Alternator voltage regulator: symptoms



1995 Micra.
Started up OK this morning, drove OK for a couple of miles. Then, the
engine suddenly cut out at a *busy* junction.
The car would not restart, ore even turn over. Symptoms were of a flat
battery. Dashboard lights were out.
The car has recently developed a tendency to stall at junctions, but
has 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 the
alternator voltage regulator was knackered. And that I needed a new
alternator.

I then drove the car home and stopped the engine. I then immediately
tried to restart the engine. Same symptoms of a flat battery. Engine
would 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 the
battery was healthy, wouldn't it still have enough charge to start up
the engine, even if the alternator was kaput?
Or is the problem that the alternator is not recharging the battery at
all? If so, why did the car start first time this morning?

Thanks
Bruce
.



Relevant Pages

  • Re: Alternator on a turbo
    ... Eliminating the drag from the alternator, water pump, PS, and AC would still not allow a starter motors to be smaller enough to save cost. ... The starter on the 2 cylinder/4 piston diesel Ecomotor probably has to be much larger and heavier than on a conventional spark ignition 4 cylinder engine. ... maybe little difference in battery size making no difference to cost. ...
    (alt.autos.toyota)
  • Re: ETA AutoQuartz cap/battery dying?
    ... drove a Prius at speed around their test track followed by an Audi R8, ... that run just fine on the original battery after 400,000 miles. ... from the battery and the engine is off, sometimes vice versa, all managed ... car at top speed?). ...
    (alt.horology)
  • Re: Strange Battery/Alt problem
    ... The light comes on because the battery voltage is too low. ... Your alternator was failing... ... car around and went back home in fear of being stranded. ... the engine off I measured 12.8 with the light still lit. ...
    (rec.autos.tech)
  • Re: ETA AutoQuartz cap/battery dying?
    ... I was watching the first episode of season 11 of Top Gear last night, they drove a Prius at speed around their test track followed by an Audi R8, 1.5litre engine in the Prius compared to the big v8 in the Audi, all the audi had to do is keep up and match the speed of the Prius, after the test the mileage was 17.something mile per gallon for the Prius, 19.? ... But, I've driven it and it's cool in a geeky way - very nice video display that shows the direction of the power flows -sometimes the car is drawing from the battery and the engine is off, sometimes vice versa, all managed very seamlessly by the computer. ...
    (alt.horology)
  • Re: 1996 SL1 Difficulty Starting - Solenoid Location/Other Thoughts?
    ... My son brought the car home on Saturday morning. ... battery/charging problems, I measured the battery voltage after he arrived ... evening with the engine warm, ...
    (rec.autos.makers.saturn)