Dynamo trouble on a friends classic

[The vast minority]

I've got a pal with a classic car whom really should have a court order banning him from owning a toolbox, If he joined the 3 wheeler forum and asked them it would go something like this. "Oy, car won't go, anyone got a big ammer wot I can borrow?

Fortunately, fearing a total burnout because this issue involves electricity, he has asked me to assist with his problem. Basically the car wont start again if he drives it with the lights on. The battery goes flat, car is fine without lights so it sounded like a charging issue straight away to me.
Voltage at the battery did rise when running but only by about half a volt, dropping to just 11 volts with lights on. I got the inspection cover off in the passenger footwell (it's a regal) and tested at the Dynamo output terminals. 0.2 at idle to 1.2 at around 2000 revs and no more with further increased revs. This is obviously enough to replace consumption of the ignition system but no more.
Belt is new and isn't slipping.

Now I suspect it's in need of a cleanup and new brushes but before I take on the job of removing the Dynamo can anyone suggest another likely cause of this low output? I'm not a Dynamo expert either so I expect my diagnosis may be wrong. Would failed windings do this or would I be looking at total failure in such a case? This is a pig of a job by the looks of it so I want to be sure before I dive in as I don't want to have to do it twice. I'd rather get a new unit to fit if the brushes and clean up might not cure it. Taking a Dynamo out of regal looks like the opposite of taking one out of a minor.

2 minutes for the minor, possibly body off on on the regal if my mate is to be believed.


Thanks
Al

[bmcecosse]

The readings make no sense to me. Battery volts please - at rest, with engine at decent revs and then again with lights on at decent revs ......I guess that is your 11 volts (which is utterly hopeless). Assuming the battery is connected right way round - has it been out recently? Then it is indeed most likely to be needing new brushes...so I suggest either a known good dynamo to swap in - or a set of brushes in stock. It's always possible that it's the regulator of course...although they are very reliable unless messed about with.

[mogbob]

Since the " charging journey " starts with the dynamo, eliminating problems there is your starting point.
Clean up and inspect the commutator, check for broken springs on the brushes and replace springs/ bushes as necessary.Get the terminals themselves back to shinny metal for a good electrical contact.Check the wires for integrity.Nothing amiss ? A drop of oil on the back bearing for lubrication.

Down the road... good earth from the battery terminal to chassis ( I presume ? non metal body ). Both battery terminals clean.The control box might be a problem.If you're familiar with them,a light clean of the internal contacts, with fine glass paper might work.Most people ,given the age of their classic, replace the whole thing.

Is does sound ,from your tests, that the dynamo is definitely suspect ,so tackle that first and see what happens.
Good luck.
Bob

[bmcecosse]

The dynamo appears to be v inaccessible - hence the idea of doing a few tests before diving in.......

[The vast minority]

Thanks for all the input chaps, I've ordered the brushes and will see what's needed next weekend
Al

[bmcecosse]

No volts readings meantime ?

[The vast minority]

No volts readings meantime ?

Sadly not, car isn't here and my mate wouldn't know how.

Al