Locomotive stalling, can anyone suggest where the problem might lie?

[AyJay]

Good morning.  I’m hoping that by sharing this problem, perhaps someone can shed light on something that I’m missing.

 

Two days ago, whilst giving a demo to my grandson, my layout started misbehaving in a strange way.

I had several locomotives on the track, two were running, all those with sound chips were on. Nothing unusual, done it plenty of times before.

Then everything cut out and restarted a moment later; this happened several times. The following day I explored the problem further.

 

I narrowed it down to the locomotive Clan Line, released by Hornby circa 2000; whilst on an extended run it would intermittently ‘stall’ on a couple of my points.  By that I mean come to a stop and then a couple of seconds later, start up again.  Anything else running would also stop.

By watching the PSX3 Powershield circuit breaker by DCC Specialities, I saw that what was happening was that an overload, or short circuit, was happening and the circuit breaker was cutting in as it should do.

So the next question is why?

 

I examined the track by eyeball and multimeter, I could find nothing amiss with the points. No evidence of shorts or open circuits. I also gently ran a brush around, in case there might be some detritus fouling the frogs or blades.

 

As you have surmised, my layout is DCC and several locos have sound chips.

The track is all Peco, OO gauge finescale. The points are all Electrofrog and they are all fitted as per instructions with the connecting links cut and the frogs wired through the common ‘switched’ connection on the applicable Cobalt iP point motor. The DCC output from the NCE controller circuit board, passes through the PSX3 before going to the track bus.  There is a separate bus from the NCE controller for the point motors, operated via Cobalt point levers and monitored on Cobalt Alpha mimics, this does not go through the PSX3.  The mains plug-in power supply has been upgraded to handle the additional load.

 

At first, I suspected the power connecting link between Clan Line and its tender.  I noticed that it appeared to be sagging. As the locomotive goes over a point, could the movement cause the connections to short together? Well I adjusted the contact and then ran the locomotive on its own, without the tender. The problem was still there.  The only thing that I could see wrong with the locomotive was that the speedo cable on one wheel was broken; but it’s probably been like that for ages and there’s nothing for the ends to foul with.  Over the last week, I had given all my locomotives a wheel clean and axle lube.

 

So if it’s the track, why does it only happen to this locomotive?

If it’s the locomotive, why does it only happen intermittently and only when it’s going over a point?

If it’s the control electronics, why has it behaved faultlessly for ages? I know that the cut-out threshold on the PSX3 can be adjusted with connecting links, but I have regularly run with everything on the track for maximum load conditions and it has not misbehaved in the year that I have had it.

 

Can anyone offer any suggestions?  I am totally bemused by this.  Thank you

[amdaley]

Without knowing what the problem is I would say concentrate your attentions on the locomotive.

The fact that the problem only occurs with a single locomotive points to this being the source of the problem.

Does it happen when running the locomotive in both directions ?

 

 

[DCB]

Something is obviously shorting,  Is it only when going round the curve of the point? Presumably its not only one point.

I had a problem with a Q1 where the layshaft which carries the double gear, spur and worm wheel had moved sideways and the back of a wheel was hitting it on certain curves under certain conditions. Could be a stray pin on a magnet or a displaced pick up strip hitting the chassis. Not sure how the 2000 MN pick ups work despite owning one for the last 20 years!

Mine just sheds footsteps and other bits while running.

[Chrisr40]

Hi, I had the same with a q1. On one point only the wheels would short but had correct back to back measurements. Solved by a blob of paint on the point in question to effectively extend the dead frog a little more

[amdaley]

31 minutes ago, Chrisr40 said:

Hi, I had the same with a q1. On one point only the wheels would short but had correct back to back measurements. Solved by a blob of paint on the point in question to effectively extend the dead frog a little more

Ayjay says he has electrifrogs so that's not the problem. 

[AyJay]

Thanks for the support gents.  When I get a few hours, hopefully tomorrow, I am going to run each of my locos for an extended period over the points in question, just to see if it really is just the one locomotive.

Meanwhile, I have been taking a look at the instructions for the PSX3.  According to the default lack of current set jumpers, the triggering threshold should be set to 3.81A.  That should be enough for all normal loads plus a bit.  But a thought occurred to me.

If there is a momentary break in continuity as the loco goes over a point, could that cause a transient voltage spike on the dcc bus?  Could this trigger the PSX3?  I guess that is a question for DCC Concepts or DCC Specialities.  If it is this, then the obvious remedy is to add the correct jumpers that puts the threshold up to the next setting, 6.35A.

As for Clan Line, this will be pre-dcc enabled, seem to remember that I had to solder in the decoder connections. I guess it is possible that a wire got trapped somewhere, I know that I did have to shoehorn a few in. Not exactly generous on space inside.

[tarifa]

Your problem appears to be similar to one I experienced with 2 Hornby locos, a Black Five and an 8F from the early 2000's.  Both have the tender pick-up and DCC ready.  The negative pickup is through the chassis.  Initially the fault pointed to the sound decoder having upgraded from the V3.5 to a D&H.  However the stopping did not cause stopping or shorting with other locos running.  I modified both loco's eliminating the pick-up through chassis.  The 8F was further modified to produce a wired pick up from the tender and it now runs without stalling.  The Black 5 on the other hand still has the original tender loco arrangement and tends still to stall randomly on curves and particularly on points.

[AyJay]

Worth considering tariff, I’ll give it a look. Clan line has a 2 wire connection, a central pin and conductive base. But think I eliminated that as a possibility by running loco without tender. I am wondering if I could have disturbed the driving wheel pickups when I cleaned and lubed it. Well I’ll look tomorrow.

[RFS]

You say this loco was manufactured in 2000. This almost certainly means it has a wheel back-to-back measurement of 14.2mm. Later locos had revised spacing of 14.5mm.  As you're using Peco code 75 this can cause a problem on some turnouts, especially slips. I have 34067 Tangmere which is from the same era and caused similar problems to what you are experiencing.  I too am using code 75 points which have all been modified as you have done. The solution is to ease out the wheels to nearer 14.5mm.

 

It would be worth doing a test with your room lights off and watch closely as the engine traverses the points. If there's a short you should see a spark so you'll be able to see exactly where it's happening.  

Edited May 8, 2022 by RFS

[Nigelcliffe]

15 hours ago, AyJay said:

Thanks for the support gents.  When I get a few hours, hopefully tomorrow, I am going to run each of my locos for an extended period over the points in question, just to see if it really is just the one locomotive.

Meanwhile, I have been taking a look at the instructions for the PSX3.  According to the default lack of current set jumpers, the triggering threshold should be set to 3.81A.  That should be enough for all normal loads plus a bit.  But a thought occurred to me.

If there is a momentary break in continuity as the loco goes over a point, could that cause a transient voltage spike on the dcc bus?  Could this trigger the PSX3?  I guess that is a question for DCC Concepts or DCC Specialities.  If it is this, then the obvious remedy is to add the correct jumpers that puts the threshold up to the next setting, 6.35A.

As for Clan Line, this will be pre-dcc enabled, seem to remember that I had to solder in the decoder connections. I guess it is possible that a wire got trapped somewhere, I know that I did have to shoehorn a few in. Not exactly generous on space inside.

 

With a OO layout, I can think of no reason to set the cut-out threshold any higher than 3.8A (and even that seems too high to my thinking).   If you set it to 6.3A, do you have a command station which delivers more than 6.3A to the track ?  If not, the PSX does nothing as the command station will cut out first.     Throwing more power (Amps) at things is usually the route to melting track and melting parts of locos when something is not able to handle the current  - your wiring and all joints in wires has to be to a significantly higher standard each time you increase the power.

 

The problem as described appears to be in your loco.  Somewhere it is shorting out as it goes through that track.  It could be wheels touching wrong-rails (wrong back-to-back settings, wheels with tyre-tread which is too fat for the track in use).  It could be other things in its mechanical arrangement causing the short circuit. 

 

 

- Nigel

 

[tarifa]

13 hours ago, AyJay said:

Worth considering tariff, I’ll give it a look. Clan line has a 2 wire connection, a central pin and conductive base. But think I eliminated that as a possibility by running loco without tender. I am wondering if I could have disturbed the driving wheel pickups when I cleaned and lubed it. Well I’ll look tomorrow.

True but the negative pick-up is through the chassis.

[Dungrange]

On 08/05/2022 at 04:24, AyJay said:

If it’s the locomotive, why does it only happen intermittently and only when it’s going over a point?

 

It sounds to me like the problem is the back-to-back setting of the locomotive.  The back-to-back setting is not particularly critical on straight track, but it is critical through point-work, which is the reason why it appears to be shorting at that location.  It's obviously intermittent because sometimes wheels touch the wrong rails and other times they don't quite.  It's actually the back-to-front distance that is critical, so the desired back-to-back dimension depends on the wheel profile, but 14.4 mm would be the desired setting for commercial ready-to-run wheels.  For finer 'kit' wheels, 14.5 mm would be the preferred back-to-back setting.

[AyJay]

This is rapidly turning into a not a DCC issue, so apologies and I'm happy if admin wishes to move it.

 

I think that you might have something Dungrange, thank you.  I have just run all locomotives over the same stretch of track, with no problems.

Then I ran the troublesome Clan Line and it very soon stalled on a point.  Remembering what was said, I checked the back to back on the driving wheels, it was 13.8mm.  Then compared with a more recent locomotive, 14.4mm.

So, my next question is, how do I safely adjust this?  Never attempted it before.

 

[RFS]

14 hours ago, AyJay said:

This is rapidly turning into a not a DCC issue, so apologies and I'm happy if admin wishes to move it.

 

I think that you might have something Dungrange, thank you.  I have just run all locomotives over the same stretch of track, with no problems.

Then I ran the troublesome Clan Line and it very soon stalled on a point.  Remembering what was said, I checked the back to back on the driving wheels, it was 13.8mm.  Then compared with a more recent locomotive, 14.4mm.

So, my next question is, how do I safely adjust this?  Never attempted it before.

 

 

Simple method - hammer and a nail.  Lay the loco on its side and place the tip of a nail on the axle and gently, very gently, tap with the hammer. 

 

If you're not happy with this, the alternative is a replacement wheelset. Plus bogie and trailing truck on the loco, and the tender wheels also need to be done too. With my 34067 Tangmere the tender wheels were also causing a problem. 

[AyJay]

I think I solved it!

Dug out a pin punch and laid the locomotive on something soft & clean.  Checked the back to back with a vernier gauge between each hammer blow. The spacing is now 14.5 to 14.6mm; also did the pony wheels.

Next , after the problem was still stubbornly there, I examined underneath with a magnifier and could see the wheels pulling clear of the contacts.

So I took the base off and removed the copper contact strips.  Cleaned them and used a pair of plyers to emphasise the desired deflection. 

Put it all back together and with the locomotive on the track with an insulation under one set of wheels, checked the continuity from rail to the terminals on the tender coupling.

Lastly, I turned my attention to the tender.  Pulled it apart, Adjusted the back to back on the tender wheels.  Cleaned and adjusted the contact strips.  Quick continuity check and put back together.

There was a lot of 'gunge' on the tender contacts.

Ran complete locomotive, starting at the lowest speed setting; ran smoothly.  Gradually increased the speed each circuit until it was racing.

Lastly,  I ran it at slow speed, forwards and backwards over my engine yard, to catch as many points as possible.

Job done.  Thank you for your suggestions all.  Hope I don't have to do this every week, I have many locomotives.