Member Since: 10 Mar 2010
Location: Wantage
Posts: 559
Alternator question
after a flat battery Ive just checked the voltage and across the battery it read 12.2 volts with the engine off and 13.82 with the engine running.
Is the higher figure about right or would it indicate a faulty alternator?
Andy
23rd Aug 2012 9:01 pm
DiscoDunc
Member Since: 08 May 2006
Location: Bristol
Posts: 16390
its about right although it could go higher
try switching all the lights and heated screens /seats on and see what it reads thenDuncan
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23rd Aug 2012 9:09 pm
Robbie
Member Since: 05 Feb 2006
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Good battery is around 12.5v and the D3 alternator peaks at around 15.8v (which is higher than most). You should always see over 12.7v when the alternator is running but it seems to settle around 13v+. Alternator goes to full output not long after start (a few seconds) and pushes out almost full power at idle. I think the protection systems kick in around 16.8v, but don't quote me on that.
Reasonably new battery in rude health:
About 10 seconds after starting:
About 40 seconds after starting:
Apologies for the poor photo but about 60 seconds after starting as shown on a cheap 12v cigar socket voltmeter rather than a Fluke:
The above are pretty typical for a D3 with a good battery and good alternator. Car had not been driven for a day and temp was about 9 deg C, although it was a little colder overnight. The voltage is regulated by the cars engine management system according to load, charging rate and temperature.
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