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Back to Back Shorts

Started by Rod in PA, April 23, 2012, 09:18:43 AM

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Rod in PA

Does anyone have a cure for back to back shorts?

I have a Bachmann HO DCC Pennsy K4.  One of the front wheels of the tender causes a short circuit  whenever it passes through the converging direction (curved portion) of a turnout from the point end (I hope that makes sense).  Depending on the direction of the curve, left or right, the corresponding front wheel of the tender shorts between the stock rail and the point rail.

I'm not sure it the problem is with the turnouts or the locomotive, or a combination of both.  The problem doesn't occur through all turnouts, and the distance between the rails are in gage.  I've noticed that the drawbar between the loco and tender seems to be a little short, or maybe its just the design of the connection, but the tender seems a bit tight following the loco through the curved portion of turnouts.

If anyone has experienced this same problem and has any recommendations for correcting it, it would be greatly appreciated.

Thanks,
Rod   

bapguy

Did you check the guage of the wheels? Also what size of turn out? IE #4,5,6,8. How many axles on the truck. Did you try turning the loco around and see if it shorts out that way as well?

Tom M.

Does this happen on only a single turnout or on all of them?  As has already been suggested, check the gauge of the "offending" wheelset with an NMRA Standards gauge.  If you don't have one of these check gauges, you can get them from Walthers or a well stocked model RR hobby shop.

If it happens on only a single turnout, check that turnout very closely.  At the point where the wheel shorts, you should find one or more "pit" marks where the back of the wheel is touching the back side of the open point rail.  To correct this, I normall take a very small flat bladed screwdriver and place the blade against the pit.  I then push on it slightly to "kink" the rail just a tiny bit.  In essence, to increase the gap fractionally at that point.  You are not looking to make a big bend.  Most often, you only need to increase the clearance by no more than the thickness of a sheet of tablet paper.

Good luck,

Tom

Jerrys HO

Rod

Good advice keeps coming. If the turnout is a Bachmann, check the rails. Someone else had a similar problem and the following day I experienced the same. When installing the turnout the rail from the adjoining track was slid back causing the turnout rail to be pushed toward the frog and cause a short. Check and make sure the rails are not touching the frog, if they are take a small flat blade and push the rail back away from the frog.

Jerry

jward

what brand is the offending switch? something tells me it is not "dcc friendly".....

on some of the older power routing type switches, the frog and both points were the same polarity. if this is the case. when metal wheels rub against the stock rail while riding on the points they cause a short circuit, this isn't noticeable on dc, but on dcc it will cause problems.  the solution is to carefully cut gaps on each of the closure rails near the frog, then wire them to the adjacent stock rail. you'll also want to use your switch motor contacts, if you have them, to power the frog.
Jeffery S Ward Sr
Pittsburgh, PA

Rod in PA

Thanks all for the info.

Some further details;  I use NCEs Power Cab, all turnouts are shinohara (18 of them), all frogs are wired around through the switch machine contacts, the problem turnout is a #4.  The only locomotive shorting out is my Bachmann HO DCC K4 (4-6-2) when it enters the curved portion of the turnout from the point end. The K4s tender has two trucks with two axles each. All of the K4s wheels and drivers are in gage.  All of my other Bachmann locos, steam and diesel, have no problem going through this turnout in either direction.  When the K4 shorts out at this turnout, it's obvious that the left wheel of the front axle of the leading truck is touching both the stock and point rails.

I've tried bending the point rail up in a more vertical position to create more space between it and the stock rail.  I've done this on other turnouts where the lead wheel of a particular car would short out, but never a locomotive until now.  Bending the point rail didn't help in this case.  Next thought was to somehow insulate the back of the culprit wheel from the point rail.  So I coated the back of the wheel and the side of the point rail with clear fingernail polish.  Last night I ran the K4 through the turnout several times with and with a cut of cars.  Didn't have any shorts.   But I'm not satisfied as this would only be a temporary fix until the polish wears off.

I'm still not sure if the problem is with this particular locomotive or the turnout,  or a combination of both.  Any further suggestions would be appreciated. 

Thanks again,
Rod

jonathan

This may be in left field, but is it possible that one wheelset in installed backwards?  I would think that would short the loco at all times.  Just a thought...

Regards,

Jonathan

jward

shinoharas were notoriously dcc UNfriendly. i never liked them, but a friend has many and in addition to the gaps in the closure rails i described above, he had to replace the throwbar with a piece of pc board with the copper cladding cut to insulate the points from each other.
Jeffery S Ward Sr
Pittsburgh, PA

RAM

#8
OK, jward just beat me to the point.  do a google search. Making a dcc freindly turnout.  It will show you how to do This step by Step.

Tom M.

I have over 150 Shinohara turnouts on my layout.  I've been using Digitrax DCC since 2000.  As long as you have gaps in the rails that lead to the frog and remove the little tiny wipers from the point rail throw bars that make contact under the stock rails they are just as DCC friendly as almost any other turnount.  In my opinion, the Wiring for DCC site goes way overboard on what the author thinks is necessary to make a Shinohara turnount DCC friendly.

Tom

Jim Banner

Rod,
Your finger nail polish test has confirmed that it is indeed the first set of wheels that short.  Why not just replace them with plastic wheels?




Tom,
I too have many Shinohara turnouts on my layout.  Only a couple of them gave any problems with DCC and required modification.  I used Alan Gartner's method which not only gaps the closure rails as you have done and removes the sliding contact tabs as you have done but also isolates the the points from one another and then jumpers each point to its corresponding stock rail.  This forces each point to have the same polarity as its stock rail so that any accidental connection between them, such as Rod has been experiencing, does not cause a short circuit.  Without the jumpers, I do not see how your point rails get any power except possibly through the notoriously unreliable contact of point to stock rail.  And if somehow they do get power, I do not understand how you avoid having the points, when open, from having a polarity opposite that of their stock rails.  With the point rails still joined by the metallic hinge and throw bars, powering the points so the closed one matches the polarity of its stock rail perforce means the open point does not match the polarity of its stock rail.  And that, it seems, is what is causing Rod's problem.  I am also left with the question:  if you do not somehow power your points, what is the purpose of having all metal turnouts?

As to which Shinohara turnouts gave me problems, they were both number fours.  The number sixes and eights have never been a problem with any locomotive and doing any modifications to them would have been a waste of time.  My hand laid turnouts in all the scales I model are all metal with points isolated from the frogs and jumpered to their corresponding stock rails.  (The only exceptions are stub switches.)  The only shorts they ever have are when operators attempt a trailing point movement with the switch set against them.  But that is a whole other story.

Jim
Growing older is mandatory but growing up is optional.

Tom M.

Jim,

I don't use any jumpers to the point rails.  Parts of my layout have been operational since 2001 and all trackage was operational in 2008.  I'm still in the process of completing the installation of all the switch machines.  I have about 50 left to do and on a couple of turnouts still controlled by ground throws I will get an occasional stall.  However, on those that are thrown with PFM/Fugurex slow motion switch machines I don't have any issues.  The throw provides adequate tension on the points and I also use the auxiliary electrical contacts to power the frogs.

Tom