Lucas C35A Regulator

[Lowbarn]

Please can someone confirm my understanding that the Lucas C35A has a simple fuse wire regulator device screwed on top.  (Summer Winter charge settings).

I think my cutout is the reason that the battery doesn’t charge. Just confused as to whether the cutout is also a regulator!

Full setup is:
1931 RN lwb saloon
Lucas C35A dynamo fitted with resistor pack
Lucas CF3 cutout
Lucas type SM5 switch panel

And some dodgy wiring that I’m still investigating!

Thankyou in advance.
Richard.

[Tiger]

The Austin7 cutout is a simple electromagnetic switch which connects or disconnects the Dynamo to the battery.
The charge is adjusted by switching in various resistors
Regulators came in a bit latter which could constantly vary the charge.
Hope this helps

[David Stepney]

The box on top of the dynamo merely contains the field coil resistor for half charge and the field fuse. The cutout box is, as Tiger has said just an electromagnetic switch to connect the dynamo to the battery once the voltage from the dynamo has risen sufficiently to start to change the battery. The cutout is fitted to the bulkhead on the drivers side.

[Stuart Giles]

As Tiger says, it's a cutout not a regulator. If there's no charge at the ammeter, I'd start with putting a voltmeter on the dynamo 'D' terminal. When the motor revs rise from tickover you should see a rising voltage, At 7+ volts you should see the cutout operate. The cutout needs to be connected to a good earth to work. If there's no output, wire the 'D' and 'F' terminals together and try to get a voltmeter reading again. Best to use an analogue meter, i.e. one with a needle; digital voltmeters aren't really suitable for this testing as the display looks like it belongs on a fruit machine as the output voltage constantly changes .


Edit: David types much faster than me.....

[Tiger]

If you don’t already know an excellent booklet for all 7 electrical problems is published by HARRY HALES.
Let me know if you would like a copy.
I think they are on the forum

[Lowbarn]

Thanks for the advice chaps, very helpful as always.
I have many books and articles, I will check if the electric guide I have is by Harry Hales.
The problem is putting all this academic knowledge into practice without blowing anything up! So far so good.

My cutout definitely doesn’t work. If I close it with my finger it stays shut permanently, even with the ignition switched off.
I have figured out that I could bypass the cutout with a manual switch in the car.

More intriguing problem today is that the dynamo is producing electric, up to 9v and cruise speed, as measured at the D terminal. However, this voltage isn’t getting through to the ammeter / battery.

I’m very suspicious of the SM5 switch panel. I don’t think it’s wired the same as the wiring diagrams in the books.

My plan for this morning is to remove the wires from the switch so that I can work out which contacts make and break when the switches are operated. It’s the only way I can see to get to the bottom of the problem. These switch units are very clever in the way they operate different circuits at the same time.


On the upside, my new LED bulbs are brilliant. Virtually no current draw compared to the filament bulbs as measured by the ammeter. I can now use the side / rear lights as daytime driving lights.
Also while fiddling with the main switch panel I found a damaged wire going to the fuel gauge, now that works properly for the first time since I’ve owned the car!

Richard.

[Stuart Giles]

My cutout definitely doesn’t work. If I close it with my finger it stays shut permanently, even with the ignition switched off.

This often indicates a problem with the cutout's voltage winding; either there's a bad earth on the cutout or the voltage winding has failed. The voltage winding is responsible for the initial operate of the cutout, the voltage winding and current winding together are responsible for its release.

[Lowbarn]

I’ve tested the thing to death on the car!, still no charge though.
I have put all the wiring back in accordance with the diagrams and everything still works so that’s good.
Next task is bench testing the dynamo. Still not convinced it’s charging.
So at this stage it could be the dynamo and not the cutout!

[Stuart Giles]

If you haven't removed the dynamo yet, have you tried operating the cutout manually with the engine running? You said previously that it stays operated, when you rev the motor does the ammeter show a charge?

[Lowbarn]

The ammeter shows no charge Stuart.
Richard.