Saturday, January 16, 2010

1005 Moves! Kinda

One truck moved under its own power. Here's the YouTube video.

The problem was this. In a DC motor, most of the energy (watts) is consumed in the armature, and fairly little in the field. A series-wound motor has all current go through the armature, than all current through the motor field. So the field has very heavy windings. Each traction motor has four wires (two for armature and two for field). Three wires go to the reverser. That is so the reverser can reverse the field relative to the armature, as that is how you reverse a series-wound DC motor.

The 1005's wiring appeared to possibly have a serious defect. In one direction, the reverser would connect normally. But in the other, it would connect the two armature leads to each other, and the two field leads across the full 600 volts. The field's heavy windings were only ever designed to be in series with the amature. They would act like a near-dead short. Something would blow up -- one would hope, the fuse. Assuming that this defect existed, which it may not

So a test was made using low power. The reverser and Westinghouse HL switch group require 600 volts (which they drop to about 80 volts via a resistor ladder) for controls. They also require air to provide the "oomph" to throw the big contactors and the reverser. These controls were connected to trolley power, and to shop air. But we did not want to apply full trolley power to the questionably wired motors. Instead, the actual motor circuits were wired to a welder. It supplied about 60 volts - enough for the motor to barely turn on its own. The whine of the welder can be heard in the video.

Now, the car is high in the air on jacks. The north-end truck was beneath the north end. (the south end truck is being overhauled.) An "extension cord" was made to connect the four motor leads to one motor. Household 120/240 volt type wiring was used, as very little current would be needed for the test given the low voltage. Greg manned the controls, and took notches of power one at a time. The truck stepped to life and began rolling in the correct direction. Test done - shut off. It was tried in the reverse direction, and again the motor rolled. This would not have happened if the motor was miswired. Test complete, no trouble found!

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