Athearn Challenger/TSU-4664N Motor Stall

[conrad]

Athearn Challenger/TSU-4664N Motor Stall

Per my 9/15 post on “My unorthodox Sound install (Athearn Big Boy)” thread I am getting ready for the winter replacement of the burned out incandescent headlight with an LED.  In preparation, I took the loco out for a run and was reminded of a recurring problem – stalling on startup.

Symptoms:  Rarely, but often enough that I have the shell unscrewed from the chassis, the loco will not start unless I rotate a flywheel by say ¼ turn.  The whistle start sequence sounds and the chuffs increase as momentum builds but no movement.  And no smoke, heat or buzzing.  A quarter turn of the flywheel/motor and off it goes.  Also (when stalled), if I return the throttle to 0 then give the flywheel/motor a ¼ turn the loco will move upon throttle command.

Tonite of course, after many many starts and stops I could only get it to stall twice.  Thus I can’t say if this only happens at very slow speeds, or when reversing directions, or when coming to a stop from express speed.  A loco with many cars, some cars or no cars.  To me, it’s random.

As I remember, I have spent a good amount of time checking for binding and have found none.  This being said I have not disassembled the loco to separate the motor from the drive train.  As Peteski said in the above thread about his friend’s Athearn Big Boy, this is NOT a loco made to disassemble. Everything seems loose.  Normal running is very, very smooth from creeping to express.  With mute on all I hear is just rail noise, no motor or gear whine.  It’s really a great running loco.

This loco, bought in 2009,  has a history of a strangely behaving Athearn (MRC) sound decoder that finally blew up in 2017.  From what I remember, strangeness included sometimes no sound and sometimes no movement.  I think I had to make many decoder resets to get it to function.  2017 came and the input diode D6, adjacent to the no. 5 pin (left side rail power, blk) failed (over-voltage?), melting part of both the decoder connector and the tender shell.

Tsunami TSU-4664N decoder info as follows:  accel/decel both set @ 60 (out of 255), Speed Table used with Start (CV67) @ 1 and linear to top (CV94) @ 110, BEMF cutout @ 0, Motor Kp @ 25, Motor Ki @ 20, Motor Control Intensity @ 255, Motor Control Sample Period @ 15 and Motor Control Aperture Time @ 15.

Athearn’s manual says it has a 5 pole, skewed armature motor so I don’t think it’s a “cogging” problem.  Could it be a commutator issue?

Conrad

[peteski]

I recently had a Kato loco (straight-wound 5-pole motor) which had a dead spot similar to what you describe. Rotate the armature (or flywheel) slightly and it would start up.  I took the motor apart, and after some resistance measurement I determined that one commutator segment was not connected to the wire attached to it.  I suspect it came from the factory that way.  In those motors the insulated magnet wire is crimped to the commutator and apparently the crimp didn't break the enamel, so the wire was not electrically connected to the commutator segment.  I carefully scraped the wire's enamel near the crimp, and soldered the wire to the commutator segment. That fixed the motor.

[conrad]

I recently had a Kato loco (straight-wound 5-pole motor) which had a dead spot similar to what you describe. Rotate the armature (or flywheel) slightly and it would start up.  I took the motor apart, and after some resistance measurement I determined that one commutator segment was not connected to the wire attached to it.  I suspect it came from the factory that way.  In those motors the insulated magnet wire is crimped to the commutator and apparently the crimp didn't break the enamel, so the wire was not electrically connected to the commutator segment.  I carefully scraped the wire's enamel near the crimp, and soldered the wire to the commutator segment. That fixed the motor.

Peteski, thanks for the info.  Looking at my Challenger bookmarks I found that Spookshow (http://www.spookshow.net/loco/athearn4664.html ) states that the motor has only 3 poles: “Up until 2017, the motor was an open-sided / skew-wound three-poler (which was a bit of false advertising on Athearn's part since they described it as having five poles in the manual) “

If true, this brings up the question of how it would run with only 2 poles.  Did your Kato exhibit any “loss of pole” symptoms?  I ask because the Challenger is really a smooth runner and can pull lots of cars.

As for resistance measurements, I have several VOM’s and one VTVM.  Only the VTVM  can measure  in tenths of an ohm.   But it is over 60 years old and I fear the electrolytic capacitors are probably bad.  I have an even older oscilloscope.  I could recap them but they haven’t been used since the 80’s.

I have previously put stripes on one flywheel and I have looked carefully at the spinning flywheel to see how it smoothly it runs at low loco speed.  Unfortunately at speed step 1 the spinning so high that my white striping becomes a blur.  Maybe I can adjust Tsunami’s motor controls to reduce the rpm’s.

And, since I was educated in electronics, I’ll have to start reading my father’s engineering text the 1923 “Principles of Direct Current Machines” by A. S. Langsdorf, M.M.E. to understand the effects of running without one pole.

On the bright side, this has made me look carefully at the burned out headlight setup.  Both lamp wires go to the motor circuit board.  Maybe I can release the headlight body and pull the wires forward.  Using them as fish wire to pull the LED wires.

Conrad

[peteski]

That Kato motor I fixed (if it stopped so the dead commutator segment was in contact with a brush) would need a manual nudge to get it started again. But while running, it would not behave all that different from a same good motor. The speed was a bit lower, bunt no pronounced cogging.

As far as a resistance measurement goes, it is difficult to  get a steady resistance reading, when the dead segment was under the brush, the ohmmeter showed open circuit.

A dead commutator segment in a  3-pole motor would result in a severely limping motor. But a commutator segment provides power to 2 winding.  More common type of failure is just a single winding being open.

As for what it in those locos, I'm pretty sure they are 5- not 3-pole motors, but it has been a while since I had one apart (I own both Big Boy and Challenger).  There were multiple runs of these - it is possible that the initial run had 3-pole motors, while the subsequent runs had 5-pole motors.  As far as the motor construction details go, sometimes  Mark's reviews might not be 100% accurate.

[conrad]

Must of had brain freeze.  Of course, with a VOM a good winding would show a short, sort of "zero".   A bad winding an open.  duh

My loco was bought in 2009.

Conrad

[conrad]

“But a commutator segment provides power to 2 winding “

Peteski, sorry but I don’t believe the above is correct.  See:

https://en.wikipedia.org/wiki/Brushed_DC_electric_motor

Conrad

[peteski]

LOL!  Are you talking about the animation model using a 2-pole motor?  That is not a good example.  In a 3- or 5-pole motor, each commutator segment has 2 wires attached, each going to an adjacent winding.  At least, that is the most common scheme of the internal  motor wiring.  I do seem to remember some motor which had the ends of the windings on the side opposite the commutator connected into a pigtail and soldered.

Most model train motors have 2 wires connected to each commutator segment.  Actually, here is a photo of the Kato motor I fixed.



You can clearly see 2 wires attached to each commutator segment (each wire going to a different winding). The arrow points to the solder joint I made to fix the motor.

[conrad]

hmm. photos don't lie

Conrad

[conrad]

Yup, here's my eat crow video.  Coils and poles in action:

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This may answer why an open coil does not completely degrade the motor performance.

Conrad

[peteski]

This may answer why an open coil does not completely degrade the motor performance.

Conrad

Exactly!  But in my case, the commutator segment was disconnected from both wires, so the motor truly had a dead spot. But it still ran, once the armature was moved (or if the motor didn't stop with the dead commutator segment directly under the brush).  A broken-in brush can connect to more than one commutator segment at a time.  The motor's performance was degraded, but it ran.

As long as you learned something here, no crow eating is needed. 

[conrad]

Nuts, just sitting down to eat crow pie with a glass of merlot.  Guess I'll skip the pie and go right to the wine.

thanks,

Conrad