Pre-war Traction dynamo

[Larry LewisParticipant]

I recently bought a 1937 BL that was sold new by Challenger Motors in Los Angeles. I am right now re-wiring the car and I must ask- the dynamo has only one wire from a small cut-out mounted on it, going back to the ammeter. Should I keep it this way or upgrade to a later type dynamo with a proper voltage regulator. I do not yet have the car running so have no way of checking its output.

[BernieParticipant]

Larry,

It sounds like you have a “3-brush” dynamo.  A clever design that relies on the dynamo to create it’s own magnetic field.  It is also self-regulating in as much as the faster it runs, the lower the output to the magnet windings and the main output reduces as a result. In your shoes I would  want to keep it.

I do have a fully reconditioned 6V unit “on the shelf”, never used since it was rebuilt,  However, in view of the distance, I would suggest you would be better having yours rebuilt locally.

B…

[Larry LewisParticipant]

Thanks Bernie, I appreciate the info. There is a local rebuilder that I will have service it.

[BernieParticipant]

Larry,

I forgot to say that, although there is an element of inbuilt self regulation, it is not as accurate as the dedicated regulator in a 2-brush circuit.  As a result, there are often two terminals on the dynamo allowing the output to be “controlled” by conecting to the appropriate terminal to suit the type of motoring and, with luck, preventing under-charging on short trips or over-charging on longer distance drives.

A cut out is required in the system simply to prevent the battery feeding back to the dynamo when there is no dynamo output.  This is often a box which looks much like a modern regulator, usually mounted directly on the dynamo body.

B…..

[Larry LewisParticipant]

Bernie- this dynamo does have that small box mounted to it, one wire in and one wire out. I see that Renelauto.fr has them but I will wait to see if this one actually works as is. I will likely replace the cut out as there is no metal cover for it so I’m guessing that it does not work.

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