booster cable

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Jumpstarting a vehicle

A jump start or boost is a term for a method of starting an automobile or other internal combustion engine-powered vehicle which has a discharged battery. A second battery (often in another vehicle) is temporarily connected to provide starting power to the disabled vehicle. Once the engine is running, it will recharge the dead battery, so the second battery can be disconnected.

Most passenger vehicles use a 12-volt car battery which provides power to a starting electric motor for the engine. When the engine is running, electrical power from its alternator restores the charge to the battery in preparation for the next start. When a battery 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.

Jumper Cables

Jumper cable connected to positive post

Long heavy-gauge cables.

Many motorists carry jumper cables (UK usage: jump leads) which consist of a pair of heavy gauge, insulated wires with alligator clips at each end. Jumper cables are available in various lengths. The size of copper conductors varies from about #10 AWG for light duty sets, to #1 AWG. The alligator clips generally have color-coded, vinyl-coated (PVC) insulation to prevent electrical short circuits. Most clips fit both top- and side-mounted battery terminals. Top-quality clips are made of pure copper; lesser-quality are made of alloys, such as zinc-plated copper or copper-plated iron or steel. Jumper cables are marked by black (-) and red (+) handles, representing the two polarities of the automobile's direct current system. Interchanging the polarities will cause a short circuit and a hazard to people and damage to one or both automobiles.

Limitations

Operation of a lead-acid battery may, in case of overcharge, produce hydrogen gas which is flammable. Jump start procedures are usually found in the vehicle owner's manual.^[1][2] The recommended sequence^[3] of connections is intended to reduce the chance of accidentally shorting the good battery or igniting hydrogen gas. Owner's manuals will show the preferred locations for connection of jumper cables; for example, some vehicles have the battery mounted under a seat or a jumper terminal in the engine compartment.

Motorists can be severely injured by a battery explosion. In the United States in 1994, a research note by the National Highway Traffic Safety Association estimated that about 442 persons were injured by exploding batteries while attempting a jump-start.^{[4] [5]}

Current from the boosting vehicle will charge the dead battery. After several minutes enough energy is transferred to allow cranking of the engine. If the connections are good and the cables are large, the boosting vehicle battery may also supply part of the cranking current. In an extreme case, it is possible to crank and start a vehicle with no battery in it if the cables are heavy-duty. Cranking current drawn through light-gauge cables in this way will damage them by overheating.

If the discharged battery is cracked, has a low electrolyte level, or is frozen, a jump start will not restore normal operation. A jump start is only effective for a discharged battery and cannot resolve other faults including a lack of fuel, a failed battery, or other mechanical problems. Even after a successful jump start a vehicle may not be able to resume normal operation if the reason for the dead battery is a failed charging system. Loss of voltage from the vehicle battery may have wide-ranging effects--from a trivial loss of radio receiver preset stations to a significant loss of security codes or engine control parameters.

Motorcycles

Many very old motorcycles (and cars) have 6-volt systems and cannot be jump started safely with a modern car,^[6] but newer designs with 12-volt systems may be jump started with a 12-volt car or truck. Car batteries can generally jump start a motorcycle easily without any help from the car's alternator.^[7] An alternative is to push start the motorcycle.^[8]

Alternatives to jumper cables

Cigarette lighter outlet

An alternative to jumper cables is a cable used to interconnect the 12 volt power outlets (cigarette lighter outlets) of two vehicles. While this eliminates concerns with incorrect connections and generation of arcs near battery terminals, the amount of current available through such a connection is small. This method works through very slowly charging the battery, not through providing the current needed for cranking. Engine cranking should not be attempted as the starter motor current will exceed the fuse rating in a cigarette lighter outlet. Many vehicles turn off the cigarette lighter outlets when the key is turned off,^[9] making the technique unusable unless the ignition key is turned to the accessory or on position to connect the cigarette lighter outlet to the battery.

Battery booster and jump starter

A hand-portable battery, equipped with attached cables and charger, can be used similarly to another vehicle's battery. It can reach 1700 peak amps.

Portable boosters may automatically sense the battery's polarity prior to sending power to the vehicle, eliminating the damage that can result from reversing the connection.

Battery charger

Motorists and service garages often have portable battery chargers operated from AC power. Very small "trickle" chargers are intended only to maintain a charge on a parked or stored vehicle, but larger chargers can put enough charge into a battery to allow a start within a few minutes. Battery chargers may be strictly manual, or may include controls for time and charging voltage. Some chargers are equipped with "boost" settings that supply a large current to assist in cranking the engine. Battery chargers that apply high voltage (for example, more than 16 volts on a 12 volt nominal system) will result in high emission of hydrogen gas from the battery and may damage it. A battery may be recharged without removal from the vehicle, although in a typical roadside situation no convenient source of AC power may be nearby.

Push starting

A vehicle with a manual transmission may be push started. This requires caution while pushing the vehicle and may require the assistance of several persons. If the vehicle battery cannot provide power to the ignition system, push starting will be ineffective. Most vehicles with automatic transmissions cannot be started this way because the hydraulic torque converter in the transmission will not allow the engine to be driven by the wheels (some very old automatic transmissions, e.g., General Motors' two-speed Powerglide transmission, do leave a solid connection between the engine and wheels, and cars equipped with such transmissions can be push started).

Voltage problem

Formerly, especially in cold climates, some jump starts were done with two series-connected batteries to provide 24 volts to a 12 volt starting motor. However, such overvoltage can cause severe and expensive damage to the electronic systems on modern automobiles and should never be used.

Heavy vehicles such as large trucks, excavation equipment, or vehicles with diesel engines may use 24-volt electrical systems. These cannot be boosted from a 12-volt motor vehicle and must not be used to boost a 12-volt motor vehicle.

Vintage cars may have 6-volt electrical systems, or may connect the positive terminal of the battery to the chassis. The methods intended for boosting 12-volt, negative-ground vehicles cannot be used in such cases.

Passenger vehicles with 42-volt electrical systems may not be possible to "boost" from other vehicles; professional assistance would be required to prevent severe damage to the vehicle and possible personal injury (see tow truck). Hybrid vehicles may have a very small 12 volt battery system unsuitable for sourcing the large amount of current required to boost a conventional petroleum vehicle. However, as the 12-volt system of a hybrid vehicle is only required to start up the control system of the vehicle, a very small portable battery may successfully boost a hybrid that has accidentally discharged its 12-volt system; the main propulsion battery is unlikely to also have been discharged.

Military Vehicles

Slave receptacle on an M1009 CUCV

Generally referred to as "slave starting" in military parlance, the jump starting procedure has been simplified for military vehicles. Tactical vehicles used by NATO militaries possess 24-volt electrical systems and, in accordance with STANAG 4074, have standard slave receptacles for easy connection. A slave cable is plugged in to the receptacle on each vehicle, and the dead vehicle is started with the live vehicle's engine running.

See also

Wikibooks has a book on the topic of Automobile Repair/Jump start

• Crocodile clip used in the cables.

References

External links

• Breakdown Advice : using jump leads safely - The AA (United Kingdom)
• AAA starter cables information
• Jump-Starting a Car - by the US Naval Safety Center
• do-it-yourself jump start
• Official Car Talk Guide to Jump Starting Your Car - by Car Talk's Tom and Ray Magliozzi, "Click and Clack, the Tappet Brothers"
• Quick & Easy Directions to Jump Start by Car Care Council