Jump start (vehicle)
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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.
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[edit] Procedure
If the discharged battery is cracked, has a low electrolyte level, or is frozen, then a jump start should not be attempted. Proper jump start procedures are usually found in the owner's manual for the vehicles.[1] Owner's manuals may show the preferred locations for connection of jumper cables; for example, some vehicles have the battery mounted under a seat, and may have 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 around 442 persons were injured by exploding batteries while attempting a jump-start.[2] Organizations such as Prevent Blindness America recommend use of splash-resistant safety goggles to protect the eyes while connecting cables.[3]
Operation of a lead-acid battery produces hydrogen gas which is flammable. Caution is in order to avoid a spark which may ignite the gas. The usual recommended sequence[4] is to first connect the positive terminals of the charged and dead batteries with the red booster cable, then connect the black cable to the negative post of the charged battery and to the frame of the vehicle with the dead battery, at a point away from the battery. This method avoids creating a spark near the battery terminals. The boosting vehicle must not touch the boosted vehicle.
By connecting the positive terminals first, the risk of accidental short-circuits can be minimized. If the negative terminals were to be connected first and the operator accidentally touches the chassis with the positive cable, a massive and dangerous short-circuit would form, possibly welding the cable to the chassis. But with the positive cable connected first, accidentally touching the chassis with the negative cable is harmless.
Current from the boosting vehicle will charge the dead battery; after several minutes enough energy is transferred that the battery can crank the vehicle. If the boosting cables are heavy gauge and have good connections, the boosting vehicle battery may also supply cranking current. In an extreme case it is possible to crank and start a vehicle with no battery in it, if the cables have low resistance. 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 out of fuel, a failed battery, damaged starting motor, or other mechanical problems with the vehicle cannot be overcome by a jump start. Even a successful jump start may not allow the vehicle to resume normal operation, since the reason for the dead battery may have been a failed charging system. Unless the cause of discharge is known, the operator of the "boosted" vehicle should have the battery and charging system checked at once.
Loss of voltage from the vehicle battery may have effects ranging from trivial (loss of radio receiver preset stations) to significant (loss of security codes or engine control parameters). A prudent motorist would be well advised to familiarize himself with the possible effects of a dead battery; booster cables may be unavailable if the keyless entry system won't unlock the trunk (boot).
[edit] Alternatives to jumper cables
[edit] 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.
[edit] 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.
[edit] 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.
[edit] 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).
[edit] 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 it's 12-volt system; the main propulsion battery is unlikely to also have been discharged.
[edit] See also
- Crocodile clip used in the cables.
[edit] References
- ^ 2004 Owner's Manual,`Toyota Camry Solara, Toyota Publication No. OM33596U, an example of an owner's manual
- ^ Injuries Associated with Hazards Involving Motor Vehicle Batteries , Road Management and Engineering Journal, retrieved from www.usroads.com on August 2, 2007
- ^ Prevent Blindness web site retrieved August 10, 2007
- ^ Horst Bauer Bosch Automotive Handbook 4th Edition Robert Bosch GmbH, Stuttgart 1996 ISBN 0-8376-0333-1, pages 806-807
[edit] External links
- AAA starter cables information
- Jump-Starting a Car — from the US Naval Safety Center
- do-it-yourself jump start — info
- Jump-Starting a Car — by Car Talk's Tom and Ray Magliozzi "Click and Clack, the Tappet Brothers"
