alternator problems

[caterhamnut]

Was left stranded in North London on Saturday afternoon whilst on my way up north to Donnington. Red ignition light had come on, and sure enough about 20mins later (trying to reach somewhere suitable to stop) we stopped.

 

We had fitted a reconditioned alternator a week before, and had done maybe 10 miles on it before the light came on and all charging ceased. (This was checked on the scene by the 'Ontime' towing chap.)

 

Bit of prior history:

A few weeks ago we had to replace our old alternator (due to similar [initially intermittant] red light/no charging stuff) This was also cracked, so needed replacing anyway. We replaced it with a nearly new alternator which proved to be faulty (or was it??!!) and then replaced this one with another newish one, kindly loaned to us. This worked fine, and with it we drove from Balham to Brooklands, spent the whole day thrashing the car there, then drove back again - all with no problems/red lights etc. This particular altenator was required by the owner, so we then fitted the current reconditioned version. This is the one which has just gone.

 

So - question is, have we just been unlucky with this alternator, and although just reconditioned it is faulty and has broken almost immediatly, OR is there something on our car breaking the alternator. If it is the latter then surely it must be intermittant, as it did not blow the other new alternator with over 100 miles driving. And if this is the problem where the hell do we start looking?!

 

Any ideas people?

 

😬26,000 miles in 13 months!

angus@tinyworld.co.uk

[Peter Carmichael]

If you have an earthing problem or an open circuit between the alternator and the battery then you will knacker the alternator regulator in short order. I now reckon three alternators have blown up on your car, so checking the wiring is a priority before spending more money on a new regulator for that alternator.

 

Each time you have fitted an alternator, you have disturbed the battery connections - the open circuit could be related to disturbing and remaking these connections.

[Peter Griffiths]

Angus

 

Have just called a chum of mine who is an ace 7 electrician and his comments mirror those pf PC

 

Peter

C7 PRG

 

 

[Graham Sewell]

I have been wondering whether my last alternator blowup was due to me using the battery master switch to shutoff the engine (I do it if I am being lazy while working on the car). I do have the 11ohm resistor connected to the master switch, but have not yet checked for resistance since I got the car back from the post-vandalism rebuild.

 

Low tech luddite - xflow and proud!

[caterhamnut]

Thanks guys. Would point out I had already spoken to Peter about this - just wondered if anyone had had similar experiences.

 

So if the damage was possibly caused by battery connection/disconnection, why did the alternator last as it did. In other words, what is the nature of a regulator failure - is it 'instant' or does it cause a slow failiure? Obviously if the same effect is being caused by a dodgy short/loose connection elswhere then it is more difficult to find. I suppose the battery theory could explain why the other alternator worked fine - or was that just luck that nothing shorted whilst that was in?

 

How do you avoid the battery connection/disconnection problem, understanding that you have to disconnect when replacing the alternator?

 

arrggh - I can get my head round most mechanical problems/principles but electrics are a pain in the ar*e!

 

 

 

😬26,000 miles in 13 months!

angus@tinyworld.co.uk

[Peter Carmichael]

The problem is if the alternator becomes disconnected from the battery while the engine is running. Just disconnecting and reconnecting during the fitting of the alternator is not the problem. The problem is with open circuits, not short circuits.

 

I am suggesting that you need to trace through your earth connections to the battery and to the engine and check the power-side connections as well.

[caterhamnut]

ok - I see what you mean now.

Where does one start?!

Is one solution (and I understand this is partly avoiding the problem - but bear with me!) to simply not use the existing wires from the alternator, and replace them (with the old ones in situ but disconnected) in which case you should be able to guarantee the cables are sound. The existing cables are buried in a taped up, hard to get at wiring loom.

 

ok - re-reading your reply Peter, it is the earth wires I need to check. Now I know where the obvious big one is, at the front of the engine to the chassis front off-side. Where are the others? How many are there? Or am I still being thick? Are you, your meter and your thoughts available later?!

 

😬26,000 miles in 13 months!

angus@tinyworld.co.uk

 

PS we'll cook

 

Donnington was great - what is it like as a '7' circuit? Looks fast.

 

Edited by - angus&tessa on 23 Sep 2002 16:28:31

[jf_renard]

Hi Angus.

 

A "monofunction" alternator has basically 3 connections:

-n°1 to the battery (-), through the alternator body and mounting, the engine and the earth strap.

-n°2 (B+, "power-side connection") direct to the battery (+), through a big wire. Sometimes it is not directly to the battery, but via the starter -> check if it's not loose there.

-n°3 (D+) to the warning lamp, then to the ignition switch then to the battery (+)

 

To light the warning lamp, you need connections n° 1 and 3 so it is likely they are OK (but costs nothing to check!)

The more likely to fail is n°2, which you could replace by a new wire (must be as big as the genuine one!). But more weight and the beginning of a messy engine bay....

 

I remember having heard that n°2 is made of 2 brown wires (wonder why 2?), but never checked on mine or a wiring diagram.

 

Hope it will help.

 

 

Jeff

Cosworth 1600 BDR

[caterhamnut]

Well, we have done a brief check of wiring and battery connections and can only come to the conclusion that a dodgy alternator is to blame. we will re-fit the newer alternator and hope it does not blow up! Thanks for the tips.

 

😬26,000 miles in 13 months!

angus@tinyworld.co.uk