Saturday, September 25, 2010

An Open and Shunt Case

Last Saturday, while running the three-car wood train on the mainline, we had noticed a problem with the 319. The #4 motor was running hot, and indeed it started smoking a little. There was a noticeable odor. Tim O'Donnell and Alex Bruchac from Cleveland were along for the ride, and helped me identify the problem. We cut out the motors and ran the rest of the trip using only the 308 and 309 for motive power.

Obviously, that's a worry. On Wednesday I disconnected all the motors and meggered them again. They were all consistent, so evidently no permanent damage to the motor was done. I also started ringing out the wiring circuits on the car, since I had surmised that it must be a wiring problem on the 319 itself. I know that these motors worked just fine when they were under the 321. I traced the motor wiring back to the field tap control and the motor cutout switch, and everything seemed to be OK. So I was stumped. How embarrassing!

Today I started by going out to Yard 14 to check on the 321. Its tarp is still OK. Another picture of a tarped car isn't very interesting, so I took a random shot (L) of the underbody.

Be that as it may, I wanted to solve the problem with the 319. I opened the motors. The brush holders and brushes are fine, and there are no obvious problems. I then started meggering the motor circuits, starting from the reverser as Tim suggested.

Warning: If you're not into mechanical or electrical details, stop here!

Two motors (#3 and #4) should have direct ground connections through the reverser, but I could only find one. There's a single ground wire coming into the reverser. And I quickly noticed that one of the fingers on the right side had no connection at all, as shown by the yellow arrow at right. That can't be right.

There is a copper shunt between two of the fingers, as seen below (green arrow) but after checking the wiring it doesn't make sense.

On the other hand, if this shunt were on the other side, it would provide the ground connection that is so desperately needed for motor #4. So I hiked back out to the 321 and opened the reverser.

Sure enough, the shunt (green arrow) is on the right side where it belongs. So I removed the shunt and fingers on the 319 and moved the shunt over to where it should be. Then I reconnected the motors (a job in itself) and disconnected the 319 from the blue cars.

This snafu explains exactly what was wrong. Motor #4 had no current flowing through its field windings, and thus there was no magnetic field in the motor, and no backvoltage being generated in the armature. The armature was just a rotating resistance bank, and heated up more the faster we went. I don't know when or how this happened, but the car can never have operated properly since then. I guess we're lucky anything we bought from Trolleyville is still in operating condition.

Having fixed the problem, I naturally wanted to test the 319 out. Since I personally have no sense of smell, I also wanted people along to notice if anything smelled wrong. Luckily, Bob Heinlein, Tom Disch, and Bob Sundelin were nearby working on L cars, and they graciously agreed to help. We ran 319 back and forth in the yard a couple of times, and it worked much better than before, in both directions. We then took it out on the carline for two trips. No problems were found.

Here we are at McCormick Place. Bob Heinlein is carefully checking for any overheating. The grids are warm, of course, and the brake shoes to some degree, but that's it.

That's a huge relief. I would like to have the 319 in regular service next year, and alternate between the two blue cars. The steps on the 319 are much easier for passengers than the awful design on the 308 and 309. We were very fortunate that the motor was not damaged. And once the wiring was fixed, this car really wants to get up and go!


David Wilkins said...

Very interesting Randy. I'm curious why this problem didn't present itself when we ran the 3 car train on July 4? Any ideas as to why?

Randall Hicks said...

Actually, it did. At that time, the problem manifested itself mostly as a sort of grinding noise in the #2 truck, so we cut out the motors eastbound. On inspection, it was found that the brake shoes were worn and the brake gear was rubbing against the motor case. After replacing the brake shoes and readjusting the brake rigging, the noise seemed to have gone away, based on slow-speed testing. So we hopefully put the train together and tried it on the main line.

sd45elect2000 said...

Luck was with you !! I think your fortunate the motor didn't flash to ground. I love the nomenclature, after all it isn't really a ground at all is it? I know on the schematics its drawn as a ground but anyone that's seen lightning travel miles along the rail knows that the track really isn't a ground. If you drove a ground rod into the the earth and really grounded the car it wouldn't run very well at all and likely hurt someone. On diesel locomotives grounds are bad and switching between working on locomotives and 3 phase building power is a thinking process that involves a lot of effort in correct nomenclature, my first clue that Alzheimer disease is setting in will be confusing electrical nomenclature I think...

Jim said...

I was on that trip with you last week - surely am glad you found the problem!

Jim Reising

David Wilkins said...

Ok, makes sense. I thought the problem was the brake shoe/rigging problem as well.

I assume from your post the car isn't as "sluggish" as she was before? I guess running with 3 motors and one big rotary resistor would slow the car down considerably.

David Church said...

You fellas just amaze me with your dedication and abilities. Now you have turned 319 into one of the best looking interurban cars I have ever seen. And a great runner as well...

We were there last week and I was just blown away by all the beautiful CA&E Cars. We rode them as much as we could, reliving many childhood memories.

Can't wait to see and ride 319 next year.