"Momentum" Circuitry in model railroad transformers

[Anonymous]

A general question:

I understand how "momentum" circuitry is used to simulate prototypical locomotive acceleration, by gradually increasing the voltage to the track. My question: Does anyone know whether this circuitry does harm to the commutator brushes, etc. of these small, DC electric motors? I wonder sometimes whether these incremental voltage increases might tend to burn out the motors much faster. Any thoughts?

[rrinker]

No, there is no more stressonthe motor with momentum than there is without. All the momentum circuitry does is put the control fromt he speed potentiometer though a resistor and capacitor before driving the control transistor. IE, you turn the throttle wide open from zero. With momentum, the voltage that should control the transistor and tell it to go wide open is shunted through a resistor and capacitor, which means the full voltage is not realized until the capacitor is charged. Gogn the other way, when you suddenly close the throttle, the capacitor supplies the voltage until it is drained through a resistor (and that's how the 'brake' function works on a typical transistor power pack - different resistors draing the capcitor. The smaller the resistor, the faster the drain). All the momentum does is slow the action of the throttle knod, it does not change the output of the power pack in any way. You can duplicate the momentum yourself if you turn the knob slowly. It won't harm the motors.

--Randy