Alternator Failure

[DGRiley]

I am on my third alternator in three months and its failed (blown) again. Always the same scenario, the alternator light comes on and the speedo and rev counter go t*ts up. Its a Lucas alternator on a 2.1 Pinto. I put a new battery on last month and had it serviced and MOT'd ready for some summer fun but cannot understand why I am suddenly getting alternator problems. Any suggestions.

[Richard M Green]

I would consider the following factors:

1) Excessive heat - Westfield under-bonnet temperatures do not help longevity of alternators: is it receiving direct (radiated heat) for example from exhaust headers?

2) Excessive speed - the ratio of crank pulley to alternator pulley size should result in the alternator staying below 12,000 rpm (ish).

3) Incorrect load - either too great or too little. Do you have a battery master switch? If so is it correctly wired so that it dumps alternator output to ground when the main switch poles are open? Is there any possibility that the alternator is being intermittantly taken off-load whilst running.  You mention instruments misbehaving; is there anyway that the alternator +12V output is becoming (even momentarily) disconnected from the battery which provides it with a load? If the instruments end up on the 'alternator side' of an unintentionally 'split' system with no or litle other load on the alternator, then you will damage the alternator and probably damage the instruments.

4) Is the exciter current (i.e. the current through the warning lamp) too great, so that the alternator gets 'full fielded'. The charge warning lamp  bulb should be rated at no more than 1 or 2 W.

HTH

Regards all

Richard