Ask the Mechanic

Cable Size Matters

(Getty Images, Photo illustration by Barry Falkner)

READER: I am a little confused about battery cables. I have an H Farmall with a 6-volt battery. It has big battery cables even though it's only a 6-volt battery. I also have a Ford truck that has a 12-volt battery, and it has smaller battery cables. Why does the 6-volt battery have larger battery cables than the 12-volt battery, which has twice the volts?

STEVE: This cable arrangement does look backwards, doesn't it? However, the starter requires a lot of work to be done. Amps are what do the work, and the volts are what push the amps (electrons) to the starter to do the work. If you only have 6 volts of push, then you need a big cable to allow enough amps to be pushed through it to start the tractor properly. But, if you have 12 volts of push, you can cram adequate amps to the starter to start the truck with a smaller cable.

If you were to take a water hose with 6 pounds of pressure on the hose and hold it in a gallon bucket, it would fill the bucket in a certain amount of time. Then, if you were to increase the water pressure to 12 pounds, you could fill the bucket in the same amount of time with a smaller hose.

But always remember, if you are smoking battery cables when running the starter that is in good working order, you simply have too small of battery cables to handle the necessary amps.

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-- Write Steve Thompson at Ask The Mechanic, 2204 Lakeshore Dr., Suite 415, Birmingham, AL 35209, or email mechanic@progressivefarmer.com, and be sure to include your phone number.

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