Dynamo

[Tiger]

More Dynamo points
About to reverse the field windings on my C35.
Some of you will be sick of this problem SORRY
HOWEVER
are the orientation of the metal field coil centres important ?
When I installed the field coils I could not see any marks on the two.
This post follows on to my “Dynamo no go” post
Regards
           Tim

[Dave Mann]

No, if you have put then in different to the position they were in originally just motor the dynamo from a battery with the polarity it will have in the car this will induce the magnetic field in the pole pieces.

[Tiger]

Dave
Do you recommend reversing the field wiring?
If you read my earlier post their is no output after repolarising but it motors fine.

[Dave Mann]

  Generator_type_4.jpg (Size: 27.64 KB / Downloads: 394)     I've never had to reverse the field connections, however any dynamo which doesn't cooperate is stripped examined repaired and rebuilt correctly. I've lost track of which dynamo you have, are you certain all the connections are correct? With no undesirable shorts or earths, the early C35 dynamo brushgear has insulating bushes which after 80 years usually disintegrate see photo. With new field coils and rewound armature there isn't much else apart from incorrect wiring or shorts to cause your problem.

[Jack in the Box]

I've never had to reverse the field connections, however any dynamo which doesn't cooperate is stripped examined repaired and rebuilt correctly. I've lost track of which dynamo you have, are you certain all the connections are correct? With no undesirable shorts or earths, the early C35 dynamo brushgear has insulating bushes which after 80 years usually disintegrate see photo. With new field coils and rewound armature there isn't much else apart from incorrect wiring or shorts to cause your problem.

Dave,
In your diagram, would you happen to know the value of the resistance between the D and F terminals please?
Thanks
Alan

[Reckless Rat]

I think it's about 6 ohms. It's the Summer/Winter charge resistor. If you haven't got one, you can buy resistance wire on the Bay of E and wind it round a pencil.

[Tiger]

Thanks Dave for your comprehensive reply.
Brush gear is the newer type with “snail springs”
Checked carefully for any shorts.
As mentioned previously the Dynamo motors very well.
The only thing I can think of is the field connection.
This was mentioned by Bob from NZ
So I will try that.
Report back later
Regards
Tim

[john williams]

Thanks Dave for your comprehensive reply.
Brush gear is the newer type with “snail springs”
Checked carefully for any shorts.
As mentioned previously the Dynamo motors very well.
The only thing I can think of is the field connection.
This was mentioned by Bob from NZ
So I will try that.
Report back later
Regards
           Tim

If the dynamo "motors", it is usually sound. Refit the dynamo to the engine, leave the "D and "F" leads disconnected. Conenct a link lead between "D" and "F" terminals on the dynamo, run the engine with anologue voltmeter connected between "D" terminal and a good earth. If votmater reads approx' 7.5 volts, it is fine, fault is in associated charging circuit.

[Jack in the Box]

I think it's about 6 ohms. It's the Summer/Winter charge resistor. If you haven't got one, you can buy resistance wire on the Bay of E and wind it round a pencil.

Many thanks. I’ll take a look. Alan

[Dave Mann]

I'd forgotten that back in the 1970s we'd arrived at Astle park traction engine rally in the rain erected our tent, new mum Sue was under the weather so I took our daughter in her buggy for a walk round. It wasn't long before I came across a crowd round a showman's engine which had no lights on, yes they'd got a battery to restore the dynamo field magnetism, and run it up with no joy. I asked about it's history to be told that the dynamo had recently been overhauled by Mather & Platt and hadn't been used since refitting to the engine. Now this dynamo had six leads going to the switchboard, two were the output from the brushgear, two were the series field and two were the shunt field. OK I said all you have to do is reverse one pair of field connections at the moment one field is opposing the other. All eyes turned to me then they switched one pair of leads and ran the engine up followed by a loud cheer as all the lights came on. So yes I have reversed the field connections but not on a Seven. Catherine in her buggy was in awe at the goings on with not a peep out of her.