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Author Topic: Steam loco 4-8-4 rebuild  (Read 702 times)
crosswire

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« on: April 22, 2021, 01:29:28 PM »

Hi,

I have a 4-8-4 that needed a new motor, DCC conversion, and traction tires. I have all the work complete and the loco works great in reverse. However, in forward, I get numerous track shorts on the DCS52 command station. Monitoring volts and amps in the DCS with JMRI, no low voltage or over current is indicated.

The loco also runs well on level track, but not forward, and not upgrade. I tried changing the decoder with no success.

Any ideas about what is going on would be appreciated.

John G.
« Last Edit: April 23, 2021, 02:58:51 PM by crosswire » Logged
RGW

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« Reply #1 on: April 26, 2021, 07:08:37 PM »

Do you have a way to run it on dc with out the decoder. This way you can check to make sure it is not some mechanical problem. For example something in the valve gear. I have had many problems only to find some thing simple like a tiny part or screw binding .

Help this helps
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crosswire

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« Reply #2 on: April 27, 2021, 08:46:10 AM »

RGW, thanks for the suggestion, I can give that a try. All this work changing and removing decoders is great practice on soldering. But, I certainly need that anyway.
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crosswire

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« Reply #3 on: April 27, 2021, 02:49:55 PM »

Going, back to the original question, restated, concerning multiple track faults: can an overloaded motor cause a track fault even if a volt meter shows 13.8 volts and the ammeter shows 1.4 amps on a DCS52?
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crosswire

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« Reply #4 on: May 02, 2021, 09:37:10 AM »

After a complete rewire, most of the track faults have stopped; however, sometimes the loco just stops at random locations for no apparent reason and will not respond to commands even though the headlight indicates the loco has power.
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rbturner

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« Reply #5 on: May 02, 2021, 10:00:21 AM »

A couple of thoughts;

sometimes a headlight, which only requires a minimal amount of current to operate will work fine while the motor which requires maybe a half an amp will not run.

This reflects a questionable connection between the wheels and track.

When there is  a wiring fault someplace a voltmeter may still show voltage present but not 'enough' current available to do any work.

I know you have re-wired recently so we'll assume that you whipped any wiring issues but maybe there is still some oxidation on the rails/wheels.

Hope this helps.
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rbturner

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« Reply #6 on: May 02, 2021, 10:13:44 AM »

I forgot to ask if you got the loco to run OK in forward?
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crosswire

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« Reply #7 on: May 02, 2021, 10:44:45 AM »

The loco runs forward ok, although 4 passenger cars or 5 freight cars up the 2% grade is the max it will do. Seems strange to see a 4-8-4 with an 8 axle tender barely making the grade with 4 or 5 cars. Oh well. This is with clean track, clean wheels and a lube job.

The problem now is the random stopping and related loss of control. The loco will make several circuits of a loop and then, just stop in no particular place. The fix is also random; sometimes, initiating a track fault near the loco will clear the problem, sometimes changing to a different loco on the DCS52 and then, changing back clears the problem, and sometimes waiting overnight does the trick.
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jward


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« Reply #8 on: May 02, 2021, 11:39:22 AM »

This sounds like a decoder going into thermal shutdown. It;s the decoder's way pf protecting itself from heat damage. WHat decoder did you use? Apparently, the motor is drawing more current than the decoder can handle. This and the sluggish performance of the motor lead me to believe you have a bind somewhere that is making the motor work alot harder than it should.
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Jeffery S Ward Sr
Pittsburgh, PA
RGW

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« Reply #9 on: May 02, 2021, 01:21:49 PM »

This was my thought. If the is a mechanical problem it can cause a  electrical problem. Just curious  did you say the engine was running at 13 volts this seems high to me as at full power with a train  the drivers should be slipping or the motor will start running hot.

Just a thought. However I have very  little DCC experance my self.
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rbturner

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« Reply #10 on: May 03, 2021, 09:47:02 AM »

Crosswire, it's hard for us to really help you because we are not onsite to see the goings on.

It sounds like you have a real stinker of a problem. I wonder why it isn't pulling better?

Something that I just thought of and maybe you already checked this; but I have run into poor pulling caused by the tender, lifting the rear of the loco up.

Is there any chance the drawbar or wiring is binding any at all? This can lift the rear on the loco up and kill traction.
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crosswire

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« Reply #11 on: May 03, 2021, 11:28:41 AM »

Thanks to Jeffery, RGW, and Bturner for your questions and suggestions, all good points.

I did remove the traction tires to allow the drivers to slip and the motor to keep running. After about 30 minutes of running with 4 cars and the drivers slipping, the motor was barely warm.

If I remember correctly, the 13 plus or minus volts is what JMRI reports as track voltage at the output terminals of the DCS52, not the decoder output voltage.

The decoder is a Digtrax DH165A0 mounted in the boiler, so no wires to the tender to lift the rear of the loco. The tender attaches to the loco with a vertical pin on the drawbar that fits into a transverse slot in the rear of the loco. This pin was too long and was causing the tender to derail. The pin has been cut off and no longer interferes with either the loco or the tender.

As for mechanical binding, there are no unusual noises or "jumpy" operation and the loco runs like a rabbit on a 2% downgrade, even with 8 cars attached, so I would not expect any binding.
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rbturner

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« Reply #12 on: May 04, 2021, 10:21:45 AM »

I re-read this whole post and the only thing I can come up with at this point is to wonder if maybe you have a funky decoder.

I put a Digitrax sound decoder in a loco once that did the same thing as you described. The engine would run fine then slow down and stop.  Then it would take off again. I considered it being a thermal shut down but the locos stall current was tested prior to the decoder install and after the install, track current was monitored with a meter. Current draw remained well below the decoder's rating.

You mentioned replacing the motor. Did the replacement by chance have noise suppression capacitors on it? I have read that the caps can affect the decoder's back EMF feature and they recommend you remove the caps from the motor.

Obviously none of this would affect the pulling power.

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crosswire

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« Reply #13 on: May 05, 2021, 04:06:00 PM »

The decoder was changed to another DH165A0; the problem persisted. I installed the used decoder in another loco, which has not experienced any problems.

The motor does have RF suppression capacitors, which may explain why the various changes I tried to CV 57,56, and 55 had no apparent effect. I did disconnect them at one point when the loco had traction tires to see if they had an effect on the motor performance. As you mention, this had no effect on the pulling power.
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rbturner

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« Reply #14 on: May 05, 2021, 08:28:36 PM »

Did the motor in the #2 loco that got the first decoder and ran fine have the suppression caps?

I am guessing not and would think the thing to do is cut them off of the 4-8-4 and see what happens.
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