High resistance leakage on hand laid turnouts

[robert3985]

I would approach this from a logical methodology, meaning, I would construct a turnout like I normally would, but...I would check it with my ohmmeter first after I'd cut the gaps in my PCB ties and BEFORE solder any feeders or you glue on your wooden ties.  Your ohmmeter should read ZERO at this point and if it doesn't, I'd make sure that the edges of your PCB ties have been scraped to get rid of the minute burr that almost always is present there.

If your turnout rails are not totally isolated at this point, then there has to be something going on in how you're gapping your PCB ties, and the most likely spots for that are at the gaps on either side of your frog between the closure point rails, or down at the closure points/throwbar area.

Make sure you clean your turnout well at this point, and once again make sure you have scraped or filed off all the burrs on the edges of the copper on both the tops and bottoms of your PCB ties.

If you usually use a lube such as Grease-Em or Neolube to any portion of your turnout, don't use it, as graphite lubes can be conductive...even pencil marks can be slightly conductive.

If your turnout is properly gapped and your ohmmeter is reading ZERO, then proceed to the next portion of your construction, but check the resistance at each step and don't do multiple steps.

If you think the paper could somehow be slightly conductive, or your ties, then check each material before you put it on your turnout.  The paper will be conductive most likely after you've printed the template on it, but check it both before and after.  Your ties might be conductive, so check 'em before you glue 'em on.  If nothing is conductive at this point, then do ONE tie with the Pliobond, and check resistance/conductivity again.  Keep checking each wooden tie as you position and glue them.

Somewhere in here, you're going to discover the step you just did suddenly made your turnout have a short, and you have to approach it in a logical, organized manner, never assuming a step isn't going to affect the electrical isolation of your rails.

I had a similar problem when I was attaching feeder by drilling a hole in my PCB ties and sticking the wire up through them and soldering it.  I hadn't gapped the underside of the PCB ties I was attaching feeders to, and the solder would sometimes creep down to the bottom copper plating and cause a dead short because I'd put both rails feeders on the same PCB tie.

The difference in my problem and yours is that my shorts were total shorts, which leads me to believe yours are caused by either the ink on your template, what your wooden ties are colored with, the Pliobond, your graphite lube or pencil marks.

Good luck!!

[bdennis]

Gents,
Thanks for your inpout so far.

In terms of my comment that the resistance is 4meg ohm. This is just the resistance on this particular turnout between the frog and one of the stock rails.
I think the issue is that when you combine all the different resistances I am seeing as individual readings into 1 total value when placed in line with a block on the BDL, then it seems to detect.

I have done some more work in removing the wodden ties from one or 2 of the problem turnouts and the issue does not change.. So the paper / wood / Pliobond is not the issue.

I have also tried to clean them using a electronics spray contact cleaner made by CRC. This seems to help but does not fix the issue.

What I did find is.. If I heat say the 2 rails that are north of the frog it self, and then test the reistance that was there.. be it a few hundred K Ohms or just short of a Meg Ohm, disappears after the rail has been heated..

I have not yet retested the ones that I heated.. So I will do that and see what happens.

I will also check the setting on my BDL's re the sensitivity.. I am 110% sure that they are all factory default.. But will check..

Im begining to think that the issue is the copper ties.. The gaps I ahve cut are, well, huge in comparison to what I ahve seen others do yet I am having issues..
Again, let me stress, there is nodead short on the turnout.. Just block occupied when connected to a BDL168...

In reply to Robert3985..
Firstly thanks for the tips..
Per the above, I have removed the ties and paper and the problem still exists..
I completely agree that there should be ZERO resistance and thats what I am aiming for.
I dont use any lube, so no issues there.

Im with you re the ties.. On the ones I have tried to fix.. I have used a new #11 knife and cleaned both edges (I think) with some but no complete change.
I have checked the tie at the frog where the rails are cut on both ends and no issues there.
I do gap both the top and bottom of the copped tie before installing.

To cut the gap I simply use a round small file and run it backward and forward until there is a clear visible gap and then turn over and repeat for each gap that is needed.

I will go and do more testing and see if the ones I have heated remain good or end up with oddresistance values again..

I have run out of copper ties and more are on their way.. I will build another turnout when they arrive to see where / when the resistance value is introduced.

Also, of note, when I build the turnouts, I dab each tie / rail joint with a liquid flux (using a small paint brush) and then cut a piece of solder about 1mm to 2mm long and place it on the join with tweasers and then apply heat with the soldering iron that is set to about 300 to 350 deg C to make the join.. The liquid flux is not near the gap that is cut but I guess it could wik along the tie..???

Keep the ideas coming guys..

Thanks.
Regards
Brendan

[garethashenden]

These are double sided copperclad ties? Do the gaps on the bottom line up with the gaps on the top? It may be worth removing all the copper from the bottom of the ties.

[robert3985]

Logically, it's gotta be either the flux or the PCB material.  I've never heard of either flux or the fiberglass/phenolic of PCB material being conductive...but who knows. 

A "Phantom Short" for sure...

[thomasjmdavis]

I hate to interject here, but is there a confusion between 12 kilohms (12000 ohm) and 12 megaohms (12000000) and 12 milliohms (.0012 ohms) or 12 microohms (.0000012 ohms)?  12 Megaohms would be on the order of the resistance of air over the width of an N scale track assuming around 50% humidity.  I can't imagine a block detector seeing it as anything other than an open circuit.  12 microohms (.00000012 ohms) would be expected to read as full contact- would not surprise me to find much larger readings over the two sides of a tight rail joiner, or over the length of a rail or piece of wire.

[bdennis]

These are double sided copperclad ties? Do the gaps on the bottom line up with the gaps on the top? It may be worth removing all the copper from the bottom of the ties.

Re the gaps on the bottom vs the top.. In most cases they do roughly line but but not 100% of them.

Logically, it's gotta be either the flux or the PCB material.  I've never heard of either flux or the fiberglass/phenolic of PCB material being conductive...but who knows. 
A "Phantom Short" for sure...

Yep I think it is a combination of both.
I have now tested the problem ones and while there is still some resistance, I have found that by heating the rails the problem in terms of detection goes away.
BUT!...
I ahve a set of 3 turnouts in 1 block (or lenght of track) and I have just found that if each turnout is connected to a different block on the BDL then they are OK. BUT, if the 2 in question are on the same block there is enough resistance to cause the BDL to detect!.. I have tried the heating the rail trick in all locations on the turnout with no luck.
As the rails north of the frog are gaped to the frog I have needed to add feeder wires.. So if I remove particular feeders, then I can isolate the issue.. But as per above, when I connect the feeder to different blocks all is well, when combined then things go bad.

So at the end of the day, I need to get ALL my turnouts to a point that there is NO resistance at all and then install (especially where the track is block detected). If not block detected then no issue.. But that is rare!.

So, enough testing for one night.. Back to the drawing board tomorrow..

I have found that I have  a spray can of throttle body cleaner that is basically methanol and Acetone..
I will put some gloves on, and try using that to clean one or 2 of the turnouts to see if that fixes my phantom resistance issue.

Again, thanks for the help..

[bdennis]

I hate to interject here, but is there a confusion between 12 kilohms (12000 ohm) and 12 megaohms (12000000) and 12 milliohms (.0012 ohms) or 12 microohms (.0000012 ohms)?  12 Megaohms would be on the order of the resistance of air over the width of an N scale track assuming around 50% humidity.  I can't imagine a block detector seeing it as anything other than an open circuit.  12 microohms (.00000012 ohms) would be expected to read as full contact- would not surprise me to find much larger readings over the two sides of a tight rail joiner, or over the length of a rail or piece of wire.

Hi,
In terms of the readings on my Fluke Digital Multi Meter.. Were talking about kilo ohms as in 12,000 Ohms and 12 Meg Ohms, as in 12,000,000 Ohms.. Not micro ohms.
Thanks for the suggestion though..

[sp org div]

Brendan
Been there done that
Its the contact cement bridging a gap under the turnout.
My staging entrance drove me nuts with false detection and it wasnt until I scraped out a piece of that adhesive and the false occupancy dropped. 
Jeff
http://espeeoregondivision.blogspot.com/

[bdennis]

Jeff,
Thanks for that..
In the few I have been working on.. I removed all the wooden ties and was left with the copper / rail skelton and the issue still exists.. So I think it is a Flux / copper ie issue..

Thanks for the tip though.

[sp org div]

Im thinking that PlioBond is hiding on the underside somewhere....
In my case, it was a gap that I cut in the rail after laying the turnout on top of contact adhesive (which had been spread thin over the plywood base).  The adhesive apparently found its way up under the railhead, and when I cut the gap, the adhesive refused to completely break free from the undersides of each rail end.  Even though it appeared to be a clean cut after close study numerous times, it was still enough to cause the false detection.  It was resilient to removal by scraping, cutting, sanding, and filing.  I like the idea of putting high current through the turnout to burn through the PlioBond.... but Im going to guess you need a voltage below 120v to keep it from arching across some of those gaps.
Good luck.

Jeff

[Lemosteam]

Maybe a continuity check across each rail gap will reveal if there is conductivity there?

[GaryHinshaw]

From reading the BDL manual, it has two sensitivity settings: the default regular threshold requires at least 22 K-ohms to trigger and the high threshold requires 10 K-ohms.  I would try placing a series of controlled resistance values across your rails (in a block w/o problematic turnouts) and see if your BDL is functioning according to this spec.  In no case should it be triggering on 4 M-ohms.

[victor miranda]

two problems...
the short detection circuit is one.
it should not think a 100k resistance is a short.
sweaty fingertips can get to 1k according to my meter.

other problem.
Is what the meter is saying.
most meters read resistance by testing the voltage across a known resistance
Some current must flow to do that.

if the copper is clad on both side AND is not cut on both sides
you will create a capacitor... large in dimension and low in overall capacity.

keep in mind that a megohm of resistance lets darned little current flow.

try this:
test for resistance for a minute and see if the resistance value goes up.
then carefully swap the leads to the opposite rails and see if you can get
a low value for resistance.

from what I have read here, your turnouts are fine as tested.
you have a problem, and  the turnouts are not the issue.

when I have strange track-work shorting issues,
I look for reverse loops and then miss-connected electrical switches.

victor

[WBRRVP]

Could it be from one of the 2 throw "bars" making contact with the head ties when the points are thrown? In the picture it looks like the 2nd throw bar (the thicker one) might contact the left head tie when the points are lined for the diverging route.

Jerry

[bdennis]

Gents,
Thanks for the tips.

To answer a few of the above.
The gap between Frog and rails is not an issue. I can run the #11 blade between the gaps. So no issues there.

All my turnouts have 2 throw bars 1 thick one and one normal copper tie to build in strength and also to enable the Tortoise thrown bar to be in the thick tie and to reduce the chance of the tie breaking. All my turnouts are solid rail with the lower part of the webbing removed at particular places to enable the rail to flex. On all the problem turnouts the throw bars dont touch the tie next to it and even if it did, all are gaped on both sides so no issues there.

In terms of BDL sensitivity. I am confident that the 5 BDL's I have, they are all working with no issues.. The wet finger test does cause detection on the BDL with the current setting on the BDL.

In terms of the resistance tests.. The values I provided were on different rails on a given problem turnout. All turnouts being tested are not installed and are tested in isolation with alligator clips onto a known good detection section..

While it is probable that if I change the sensitivity of the BDL will fix the issue, my concern is that ALL these turnouts should not have any resistance on them with tested in isolation (not installed on the layout). I would prefer to get to the bottom of the issue I am seeing with the multi meter before I install them and potentially create problems for my self over time.

In terms of testing each rail on each turnout, the resistance is not stable.. it changes if the leads are held on the rail over a few seconds/ 20 second etc.. In some cases the Meter reads a negative number and if I reverse the leads then it turns into a positive number. So this goes to the potential of being a capacitance issue.

I just tested a few ties that I have cut the gaps and not installed. A few did have a dead short over the gap and I was able to see the error in the cut and was quick and easy to fix. I will now introduce flux to the tie and test that in isolation.

I have a friend that has a meter capable of testing capacitance, so I will loan that and see what comes of it..

I think I have answered all questions / suggestions.. So thanks to all and keep them coming.