Alternator diodes?

[814XUW]

Hello all, thanks in advance for your advice.
I did try the search function but found no specific answer to my question.
Tonight my Morris, with headlights etc on, developed a glowing ignition light. I found that the light went out with high revs, but glowed at idle/lower revs.
I do have an ammeter fitted, and it showed a 20 amp approx. drain while the ignition light was on and with high revs this would flick to an approx. 20 amp charge (though the needle was darting all over, though it's always been a little sensitive/flickery).
I pulled over right away to check the fan belt wasn't slack and check the connections, which were all fine. I then discovered that the ign warning light no longer comes on at the first position of the ignition switch, though glows when started/running.
After returning home it was still glowing at idle/lowish revs but went out with high revs, though it appeared to never show greater than a 5 amp discharge by the ammeter (though that could be just a gauge inaccuracy).
The alternator is less than twelve months old. I assume that what has happened is that the diode pack in the alternator has failed, but thought I'd best check before writing back to the supplier that sold me the original alternator requesting that the new one come with a warranty.
The battery is an oldish one (in that I've never changed it in ownership) but has always started the car and never given any trouble, though it is in daily use.
I should mention all battery connections are tight too, and the alternator uses one of the purpose made looms running through the ammeter to the correct terminal of the solenoid, as opposed to a bodge of 'home brew' wiring.

[bmcecosse]

More likely the brushes in the alternator are sticking. Failed diodes would stay failed - not come and go. Check the brushes...

[kennatt]

if its less than 12 months old,don,t touch it just take it back and get them to test it,it should be replaced if faulty.If you take it to bit you may invalidate the warrantee

[bmcecosse]

Reading it again - I can't see how the alternator loom'runs through the ammeter' - but hey ho! As above - if less than 12 months it should be a warranty job. Who supplied it?

[814XUW]

Thanks both.
The wiring loom was supplied new by ESM and should, by design, go to the battery terminal of the solenoid.
Since it has an ammeter, I've added a smaller ring terminal to the end of the loom and connected it to the back of the ammeter, so it can 'read' the charge.
Typically this has happened the day before I'm out of the country for two weeks, so I will have to chase it up on my return.
The alternator was supplied by either Accuspark or BBClassics (I forget now) from eBay (seeing some good reports on their electronic ignition kits I assumed this would be a good bet).

[bmcecosse]

The ammeter could only read the alternator supply amps then - if not connected between the solenoid and the battery...

[IslipMinor]

Mmmm! We have an 18ACR that was supplied during a classic car run around Europe a few years ago, and on the way down to the ferry in Portsmouth last week for this year's run around France, the ammeter started flicking about. A week later and it is still doing it, and I hope it will continue to charge until we get back in 4 day's time.

I have put it down to a dodgy regulator, as sometimes the ammeter is completely steady and sometimes flicks from minus a few amps to plus a few amps - is much worse if there is a load, e.g. headlights on.

When we get back I will get an overhaul kit that seem to be available on eBay for <£20.

[bmcecosse]

Very easy to check the brushes are not sticking on the ACR alternator. Probably worth doing rather than worrying for the next 4 days! A whack on the side of the alternator may just settle them ......

[814XUW]

I can tell you that the ammeter shows a charge/discharge in the usual fashion. It has never given any trouble and actually I'm very glad to have fitted it, with regards to the recent alternator problems. As far as I'm concerned it's working as well as it can be! I'm fairly certain the wiring for it is not the source of my current problem in any case.
Islipminor, sounds very similar to the trouble I've had. Thankfully it does charge (albeit intermittently) so was able to continue the journey with no worries. All the best with your problems, and a safe journey also.
I'll try tapping the alternator with a soft mallet and see if that helps at all (as this is unlikely to invalidate any warranty!) and will contact the supplier as soon as I'm able.
Thanks all for your input.

[kennatt]

problem with most (NEW) alternators is that they are actually recons,and it depends on how much has actually been replaced.

[bmcecosse]

If you switch on the headlights - engine not running - what does the ammeter show?

[IslipMinor]

Update - the alternator survived the whole trip, but on the way back from Portsmouth to Oxford late Sunday night, the regulation was all over the place. The ammeter was flicking from a 30A discharge (headlights, ignition & heater) to a small charge all the way back.

Checking it over the brushes seemed fine, so looked at a 'repair' kit. Whilst looking for them, came across a number of suppliers offering a new, not reconditioned (but Far East made) 'Lucas Type' A127 75A alternator (the 'modern' equivalent of the ACR range) for ~£60 outright for the RH version, no exchange required. It came complete with fan and pulley from the supplier I chose, which is important as the A127 has a 17mm armature spindle, and the ACR/A115/A133 all have 15mm.

So decided to get one, which arrived this morning. The wiring already has 2 x 35A cables from the alternator to the starter switch, via the ammeter, so enough capacity for the new unit, and with exactly the same mounting and plug arrangement, it was fitted an hour or so later.

As you would expect a rock steady charge, with ~30A available on tickover! This means that with ignition + dipped headlights (2 x 80W) on, it still leaves around 10A available to charge the battery, if required. Very comforting.