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Alternator going full field

PostPosted: Wed Jun 17, 2009 4:55 pm
by Noel/MOKU
I have a 453 GM diesel in my trawler. I have owned it for 15 years with no problems. It has the original 60 amp Delco alternator and external tranistorized Delco regulator.
Since last August I have been unable to run more that an hour and a half before the alternator pegs the amp guage and produces 17.5 volts. The problem has been intermittent - I've put as much as 20 hours on the hour meter before a failure.
To troubleshoot the problem I have:
- worked with two different shops - one tested all parts and sold me two new regulators; another repaired contacts on the diode plate, replaced the rotor and tested all three regulators and determined only the newest one was bad.
- replaced the oil pressure switch.
- replaced the ignition switch.
- inspected all wiring twice.
- cleaned and replaced all questionable/aged terminal ends.
- ohmed and replaced all questionable/aged wiring.
- load tested the two 8-D batteries twice.
- checked the specific gravity of both batteries.

On my last test run the alternator went full field after 1 1/2 hour. I reduced rpm to limit the charging and systematically turned off circuit breakers and fuses to isolate possible faults to ground. Shedding load did not eliminate the full fielding. I shut down the engine and changed to my spare regulator and the system began performing correctly.

I'm out of ideas and my friends are tired of listening to my sad story - so I'm approaching a new audience.
Has any one a clue as to how I may solve this problem or offer me a new direction to explore?


Re: Alternator going full field

PostPosted: Thu Jun 18, 2009 10:41 am
by Coulomb
With a digital voltmeter you could find out what is happening in a few minutes.

Best Guess:
You may be losing a connection to the regulator that senses battery or alternator voltage so the regulator turns on thinking the batteries are low. This input to the regulator is a low current one, so any small amount of corrosion will create an intermittent connection. Probably unplugging one and plugging in another scrapes enough to make a good connection - for awhile.

A fuse in any low current connection can also play the same game.

Re: Alternator going full field

PostPosted: Fri Jun 19, 2009 10:38 am
by Noel/MOKU
Thank you for considering my problem. I have been doing what you suggested for 10 months now and found nothing. Today I plan to re-wire the regulator voltage circuit. (it is currently sensing from the output of the alternator - machine sense - changing it to a battery sense).
I also have another regulator on order - which I just found out got directed to the east coast by mistake - I'm hoping with all new parts it may be cured.