AF 312 armature shorts only in reverse.

Im a ogauge guy but I volunteered to clean up a flyer steamer. Would not run at all. I looked at eunit first, cycles and contacts okay. Took boiler off and brushes one brush was getting hung up. Still jamming. Cleaned gears and oiled. Now works forward great, but smoke or arc on armature plate in reverse.  Does this mean armature shot or something else?

Original Post

Sounds like the commutator face is touching the rear bush tubes.  Can't remember now but when going forward the armature is pushing forward but when going in reverse the armature pushes to the rear. Have a look to see if this is the case. Again can't remember at moment but if you have the wrong armature in it this will cause the problem. I think the armature on this has a brass oil slinger that touches the rear bush/bearing and still gives clearance for the commutator to brush tubes.

My Google search, found about brush tubes, but there was not that much movement. The arc and smoke happens as soon as the eunit switches without any movement in other direction.  Really confused, because it runs forward does that mean the armature is good? Isnt The motor using all the same windings to make it go in reverse?

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I would check the armature by changing it to a good used one if I suspected the armature. If it goes OK in one direction I would be tempted to say it is good. How much forward/back movement does armature have, can you see the commutator distance from the tubes?

if it looks OK I would then be looking at config of the wiring to the reverse unit compared to either a diagram or a known good worker.

What number is the engine? You say one brush was jamming, did you take both brushes out, clean tubes, clean brushes and make sure springs are OK? If not then it would be a good idea to do so. It could be that the brush is not making contact properly in reverse, could be it makes contact just in forward and is just light in reverse and is causing the arcing.

It is possible that the brush springs are weak and or the brushes are too short from wear.  What happens is that the motor when in reverse pushes out against the brush plate and may actually contact the brass brush tubes causing the arcing / shorting you mention. With the boiler off the frame use your fingers to move the rear driver forwards and back and observe the movement of the armature in and out. There needs to be some play however the face of the commutator should not touch the brush tubes. If it does than new brush springs may be in order.  Additionally there should also be one or two washers on the gear end of the armature, if missing than the motor will not run correctly.

Thank you, all.

spacers there, I will check all again. i dont have another to compare.  I did find wiring diagram online and will look that over when I get home from work.

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Ukaflyer posted:

Sounds like the commutator face is touching the rear bush tubes.  Can't remember now but when going forward the armature is pushing forward but when going in reverse the armature pushes to the rear.

Nope. In the forward direction, the armature pushes towards the brushes. In reverse, the armature is drawn towards the gears/forward.

RoyBoy

RoyBoy posted:
Ukaflyer posted:

Sounds like the commutator face is touching the rear bush tubes.  Can't remember now but when going forward the armature is pushing forward but when going in reverse the armature pushes to the rear.

Nope. In the forward direction, the armature pushes towards the brushes. In reverse, the armature is drawn towards the gears/forward.

Thanks for confirming the way the armature moved, I just couldn't remember and wasn't in a position to go and look.

So this now seems that the stuck brush is still the problem if it hasn't been sorted. The armature pushing back in a forward direction is making contact OK and going in reverse is now pushing the armature forward and the brush is not making a full contact because it is partially stuck. A nice easy fix then.

The best thing I find for cleaning the tubes is to have the brush plate assembly removed and use a Q tip. The ones we have over here are slightly too large to get in the tube but if you just roll each end in your fingers a little bit to make it a tad smaller, then you can just push one end in and rotate as it goes through to clean all the oil and carbon off and then just follow it through so that the other end gives it a bit of a polish when that end goes through.

 

Just a shot in the dark, but are the fingers on the reverse unit drum in their correct position and is there any "crud" on the drum?  With enough build-up of crud, there may be electrical conductivity between the brass sections.  The fingers should be nice and clean with no holes on the contact areas of the fingers (but tha'ts not all that necessary - I've seen "holey" fingers work without shorting out).  The fingers should be in the center of their respective brass contact segments.  Also make sure also that there is no contact between the fingers and other parts of the motor frame. 

Sounds like kind of a fun problem in troubleshooting.  At least for me, who isn't trying to diagnose the problem.

 

 

 

To check the armature, take a meter reading off two plates at a time. Each pair should have the same approx. ohm value and none should read continuity to the shaft. Make sure commutator's gaps are clean (brush them, etc) 

I'd suspect brush tubes or wiring though.

"Still trying to not shoot my eye out"

 

"Nursing insomnia one railcar at a time"

My aroma therapy? Smoke Pellets.

 





If this locomotive has the 4 prong plug from the tender to the engine cab, turn it upside down--it might be in backwards! At one point ACG put a red dot of paint on one side of the the plug and the receptacle to keep it oriented correctly.

S'incerely,

David "two rails" Dewey

Obviously a number of things can cause an engine to run well in one direction, but not in the other.  One thing among several to look for when something electrical in nature is observed, is whether all three armature segment wires are soundly soldered to their respective post.  I've had it happen where one or another is ever so slightly loose.  When spinning in one direction reasonably good connection gets made, but in the other not so good, and the engine ran sporadically.  With all three soldered soundly - smooth running in forward and reverse.

Let us know how it goes and what resolves your issue.  

PS  4-pin plug orientation matters on 5-wire AF steam engines.  If they are not red-dot aligned, you will get sub-optimal performance.  With four-wire engines the plug orientation doesn't matter.       

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