Non standard alternator; problem diagnosis?

Hi,

I normally hang out on the Discovery forum for my D4 with occasional forays into the Defender world when helping my youngest with his TD5 110. I do have other cars, and as you can imagine - problems.

Latest is an alternator problem on an Austin 7. Yes I know they're supposed to have a dynamo but they were 6v, crap at charging and fragile. A company made some 'look alike' 12v alternators for these as a retrofit which is what I've got. It is more complex to change out compared to a normal belt driven one as it is gear driven with the distributor being driven from the other end, which also makes it a pain in the arse to remove and refit/set up. The company have stopped making it and withdrawn all support.

Mine did originally work and nicely balanced the ammeter reading but then the red light started flickering and eventually became always there.

I've stripped it down (a few times in fact) and cant find a fault. Can I draw on the enormous collective experience of those on this forum? Can you help please, am I missing something stupidly obvious?

The rotor coil has continuity at 4 ohms with good continuity out through the sliprings and brushes (which I manged to renew with a generic brush box item). The stator coil tests out similarly, though I haven't split out the separate coils in it to test individually. The diode pack has continuity in one direction and a very large resistance in the opposite direction. I've tried different regulators, cutting and grafting them from proprietary items (but can't work out which way to connect the two live wires - but neither alternative brings the alternator back to life). The alternator has a good earth to the engine and back to the battery.

If there's something down I'll have to either fix it myself or graft in a spare from something else though the rotor, stator and diode pack are very bespoke to the very small 3.5'' diameter body.

Am I missing something or not testing an aspect correctly and meaningfully?

Can you please advise how to test out each of these components?

Thank you, Dave

Hi there,

500 'Views' but nobody has any advice? I can't believe that the collective experience on this forum doesn't cover basic tests of an alternator. Or has the Replacement Society taken hold and we just ditch anything where a bolt in part is available. From other ingenious solutions to obscure problems posted elsewhere on here I suspect not.

I'd really appreciate it if you could offer some advice, I'd like to fix this over the Winter.

Thank you, Dave

Sounds like you know more about it than anyone else on here.
Is there not a forum for that make of car?

lynall said:

Sounds like you know more about it than anyone else on here.
Is there not a forum for that make of car?

Click to expand...

Thanks for the response Lynall. Yes there is an Austin 7 forum but most on it are heavily into 'originality' - and I get abused for wanting to do away with the fragile low charging 6v dynamo. I now probably know more about this alternator conversion than anyone else other than whoever put it together in China. But it is just a conventional alternator and there will be a way of definitively testing the sub components; am I missing something? The days of an Auto Electrician's shop being full of scruffy dismantled alternators and starter motors seemed to have passed, cheap unit replacements now seem to be the norm - and have we lost the knowledge on how to test and fix these things?

Thank you, Dave

if your sure the core is ok and replaced what you can. if its gear driven have the gears worn down and reduced your output more so than the core being the issue?

how are you bench testing it and getting it upto speed needed to test the output?

https://www.alternatorsnorthwest.com/ will test for free maybe they can shed some light for you.

Speedex750 said:

Thanks for the response Lynall. Yes there is an Austin 7 forum but most on it are heavily into 'originality' - and I get abused for wanting to do away with the fragile low charging 6v dynamo. I now probably know more about this alternator conversion than anyone else other than whoever put it together in China. But it is just a conventional alternator and there will be a way of definitively testing the sub components; am I missing something? The days of an Auto Electrician's shop being full of scruffy dismantled alternators and starter motors seemed to have passed, cheap unit replacements now seem to be the norm - and have we lost the knowledge on how to test and fix these things?

Thank you, Dave

Click to expand...

we used to have two alternator/starter motor repair places in the town I live they both went about 10 years ago
Suspect most people do the same as me stick a new brush box in it and if that does not fix it stick a new unit on.

It might pay to ask on the migweldungforum as they have some really knowledgeable electrical people on there, and they love different stuff.

Thank you for your responses.

The gear drive is fine, it's definitely driving the thing round. I haven't tried bench testing it, I take it to bits, try something different and reinstall it. I could perhaps drive the input with a socket and drill so may try that next time it's off. Thanks for the tip about the MIG forum, I've posted the problem on there and will see what emerges. I'll post what comes especially if there's helpful advice, I get frustrated with problem threads that don't conclude with what to do to fix something similar.

Thanks again, Dave (Speedex750)

Does it have/need an “exciter” wire to start it charging like a standard alternator?

What does it have by way of a rectifier ?