Jump start (vehicle)

Jump start (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 the "dead" (discharged) battery, to provide the initial charge required to start the engine. Once the engine is running, it will recharge the battery, so the second battery can be detached. However, if the engine stops running too soon, the battery may not have built up enough charge to restart the engine, so a further jump start may be required.

Most passenger vehicles use a 12-volt battery which provides power to a starting 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.

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 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. Good quality jumper cables will have large copper conductors and well-made alligator clips, and insulation that remains flexible at low temperatures. Longer cables require less maneuvering of the boosting vehicle to allow connection of the two batteries.


If the discharged battery is cracked, has a low electrolyte level, or is frozen, a jump start should not be attempted. Corroded terminals will increase the voltage drop during cranking and will contribute to starting difficulty. Proper jump start procedures are usually found in the vehicle owner's manual. [ 2004 Owner's Manual,`Toyota Camry Solara, Toyota Publication No. OM33596U, an example of an owner's manual] Owner's manuals may 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. [ "Injuries Associated with Hazards Involving Motor Vehicle Batteries ", Road Management and Engineering Journal, retrieved from www.usroads.com on August 2, 2007] Organizations such as Prevent Blindness America recommend use of splash-resistant safety goggles to protect the eyes while connecting cables. [ [http://www.preventblindness.org/safety/battery.html Prevent Blindness web site retrieved August 10, 2007] ]

Operation of a lead-acid battery produces hydrogen gas which is flammable. Caution is needed to avoid a spark that may ignite the gas. The recommended sequence [ Horst Bauer "Bosch Automotive Handbook 4th Edition" Robert Bosch GmbH, Stuttgart 1996 ISBN 0-8376-0333-1, pages 806-807 ] is to first connect the positive terminals of both batteries, then connect the negative post of the charged battery and make the last connection to the frame of the vehicle with the dead battery, at a location away from the battery. By not connecting the last clamp on to the dead battery, the risk of ignition is reduced. The described sequence of connections is intended to reduce the chance of accidentally shorting the good battery.

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 will damage them by overheating.

A jump start is only effective for a discharged battery. Other faults such as lack of fuel, a failed battery, or other mechanical problems cannot be overcome by a jump start. 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. Unless the cause of the battery discharge is known, the operator of the boosted vehicle should have the battery and charging system checked.

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. A prudent motorist should familiarize himself with the effects of a dead battery; booster cables may be unavailable if the keyless entry system won't unlock the trunk (boot).

Booster Cables

Booster cables consist of a pair of heavy wires, terminated in spring-loaded clamps for connection to battery terminals (or grounded metal parts of the vehicle frame). They are available in varying lengths. The size of copper conductors varys from about #10 AWG for light duty sets, to #1 AWG. The clamps, or jaws, generally have color-coded, vinyl-coated (PVC) insulation to prevent electrical short circuits. Most jaws fit both top- and side-mounted battery terminals. Top-quality jaws are made of pure copper; lesser-quality are made of alloys, such as zinc-plated copper or copper-plated iron or steel.

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 outlet) 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 made since 1990 switch off the cigarette lighter outlet when the engine is stopped, making the technique unusable.

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 is called a battery booster and jump starter). It can reach 1700 peak amps.

Portable boosters may automatically sense the battery's polarity prior to sending power to the vehicle, eliminating the costly damage that can result from a simple jump-starting mistake.

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 allow source of a large amount of 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 gassing of the battery and may damage it and will cause high emission of hydrogen gas. 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 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 Vechicles

Generally referred to "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

*Crocodile clip used in the cables.


External links

* [http://www.aaa.com/AAA/023/hmc/cc/archive/603Battery_Basics.htm AAA starter cables information]
* [http://www.safetycenter.navy.mil/safetips/a-m/carbattery.htm Jump-Starting a Car] — from the US Naval Safety Center
* [http://autorepair.about.com/cs/doityourself/a/bljumpstart.htm do-it-yourself jump start] — info
* [http://www.cartalk.com/content/features/jumpstart/ Jump-Starting a Car] — by Car Talk's Tom and Ray Magliozzi "Click and Clack, the Tappet Brothers"

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