Charging resistance- help !!

[dhindley]

Does anyone know what resistance value (Ohms) the half charging resistor, shown fitted at the side of the light switch on the wiring diagram, is for a 1935 single with magdyno.
This model does not have a regulator.
Have searched the web but can't find the answer.
I have access to power resistors and will fix one in an alternative unobtrusive place, once I know what value to use.
Just completing final build of LH 250, only wiring to sort out.
Hope I can thank someone in advance.
Dave Hindley

[nevhunter]

You might have to address more than the resistance. I think they are wound wire and get hot so require to be able to cope with that. Nev

[bruce.carrad]

I have measured one I have at about 4 Ohms. An old stove element with coiled element would be a suitable doner.

[nevhunter]

Cortina with ballasted coil has a resistor in series with the coil primary that is of the type you need. I have a 30 Lucas headlamp that has something. I will get into it but give me a little while.. Some small cars had them in the head lamp switch about 1937. Standard, Morris etc Nev

[iansoady]

I had one of these systems on the Sunbeam I restored a couple of years ago. I measured the (original) resistor as 8 ohms.

A modern one with a heat sink should do the job OK although it won't keep the back of the light switch warm!

It took me a while to get to grips with the 3 brush dynamo circuit layout as the field control is on the earth side rather than the live and the battery live side is permanently connected to the internal cutout.

Very satisfying to get it working as intended however.

[dhindley]

Thanks Ian and Bruce for the resistance values, looks like the region of 4 to 8 ohms.
Modern power resistors are encapsulated in thermally conductive metal housings which are then bolted to a heat sink, to be placed somewhere out of sight.
I have some 6 and 8 ohm power resistors so will start with higher value and see what the outcome is
Many thanks
Dave

[iansoady]

TBH it's a very crude system anyway as the resistance is too high at low engine speeds and too low at high speeds......

[nevhunter]

This set up is used with the adjustable 3rd brush and compensates for having the lights on by increasing the charge rate . It's simple and does not employ the regulators used on later models which if they work properly look after the charging for you. Nev

[ian.scott]

Eiher a different 3 brush dynamo was supplied to export markets or you are wrong . I have a 3 brush dynamo on my 35 VH and a spare . On both of these the 3rd brush is fixed ,not adjustable. The 3 brush dynamo fitted on pre- war Fords was a dynamo with an adjustable 3rd brush and an external relay to prevent the power running back to the dynamo.

[iansoady]

My 3rd brush was fixed as well and looked much like Ian's photos.