I Need Any Experienced Opinions - Even Guesses

[DougC]

All:

I've got a peculiar problem that I've never seen before in 40 years of model railroading, and I've not been able to figure this out. Your input will be greatly appreciated. First, here's the background facts.

I run HO DC only, track is all Atlas 100 NS flex, track turnouts are Model Power NS #4s (been in service 17 years and doing fine), ALL rail joints and feeder wire/rail connections are soldered, and I have four level loops with one train on each.

I run the diesel engines in pairs (two locos per train) on the three larger loops, 60- to 70-car trains per loop, and run them slowly (scale 10 to 15mph), and it takes between 2.5 and 3 minutes for each to make one circuit of its loop.

All of my engines are either Bachmann or Atlas Trainman, and they are not cross-paired by manufacturer - generally they don't like to work with each other.

The Bachmann engines are GP30s, GP35s, GP38-2s, SD40-2s, and FTs

The Atlas Trainman engines are GP38-2s and RS32s.

With all the engines I've discarded the DCC boards and the 2 headlights, installed one 3-13 volt directional soft white LED headlight on the front, and added 2 to 3 ounces of weight, per loco. No BFS is used.

The power for each of the 4 loops is one MRC Tech 2 Railmaster 2400.

And on loop #3 I have an ampmeter and a voltmeter connected.

The layout has been in an air conditioned room for 13 years.

Here's the problem. The trains (run almost daily for about 45 minutes) will operate for one to five months just fine, then on one of the loops (and this varies) all of a sudden the pair of locos (either Bman or Atlas Tman) will speed up to about 25 to 35mph for about 15 to 30 seconds, then slow back down for 10 to 20 seconds, then will do this again, and generally keep on doing it. I take these off and replace them, and the replacement locos do NOT do this. Also after the guilty loco pair sits a few days or more I put them back on a train and run them (on any loop), and they are fine for another few or more months.

This happens randomly on any of the 3 major loops. Weird behaviour.

And here's a kicker. When this happens on Track 3 I check the meters, and if on Tracks 1 or 2 I immediately pick up the loco pair and put them on track 3 where the meters are and have them pull that train (removing the existing 2 locos). With Bman OR Tman engines doing the "surge dance" on Track 3 the meters are always rock steady! With a pair of Tman GP38-2s it's .5 amp at 4 volts. With Bman engine pairs it's .25 amp at 4.5 volts.

Have any of you experienced this? If so please chime in. Also any guesses would be appreciated. I'm baffled.

If you have any questions ask away. Thanks for your help.

DougC

 

[rodnok1]

Very odd indeed. I do have a bachmann that acts strange when it gets hot. It picks up quite a bit of speed. Haven't checked it but my guess is the brushes are worn or the bearings finally tighten up and it starts working like it should. It sounds like you have eliminated power problems to me. Probably is just right conditions are allowing engines to run more efficiently. You run them slowly you said. Maybe someone has insight into how transformers handle this over a long time. Possibly the transformers are wearing out or becoming overly sensitive? Just a thought, but I would put a diff power supply on one.

 

[bnsf971]

I've noticed this a few times, and it has turned out to be carbon buildup on the commutator plates. It would do this in combination with a small amount of lube oil that got from the motor bearing to the commutator. After letting the engines sit around for a while that oil/carbon/gunk would dry up and flake off, allowing the engine to run normally again.

 

[DougC]

Rodnok1:

Thanks for your input and sharing that one of your Bmann engines does the same. (I'm not glad it's behaving oddly for you too; just glad I'm not the only one experiencing this - see bnsf971 comments also.)

Yes, possibly heat buildup could trigger something. As we all know the motors are basically inside a shell where very little if any air gets circulated. On the other hand, the loco surging should then theoretically happen every time when running and the motor gets to its critical "hot" temperature. This doesn't happen. On the other hand, heat could cause the oil in the bearings to wick easier (see comments below.)

As info a couple of times I've changed out from an MRC to an Athearn power pack when this happens: no difference, the locos keep surging. So I guess with your input and bnsf971's input this seems to be specifically a locomotive problem, and interestingly enough it currently includes two different manufacturers. I'm betting that the motors for Atlas Trainman and Bachmann are made in China and probably at the same manufacturer.

Another thought: I run my locos in pairs. When one gets "surge urge" I guess it has enough muscle to increase not only its speed but enough to pull or push the other loco and their train to go faster. It's almost like shifting to another gear.

bnsf971:

I'm not ignoring you but chasing down and extrapolating on rodnok1's input.

Thank you very much for your input.

From what you said above I bet you've nailed it. So, you've "earned" some more questions from me.

- Did you disassemble the motor to find this?

- Is it easy to disassemble and reassemble these motors? (Bmann and Tman)

- Were you able to clean the commutators? (I know you said you let them sit and the carbon will dry up and flake off.)

- If you've been inside the motors have you thought of a way to prevent oil from working its way onto the commutator? Or are the motors designed such that the commutator is so close the the motor bearing that oil can easily reach/wick to the commutator face?

- From a casual visual inspection of the motors' exteriors it seems that the commutator faces are very difficult to reach from the outside without disassembling the motor. Have you been able to reach the face without disassembly? It would offer an option to easily clean the oil off of the commutator faces, but I can and do live with letting the locos sit for a while.

Lastly, one potential "solution" is to be extremely skimpy with the oil on the bearings. Problem with that is enough oil has to be used to get the squeals and squalls out, particularly on Bachmann engines.

With these small motors I bet there is enough friction between the commutator and the brushes to keep the locos' speeds down some. BUT when a very light coating of oil is added to the commutator face the commutator/brush friction decreases, hence the motor's and loco's speeds increase. One would think the oil would act like an insulator, but in over 17 years I've found that adding a very little amount of light oil to the tops of the rails makes the trains, including the engines, run better and does not affect the locos' electrical pickup or traction negatively at all.

Bottom line is I MAY be using too much oil. Why "MAY"? I bet it wouldn't take much oil at all to get through the bearing, and since the oil is very light it could easily wick down the drive shaft and up onto the commutator. That is, it keeps going until is volume momentum is thinned out/dried out enough.

Thank you both very much.

And does anyone else have any experience or a suggestion? (other than, "Use less oil you dummy.")

DougC

 

[bnsf971]

bnsf971:

I'm not ignoring you but chasing down and extrapolating on rodnok1's input.

Thank you very much for your input.

From what you said above I bet you've nailed it. So, you've "earned" some more questions from me.

- Did you disassemble the motor to find this?

- Is it easy to disassemble and reassemble these motors? (Bmann and Tman)

- Were you able to clean the commutators? (I know you said you let them sit and the carbon will dry up and flake off.)

- If you've been inside the motors have you thought of a way to prevent oil from working its way onto the commutator? Or are the motors designed such that the commutator is so close the the motor bearing that oil can easily reach/wick to the commutator face?

- From a casual visual inspection of the motors' exteriors it seems that the commutator faces are very difficult to reach from the outside without disassembling the motor. Have you been able to reach the face without disassembly? It would offer an option to easily clean the oil off of the commutator faces, but I can and do live with letting the locos sit for a while.

Lastly, one potential "solution" is to be extremely skimpy with the oil on the bearings. Problem with that is enough oil has to be used to get the squeals and squalls out, particularly on Bachmann engines.

With these small motors I bet there is enough friction between the commutator and the brushes to keep the locos' speeds down some. BUT when a very light coating of oil is added to the commutator face the commutator/brush friction decreases, hence the motor's and loco's speeds increase. One would think the oil would act like an insulator, but in over 17 years I've found that adding a very little amount of light oil to the tops of the rails makes the trains, including the engines, run better and does not affect the locos' electrical pickup or traction negatively at all.

Bottom line is I MAY be using too much oil. Why "MAY"? I bet it wouldn't take much oil at all to get through the bearing, and since the oil is very light it could easily wick down the drive shaft and up onto the commutator. That is, it keeps going until is volume momentum is thinned out/dried out enough.

Thank you both very much.

And does anyone else have any experience or a suggestion? (other than, "Use less oil you dummy.")

DougC

I pulled apart the motors, and found a bunch of gummed up gunk in some, and gummy powder in others. I blew out the "powder" (cough, gack, wheeze). I was able to clean everything out, and have had good luck using conductalube on the commutator plates and brushes.
If one drop is enough, two drops is too much.

 

[DougC]

bnsf971 (Terry)

Thanks for the further info. Sounds like many of the motors are purchased with factory gunk already in them. If I get brave I might try to open up one of the motors.

DougC