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Thread ID: 101562 2009-07-19 08:35:00 Jumpstart question for newer cars Nomad (952) PC World Chat
Post ID Timestamp Content User
792946 2009-07-19 08:35:00 Hi,

I left the interior light on, the mechanic said newer cars tended to have auto switch off functions? Mine obviously didn't .

I went to the gas station and borrowed a jump box and that didn't work .

I then rang road side assist and paid them cos I am not a member, and he did some test with the multimeter and then jumpstarted it with his truck, I thought cars couldn't be jumpstarted with electronic ignitions?



:p
Nomad (952)
792947 2009-07-19 08:44:00 you can jumpstart any car, the problem with modern cars is the risk of killing the computer. robsonde (120)
792948 2009-07-19 09:01:00 Few people worry about the so-called risk of killing the computer in cars, and I have never actually heard of it happening. You should be fine if you do it correctly.

They do however sell "computer-safe" jumper leads. I am not sure how these work, and personally I just use normal ones without any problems in the event that I need a jump or to give one.
george12 (7)
792949 2009-07-19 09:20:00 I cant see how jump starting a car with a computer would make a difference, when your jump starting you can only get whatever the battery is rated through the car, unless im clueless. Personally Ive never had a problem hueybot3000 (3646)
792950 2009-07-19 09:37:00 I cant see how jump starting a car with a computer would make a difference, when your jump starting you can only get whatever the battery is rated through the car, unless im clueless. Personally Ive never had a problem

I agree but people who are not idiots have told me it can happen, and they DO sell special jumper leads to prevent it. Supposedly something to do with a voltage spike when you connect the leads I think, though I'm not sure how such a spike would happen.
george12 (7)
792951 2009-07-19 09:38:00 As long as you dont connect the leads while the helping car is running all should be fine hueybot3000 (3646)
792952 2009-07-19 09:45:00 Does anyone know how to test it with a multimeter?
The guy was saying it should not be so low ... then he found my interior light was still on then it tested it again and it was fine. What were these two test? Is that just checking the voltage before and after starting? The one after should be higher? 12+.

If a battery was really flat, like lights left on overnight, would the meter give a 1 or 2V ??
Nomad (952)
792953 2009-07-19 09:47:00 One would be straight across the battery and one would be the earth to the car I assume, someone else can clarify though hueybot3000 (3646)
792954 2009-07-19 10:00:00 I know how to connect it. Here is a question, if the battery is so dead that the lights don't turn on, what is generally the voltage from that? And, how does one tell if you need a new battery or if the battery is ok once it's jumped and the alternator kicks in? Nomad (952)
792955 2009-07-19 10:51:00 Generally an interior light should not kill a battery very quickly. If you car is not running the battery voltage might even drop to about 11.5 volts, if it got down below 10v I doubt it would start the car. When it runs the alternator will bring the voltage up to about 14v. 2V is pretty dead.
However if your battery is not retaining charge you could try checking the water level of the battery and top up if necessary however the most likely thing is that the battery is simply past it and do you want the grief of being immobile.
Just head off to a genuine car battery shop and get them to check it and buy a new one if it is dead.
Ofthesea (14129)
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