New DCC Layout Short Circuit

[Quikbrew]

So, finally completed wiring-up my layout. I'm a newbie, so have tried to keep it simple(!)

• It's based on the Hornby TrackMat with all of the Extension Packs up to and including F.
• Have droppers (feed and return) soldered on every piece of track
• Single Bus wire using DCC Concepts Twisted Bus Wire
• Droppers connected to bus via DCC Concepts Bus Terminal Tags

 

Everything looks fine and connected correctly, but I've got a short circuit across the rails over the whole layout.

 

I'm pulling my hair out! Any thoughts? Am I doing something wrong or missed something?

 

HELP!!!

[Pete the Elaner]

I don't see any mention of insulated rail joiners.

Some may argue that with dead frog points, you don't need them but, since you have a short, it seems like you do.

[johnd]

Have you put insulated(plastic) rail joiners on the Vs on the points ?

 

"Have droppers (feed and return) soldered on every piece of track" if this is the case then insulated rai joiners are required to the V's on every point.

Edited December 23, 2022 by johnd

[JimFin]

Just based on my own experience, good chance you have got 1 pair of droppers cross connected.

 

[AndrueC]

53 minutes ago, johnd said:

Have you put insulated(plastic) rail joiners on the Vs on the points ?

 

"Have droppers (feed and return) soldered on every piece of track" if this is the case then insulated rai joiners are required to the V's on every point.

Is that peculiar to Hornby track? My previous layout used N scale Peco Settrack and there was no need for insulating joiners anywhere. Although the Vs look like they are one piece they actually have a very small gap between them.

Edited December 23, 2022 by AndrueC

[Quikbrew]

Pete the Elaner and johnd

 

Thanks guys. I did wonder about this. I was advised by a supplier that these weren't required for the Hornby points. I'll get some. Fingers-crossed!

 

Cheers!

[Quikbrew]

12 minutes ago, JimFin said:

Just based on my own experience, good chance you have got 1 pair of droppers cross connected.

 

JimFin

 

Checked, checked and checked again! Definitely no cross-connections.

[Michael Hodgson]

There are learning points here. 

If you can't see which wire goes where, it's very difficult to fault-find, especially on a large layout.

• It's a good idea to colour code your wires.  Red to one rail, black to other.  Check that they all go to the correct rail and to the correct bus wire.
• Don't wire the whole layout in one go - test as you go; if there is a fault you'll have to disconnect one feed at a time till the probelm goes away
• Don't feed too big an area directly off one bus.. Suppose the short is a bit of metal across the rails - you need to know which part of the layout to search; so a few insulated joiners & overload cutouts or isolating switches to break it into zones like a conventional will help with fault finding withoit stopping the whole layout.

 

Edited December 23, 2022 by Michael Hodgson

[Quikbrew]

AndrueC

 

The Hornby ones have a plastic Vs too.

 

Also, should I only put droppers on the toe end of the points?

[Quikbrew]

Michael Hodgson

 

Thanks for the tips. I have coloured coded the wires as you described.

 

There is only one bus wire, but it's only a small layout, so I thought (and was advised elsewhere) that it would be sufficient.

 

I have learned a lot since I started with this project and I think I would do a lot of things differently if I was starting now. I am considering starting again from scratch. Will have a think about it before I ripp it all up though!

[AndrueC]

36 minutes ago, Quikbrew said:

AndrueC

 

The Hornby ones have a plastic Vs too.

 

Also, should I only put droppers on the toe end of the points?

The Peco turnouts have metal Vs but with a very narrow gap between them then an entirely plastic 'frog':

Peco Insulfrogs normally only need power at two places - the outside rails. As long as the switch rails are making good contact the corresponding V arm will be appropriately energised (so in the above picture from top to bottom at the left you have P1,P2, <nothing>, P2). However over time the switch to stock rail contact can get dirty in which case providing power to each arm of the V would help.

 

However you should also note that this default configuration cuts power to one of the routes (in the above image the root horizontal left effectively has no power). This is useful for DC because it means if there is a siding to the immediate left we've now stopped any loco on it from moving. But for DCC we don't want or particularly need that and therefore we would normally ensure that there was power to that route. Most likely through ensuring that both rails of any 'siding' have droppers. Ensuring that the V arms are separately powered will improve reliability because then you aren't reliant on the switch rails making contact.

 

Whether you rely on droppers or fishplates is up to you but my experience of fishplates means that I use droppers everywhere so in the above configuration I actually would attach droppers to each of the arms of the V but a lot of people wouldn't bother.

Edited December 23, 2022 by AndrueC

[ITG]

2 hours ago, Quikbrew said:

Everything looks fine and connected correctly, but I've got a short circuit across the rails over the whole layout.

Actually, it’s probably not across the whole layout. It’s likely in one place, but because the whole layout is connected up, you cannot see where it is. There is no substitute for disconnecting parts of the layout, perhaps half, and then seeing in which half is the short. Then split that half again. Sooner or later you’ll find the short!

I have no experience of dead frog points, but surely if, by definition, the frog is dead, then the lack of insulated rail joiners cannot be causing the short, can it? The toe end of the points will be drawing power through any NON-insulated rail joiners (maybe not the best connection but probably unlikely that new ones are failing, and in any case, they alone won’t cause a short).

A track plan and wiring diagram would help - you haven’t by chance created a reversing loop?

[AndrueC]

11 minutes ago, ITG said:

I have no experience of dead frog points, but surely if, by definition, the frog is dead, then the lack of insulated rail joiners cannot be causing the short, can it?

My experience suggests not. I suppose if the V was a solid piece of metal it could but it seems to me that's a perverse way of designing a dead-frog turnout because it would mandate some form of polarity switching. It seems to me that all dead-frog turnouts must have electrically isolated V arms with each arm of the V being electrically connected to its corresponding switch rail.

 

I suppose you could also build a dead-frog turnout where the V arms are not connected to the switch rail but that again seems to be asking for trouble as it makes you reliant on the switch rail contacts.

 

There are a couple of ways in which any turnout can cause a short when rolling stock crosses it but as we appear to be talking about a permanent short those can be ignored.

Edited December 23, 2022 by AndrueC

[AndrueC]

Actually I just had a thought. I don't know if this is possible in OO or not but one time I was waving a soldering iron about (as you do ☺️ ) and unbeknownst to me a drop of solder fell off it and landed in the middle of a section of track. It splashed just enough to bridge the gap and cause a short. The drop happened quite some way from where I was last working so the moral of the story is:

* Be more careful.

* Don't assume that the fault has been introduced where you were last working ;)

I think that this is less likely with OO track unless you're in the habit of loading up a really, really large blob of solder ;)

Edited December 23, 2022 by AndrueC

[Quikbrew]

AndrueC, ITG

 

Thanks guys. Lots of good stuff here.

 

There is no reversning loop.

 

I haven't got a circuit diagram, but layout plan attached

 

No drops of solder either 😉

[smokebox]

There is the possibility that you have a faulty point.  There is known to be some Hornby points that have an inbuilt short circuit problem.  You would need to remove each point one by one to find the faulty one.

[Dungrange]

@Quikbrew

 

My initial thought was that there must be somewhere that insulated rail joiners are required. 

 

Although the frog itself is 'dead' or plastic, there will be crossover connections within the frog between the exit rails and the corresponding closure rails (the ones that run between the switchblades and the common crossing).  The points are designed to be self isolating when used as part of a train set.  That is, you feed the power to the toe end (the end with the switchblades), which means that both stock rails (the outer rails) will be live.  One will be positive and the other negative.  Within the point, one of the switchblades will be touching the adjacent stock rail and that routes power from the feed via the stock rail, switchblade, closure rail and through a wire in the frog to the exit rail, which means that whichever route is set will be live.  The other switch blade will not be touching the other stock rail and therefore the closure rail and exit from the other route (the one not set) will be isolated.

 

However, by wiring droppers to every section of track, you have effectively bypassed the self isolating feature of the points, so that all track is live.  However, looking at your track plan, I can't see anywhere that feeding power back into the normally isolated frog, closure rail and switchblade should matter.  Therefore, if you're certain that there are no crossed feeds, then I think a possible faulty point is the problem.  The fault would be that the two crossover wires within the frog are not isolated from one another.  When used in a DC train set, this might just produce a siding where a train can't be isolated, but in your case, it's causing a short.  The remedy is to find the faulty point and either replace it, or wire it as an Electrofrog point with insulated rail joiners on both sides of the V.

[AndrueC]

25 minutes ago, smokebox said:

There is the possibility that you have a faulty point.  There is known to be some Hornby points that have an inbuilt short circuit problem.  You would need to remove each point one by one to find the faulty one.

Oh that would be annoying. Could the short be detected by jamming all the turnouts open (stick a bit of card between the switch and stock rail) then releasing one turnout at a time and testing both routes?

 

As regards removing track when I first had to do it I tried to lift the track out resulting in damage to fishplates and even some of the track. What I've now learnt is that you just have to slide the fishplates back out of the way then you can just raise the turnout. Replacing is the reverse. Drop the track into place then slide the fishplates back across.

 

The fishplates will be blocked from moving in a lot of cases by the the sleeper chairs but it's usually fairly safe to temporarily lift the track or just let the fishplates barge underneath. And if you do this then tweaking the fishplates with pliers afterwards might be a good idea to try and ensure good contact.

 

In theory you could use this to break the track into sections. Slide back two fishplates then insert a thin piece of paper between the rails temporarily. Unfortunately if you have droppers on every section of track this won't help because the bus will ensure continuity.

Edited December 23, 2022 by AndrueC

[Quikbrew]

Smokebox, Dungrange, AndrueC,

 

Many thanks for all the useful information. I'll do some investigation based on your advice and let you know how I get on.

 

Cheers!

[Quikbrew]

Well, that was a LOT quicker to fix than I expected!!! Faulty set of points! (pictured) Thanks for the early Christmas present guys!!!

 

Have got it powered-up, just DC, to test and my little Hornby 0-4-0 tank engine is whizzing around like a good 'un!

 

So, do I still need the isolated rail joiners after each set of points then?

[RobinofLoxley]

Hello Quickbrew - I was 3/4 way through a fault finding process for you when you posted!

 

Running DCC style you shouldnt need any insulated joiners. You have a common bus supplying power and signal to every part of the layout. The insulations make to difference in that sense.

 

If you run it DC with locos on two loops, you need insulated joiners where the turnouts connecting the loops meet.

 

Curious how the faulty turnout created the short. Dodgy/broken blades?

 

[smokebox]

16 minutes ago, RobinofLoxley said:

Curious how the faulty turnout created the short. Dodgy/broken blades?

I believe the fault is inside the moulded plastic frog section

[Quikbrew]

RobinofLoxley

 

I'll be running it DCC. Once I get the track back down properly again, then I'll be converting my DCC ready Scotsman (already have the decoder and speaker) and then connecting-up my NCE Powercab.

 

I thought that was the case.

 

Not sure what the actual fault with the turnout is.  I did notice that it was stiff to move, but I can't see anything obviously wrong on the outside 🤔

[Quikbrew]

4 minutes ago, smokebox said:

I believe the fault is inside the moulded plastic frog section

That would make sense. Do you reckon I should tell Mr Hornby? 😅

[smokebox]

I think they are aware 😃