Charging,?.

[Bela]

....

The dynamo is regulated when the battery is in the circuit - 6 volt battery means a 6 volt system, 12 volt battery is a 12 volt system.

The cut out senses the difference between dynamo and battery, when dynamo voltage reaches battery voltage, the cut out closes and the dynamo is supplying voltage to the required level.

Austin missed a cost saving trick when in production - you just fit a 12 volt bulb in place of the "ignition" light, you don't need an odd voltage bulb and dropper winding....

@"slack Alice" Simon

If the insulation of a device is designed for a voltage it is not sure to resist to the double voltage. That is not a problem at cars because a 6V starter can also be used with 12V. I guess it is no problem with a dynamo.

But a dynamo must be regulated. As far as I know the cut out prevents from discharging and some pre war dynamos have a build in regulation. Later boxes have a voltage regulation and a cut-out function.  Charging a battery must end at a specific voltage. That's what a regulator must do. What is the base of your statement.  I still want to learn what happens in pre war cars and how it works. Any hints in the www?