MG
The Classic Marque

Thanks Willy and Bill. Right, voltage spikes. Makes sense. And takes us right back to the title of Flip's thread.

In which case the regulator on the China alt' might have suffered too I guess.

Well I'll have a new one in the set I've ordered, plus, two older ones (that may well be ok) to replace it with if it is fried.

I *think* that if the diode earth suddenly fails then there is likely an instantaneous voltage spike at the stator output, due to a sudden current collapse self induction event. This would easily over-stress at least one of the diodes, maybe more. So a sudden failed earth isn't good.

an----alternators in general don't hack running with an open circuit---If you run an alternator, for example, with the main power lead disconnected it'll fizz one or more diodes very quickly.
Running with any open circuit in or from the alternator confuses the voltage regulator and voltage goes sky high beyond the operating capacity of the diodes--pffft

Same result from electric weldi...

It's 580 ohms using the 2k ohm range on the digital multimeter (1 volt small current) David. Not accurate I know. I just used it to compare all 9 diodes to eachother, and to the other diode packs. And it showed the open circuit dead diode, which is all I was looking for.

Can anybody explain the dead diode because the rectifier pack lost its earth connection? I can't work out why.

<...

Anam,

That 580 Ohms is likely to be 580 milliohms otherwise it would be dropping an enormous amount of heat into the diode pack.

No reason really Bill.

Here's a test on the working diodes in the faulty China pack, with the diode function. Display is in mV.

Skin screen every year for me. Every 6 mos for my wife. Has picked up a couple of pre cancerous spots on me , several on my wife.

Thanks for the reminder Len. It pays to be vigilant.

Regards, Tom

I wondered why you didn't use the diode test function on your meter? You'd get infinity in one direction and about 0.6v the other way for a good diode.

2nd. What was wrong with my old lucas alternators?

For now, I'm assuming the regulators are both working as they should.

Having tested both diode packs, and found those to be good, I took the brush boxes off.

Knackered outer brushes on both alternators, but the centre brushes are hardly worn at all. Foxed me at first, until I thought about it.

The outer brush we...

Fortunately, both my old faulty Lucas alternators have good rectifiers. All diodes test to about 580 ohms.

So I soldered one of the old good rectifiers into my newer but faulty unbranded China alternator..

I'll test it as soon as I take delivery of a new angled spade connector for the loom plug, --- I broke it. Lol.

Meanwhile, I still can't work out why the nut securing...