Alternator voltage regulator: symptoms

bruce_phipps · 2008-09-07T12:43:55+00:00

1995 Micra.Started up OK this morning, drove OK for a couple of miles. Then, theengine suddenly cut out at a *busy* junction.The car would not restart, ore even turn over. Symptoms were of a flatbattery. Dashboard lights were out.The car has recently developed a tendency to stall at junctions, buthas always restarted immediately.Anyway, I called Green Flag out.The mechanic put a booster on the battery and the car restarted*immediately*. He measured the battery voltage: over 14 Volts.He then did some measurements on the alternator output and told me thealternator voltage regulator was knackered. And that I needed a newalternator.I then drove the car home and stopped the engine. I then immediatelytried to restart the engine. Same symptoms of a flat battery. Enginewould not turn over. I read the battery voltage, it was 12.4 V.So, is it the battery, or the alternator that is faulty? If thebattery was healthy, wouldn't it still have enough charge to start upthe engine, even if the alternator was kaput?Or is the problem that the alternator is not recharging the battery atall? If so, why did the car start first time this morning?ThanksBruce

Sep 07, 2008 25 Replies

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bruce_phipps 18 years ago

More voltage data. Ignore this message if you are easily bored :) The Haynes manual for the Micra gives the following voltages for battery charge condition:

12.5 V poor 12.6 V normal 12.7 V good 12.2 V to 12.4 V partially discharged less than 12.2 V discharged

I took my battery out of the Micra. The voltage was 12.52 V, according to my multimeter. I connected the battery to an entry-level Halfords battery charger. The charger lit up green, indicating that the battery was charged. Anyway, I left it charging for 20 mins or so and it was soon up to

13.2 V. I then stopped charging the battery.

I'll try it back in the car tomorrow. Hopefully I can get the engine fired up. Then I can take some measurements on the alternator.

Bruce

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bruce_phipps 18 years ago

That's the price range I was looking for! Do you recommend I try some of the firms that advertise in the back of AutoTrader? Will they have alternators removed already, or does the customer have to do it? I've bought panels before from a scrappy and they have removed 'em for me. Bruce

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