How were dynamos on steam vehicles controlled?

[EricMark]

There Seems to be only two wires on the dynamo, guy with it had no idea on how it was controlled, with cars turning on the ignition would motor the dynamo on a free wheel and one would adjust third brush to set output, since to stop engine you turn off ignition it also disconnected dynamo.

However with steam the engine stops every time the vehicle stops, so the car system would not work, larger steam engines had a steam turbine to generate electric. Again no idea of how controlled, local railway have hired an engine 1900 vintage it has 6 large headlights and a steam turbine with switches so you can select the lights, so would assume it needs some regulation but as to if electric or steam or both are regulated not a clue.

 

[Lister1987]

Get the make/model of the vehicle and hit up steam engine enthusiasts or your nearest hertiage railway and they'll be able to advise.

 

[EricMark]

I work at the local heritage railway every Wednesday and the steam turbine from one of the engines is sitting on a pallet waiting repairs, I was hoping to be able to reinstate this at some point, but no one seems to know how it was controlled.

In the main knowledge is gleamed from people who worked on standard gauge railways, but in the UK the old steam trains only had oil lamps, the massive head lights seen on the Beyer Garratt engines and the like were fitted for use in South Africa and other places abroad, Zillertal that has working lights does not belong to local railway it is hired in, so don't think they would be too pleased if I stripped it down to see how it worked.

As an auto electrician I have seen many ways to control the output, including bucking coils, and it would be very hard to work that out if you have never seen it before, so I was hoping some one has some knowledge and can give me some pointers.

 

[FatAlan]

Watt Guvnor! ... I think that’s another steam engine control mechanism

 

[DPG]

We'll need a steam engine section on the forum if this keeps up.

 

[Lucien Nunes]

Two wires could be field and armature, with common return via the casing / chassis earth, as per a normal automotive dynamo working with its control box containing regulator and cutout.

Any engine-driven or axle-driven dynamo that charges batteries needs a cutout (relay), to stop the dynamo motoring from the battery. A standard automotive setup has a voltage coil (across the dynamo output) and a current coil (in series with the contact, between the dynamo output and battery / load). The dynamo is isolated from the battery until the output voltage reaches the 'cut-in' voltage, set slightly higher than the normal system voltage, at which point the voltage coil on the cutout closes the contact. Current then flows towards the battery / load, through the current coil which adds its MMF to the voltage coil MMF, creating positive feedback and hysteresis to hold the relay closed. If the speed reduces and the generated voltage falls below the battery OCV, the armature current reverses and the machine begins to motor. The current coil MMF now opposes the voltage coil MMF and the flux in the relay falls suddenly, opening the contacts and isolating the dynamo again.

An automotive control box will typically have one (voltage only) or two (voltage and current) regulators, with contacts that interrupt a bypass around a resistance in the field circuit when the voltage / current exceeds a threshold. There's no positive feedback so they oscillate around the set point, adjusting the field duty cycle to suit the conditions. Rolling-stock regulators were often complex beasts with servo-motor driven multi-step resistances and various arrangements to optimise the charging conditions to the battery and load status and minimise voltage variation at the lights while making best use of the available generation. The configuration depended on whether single or dual battery working was used. There's some stuff online about Stone's, Tonum etc. systems if you search.

 

[EricMark]

Thank you that is rather complex compared with automotive systems, going to take some careful reading. I have the full Lucas workshop manual but the Lucas stuff is rather simple compared with the systems you show.