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Locos keep stopping at the same point in space


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An unusual incident has left me wondering whether to call an electrician, a CERN physicist, or the Ghostbusters. I have decided that RMWeb could offer equally sage advice. I am in the process of building a layout, which will eventually be DCC, however I have not yet wired it up. As a result, when my new ViTrains 37 arrived in the post today I got out my reliable H&M Duette and plugged it into my fiddle yard with a track power clip. The loco ran normally at one end, before reaching a stretch between two droppers (currently not connected to anything, as I stated earlier) it slowed down, with the lights dimming considerably, before speeding up once it had cleared this section. This occurred in both directions. I wondered if the track had become dirty, or perhaps I had accidentally put PVA on it (although there was still some conduction, as it kept on moving, albeit at a lower speed). I tried it on another track. When it reached the section parrallel to the place where it had slowed before, it slowed, before speeding up again once it was clear. This occured on all four tracks (three are Peco-made sections, one Hornby). Deciding that the issue may have affected all tracks, I got out an untouched piece of Peco flexitrack which will eventually be laid elsewhere, and put it parrallel to the fiddle yard tracks. The loco slowed down in the same position. I also ran a Hornby Duke of Gloucester down the first track of the fiddle yard and the new piece of track, observing similar results. Further exprimentation showed that in the bad zone the two locomotives would not start unless the controller was turned up much higher, but again conduction was evident due to a hum from the motor, and that at low speeds the locos would stop dead.

 

I wondered if there was an electric or magnetic field which was somehow impairing the function of the locomotives. I have never heard of this happening, but had no other explanation for the strange behaviour. The most likely sources of such  fields, I decided, were the controller and a set of magnetic darts in a nearby drawer. I moved both to sit next to another section of track, but nothing changed. I cannot think of any other obvious sources of interference nearby. I tried moving the track power clip, which also had no effect (in fact the area the locos were stopping was near to the initial location of the clip).

 

Can anybody suggest what may be causing this unusual behaviour? I would be very grateful for even the most unlikely of suggestions (for I am completely out of ideas). Thank you very much in advance for any help.

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So although you mention droppers, they are not wired to anything, so the power is coming only through the rails and fishplates? Is the board the track is laid on flat, I assume all the track is glued or pinned down at this point. If the baseboard is bowed at all there can be a bad contact at the fishplates. Doesnt sound quite right as a piece of flexi produced the same result.

 

You will get comments about testing modern stock with a Duette I predict

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Intriguing.

 

I think it would be worth trying to be certain that it isn't a mechanical effect first.

 

Definitely no dips or bumps? No track tight to gauge? Sure that the test loco hasn't got a mechanical problem that causes it to go through a tight-spot in the gearing after a particular distance? Tight curvature in the track?

 

Then electrical. Poor quality fishplated joints? Dirt, corrosion etc? dodgy connection in a common-return circuit (dry soldered joint, or loose screw in a chocolate block)? Low resistance between the rails, creating a semi-short-circuit, caused by something like damp, or the un-terminated droppers contacting something below the board, although that ought not to work as a "zone" affect?

 

Then magnetic. Have you got a compass that you can move about in the area? I'd be looking for things with permanent magnet motors, maybe a battery powered drill or screwdriver left lying there, or even under the board.

 

I'm sure you've covered-off a lot of this already, and can think of more possibilities, but these things often become clear if you go by small steps.

 

Do let us know what you find!

Edited by Nearholmer
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Can you disconnect the controller from the fiddleyard and connect it to the opposite length of track. Then see if the same thing happens at:

(a) The exact same position on the track, or

(b) A similar distance along the track?

 

As the ViTrains 37 probably isn't new, could there be a stay-alive within?

 

Edited by Damo666
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Do you have a multimeter? In which case I would suggest taking the engine off the track and then measuring the voltage along the route to see if it's consistent. 

Edited by RFS
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When getting this on loose lay layouts at shows (usually suddenly at 09:57 right as the doors are about to open) the tried and tested method is to get a long length of wire (ideally with a crocodile clip on at least one end). Clip one end to a 'good' section of track or power feed and, while running a loco, work your way towards the 'bad' section touching the rail as you go and watching for a change in performance. If it picks up you have a voltage drop across a joint(s) or just due to distance and need an extra feed. (If nothing switch side and try the other rail)

 

Odd to be across so many lines and more normal with old steel track but possible with modern stuff I guess.

 

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The more I read this, the more I suspect that the OP has all the rails of one polarity commoned in his FY, and that there is a poor joint in the common connection somewhere - its the only way I can see that all roads would be affected by a common electrical problem.

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Sorry, I had forgotten about this thread. Roasting the Duette might be a good idea. I tried running both of the aforementioned locos on another section of track, with similar results. At this point, the only common factor was the controller. The only other DC controller I could have used was some ancient Triang rubbish, so I took the decision to chip the 37. It seems to be working so far, although I still have some wiring to do.

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Don't knock the ancient Triang rubbish, I have several of them from the 1960s, it was the Triang/Hornby Westminster and the like which brought real uncontrollability and the H&M Duette which introduced real unreliability.  At least the TRiang ones usually have a pop out overload button. When shorted Duettes just auto reset until the rectifiers fail....   

Ah, sorry, please ignore this post, I have just bought a Duette cheap on eBay as part of a job lot which I shall now sell on.  Great piece of kit. Ideal for roasting on a spit as a sacrifice.

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Have you tried the thumb test.

With power to the track and a loco as a running load run your thumb round each rail. If it gets hot at a joint then there is your loose fishplate. Tweak it tight with a flat bladed screwdriver or nip with pliers. If you bleed then the rail joint wasn’t properly assembled. 

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On 14/01/2021 at 20:42, RFS said:

Do you have a multimeter? In which case I would suggest taking the engine off the track and then measuring the voltage along the route to see if it's consistent. 

 

Measuring voltage will be unrevealing in this instance. If there is a poor connection somewhere in the track/joiners, this will cause a problem to a low resistance like a loco motor, but insignificant compared to the very high resistance of a voltmeter. The meter will therefore be very unlikely to show a difference between where it runs well & badly if it is used in this way.

 

A multimeter is more than a voltmeter. Using it to measure resistance is much more useful for this purpose:

 

Remove the Duette & attach a wire across the terminals it connects to.

Using the multimeter to measure resistance instead of voltage, measure this across the track at various points around/along the layout particularly where it runs well & runs poorly. If a resistive joint is the problem you will see a difference between the 2 readings & the location of the problem will be very easy to find.

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Thank you for the advice, but it's now sorted. The combination of the Duette and modern locos seems to have been the issue. With the layout 95% wired everything is working on the intended DCC system.

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13 minutes ago, DK123GWR said:

Thank you for the advice, but it's now sorted. The combination of the Duette and modern locos seems to have been the issue. With the layout 95% wired everything is working on the intended DCC system.

 

Good to hear although I was sort of hoping you'd discovered a hitherto unknown physical phenomenon :)

 

You can actually use a voltmeter to debug problems like this and it's actually better than an ohmeter. You just need a 27 ohm power resistor attached to crock clips by flying leads to represent the motor load. You clip the resistor across the rails and measure the voltage drops around the complete circuit with the controller turned on. You can quickly find a bad connection. For example, half a volt across a fishplate is a problem. You also might be surprised at just how much voltage is dropped along three yards of track. 

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1 hour ago, AndyID said:

 

Good to hear although I was sort of hoping you'd discovered a hitherto unknown physical phenomenon :)

 

You can actually use a voltmeter to debug problems like this and it's actually better than an ohmeter. You just need a 27 ohm power resistor attached to crock clips by flying leads to represent the motor load. You clip the resistor across the rails and measure the voltage drops around the complete circuit with the controller turned on. You can quickly find a bad connection. For example, half a volt across a fishplate is a problem. You also might be surprised at just how much voltage is dropped along three yards of track. 

 

Why would that be better than measuring resistance? Few would have a power resistor in their toolkit.

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22 minutes ago, Pete the Elaner said:

 

Why would that be better than measuring resistance? Few would have a power resistor in their toolkit.

 

For three reasons.

 

To measure low resistances properly  the meter's probes need to make very low resistance contact otherwise the results will be inconsistent.

 

The second reason is that most inexpensive meters do not measure low resistances very well. 0.1 ohms is typical for a decent DVM but inexpensive analog meters might only measure tens of ohms.

 

The third reason is that most people easily understand a voltage drop whereas a resistance is often more obscure. For instance a 2 volt loss between the controller and the loco will strike most people as being a serious problem.

 

BTW, I don't but a lot of power resistors. I bought a 250 foot spool of 28 AWG Nichrome 60 wire on Ebay instead.

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Don't forget the bulb. Take a car brake light bulb, attach a short piece of wire to one terminal. Turn up the controller, sit one terminal of the bulb on one rail and the wire on the other. It should light up, or at least glow. move it to random different places around the track, or slide it round the whole layout. You will soon see if there is any resistance, and can pinpoint it quite accurately. The bulb draws enough current to be very effective. 

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