PVA woodworking glue and short circuit

 
  3333 Station Staff

I am in the process of getting my layout up and running after a decade or so of not having one.  My previous one was DC so am on a bit of a learning curve as this one will be DCC. I have completed the carpentry stage have laid the track and tested it on DC. It ran with no problems. I have added droppers and used PVA glue  (Selleys + woodworking glue) to secure the track to the trackbed (trackrite foam), this was approximately 36 hours or so ago. I have one of those squakers from Jaycar to test for shorts and since adding the droppers and PVA it has a very faint squark. I have checked for any loose material and throughly vacuumed the track but still the squark.

Do not believe it is the droppers as I took great care and they are not connected to any BUS yet. I suspect the PVA glue that may have bridged the two rails and has not completely dried out.  I tested some PVA on a bit of scrap track and tested before (no squark) and after the glue (a squark).

Has anyone experienced this and how long does it take to dry and eliminate the short/squark. Any assistance and/or advice would be appreciated.


This is only my 2nd post but have been lurking and learning from members who are far more experienced and technically savvy than I ever will be, so if this is a stupid question please go easy on me.

I have undertaken a search on this forum and google but could not find anything meaningful.

Thanks in advance

Paul

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  TheBlacksmith Chief Commissioner

Location: Ankh Morpork
Not a silly question at all. There is nothing chemically in PVA adhesive that should create a short circuit except water.

The 'squarker' you mention is a very crude tool for measuring resistance and would give absolutely no indication as to how much of an electrical path it is measuring. I suspect that if you were to pour a small puddle of water on a bench top and measure it with the device, you would get a 'squark'. I suspect that it is measuring the water content of the PVA adhesive. Once it dries thoroughly, could be up to a week, it should not give you a problem.
  Aaron The Ghost of George Stephenson

Location: University of Adelaide SA
Many adhesives are initially conductive, PVA is one, silicone is another. As the Blacksmith states once they are fully dried they generally turn to a non conductive state. Don't panic until you are absolutely sure the adhesives are cured and you still have a problem.
  Aaron The Ghost of George Stephenson

Location: University of Adelaide SA
As if to illustrate this, tonight I ballasted probably 12 linear feet of track, previously, this entire part of the layout (it's a completely isolated section) was a perfect open circuit between the rails. For the purpose of the exercise before I began ballasting I put approx 15V DCC across the rails whilst measuring the current flowing. Before glueing the ballast the current flow was zero, a perfect open circuit.

As I flooded the ballast with the general PVA + water + detergent combo the indicated current increased to about 18-19mA which is about the equivalent of a 750 ohm resistor across the track - this also set my current detecting occupancy detectors into a false trigger ie they thought there was a loco or train in the track... When I left some few hours later the current had dropped as the glue dried to 8mA or the equivalent of something just less than a 2000 ohm resistor across the tracks, some detectors were false triggered, some were not.

Tomorrow night I suspect (hope) the current will be reading zero again!
  3333 Station Staff

Thanks to Blacksmith and Aaron for providing a prompt and reassuring response.

I connected up the DC power supply and controller which have a cut out for shorts. Did not cut out so ran a couple of locos and all went fine.

Thanks for the help much appreciated

Regards

Paul
  John_Bushell Chief Commissioner

Location: Brisbane
Thanks to Blacksmith and Aaron for providing a prompt and reassuring response.

I connected up the DC power supply and controller which have a cut out for shorts. Did not cut out so ran a couple of locos and all went fine.

Thanks for the help much appreciated

Regards

Paul
3333
Paul,

Thank you for asking the question.  I have been messing around with trains for many years, but I had not heard of that quirk.  If you ask the question there are enough smart people here who can usually answer.

There is no stupid question, apart from the question that you do not ask.

Best regards,
John
  Kevin Martin Chief Train Controller

Location: Melbourne


Has anyone experienced this and how long does it take to dry and eliminate the short/squark. Any assistance and/or advice would be appreciated.


Paul
3333
As to time scale, it could be anything. The temperature and humidity would make a large difference as to 'how long'.

Glad its all sorted for you, Paul. Next time someone asks a similar question, you'll be able to jump in with an answer. Its all about learning & passing on knowledge.

Kevin Martin
  Aaron The Ghost of George Stephenson

Location: University of Adelaide SA
And tonight I was at the layout, and having cleaned the glue of the tops of the rail (incidentally, I use GP thinners and no abrasive) but I forgot to look for leakage current. I will do tomorrow night, if I remember.
  hosk1956 Deputy Commissioner

Location: no where near gunzels
Paul,

Thank you for asking the question.  I have been messing around with trains for many years, but I had not heard of that quirk.  If you ask the question there are enough smart people here who can usually answer.

There is no stupid question, apart from the question that you do not ask.

Best regards,
John
John_Bushell
I too have been playing with trains for many years and have ballasted-dare I say-miles of track in those years and I have never struck this phenomenon, perhaps as mine were mostly club tracks they had a good chance to dry out before operations resumed.
Having said that, I was in a club that was in the Mt Lofty Railway Station many years ago, that was a very dank building in winter which was only opened up fortnightly and then at night generally, we ballasted some track and it was still wet the following fortnight, it dried out in that evening though once all the heaters were on and a few bodies added warmth and some air circulation-true story.

Wayne
  Aaron The Ghost of George Stephenson

Location: University of Adelaide SA
It probably happens in all cases, except I would think most of us (especially in DC days) ballast with the power off and don't try operating again until the glue hardens and the rail surfaces cleaned. I certainly have always ballasted my track with it not live.

The leakage currents I measured were small, if I tried to run a train with such leakage through the glue there would probably appear to be no apparent issue. Devices more sensitive to current flow, like the OP's buzzers, my occupancy detectors and my oscilloscope can 'see' the current, but your controllers or DCC system are hardly going to notice.

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