Dynamos

[Martin Nash]

Can anyone help please. I had a dynamo problem on my chummy. It didn't appear to be charging. Sent it off and it was overhauled by ARMOTO. Refitted to car but still no charge. Did usual checks with help from Adam at ARMATO. Joined (bridged) F and D terminals and put volt meter from bridge to earth started engine - no voltage!!

Removed dynamo and clamped in vice. Did the same test, spun it up with a hand drill and got normal output from dynamo. Put it back into car and tried again. No output again. Thought that the dynamo was not being properly earthed so rigged up a cable from the dynamo securing bolts to a good earth but with no effect.

Removed dynamo and ran test once again and sure enough it works perfectly. I have checked that the armature is rotating when dynamo is  fitted to the car. 

Can anyone shed some light on what may be happening.

Best regards

Martin Nash

[Bela]

If it works with rotating armature on the bench and not in the car it may be there is a short in the wiring. No smoke or hot dynamo?

[Ken Morton]

Looks like the cut out is not working. Had the same trouble myself until I checked the cut out.
Ken Morton --1927 Chummy

[Martin Nash]

Thanks,

That's the mystery. I have tried it both ways i.e with the cutout connected and disconnected as per the bench test.

Martin Nash

[Peter Clayton]

May not help but have you polorised the dynamo by flashing the field coils to the polarity of the car?

[John Mason]

Did you put your earth test wire on the dynamo direct to the battery. If you only put it to a good earth on the body or engine you should check the earth strap from engine to body and also earth strap from body to battery. Once you are certain the dynamo is earthing back to the battery do all the checks again that Adam at Armani suggested.

John Mason

[Charles P]

Was it a digital multi-meter?
They can be flakey on this type of test. A bulb or analogue meter is better

c

[John Cornforth]

Hi Martin

There is a possibility that your voltmeter if digital is being upset by ignition interference Try a moving coil (pointer) voltmeter, or even a lamp, between the bridged D+F and a scraped clean part of the dynamo casing.

[Denis Sweeney]

On the subject of dynamos, during the restoration of my early type Ruby I was fortunate that the dynamo On the car needed very little attention apart from a good clean and some new brushes (touching wood with both hands) she is running fine.
However a large number of various spares and odd bits came with Ruby including a couple of dynamos and starter motors in various levels of decay.
I am now thinking it would be a good idea to have the best dynamo refurbished as a spare and note Armato noted in Martin’s original post, can anyone offer any recommendations for rewinding and refurbishing a dynamo and highlight any pitfalls.

Any advice most welcome
Cheers Denis S

[Martin Nash]

John and Charles

Many thanks for this. If it is the multimeter (being influenced by the ignition system) then and we can establish with a regular voltmeter or even a lamp that the dynamo is charging then the fault lies in the cut out box. I will try tomorrow. will advise.

Also will check earth straps although I think these are sound.

Martin