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Although most car battery ratings in Cold Cranking Amps (CCA), are from 540-880, less is required to just crank the engine and the dead battery will usually still be able to supply 100 or more amps, so the jump start cable only needs to support 85-150 amps..


4 cylinder gasoline engine 160 amps
6 cylinder gasoline        210 amps
8 cylinder gasoline engine 250 amps
4 cylinder diesel engine   350 amps
6 cylinder diesel engine   450 amps
8 cylinder Diesel engine   650 amps
Source: Portable Jump Starter Comparison Chart | CarBatteryHelp.com

Cables:
Jumper cables vary in size from AWG 4 to 8. (You may see #10, but it is not recommended).
If the car you're jumping is only a 4, maybe 6 cylinder "Short and thin" (8 gauge) should work. Anything larger needs "long and thick" (6 gauge or lower).

Cold weather starting can add as much as 60% more starter power draw, while a lead-acid battery can lose more than 50% of itŐs cold cranking amps.
However, cable resistance goes down in colder temperature (about 10% less in 32°F vs 7732°F), but not enough to compensate for the above. Ohms per 1000 ft. <
AWG 32°F 77°F
8 0.9203 1.018
6 1.463 1.619
4 2.327 2.575
2 3.700 4.094

Cheap wires have cheap clamps, which are a pain-in-the-butt to use as well as they are less likely to stand up to time. Cheap clamps are copper plated. Better clamps will be solid copper, which will transmit electricity much better. After utilizing a plated set a few time, the copper can be worn off down to the steel substrate, which does not transmit the electricity nearly as well, meaning your cables won't work very well.


Jump Start Procedure:
See: Car Talk Jump-Start Instructions

Short version:
Read your owner's manual. Some manufacturers do not allow jumpstarts, and some have fuses that need to be removed before jump-starting, or other steps that need to be taken before you can successfully jump-start the car.

  1. Turn off lights on the dead car.
  2. Turn ignition off on both cars.
  3. Put on safety gear (eye protection and gloves).
  4. Connect cables according to the diagram below.
  5. Start the good car's engine If you have heavy duty cables (AWG 2-6) you can try to start it immediately.
    If you have thinner cables wait a minuet or two to charge the dead battery. Pushing the gas pedal of the dead batter car will help charge the battery.
  6. Try to start the dead car.
  7. If the car doesn't start on the first try, shut the supply engine off and disconnect the last connection temporarily while you slightly twist or wiggle each of the four clamps to help ensure a good electrical connection.
  8. If it still doesn't start let it charge for a little longer, 2-5 minutes.
  9. When it starts disconnect the cables in the oppisite order from connecting.

Jump Start Batteries:

Links:
Car Batteries and Batteries in General
How Do I Jump-Start a Car? | LifeHacker.com
Car Talk Jump-Start Instructions
Jump Starting A Car | DrivingTips.org
Wire Size
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last updated 14 May 2007