Strange alternator issue

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Can tell where the 480 was built
Posts: 337
Joined: Tue Feb 28, 2012 3:25 pm
Location: Northants

Strange alternator issue

Post by Ade » Wed Nov 11, 2015 10:34 pm

Having recently experienced a catastrophic bearing failure in my alternator I decided that I must procure a new one. I went to GSF and got quoted silly money and so I thought if take my chances at a favourite breakers yard of mine (twigworth breakers near Gloucester, who, sadly, are soon closing and well worth a visit before they do) who do (or rather, did) a line in recon alternators. As they are in the process of shutting down for good they simply had piles of old stock of reconditioned alternators and starters that they were no longer able to identify and so I had to hunt through to find a likely contender (which I did, and at £50 a bargain).

Mechanically the unit is identical to the original item and also shares the same basic electrical construction but for one thing.......

The voltage regulator on the old unit was of the single wire type (ie just a feed for the batt light) and nothing else and so I assume the 'self exciting' variety. The voltage regulator on the new unit is of the two wire type (a 'hot' from the ignition to activate the charging and a batt light feed).

No problem I thought, ill just swap the voltage regulators over and happy days (the reg on the failed alternator was not that old, I had replaced this not too long ago to remedy an overcharging situation and it still had plenty of carbon left)

Having done this, I connected it all up and started her up. My voltmeter (confirmed by multimeter) was indicating that there was an amount of charge going into the battery but not really enough (around 13.2v) and my batt light was still illuminated. Having been unable to achieve proper charging by swapping the regulators over, I put the other one back on and ran an ignition 'hot' to the B+ terminal on the regulator and it is now charging perfectly with no warning light. If I don't have the ignition 'hot' it simply does not charge and I get the corresponding batt light.

Although I have a perfectly workable solution, I don't like having to add wiring to a car and plus I am baffled by why swapping the regulators over did not work. Bear in mind I know the regulator to be good as electrically, there was nothing wrong with the old unit, it just suffered bearing failure and went rattly, it was still charging and regulating fine at time I removed it from the car. Visually at least, the two units are absolutely identical apart from the regulators with which they are fitted. Any thoughts or theories would be greatly appreciated, really scratching my head on this one, I have a good enough working knowledge of electrics to have managed to keep my 480 alive for a long time without assistance but am by no means an expert so if anyone that is can shed some light on this, I would be most grateful.

Cheers all.
O.C. 480 D.

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