumb, cranking amps for:

 

4cyl - 80 amps

6cyl - 120 amps

8cyl - 180 amps

 

Depends on compression and cam, etc but that's a rough guide

[wagoon 2,429]

Thanks for that.

[gromet88 3,042]

The Mrs says its not the size, its the way you use it??!!?

[wagoon 2,429]

Is that just to you you feel better?

[bear351c 10,270]

 A bloody decent set of jumper leads will often mean the difference between working and failing.

 

So right !!!   I've seen so many guys trying to jumpstart a car with those $20 cables from Supacrap, when I lend them my welding cables, their jaws drop.

All sorts of excuses, .......bad connection, battery is flat, blah, blah, blah...