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Battery Cable Sizes


It really depends on the acceptable voltage drop. Voltage drop is the product of the resistance of the cable times the current passing through the cable. The shorter and/or larger diameter of the cable the less resistance. Therefore less voltage drop. And of course the longer and/or the smaller diameter the cable the more the resistance. Therefore more voltage drop. Generally the ground cable is shorter than the cable runing to the starter. With that said you would think that the ground can be of a lesser size. But if you consider that copper battery cables have less resistance than iron and half of your ground path is iron which is of a higher resistance.

After read all this, you're probably saying that this guy is over thinking the question. Maybe I am. But the bottom line is the first line; It really depends on the acceptable voltage drop.
 
Current flows FROM the more negative to the more positive, or from the frame to the battery, so go equal to or greater than.

Oddly enough, every time that I view a lightning strike, my eyes tell me that the bolt went from the sky to the ground, but actually it does just the opposite. Voltage is constant, current flows...from the more negative to the more positive. I guess that's why people that get struck by lightning and live to tell about it say that they felt something like static electric just before they got flattened. By the time you can feel the current flowing through your body and your hair begins to stand up...too late, you're about to get barbecued.

Mark
 
You're correct. I made a mistake above when I said equal to or greater than. They should be the same size, and bigger is always better.

Mark
 
Why would you want it smaller?? as the smaller the cable the greater the resistance and the more cable voltage drop. This assumes you're talkin about a 6 or 12 volt system and NOT any small jumper to frame ground as used on the 24 volt system.

John T
 
If they are the same length, they should be the same gauge. But if one is significantly shorter than the other, it can usually be smaller gauge. I say "usually", because regardless of length, each cable needs to be of sufficient gauge to handle the starting current without burning up. But usually it is voltage drop, not ampacity that dictates minimum gauge for starter cables. Regardless, it never hurts to go bigger.
 
Remember types of end lugs are very important. Connections of a crimp on open wire is a joke. Such as the one Chrysler put on a new mini van we bought in '09.
 
I made all my cables up with welding cable. You can buy end's, solder them and then be sure to use shrink tube at the ends. Red for positive black for negative. I like the welding cable because it's good sized and it's very flexible.
 
I think lightning can go either way. I was out on the porch watching the lightning one night. It suddenly went from pitch black to bright white even with my eyes closed. Then I heard a buzzing sound come down from the sky and ended with a smack in the mud. Then boom, boom, boom, etc. down the same path. Decided when I could see again the I should go inside the house.
 
4020,

In an ideal world, everyone will want the biggest cables and shortest cables for a starter.

I wanted just the opposite. My farmall C sheared off two starter drives. It's a 6 v starter and a 12 v battery. I couldn't find a 12 v starter for my Farmall, so I did a little experiment. I took my weakest and oldest 12v mower battery that measured less than 200 cca. I used 10g wires instead of cables. The mower battery and wired doesn't over power the starter. Tractor has a mag and it fires right off. Been doing this for years. Thinking the mower battery should fail. It's my oldest battery and like the Every Ready bunny, it keeps on cranking.

I wouldn't recommend using wires and a mower battery if you have a diesel or large engine.
geo
 
I went with 4-0 on my 3020. Probably 2-0 woulda been plenty big, but I was splitting an order w/ somebody who wanted bigger. Second the welding cable approach. I moved the battery right up by the starter, significantly shortening the run and allowing a bigger (more amps) battery.
 
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