Le Mans 9 Dynamo

[casadecabra]

The dynamo that was fitted to my 1934 Le Mans 9 when I first acquired it (many, many years ago) has three external terminals as ilustrated on the photo below. I suspect it is not original as all the pictures and the wiring diagrams I have seen show two terminals, although the flange and shaft fit my engine. The nameplate is inscribed 'C.A.V. Bosche Type DDC166 12 Volt'. I cannot find any marking on or adjacent to the terminals.

While I have a reasonable working knowledge of mechanical things I am a dunce when it comes to electrics and electronics. Can anyone tell me if I can use this dynamo and, if so, how I should wire it in.

David B

[jeans_old_man]

Probably not worth the trouble. The correct Lucas part number is C45H/0 or C45H/2. If the part number is followed by BP0 it indicates that it is specifically for a Singer. Hardwick's are offering dynamos for a very reasonable £150.

[casadecabra]

For the record it seems likely that dynamos with three external terminals were on occasion fitted to the nines as original equipment. Possibly if the Lucas C45s were out of stock? It transpires that it is very simple to use three terminal dynamos as an alternative to the two terminal version. All three terminals are isolated from the dynamo body and one of the larger terminals simply needs to be earthed to the dynamo body itself or the car chasis. Often the earth terminal is helpfully labelled 'D-' but if not Paul Billington of Ribblesdale Auto Electrics suggests the following:

The dynamo is insulated with the 2 larger terminal being pos and neg and the smaller being field.
I have seen dynamos where the pos and neg have been either way round.

To identify which is which disconnect all wires from the dynamo and put a volt meter across the terminals (engine running) . When you get a positive build up of voltage on the volt meter ( armature reaction ( 1-3 volts) that will give you the termination. If it goes negative swap the probes round.

Next link the the field terminal to positive and re-test with the volt meter and you should get full voltage build up.

My thanks to Paul and also to Dick Preston of the Singer Motor Club for their help with this query.

Thanks Brian for your suggestion that Hardwick's have C45Hs in stock. Unfortunately Steve has informed me that they no longer have any available.

David B