Charging (or not)

[RupertW]

Hello all, 

Looking for some pointers on my '34 box saloon which has stopped charging. 
It seemed to be charging normally last time I used it, but this time round the ignition light would not go out, and the ammeter was not showing a charge. I tried manually holding down the cut out and this didn't cause it to charge either. As far as I can see there's no fuses blown. 

Is this likely to be down to the brushes and is it normal for them to fail suddenly rather than a slow decline? I've taken the cover off the dynamo and from a very quick look, it looks far from brand new, but nothing obviously wrong to my very untrained eye. 
Is there anything I should particularly be looking for to tell if it's the brushes, and does replacing them involve removing the dynamo? Is there anything else obvious I might be missing to explain the lack of charging? 

Any help appreciated as always!

[Graham Barker]

I had a similar failure on my 37 Ruby. The cause was a broken wire from the third brush.

[Bob Culver]

Is the cutout earth connection good? When you say held down the cutout what exactly? Normally if prodded it will lock down until prised open or the battery disconnected. If not a disconnection somewhere
The basic dyn test described here many times is very simple. With all disconnected and the output and field terminals joined, then  as the motor is revved the voltage from the link to earth should soar well above 6v. Can check with a 12 v bulb.The car must not be operated for long in this state; the main output lead must be reconnected

[Tiger]

Rupert
It might be worth a look at Harry Hales guide.
It’s a great starting point with 7 electrics.
Apologies if you already know
Regards
Tim

[David Stepney]

I had a similar problem with my RP some little while ago. The dynamo suddenly stopped charging. examination of the dynamo revealed that the third brush had broken into pieces. A new set of brushes and we were back to normal. And, yes, one has to take the dynamo off the car to do the job effectively and re-time the engine afterwards.

[RupertW]

Thanks all for the pointers - electrics definitely aren't my strong point, so even the most basic of advice is appreciated.

When I say I held down the cut-out, I mean the arm that should disconnect when revved, and disconnects when revs drop to prevent discharge. I can previously recall it not operating properly and requiring some manual persuading to get going again, but I don't recall it ever needing prising back apart once back at idle.

I'm not familiar with the Harry Hales guide, so any links to where I could get one would be welcome.

I think the engines probably overdue a bit of a refresh at this point so I might take this as an opportunity to take the engine out and sort a few other bits while I'm there.

[Bob Culver]

Hi Rupert
I was referring to the situation with engine switched off. Best to diagnose on the car when it can be run at speed (and in the corrct direction!)
AS with all enquiries on here it is hard to know the level of experience of the enquirer so hard to pitch the reply, althogh others also read. 
Compered with the nightmare of moderns the Seven electrics are joyously simple (even if you have solenoid dip lamps!).
A 3rd form grasp of volts, amps, ohms, watts helpful and esily picked up as many have forgotten.
John Cornforths circuit diagram will likely prove very helpful as it covers such puzzles  as the internal function of the rotary switch.
(some minor differences from RP)

[RupertW]

Just to dig this out again, I've since removed the dynamo and it's all looking well past its best. Can anyone recommend someone to overhaul it for me, preferably with a reasonably timely turnaround time who I can post it to? Many thanks

[Chris KC]

I believe Vince Leek is the go-to guy for dynamos

[John Mason]

Whatever you do. DO NOT repeat DO NOT. Go to Classic and Vintage Dynamos of Shirebrook, Nr Mansfield. They are cowboys I got a Dynamo back but it wasn’t the one I took in.

John Mason