Dynamo charging problem

[k. rogers]

I wonder if any of you knowledgable people might be able to help before I resort to my local auto-electrician? The Weasel suddenly showed no charge while on a run on Monday. I checked the wiring for loose connections but found nothing. The brushes are free in their sockets and the commutator appears to be clean. Both the dynamo and cut-out were rebuilt about four years ago and have performed faultlessly, until now.
I would be grateful for any suggestions.

[george garside]

have you tried running the engine ( at a normal charging speed) with the cover removed from the cut out so as to see whether the cut out closes as engine speed rises to charging speed. If it doesnt try closing the cutout i.e. holding it in charging position to see if when so doing a charge takes place - if it does charge with cut out held closed its a faulty cut out.

another thought is that it could be a faulty ammeter - have you checked connections on ammeter behind dashboard. Might be worth putting a meter accross battery terminals to see if you get a higher voltage reading with engine running.

george

[k. rogers]

Thanks George, I will try this when I'm next in the garage and report back!

[Tony Fearn]

Hi Ken (and George).

Is the Weasel's dynamo a third brush type similar to Mary Ellen's, and does it have a similar cut-out, or a regulator box?

Tony.

(Don't get too excited, I know nothing about auto-electrics, just a few anecdotal observations about past problems with M.E.'s charging).

[k. rogers]

Yes Tony, it's exactly the same! Typical to get this just before Bideford, mind you, I went a whole season without the dynamo charging when I first had the car so it isn't really a disaster!

[k. rogers]

I have held the cutout points together and revved the engine to see if there is any charge and the ammeter is showing none, in fact there isn't any magnetism which is normally generated by the current from the dynamo needed to pull the points together, so I should think the dynamo is at fault. Holding a meter across the battery shows no increase in output when the engine is revved either! The handbook refers to a dynamo fuse - does anyone know where it is situated or is it inside the actual dynamo housing?

[Forumadmin]

Disconnect all leads to dynamo. Normally a dynamo has two brushes that run on the commutator which converts the alternating current into pulses, all of same polarity.You should check continuity of the brushes and each winding of the armature coil by turning the armature slowly. You should see about eight pulses as you step around one cycle. If you do not it is probably the brush. They do wear!
Note the field coil is in parallel with the armature coil so there is never an open circuit. Of course spinning the armature should generate a voltage also which might upset the ohmmeter, so put it on volts and indeed see if you get some.

[k. rogers]

Think I may have found the problem! After checking that all was well with the brushes, I had a look behind the dash following George's comments and found a loose wire which I traced to one of the connections on the cut-out - it's a red & black one and after checking a wiring diagram looks like it connects to the same point on the ignition switch as another wire of the same colour which goes to the horns. This could explain the sudden failure as I may have pulled this wire when fumbling to zero the trip meter before the run on Monday! Presumably this will complete the charging circuit? I will keep you posted once I've been back to the garage.

[Tony Fearn]

There you go Ken.

As I said in our telephone conversation, try ALL the simple things first.

Well done George.

Tony.

[k. rogers]

Finally found the time to sort the loose wire out and success - I have charge again! A lovely job it was, too: on my back, under the dash, working in my own shadow most of the time and trying to get 3 wires in the same hole with one hand and getting the little screw to tighten down with the other! Still, it's done now and I can concentrate on more servicing before Bideford. Looking forward to seeing you all there!

[Tony Fearn]

I've had all the front down on Mary Ellen so that I could mend the leading edges of the front wings at night school.

All is now back together again and the wings are re-sprayed.

Whilst I had the spray gun with the black paint in it I sprayed a few other items, one of which was the cover for the cut-out which I replaced.

On starting the engine and running the car to the MOT place I found that the ignition light stayed on and the ammeter didn't show a charge.

I checked all the points we discussed in the above posts and still the ignition light stayed on and there was no charge showing.

After a (perhaps not divine) inspiration I removed the cover over the cut-out and lo and behold the ammeter showed a charge and the ignition light went out, but I don't know why.

I'm running without the cover on but would be interested in reasons why removing it allowed the dynamo to show a charge again.

M.E. passed the M.O.T by the way, as did the Rapier three days later.

Tony.

[Forumadmin]

I think the cutout has a thermal device in it. Could this be the cause?

[ian Howell]

Tony: -

YEARS ago ( 1963ish) I had a similar problem with the voltage regulator on my Bradford.

It turned out to be one of the brass links on the back of the regulator, which had a hairline crack in it that disappeared when the vehicle was empty but appeared as soon as you got in to drive it!

It also disappeared when we loosened the regulator from the bulkhead - a bit like your cut-out.

Hope this helps.

[Keith Andrews]

Bit off subject...
About 25 yrs ago the orginal generator in the camaro...well not sure if was the generator or relay...stopped working, so I threw a 2 wire alternator in in the mean time...the generator is still put away and the relay cover still not taken off to look.
The wiring was simple...main wire to battery, sec wire on one terminal and a jumper wire from there to to the feild coils terminal
Anyone done this conversion on the jowetts?