Section : Electrical Equipment

Alternators, dynamos, lights, wipers, etc.

Alternator overcharging ?

Posted By : Steve Parsons, 29-Apr-2004, 10:45pm

I have an alternator conversion fitted to my mk 2 Vitesse, and i think it is overcharging.The ammeter shows a charge at 30 amps @ around 2000rpm [no electrics used], I have checked the charge rate with a voltmeter and get a reading of 17.5 volts which i assume is too high, 14.2 volts being the norm. [Battery fully charged].
I have replaced the alternator, but get exactly the same readings, can anyone point me in the right direction please?

Followups :

Alternator overcharging ?

Posted By : David Rumens, 30-Apr-2004, 09:17pm

Yes you do appear to have to many volts coming out of the Alternator. Firstly ensure the ignition light is connected and working.

If you still have the fault after this it would normally be caused by the regulator in the Alternator, but if you have changed the Alternator then this should solve the problem.

So I wonder which Alternator you have fitted on your Vitesse.
- Alternator overcharging ?
  
  Posted By : Steve Parsons, 30-Apr-2004, 10:45pm
  
  Dave,
  The ignition lamp works fine, but I will check the type of alternator fitted over the weekend, I don,t know if this is any help but after I fitted the new alternator the charging rate seemed to be fine for a few miles, then started overcharging again, that is according to the ammeter?
  - Alternator overcharging ?
    
    Posted By : Philip Wright, 01-May-2004, 12:12pm
    
    Hi Steve
    
    I had similar problems to what you describe when I replaced the alternator on my Spitfire. However, I took the replacement back, swapped it over and the replacement has been fine. Maybe its something to do with dodgy non O.E. parts?
    
    Phil
    - Alternator overcharging ?
      
      Posted By : David Balfour, 01-May-2004, 12:57pm
      
      I'd suspect a short circuit, because 30A is a lot of current.
      
      If the battery is fully charged then it simply wouldn't draw that sort of current, and thus it must be going somewhere else.
      
      If this is the case, the short may have knackered both the alternators (sorry ). However, I had a reasonably serious short once, and the alternator didn't seem to mind.
      
      I'd suspect one of the 'hefty' cables as the problem - a smaller one would melt with 30A through it, stop conducting and act as a sort of crude fuse. Is the battery holding its charge ok overnight?
      
      I may be way off the mark here, of course...
      - Alternator overcharging ?
        
        Posted By : David Rumens, 01-May-2004, 05:34pm
        
        The key is the 17.5volts output from the Alternator. If this voltage is correct then the battery will continue to draw current untill it over-heats and then fails. Not nice!
        
        If it is a Lucas 16ACR then it does sound like the internal regulator has failed. Make sure your number one plug lead is not drapped over the rear of the Alternator as the high field generated by the high voltage will destroy the internal regulator. I found this one out after two Alternators. Watch after market plug leads as they are longer than the E.O. type.
        
        The other factors that will destroy the internal regulator are welding on the car, running the car with the battery disconnected and intermittent connections to the Alternator.
        
        If it is not a Lucas 16ACR then - some Alternator have a sensing terminal that must be connected to the battery. If this is left un-connected the regulator will not work and the output voltage would go high. Hence me asking what Alternator it is.
        
        Just some thoughts