Are CFR and CF3 cut outs interchangeable

[richard tatton]

My Lucas CFR cut out and fuse unit has been very erratic. I have a Lucas CF3 unit and wondered if I can carry out a replacement as the wiring connections seem very different. The dynamo is Lucas C35A. Any advice on whether I can swop over the cutouts? Many thanks.
ps I know the present wiring could look better!

[David Stepney]

Yes, Richard, you can, but you will need to interpose a resistor between the D and F terminals on the dynamo of about 2 ohms. Otherwise, when you switch from full to half charge, you will have no charge.

The difference between the cutouts are that the CFR has a built in half charge resistor and the CF3 doesn't.

[richard tatton]

Thanks for that David. I may be better sourcing an exact CFR like I currently have or finding someone who would like to exchange the CFR3 for one.

[Howard Wright]

Hi Richard

You may want to replace the whole cut out mechanism with a diode.  I use one like this in my special and carry a spare in both the Special and RK.  It can be. Easily hidden in the existing box

https://www.themagnetoguys.co.uk/smart-diode-cut-out

Cheers

Howard

[Nick Lettington]

Hi Richard

You may want to replace the whole cut out mechanism with a diode.  I use one like this in my special and carry a spare in both the Special and RK.  It can be. Easily hidden in the existing box

https://www.themagnetoguys.co.uk/smart-diode-cut-out

Cheers

Howard

That's almost too good to be true Howard!

Has anyone produced a wiring diagram that shows how to integrate the ammeter and warning light?

[Howard Wright]

Hi Richard

You may want to replace the whole cut out mechanism with a diode.  I use one like this in my special and carry a spare in both the Special and RK.  It can be. Easily hidden in the existing box

https://www.themagnetoguys.co.uk/smart-diode-cut-out

Cheers

Howard

That's almost too good to be true Howard!

Has anyone produced a wiring diagram that shows how to integrate the ammeter and warning light?

Hi Nick

I just take the wire from the switchbox to the cut out, insert the diode, and join the other wire to the dynamo lead. The ammeter is generally in series with the main lead from battery to cut out and the warning light comes off the ignition side of the ammeter.

Hope this helps

Howard

[richard tatton]

Thanks for the suggestion Howard. I've ordered one.  I  can see the wiring diagram they suggest but can it be wired into the regulator otherwise I'll need a long wire to reach the battery negative (I'm +ve earthed) and another to the dynamo which I don't think they intend. Someone on here mentioned they wired between D+ and A of the cutout.

[Howard Wright]

Hi Richard

I’d be wary about using the original cut out as a connector.  It may fail as a direct short and the diode would be useless or worse damaged.  I shortened the tails on the diode and used chocolate box connectors to connect the lead from the switch box and lead from the dynamo.  That way I could be certain nothing else would interfere with the diode.

It looks like will need other feeds to supply ancillaries through the fuses. If you don’t have a Woodrow manual I recommend you get one. There will be wiring diagrams for your car.  On both my cars 1930 and 1929 the wiring is much less complex and the wires easily identified and mercifully no ancillaries from the cut out  .

Cheers

Howard