Texas, excellent, thanks you
Using 1.5V light bulbs one can get almost constant lighting using four diodes.
Make two sets of two diodes in series of each other. ------>|----->|-------
Connect these in parallel with each other only in reverse polarity.
---------->|----->|--------------------- MOTOR ------------------ | | ----|<-----|<------
Connect this in series with the locomotive motor. The motor is a ballast and the diodes produce a voltage drop of 1.4V in each direction.
Finally connect the 1.5V light bulb for the headlamp in parallel with the two sets of diodes.
---------->|----->|--------------------- MOTOR ------------------ | | ----|<-----|<------ | | ---- lamp -------
The lamp should light and stay at a constant brightness as soon as the track voltage exceeds about 2 volts. As expected the motor will be deprived of 2 volts of power. The top end speed will be reduced. How it impacts the low end smoothness and control will depend on the motor and controller.
To make it directional requires two more diodes.
Thanks all you
Can you cope with no lights when the DMU is stopped or at slow speeds?
The easiest way is to use LEDs with resistors and diodes in series connected to the wheel pickups. One set for each direction and colour. Diodes will need to be the right way around using the try it and see method. Otherwise you need some electronics to provide the constant voltage. Try googling constant lighting circuits. I think Rob Paisley's site has some.
cheers
Alan Jones in Sunny Queensland (Oz)
What diesel locomotive are you talking about? Basically with DC you just wire track power to the light board on the loco. If the bulbs are 12volt you'd be pretty much good to go, if LED or lower voltage bulbs you'll need resistors to protect them.
Springfield PA
Please, how do I get constant lights in a Diesel Multiple Cars (2 units), in the circuit for the front lights (white) and in the circuit for the rear lights (red)? It will run only in DC. Thanks you