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Checking charging system

My car's playing up a bit - seems that either the battery's not got enough charge in it, or the alternator's not producing enough juice straight after starting, and it can cough and splutter a bit if you don't rev it. This also gives a nice dim then bright headlight effect as the revs rise.

And today I found out that if you start the car and drive it round the corner into a petrol station, it's not got enough juice to start again. Alternator was recently changed to a new used unit as the original had a cracked casing, so I can't be sure that's sound, and the battery is under year old, but the car has done a lot of standing.

Reply to
Doki
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Do you have access to a digital multimeter? If so, you could make the decision as to whether the battery or the alternator is at fault within minutes.

If not, and you intend trying to fix car electrics in any way, then I would recommend you get one.

Chris

Reply to
Chris Whelan

Yep. Thought it went without saying that if I were going to be checking the electrics, I'd have a multimeter :).

Reply to
Doki

OK. Leave it overnight, then before starting it check the battery voltage. If it is lower than 12.5 or so, repeat the following night but with the battery disconnected overnight. If it is significantly higher when left disconnected, suspect something is draining it. If it is still lower than

12.5, the battery is not holding its charge.

If the voltage is above 12.5, start it, and see what the voltage is. It should be in the range of 13.5 to 14.4 volts. If not much higher than the standing battery voltage the alternator or wiring is likely to be faulty.

With the engine still running, switch on headlights and heater blower. The voltage will be lower, but should still be more than the standing voltage. If not, suspect the alternator.

HTH

Chris

Reply to
Chris Whelan

& check the earth straps to the alternator & the chassis are intact.
Reply to
Duncan Wood

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