Phantom movements

[brober]

Hi, looking for some advice on a particular issue I have.

When one of my engines stalls (usually on a diamond crossing) the PSU (a Gaugemaster PA2) goes into overload mode, which is fair enough. But, this seems to cause one of my other engines to momentarily surge forward at full speed for a fraction of a second elsewhere else on the layout. It is not always the same engine but is usually one of two that seem to be susceptible. It doesn't seem to matter where on the layout there either. There is no commonality in the DCC chips installed in the engines as they include, Hattons, Hornby and DCC Concepts. I have looked at all my bus wire/ dropper connections and polarity and all seem to be fine.

I would be grateful if someone can give me any pointers as to the cause of the issue or what further checks I should be doing.

Many thanks

Bruce

Mod Note: All posts moved to the DCC forum area as this is a DCC item.

[Flashbang]

Hi
Its not stalling its stopping due to the short circuit the wheels are causing as the metal wheel is able to touch both rails of opposing polarity at the diamond crossing itself.

How to resolve...
A) Check problem locos wheel Back to Back distance and adjust as necessary.
B) Apply a coat of nail varnish to each rail tops at their closest position at the diamonds frog area. Only about 1mm of rail top is needed to be painted. The varnish will wear away quite quickly and will need retreating frequently and especially after any rail cleaning.
C) Drastic action, of carefully cutting away about 1mm of metal rail top at the diamonds frog and replace it with a small amount of Epoxy Resin. Once cured and hardened, file and trim the resin to match rail profile.

Your locos surging forwarded or occasionally taking off uncontrollably is caused by the short circuit creating a spike of power on the rails/DCC bus. The decoder "Sees" the spike as being a data signal and thinks the DCC full rail volts is a request to move at full speed.
Three methods to stop this are..
1) Turn Off DC operation in the locos decoders via CV29.
2) Fit Bus filters to the ends of the DCC bus wires - Filters are nothing more than a 120 to 150 Ohm 2 or 3 Watt resistor and a 0.1uF Ceramic capacitor in series. See link to item
3) Paint or open up the area of insulation at the diamonds frog areas as per B or C above.

[Bufferstop]

Exactly my thoughts Flashbang. Cure the cause not the symptom, quite a few locos still in production have a wider tyre width than is strictly necessary, if it weren't for the wheels being plated I'd suggest putting a slight chamfer on the culprit's wheels.

[Bigmet]

... what further checks I should be doing...

The well known 'coin test' on and around the diamond crossing. Really, your DCC system should trip the power immediately there is a short, and if it doesn't then there is probably too much impedance in that area of the layout, need to look at the bus to rail connections.

With the DCC system tripping whenever there is a short, you have to fix the problem which can be by the methods described, or by replacement of the track piece with a live crossing track piece which will not lead to such short circuits.

[brober]

Capacitors and resistors bought. Off to change CVs as well. Said to her indoors I want to paint my rails, can you lend me your nail varnish please? Won't say what she replied!!

Bruce

[Flashbang]

Hi
Pop into your local Pound shop and buy your own. Colour is of course your choice, dear! Ha ha

[brober]

Ok.... I have programmed all locos to CV29=2 (normal running and no DC operation) and fitted the bus end filters as suggested to both ends of my two bus wires. I have one bus to feed the outer twin loop tracks and another to feed the inner twin loop tracks). I still get phantom movements on some locos when an overload occurs, and not necessarily associated with the diamond crossing issue. A simple induced overload is employed to test the possible effects.

Any other thoughts as to why this is still occurring?

[Flashbang]

Hi
Why do you need two separate DCC rail bus circuits? Normally one pair of suitably sized wires act as the Bus pair, feeding everything track wise!

What exactly is meant by "Phantom Movements"? Is it just a small movement like a sort of shudder or does a loco take off uncontrollably?
Is it only one loco doing this or all on the tracks?

When a short circuit occurs the PA2 (Squared) should immediately shut down and its display show SvdA. If it doesn't shut down immediately your DCC Bus wiring is not correct. It is absolutely vital that the instant a short is applied across the rails anywhere on the layout the PA2 shuts down immediately.
To test this... Remove all locos from the tracks and turn on the PA2. It should start up correctly. Assuming it does, then take a coin and dab it on and off across the two running rails. The PA2 MUST shut down immediately. If it does shut down then reset the PA2 and try the coin test at other locations around the layout. With every test the PA2 must stop working immediately.
Any failure of the PA2 to trip out means there is a serious wiring problem. Possible causes can be undersized bus wires. Poor connection bus wire to dropper wire. Poor connection dropper wire to rails. All need to be investigated and corrected before using the layout again.

[brober]

I used two bus wires as I felt I could isolate any problems more easily and the layout I have, and its development, lent itself to that. I assume that there is no downside to having two buses? The bus wires are all 32/0.2 so I believe that that would not be the issue. All my droppers are 16/0.2 so again I don't think that would be a cause of the problem. All drapers are soldered to the rails so I believe that connection is fine and all droppers are correctly paired to their bus wire (i.e. red to red, black to black). Where I suspect I may have an issue is the connection of the dropper to the bus. I used Scotchlok connectors (which in retro was not the best way and one I would not use again) as I was not comfortable soldering below the baseboard working overhead and lying on my back. But to cause a short? Is that really likely when you are connecting sheathed wires together? I can certainly have a look over these connections and ensure they are not touching but to replace all these connections (and there may be in the order of 400 of them) with, say, terminal block connectors is not really practical IMO.

The "phantom movement" occurs when the short happens (and the PA2 displays "Ovld") and causes one of three locos (not always the same one) to surge forward for about 6". The PA2 shuts down all locos when in overload mode and therefore I believe it is working properly. When the short is removed the PA2 and all running locos resume as they had been running. It is not always the same loco nor is it a particular brand of decoder that seems to be a common factor.

It may be an issue I learn to live with until I can replace the Scotchlok connectors over time.

[Bufferstop]

If your DCC supply can withstand, without tripping, the sort of transient short circuits that can be generated by wheels passing through pointwork, it's an indication that your track and busbars have more than an ideal level of resistance. They need some extra current carrying capacity, this would convert the random behaviour into a trip and restart, which in turn points to the need to sort the problem that causes it, wheels shorting at the pointwork.

[Bigmet]

...Where I suspect I may have an issue is the connection of the dropper to the bus. I used Scotchlok connectors (which in retro was not the best way and one I would not use again) ...

Got a multimeter? With power off measure from all the rails of the diamond crossing to the relevant track output on the DCC system. Then compare from the rails of nearby track pieces to DCC system output. If impedance is significantly higher on the diamond, then that's relatively few connections to renew, or you might replace the diamond; or give it wire linkages between the rails that may well only be connected internally by flaky contact strips .

Story relating to the latter, many years ago took my DCC system and several early Heljan 47s I had decoder equipped for a friend, for a first DCC demo on his existing layout, all Hornby system 6 track. (He hadn't decided at that point which DCC system to purchase.) All went swimmingly, until the final lash up of all four 47's quickly melted the plastic base of the one diamond crossing on the layout, the only piece of pointwork on the section where the lash up was made up, caused by heating at the multiple contact points of the internal wiring. A combined effect of the 500mA + draw of each loco, and a layout with one feed per section, typical 'old time' DC wiring. Neither the diamond crossing or the wiring were designed to cope with this possibility.

[Bufferstop]

I've witnessed an 009 point blade start to glow red when it was feeding a short circuit about a metre away without drawing sufficient current to overload an H&M Powermaster. There should have been a substantial feed between the two but a failed solder joint left the poor little point blade to carry the lot.

02/08/21 Edited to insert the word "feed" in the last sentence,

[Peterm]

My solution would be to replace the diamond crossing with an electrofrog (live crossing) version with insulated rail joiners on all 8 rails and then feed it directly from the bus wires. Wiring these isn't as complicated as some people make out.

[brober]

I didn't think you get code 100 electrofrog crossings.

[brober]

I've had a look at flashbang's website. Is it really as simple as adding a few wires from the DCC bus to a dpdt switch and soldering a couple of wires to the diamond crossing frogs and a few additional IRJs? I would be happy to try that if it solved the issue.