Reduce voltage to DC Motor

[chado0044]

I am helping to restore a 1950 Diesel-Electric Locomotive. It has an oscillating headlight. The motor for the headlight is nameplate rated 30 VDC. The locomotive electrical system is 64 VDC. The motor appears to be shunt connected. Before I came on the scene, someone tore the unit apart with no apparent interest in ever putting it back together. There are two wire wound resistors that were somehow connected to the motor. One resistor is 100 ohms fixed. The other has a slider so it can be adjusted to between 0 - 100 ohms. The adjustable resistor is a larger wattage than the fixed. The motor is definately a 30 V motor. I hooked up a dc power supply, and the motor runs great at 30 V. Boost the voltage to 60 and motor smells like there is arcing at the brushes and the whole motor gets hot. Somehow these resistors hook into the motor to make it work on the higher supply voltage, but I don't know how. Can anyone help?

 

[jbartos]

Suggestion: Visit

http://www.trainweb.org/gyra/warnlts.htm

http://www.trainweb.org/

etc. for more info
Does that light or motor have any nameplate?

 

[jbartos]

Suggestion: Visit

http://www.thomasregister.com

and type Locomotives: Diesel-Electric under Product or Service, which will return 20 companies to approach to for information or a spare part

 

[jOmega]

It would seem logical that the large wattage adjustable resistor was connected in series with the motor armature. Its purpose is to drop the voltage from 64 down to 30v. or less.

The smaller, non-adjustable resistor was most likely installed in series with the shunt field and its purpose is similar; that is, to drop the voltage to the appropriate value for the shunt field.

 

[DanDel]

It is possible that the resistors were used as a voltage divider circuit to produce 30V from the 64VDC source. If the resistors were connected in series across the 64V source, there would be 32 volts available at the junction when the slider is set at the 100 ohm point on the adjustable resistor. Adjusting the slider slightly should give 30V.
The load current of the motor at rated voltage and actual wattage of the resistors would be needed to determine exactly how to connect the system. The voltage at the junction will change depending on the motor load.