Jump start

A jump start is a colloquial term for a method of starting an automobile or other internal combustion engine-powered vehicle having a discharged battery.

Most U.S. passenger vehicles use a standard 12-volt DC battery which, when the driver turns the ignition key, an electric motor engages the teeth on the flywheel briefly turning the flywheel which is connected to the crankshaft and powers the spark plugs until ignition is achieved and the engine can produce its own electrical power from its generator or alternator.

When a battery fails or is discharged, such as by inadvertently leaving one's headlights switched on while parked, the car's engine will not "turn over" when the ignition key is turned. Many motorists carry "jumper cables" which consist of a pair of heavy gauge wires with alligator clips at each end. An automobile with a good battery (owned, perhaps, by a Good Samaritan), is parked near the car needing the jump start and the cables are attached in this order:

• One cable attaches to the positive (+, red) terminal of the dead battery, and then to the positive terminal of the live battery.
• The other cable attaches to the negative (-, black) terminal of the live battery, and then to the engine block of the car with the dead battery.

With a safety cable, such as the one shown in the picture, the two pieces are connected together. The safety cable has color coded alligator clips and the connectors are polarized so that they can only be inserted in the correct orientation.

Since the entire engine block is grounded to the negative terminal, the cable need not be connected directly to the dead battery's negative terminal, and in fact it would be unwise to do so as sparks from the connection (when the circuit is completed) could ignite the battery (highly explosive hydrogen gas can be given off by a battery). A good connection point would be a piece of unpainted metal at least eighteen inches away from the dead battery. Some engines have eyelets which are used to attach chains when the engine needs to be lifted out of the car; these make good connection points for the jumper cable.

(Many auto manufacturers specify methods of jump-starting their autos, such as a different sequence of attaching or detaching jumper cables. For your safety, please read your owner's manual!)

The "good" car is then started, and the dead battery is allowed to charge for a few minutes. Then the car with the dead battery can be started, the cables carefully detached, and the formerly-stranded motorist goes on his or her way. If the original cause of the dead battery was simply a drain such as the headlights being left on overnight, then the car's generator should take care of finishing the recharge and keeping the battery charged; but if the battery is damaged or old or there is some problem with the car's electrical system, then the motorist should keep his engine running until he can buy a new battery or reach a service station.

In localities or in situations lacking in Good Samaritans, there is always the auto club, for its members. In mid-town Manhattan, New York City, standing next to a parked vehicle and holding up a set of jumper cables is likely to result in a taxi-cab stopping within a minute or two. The cab's driver is likely to sound surprised if the person with the cables needs to ask what the charge for the jump start will be. (In the late 1980s, the answer was $5.)

Jump Start is also a comic strip by Robb Armstrong. Jumpstart is also a series of educational software produced by Knowledge Adventure.