You wont find automatic voltage control on a full size engine, just a variable field resistance and a attentive engine driver.

An electronic regulator and the original mechanical regulator will both hold a pre-set voltage provided that the input voltage is higher.

So.......................... you won't get the pre-set voltage if the speed is too low.

That end of things I understand the regulator cannot 'create' voltage.. I was more confused about the other end of the 'graph'....

Once the Dynamo is generating over 12v are you saying if the field winding is then kept at 12v the generated voltage cannot rise above this no matter if the speed is increased?

Yes but the Regulator itself has an Input Voltage limit rating see "Absolute Maximum Ratings" on the PDF link below.

In theory the Regulator would fry if the maximum voltage was exceeded but would a miniature drive the dynamo fast enough? .


http://www.farnell.com/datasheets/19...508.1502905985

As i posted on this forum on the same subject but for a 2 ins Showmans engine , I found the easiest route was a 12/24 volt wind turbine

Hi,
I don't think your getting what I'm asking. I fully understand how voltage regulators work.


The thing I don't know about is the Dynamo itself.

Does holding the field windings at 12v hold the generated output at 12v and it makes no difference if the speed is then increased?

No , voltage will increase with speed . The idea is to control the voltage by varying the strength of the magnetic field . The field is , most of it , produced by the current in the field windings which surround the iron pole pieces . So you can vary the strength of the field by varying the current through the field windings .

All the regulators work this way . The old CVC boxes have a make and break mechanism operated by an electromagnet taking the dynamo voltage . This operates against a spring to break the field circuit at a set voltage . The voltage then drops , and the circuit is reconnected by the spring . This sequence is then repeated , in the same way that a bell buzzer works . Otherwise one could have a variable resistance in the field circuit which could be operated manually .

The whole idea is that it is easier to control the voltage by controlling the small current through the field windings than to put a heavy resistance in the main circuit .

You have explained correctly how regulators work but surely you mean, The dynamo voltage will increase with speed but the over voltage will be dissipated by the regulator ?

PS. 12 Volts is just a nominal figure, the old type regulators were usually set to cut out at around 16V.

No , there will be no overvoltage , because the power of the magnetic field will be reduced by the regulator , and therefore the voltage produced by rotating the armature within this field will be reduced .

A dynamo works by rotating a coil of wire - the armature - between the poles of a magnet . This induces a flow of electricity through the armature . In order to produce a decent magnet the pole pieces of the magnet are themselves wound with wire . Feed a current through these windings - the field windings - and you have an electro-magnet . The strength of the magnetic field between these pole pieces depends on the strength of the current fed through field windings . So - vary the field current - vary the field strength - vary the output of the dynamo .

Have you got that down ?

Now , for your homework ............. . .

I haven't made it clear that the electronic regulator would need "tweeking" and some more components to monitor the output and regulate the field accordingly.