Starting your car with jump leads is simple: get another car alongside, connect up, start the engine and you’re away. But I now know the downside.
An apparently normal jump-start started a fire that could have killed me, wrecked my Aston Martin DB7 and BMW 730i, and burned down my garage. As it was, £2,000 of damage was done to the Aston and I now appreciate the need for adequate jump leads, the correct procedure and the potential for damage to both cars.
Many Astons have starting problems. Their electrical systems drain a 12-volt battery if left for more than a few days, and only the newest ones have a sleep mode. In four years of DB7 ownership I have got through three batteries.
I already had a trickle charger to plug into the cigarette lighter, which was fine except that I had to feed the lead through the window, which entailed leaving the alarm off. Aston Martin has now supplied a charger that feeds a socket in the boot and exits under the lid so the alarm can stay on.
Last winter, however, I was without this device and my Aston’s battery was flat just a day after a 200-mile run. With the car in the garage, I reversed the BMW up and took out my “heavy duty” jump leads. I connected them to both batteries, started the BMW, went into the garage and switched on the Aston.
It didn’t start, but flames and acrid smoke shot from its boot toward the BMW as the leads’ coating melted, scattering gobbets of flaming plastic. The fire hazard was somewhat intensified by the paint store on one side of the garage and a heating boiler and shed full of dry firewood on the other. I was stuck at the back of the garage and to escape I would need to squeeze past both vehicles.
I killed the DB7’s ignition, broke the jump-lead connection (the crocodile clips were coming away from the wires) and ran past the Aston. I then drove the BMW clear, smothered the fire and shakily rang the RAC.
The patrolman looked tearful as I explained how close two prized cars had come to destruction; he said I was lucky to get out alive. He reassured me I had connected the jump leads correctly, then diagnosed the causes of the fire.
The leads might have looked superficially sturdy, but their aluminium cores could not handle the amps generated by a modern alternator. He also said the Aston’s battery was too flat to cope with a hefty charge-up generated by the BMW, which had detected a flat battery and was belting out the amps to charge it up. He said that I should have connected everything without the cars started, then gone for a cup of tea while the battery acclimatised.
I rang the AA’s technical department to find out more. They first advised me the safe order to attach jump leads: clip the positive/red jump lead to the positive/red terminal of the flat battery, then the other end to the positive/red terminal on the good battery. After that clip the negative/black jump lead to the negative/black terminal on the good battery and the other end to the negative/black terminal on the flat battery.
To be absolutely safe and avoid the very small risk of an explosion caused by a spark igniting the hydrogen coming off the charging flat battery, don’t attach jump leads to that battery, but instead clip the red lead to a distributor box under the bonnet and the black to the engine. If you are trying to jump start an old, classic car, be very careful that you are dealing with the same wiring polarities, as many of them have positive earths. The AA also said that it is best to connect up, run the engine of the donor car, switch off after 10 minutes, disconnect the leads and then try to start the car with the poor battery. Remember to keep the jump leads clear of rotating engine parts and hot exhausts.
The AA said it is best policy not to try to start the car with jump leads still connected and also to keep both ignition keys in your pocket, as occasionally, when systems kick in, they can activate the central locking.
My BMW was almost unscathed, but the DB7 was taken away for evaluation and repairs; by chance its overhaul and MoT were due. The damage was superficial, except to the CD stack, but the fire had knocked out the electrics, so a new radio was needed, too. Aston Martin also fitted the beefiest battery it could find.
I now have my DB7 back and I shall now use my trickle charger religiously, but I also have a set of very expensive copper-cored jump leads and two fire extinguishers in the garage. Better safe than sorry.
This article was published in 2005.
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