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No need to book, just drive in - or book online

How To Jump Start a Car

Are you one of the many who worry about jump starting a car when the time comes?

Read this to learn why cheap jump leads aren’t necessarily good value, and the dangers associated with jump-starting a car.

Jump-starting a car incorrectly can not only cause electrical damage to your vehicle, but it can also be very dangerous! Read below to learn the correct technique, but before we get to that it is worth considering the type of jump leads that you have in the boot of your car.

Why you shouldn’t buy cheap jump leads

One of the big problems with cheap jump leads can be that the quality of metal wire inside is very poor. This has two implications, firstly you will find that their performance in charging the drained battery is low, but more importantly, they could be dangerous. When you are jump-starting a car there is a large amount of amperage (electrical current) flowing through the wires. In a performance/quality set of jump leads, you will find that they have a high number of thick copper (low resistance metal used in domestic electrical cable) strands running the length of the lead that will withstand the high amperage. In a budget set, a cheaper metal will often be used with a higher resistance, meaning it gets very hot, so hot it can cause damage to both your car and even you!

“Our old minibus at work had burn marks on the front from where our old handyman (handy in the loosest sense of the term) used cheap jump leads. I told him not to but he wouldn’t listen, they had such high resistance that they melted the insulation and burned the paint off the bus.”

A comment from The Mini Forum

Good quality leads will have a braided cable inside each clamp joining the two parts. Without this, the hinge rivet is the only thing carrying current from one side of the clamp to the other and this is not likely to make a good connection. Effectively the only point of connection to the battery post or the panel is the teeth of one half of the clamp, giving a total amount of about 4mm in contact with the battery terminal. Get leads with good quality clamps and always make sure they are well connected to each vehicle to get the most possible cross-section of contact.
Getting a set of anti-surge jump leads will ensure that you are prepared for most eventualities and will protect both cars from damaging energy surges.

How to Jump-Start a Car Safely

Before you begin jump-starting a car, make sure that the ignition and anything electrical i.e headlights are turned off on both vehicles and put the keys safely in your pocket.
  1. Make sure that the vehicles are not touching each other and that the jumper lead clamps do not touch each other or any part of either vehicle – except as outlined in the following procedure.
  2. Connect the red lead to the positive (+) terminal of the discharged battery.
  3. Connect the other end of the same red lead to the positive (+) terminal of the booster battery.
  4. Connect the black lead to the negative terminal of the booster battery.
  5. Connect the other end of the same black lead to a solid stationary metal component on the engine of the vehicle with the discharged battery.

If your car battery is located in the boot, refer to the vehicles handbook as it will typically have dedicated jump starting connections in the engine compartment.
Important safety information to consider when jump starting a car:

  1. Always make sure you connect the negative terminal lead to a good earthing, NOT the discharged battery, fuel lines of air conditioning pipes
  2. Do NOT allow the jump lead clamps to touch each other or any moving parts, you don’t want them to short circuit
  3. Be careful with loose clothing that may hang over the battery terminals, always either remove or tuck scarfs etc into your jacket
  4. Never leave an engine running unattended. You must be present to ensure that it does not overheat and only run an engine in a well-ventilated area
  5. Wait for at least three minutes for the voltage to equal across both batteries
  6. Start the engine in the vehicle with the discharged battery (do not start the engine of the vehicle with the good battery) and let it run at idle for at least ten minutes, with all accessories switch off, to charge the battery. If the engine cannot be started at this point refer to the note below
  7. The AA suggest that you then switch the ignition off on both cars and disconnect the jump leads in the reverse order that you connected them. Then attempt to start the engine of the vehicle with the discharged battery. If the engine will not start there is a reasonable chance that the battery or the alternator is faulty, or, the battery is still insufficiently charged. It is common practice, however, to leave the car with the weak battery ticking over for a few minutes to allow the battery to charge sufficiently. Either way, ensure that the jump leads DO NOT touch each other.

If you are having difficulty starting the discharged battery it could be a couple of things. Possibly the charged/healthy battery does not have enough amperage to start the discharged/weak battery. When jump-starting a car, consider the size of vehicles that you are using, a small hatchback won’t be sufficient to jump-start a large 4×4.
Always refer to your owner’s handbook for detailed information about specific vehicles. Some modern vehicles cannot be used for jump starting a car because of the complex electrical systems. Attempts to boost another car’s battery could cause significant damage to the engine electrics.
Finally, make sure that your jump leads are up to the job. Remember to purchase reliable and heavy-duty booster cables that you can trust in your time of need.

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