Very hot alternator

[Clifford Pope]

The car has been out of action since the start of covid, but I have been starting it every few months and getting it up to temperature.
Quite recently it has become very difficult to start, splutters and misfires, but usually finally settles down and runs smoothly.

Today it did the same, but then started misfiring very badly and finally cut out. I've been beginning to suspect dirt in the fuel from the original rubber fuel feed pipe connectors breaking up. I've got a new set ready and had intended draining and flushing the entire system and replacing with new.

But that's another story. This time I noticed a hot electrical smell, and the alternator was very hot - far too hot to touch, after only "running" for about half a minute. Only the ignition was switched on, so it should have had virtually no load.
It's a Mk 1, converted to alternator some years ago, and only done a small mileage since. I left the ammeter in place, but the charging current never took it off-scale. It now however suddenly charges at a much higher current, suggesting to me that some fault has occured in the alternator. The battery had been fully charged just before starting, so there was no need for a high charge rate at all.

How do I test the alternator statically - what should the coil resistances be? Any other ideas please?

[Mike Stevens]

First of all measure the voltage across the battery with the engine stopped and also with it running. It sounds like the alternator regulator is giving problems and producing a too high voltage which will eventually damage the battery.

With the engine stopped the battery voltage should be somewhere between 12 and 13V, depending on the state of the charge and how long it is since it was last charged. When running somewhere between 13 and 14.5 is about normal, but much more than that is not!

Cheers,
Mike.

[Clifford Pope]

" When running somewhere between 13 and 14.5 is about normal, but much more than that is not!"

So 18 and rising when revved would indicate something wrong with the regulator? !!

I take it the regulator is somewhere inside the alternator - is it fixable, replaceable, or would this mean a new alternator?

[johnnydog]

I have a Lucas 15ACR (a very early Mk2 alternator with the early connector block with the 'loop' cable) on my J reg. 2000.
Several years ago whilst on the first Northumberland National, it started over charging, which I only noticed due to the higher than normal reading on the voltmeter in the car. The battery was hot to the touch. It actually damaged the battery on the journey home dispite putting the heater fan, headlights and radio on (no heated rear window unfortunately!) I took the alternator to an auto electrical business near me, which fully overhauled it, and it looked like new when I got it back. It was less than £50 which I though was good value, and it kept the originality of the car and avoided the need to change the block connector had I opted to fit a later Lucas 17 ACR alternator.
It's been fine ever since.
Worth trying a known good used one first if you didn't want to go down the overhauling route?

[Clifford Pope]

Thanks very much; I'll try your suggestions.

I've taken the end cover off and immediately noticed what I think is the rectifier looks burnt and sooty.
If the voltage has been getting higher steadily then I've just read this could explain the way the contacts and capacitor don't seem to last long.
On thinking about it that could also be the cause of headlights burning out fequently. I'd put this down to old stock aging in storage.

[Mike Stevens]

Th rectifier pack looks like 3 square metal plates bolted together with one fixing though the middle (in fact there's 9 diodes in there, 6 wired as a 3 phase bridge and the other 3 wired much the same to power the regulator and field coil). The regulator is normally a square metal box about 2" square and maybe 0.5" thick. the open side of the box is probably filled with potting compound- not the stuff you use in a greenhouse, but the stuff that sets hard to hold everything in place. A number of wires come out of it, perhaps 3 or 4. It's the regulator that has failed and you used to be able to get spares easily. Good luck with getting it fixed!

[Clifford Pope]

I've replaced the alternator, and it works perfectly. At first the engine would hardly run, with no power, would barely idle, and cut out if I touched the accelerator. But then I realised the high voltage had probably damaged the condenser, which I've also now replaced and it runs beautifully. So that's all good.

What's not so good is that it refuses to restart. It will occasionally give a little kick just as I release the key, which I've just read is a common sign of a failed battery. It uses all its effort in turning the engine, but drops the voltage so low while turning the starter that there is no spark.
It appears therefore that the alternator has gradually been failing over the past two years, causing an increasing appetite for condensers and also damaging the battery.