Author Topic: Questions about lack of wheel conductivity and metals  (Read 3305 times)

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mmagliaro

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Questions about lack of wheel conductivity and metals
« on: July 15, 2016, 05:53:15 PM »
0
My questions are never easy ones. 

So... I have created all new tender trucks for my 0-6-0 project.  I have made my own wheelsets, sideframes, the whole darn thing.
It looks nice and it runs... almost

The problem:

I am having some intermittent conductivity/stalling issues.  And I should point out that I had these same issues
even when I used Kato Mikado trucks under the tender.   That's important, because it strongly makes me believe that
my problem has nothing to do with my new trucks.  It is something fundamental I don't understand about wheels,
metal, and pickup.

Recall that the tender pickup/truck system looks like this:



So, with rails perfectly clean, freshly wiped with alcohol, wheels freshly cleaned the same way,
it runs beautifully, down to a certain point.  But if I make it creep along at, say, 3 mph, every once in a while, it will
stall.

Important facts:
1. When it stalls, current draw is zero, so it is lost pickup, not a mechanical bind.

2. It does not always happen at the same place on the track

3. When it stalls, I can take a whisker of fine wire, jumpered to the rails, and touch a wheel on the tender, and it will
start up, meaning that that wheel had lost contact on that rail. 
The whisker is important, because it allows me to touch the wheel
without mechanically moving the engine or wheel.

3a.  To double-confirm this, I tried touching the wheel with the whisker over and over WITHOUT the other end of
the whisker being connected to the rails, and the engine does not start up again.  So I am definitely not nudging anything to cause it to get going.  And as soon as I connect the whisker to the rail and touch the wheel, it runs.

4. I tested this many times, touching the wire to a different wheel every time.  It makes no difference which wheel I choose.
It always starts up. 

This means, to me anyway, that the lost contact cannot possibly be in the axle points, cones, the "thumbs" that go up into the tender or the tender floor strips or anywhere else.  If hot-wiring to a wheel makes it go, that means that the wheel
has lost contact with the rail.  And in fact, since I tried this over and over with different wheels,  it means that ALL FOUR wheels on one side have lost contact with the rail.

===============================================
Whew.

Now to my confusion. 

How on earth is this possible? 

4 nickel-silver wheels on nickel-silver rail, all clean, with a good amount of tungsten weight on top of them, and they are all not conducting?  I could easily see it if there were only 2 wheels, but 4? 

Oh.. and I should point out that all the wheels on this thing consistently roll beautifully.  I don't have any dragging or wheels that don't touch or won't roll.  I stackied an extra 20g of weight on top of the tender just to see if that would make
any difference.  Nope.  The problem doesn't change at all.

This engine is powered by a 3v motor that is zener limited, so the voltage from track to wheels during these tests
is about 7.5 volts.  In other words, I am not trying to power this engine on the hairy edge with only
1 volt on the rails.

What do I not understand about conductivity between a wheel and a rail?



« Last Edit: July 02, 2017, 03:24:20 PM by mmagliaro »

central.vermont

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Re: Questions about lack of wheel conductivity and metals
« Reply #1 on: July 15, 2016, 07:55:28 PM »
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Wow this does sound weird Max. :o
So the only thought I have on this is this. You say you have made all parts and I am assuming the wheels also? I am wondering if it could be the contour of the wheels not letting them touch on the top of rail head. What the problem could be is it is touching on the inside lip of the rail where there could still be a dirty issue. Just throwing this out there.
I kinda feel like a student telling the teacher you have it all wrong.  :D

Jon

peteski

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Re: Questions about lack of wheel conductivity and metals
« Reply #2 on: July 15, 2016, 08:13:07 PM »
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Going by your findings I would say that something non-conductive and microscopically small gets between the wheel and the rail.  Something large enough to prevent 3V from arcing across it.  :D  The only thing that surprises me is that it happens to 4 wheels at the same time (since all 4 wheels are set up for picking up current).  Also surprising is that you can make it move again by just jumping across one wheel (always on the same side?). Weird. It almost seems that you are jostling the wheel-set ever so slightly.

What that insulating substance is - I don't know. Maybe particles of dust or abrasive, or maybe particles of metal oxides. I have feeling that if you polished all 8 wheel treads to a mirror like shine and did the same with the rail head, the problem would be solved (at least for some time period).   Or if you spread a thin bead of mercury over the rail head, that should work too.  :D  Just kidding about the last one (but I really think it would work).

How about increasing the mass of your tender?  Will that make it more reliable?  Load it up with lead and see how it runs.
« Last Edit: July 15, 2016, 08:20:36 PM by peteski »
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mmagliaro

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Re: Questions about lack of wheel conductivity and metals
« Reply #3 on: July 15, 2016, 08:14:03 PM »
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Wow this does sound weird Max. :o
So the only thought I have on this is this. You say you have made all parts and I am assuming the wheels also? I am wondering if it could be the contour of the wheels not letting them touch on the top of rail head. What the problem could be is it is touching on the inside lip of the rail where there could still be a dirty issue. Just throwing this out there.
I kinda feel like a student telling the teacher you have it all wrong.  :D

Jon


Don't worry about throwing things out there!  (and that goes for everybody).

But remember, I tried this originally with Kato trucks and Kato wheelsets and got the same behavior, so I have eliminated
my wheels as the source of the problem.

jdcolombo

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Re: Questions about lack of wheel conductivity and metals
« Reply #4 on: July 15, 2016, 08:17:10 PM »
+1
Hi Max.

How are the tender trucks attached to the tender floor?  Do they have "play" that allows them to rock a bit from side to side (not front to back, but side to side)?  If they are attached to the floor with screws, have you tried loosening the screws a turn to allow more free play from side-to-side?

If you've done all that, then my next step would be to clean the rails not with alcohol, but with 600-grit sandpaper.  I know this sounds terrible, but I've found that sometimes there are deposits on NS rail that alcohol or other liquid cleaner simply won't remove.  The 600 grit will not roughen the surface of the rail - I've used it to clean rail for years - but rather "polish" it.  Don't use anything less than 600 grit, and if you can find 800 or 1000, use that.

If none of this works, I'm out of ideas.

John C.

Curtis Kyger

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Re: Questions about lack of wheel conductivity and metals
« Reply #5 on: July 15, 2016, 10:51:57 PM »
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Personally, I've found that after a bit of time, track leaned with alcohol will tend to tarnish -- although that may only be the case in combination with high humidity or perhaps alkalinity of the air as it was in an unfinished basement.  Perhaps this is happening with your rail; that it runs fine until the rail tarnishes (???).  I found that after using alcohol, I would need to go back and wipe the rails with a soft cloth ad then results were much better.  However, I have since moved on to cleaning the rails with Lacquer Thinner and am very happy with the results.

Lemosteam

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Re: Questions about lack of wheel conductivity and metals
« Reply #6 on: July 15, 2016, 10:56:03 PM »
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Maxx have you checked continuity through each electrical path with a probe?

Wheel to rail, wheel to axle shaft, axle shaft to pickup, pickup to wire? wire to rail wire to wheel, etc?  maybe there is a broken strand in that wire...

nkalanaga

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Re: Questions about lack of wheel conductivity and metals
« Reply #7 on: July 16, 2016, 01:51:45 AM »
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To go with John's questions about the truck mounting, how tight is the drawbar?  If the loco leans to one side, does the tender lean with it? 

I had that problem with first-run Kato F units, with the flanges turned down, when first laying my track.  The rear trucks kept derailing at the points on ME #6 turnouts, and I couldn't find the problem.  It turned out that the trucks couldn't rock, and when the lead truck went over the frog, that side was raised slightly.  Going through the curved side, that raised the rear truck enough to go over the point, rather than follow it into the curve.  I spent weeks trying to figure out what was wrong with the points, and why it only affected Kato F units, when the points were fine all along.

On the plus side, I have very few derailments.  Once I could get a 4-unit set of Fs around the layout reliably, everything else ran perfectly!
N Kalanaga
Be well

svedblen

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Re: Questions about lack of wheel conductivity and metals
« Reply #8 on: July 16, 2016, 04:10:25 AM »
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I once had a similar problem: https://www.therailwire.net/forum/index.php?topic=36450.msg455636#msg455636
But then the problem always occurred at the same spot and was partly due to a narrow track gauge. Maybe not applicable in your case.
Lennart

Maletrain

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Re: Questions about lack of wheel conductivity and metals
« Reply #9 on: July 16, 2016, 08:56:14 AM »
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What track are you using?  It sounds to me like you might be having problems with your wheel flanges riding on the plastic “spike heads” that hold the rails to the ties.  When the tender shifts to one side so that the flanges do not make contact with the rails, and the plastic bumps raise the wheels off the tracks just a tiny bit, you lose electrical contact.  Since that is intermittent, it would only be a problem when moving at a crawl.  The smaller the rail, the more likely this is your problem.

Rasputen

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Re: Questions about lack of wheel conductivity and metals
« Reply #10 on: July 16, 2016, 08:58:49 AM »
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You could disconnect the tender from the locomotive and mount a light bulb on it instead.  Then, gently push the tender around.  It sure sounds like the drawbar is too tight and lifting the tender wheels.

sp org div

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Re: Questions about lack of wheel conductivity and metals
« Reply #11 on: July 16, 2016, 09:51:30 AM »
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Wow this does sound weird Max. :o
So the only thought I have on this is this. You say you have made all parts and I am assuming the wheels also? I am wondering if it could be the contour of the wheels not letting them touch on the top of rail head. What the problem could be is it is touching on the inside lip of the rail where there could still be a dirty issue. Just throwing this out there.
I kinda feel like a student telling the teacher you have it all wrong.  :D

Jon

I will second, cleaning the inside of the railheads.
Had similar problem after weathering track and baffled me for awhile.
Apparently the shape of the flange wheel / flange, and where it rides on / against the railhead is not just the top.
Jeff
« Last Edit: July 17, 2016, 01:52:27 AM by sp org div »

ednadolski

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Re: Questions about lack of wheel conductivity and metals
« Reply #12 on: July 16, 2016, 09:52:21 AM »
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What do I not understand about conductivity between a wheel and a rail?

How have you measured that the current is going to zero?

To further isolate that it is a tender pickup problem, I would suggest connecting a pair of free wires directly from the power supply to the motor leads, and see if that improves the operation. Then, try with the wires connected to a separate, independent pickup truck that is known good/reliable (if you have one).

If both of those work, then it sounds to me like there is something mechanical that may be causing some of the wheels to lose contact (even tho that may be very hard to see), and/or there is perhaps something resistive in the pickup paths.  Do you have any images showing the electrical pickups?

With my GP9 I used home-brew electrical pickup strips, and even with all-wheel pickup the operation was spotty until I added a small amount of conductive grease to the contact points.

Ed



ednadolski

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Re: Questions about lack of wheel conductivity and metals
« Reply #13 on: July 16, 2016, 09:56:46 AM »
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Just another thought (i.e. guessing) FWIW - what about the motor itself?   Could you be having some kind of small particles of carbon or other contaminants building up on the brushes?  This may not be the source of the track contact problem but perhaps could be a factor in making worse.

Ed
« Last Edit: July 16, 2016, 10:34:55 AM by ednadolski »

Big Train

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Re: Questions about lack of wheel conductivity and metals
« Reply #14 on: July 16, 2016, 11:47:37 AM »
+1
Just throwing this out, as requested, ......clean the wheels and rail with Conductalube, Wahl clipper oil, or WD40? Sometimes a little, and I mean a little, application of oil can help I've found.