I've got an alternator where the output voltage measures over 14v, but the idiot light doesn't go out, so I'm thinking a diode or something has failed.
Would putting a new regulator solve the issue?
Thanks.
Regards,
Jim
Alternator fault
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Bruce.m
- Posts: 1070
- Joined: Sun Aug 11, 2013 1:44 pm
Re: Alternator fault
Why?
The idiot light has the alternator on one side and the battery on the other.
If the voltages are the same, the light goes out.
If the alternator / battery voltages are different (either way) it lights up.
Nothing fancy or digital about it.
That might be a broken wire or more serious.
The light is the start of the investigation process not the end.
The idiot light has the alternator on one side and the battery on the other.
If the voltages are the same, the light goes out.
If the alternator / battery voltages are different (either way) it lights up.
Nothing fancy or digital about it.
That might be a broken wire or more serious.
The light is the start of the investigation process not the end.
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vwjim
- Posts: 389
- Joined: Thu Jul 04, 2002 12:01 am
Re: Alternator fault
Thanks for the reply.
I know all of that, what I didn't know if the trio diodes are part of the regulator or not.
I've now removed the alternator. The trio diode (usually 3 in one package) is on the rectifier plate. Not the 6 larger power diodes on the rectifier plate. The trio is made up of 3 small wire ended plastic packaged diodes connecting to the 3 phases and a single connection to the D+ terminal.
These have failed, so the idiot light circuit stopped working.
I know all of that, what I didn't know if the trio diodes are part of the regulator or not.
I've now removed the alternator. The trio diode (usually 3 in one package) is on the rectifier plate. Not the 6 larger power diodes on the rectifier plate. The trio is made up of 3 small wire ended plastic packaged diodes connecting to the 3 phases and a single connection to the D+ terminal.
These have failed, so the idiot light circuit stopped working.
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telforddorr
- Posts: 7
- Joined: Mon Jan 13, 2014 11:36 am
Re: Alternator fault
Point to consider: when the alternator is operating correctly, the output of the diode trio is just like the main diode output, with one exception - the diode trio is rated around 5 amps maximum load. The alternator inductance will not limit the diode trio current, as it will with the main diodes. Thus, any excessive load on the diode trio, especially a short of some kind, will pop the diode trio diodes like flashbulbs. Any time you have a diode trio failure, it would be wise to do a thorough check of everything connected to the alternator D+ terminal blue wire, looking for issues.
For more VW electrical, see http://telforddorr.com/ (available 9:00am to 9:00pm, PST)
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vwjim
- Posts: 389
- Joined: Thu Jul 04, 2002 12:01 am
Re: Alternator fault
That's probably why it has a fault then, as the vehicle it came off has horrendous electrics.telforddorr wrote: ↑Mon Nov 16, 2020 1:23 pm Point to consider: when the alternator is operating correctly, the output of the diode trio is just like the main diode output, with one exception - the diode trio is rated around 5 amps maximum load. The alternator inductance will not limit the diode trio current, as it will with the main diodes. Thus, any excessive load on the diode trio, especially a short of some kind, will pop the diode trio diodes like flashbulbs. Any time you have a diode trio failure, it would be wise to do a thorough check of everything connected to the alternator D+ terminal blue wire, looking for issues.