Help needed with a phantom short

[Marcyg]

Hi all, really hoping someone has an ideas about this as I been struggling with it for a while. I seem to have a short circuit that comes and goes. The layout is powered by an NCE SB5, to which 4 EB1 circuit breakers are fitted. A DCC bus (twisted pair) then goes round to the back of the layout, to 2 Tam Vally Depot boosters, which control the fiddle yard through 5 EB1 circuit breakers. The points are controlled through Megapoints system, but this fault happens whether its powered up or shut off. The points on the scenic side are electrofrogs, with Gaugemaster auto frog switches underneath.  When it started, trains would randomly cause a short on the fast lines, circuit breaker 1 on the scenic side. At first I thought it was specific models, namely ones with TTS chips, but after some testing, its not that. I have Lenz, ESU, TTS, Lais and Hattons chips, and all can randomly be effected. Then I looked at the circuit breakers, swapped them over, changed which line they control, nope, not that either. I run a lot of older Lima stuff, so could the wheels be shorting the points? Nope, trains were cutting out on plain track too. By now the problem has migrated to the releif lines, which are on a different circuit breaker. The short is almost acting like a trickle short, it builds and builds until it trips. Some research I found the EB1s have a ridiculously short trip time, sound locos on start up can cause the factory set trip to time out , so I set them to a longer trip time. All the while, the short is coming and going randomly. Had some friends over and we had up to 8 trains running at one time for 6 hours, no trip, then it would all of a sudden act up for no reason. Then it would go away again. The other night, the problem seemed to manifest itself on the fiddle yard too as well as the scenic side. I by-passed the circuit breakers and everything run fine. No cut outs, but no gene smoke either from anything shorting out. I used to have termintion filters on the ends of each bus, as the layout is 45ft, there are sopme long runs, but a rebuild saw some of those disappear. I cant remember if these had an effect on it or not...  Im completly stumped and its driving me mad! Any help would be greatly appreciated.

[Dagworth]

Is it the EB1s tripping? I had a pair of EB3s on Ravensclyffe and found that any double power bogied loco (eg Hornby 86s fitted with two power bogies) would cause them to trip out for no reason. In the end I scrapped them and the layout has run fine since.

 

Andi

Edited November 18, 2020 by Dagworth

[Marcyg]

Yes it’s the EB1s tripping. At first it seemed to only be sound HSTs, so thought it was the draw of 2 chips. But now it’s single locos too. I’d love to do away with the EB1s but I fear I’d melt something

[Dagworth]

I'd bypass them permanently, or replace them with switches to help with fault tracing. Once done then make sure that a coin test at the furthest extremities shuts down the DCC system immediately. Once you've done that then go back to playing trains.

 

Andi

[Marcyg]

Does the SB5 have built in protection then?

[Dagworth]

4 minutes ago, Marcyg said:

Does the SB5 have built in protection then?

My reading of the SB5 manual says that the P514 power unit supplied with the SB5 has the short circuit protection. 

 

The manual also suggests using car tail light bulbs as short circuit protection on the SB5 outputs!

 

Andi

SB5 Manual.pdf

[ISW]

4 hours ago, Marcyg said:

Im completly stumped and its driving me mad! Any help would be greatly appreciated.

This has all the hallmarks of a lose wire or stray strand of wire somewhere. I'd be looking over all the wires to/from the layout that are capable of movement for such things. Chocolate blocks are a common source of stray strands of wire. Normally, you'd isolate part(s) of the layout to try and narrow the search down, but from your descriptions it's so illusive that probably wouldn't work, or would take forever.

You may also want to look over the short-circuit detectors for any stray wires or potential for shorting by other nearly wires, including any excessive flux (I had a short on my layout and I found it was a short caused by me not cleaning off the flux properly after soldering some components to a piece of stripboard).

 

Ian

[Marcyg]

12 hours ago, ISW said:

This has all the hallmarks of a lose wire or stray strand of wire somewhere. I'd be looking over all the wires to/from the layout that are capable of movement for such things. Chocolate blocks are a common source of stray strands of wire. Normally, you'd isolate part(s) of the layout to try and narrow the search down, but from your descriptions it's so illusive that probably wouldn't work, or would take forever.

You may also want to look over the short-circuit detectors for any stray wires or potential for shorting by other nearly wires, including any excessive flux (I had a short on my layout and I found it was a short caused by me not cleaning off the flux properly after soldering some components to a piece of stripboard).

 

Ian

I tend to agree, it’s just finding it. At least with DC a multimeter could be used, DCC is a little more complicated...

[ISW]

6 hours ago, Marcyg said:

I tend to agree, it’s just finding it. At least with DC a multimeter could be used, DCC is a little more complicated...

Given its illusive behaviour I doubt whether a multimeter will ever find your short. That's why I concentrated on a 'physical' examination of the cabling, using a magnifying glass if necessary. Start at 'any' wires that show visible wire strands (ie: the sheath is not 100% coverage at the termination point).

 

Ian

[Dagworth]

I don't believe you have a wiring fault causing a short at all, if you did it would stay in the same place. I think it is simply the EB1s being temperamental.

 

What hasn't been mentioned is the action taken to clear the short from the EB1s, is it just a case of killing global track power from the hand set for a few seconds and then restoring and it all comes back as normal?

 

Andi

Edited November 19, 2020 by Dagworth

[Marcyg]

22 hours ago, Dagworth said:

I don't believe you have a wiring fault causing a short at all, if you did it would stay in the same place. I think it is simply the EB1s being temperamental.

 

What hasn't been mentioned is the action taken to clear the short from the EB1s, is it just a case of killing global track power from the hand set for a few seconds and then restoring and it all comes back as normal?

 

Andi

I don’t do anything, it clears itself. The effected train stops, usually only one EB1 trips. Trains sits there for a second, then starts again, moves several feet, then stops, restarts and away it goes. 

[Dagworth]

That’s definitely not a symptom of a wiring fault. I really am convinced it’s the EB1s themselves, especially after my own experiences with the EB3s tripping spuriously when we’ll within the current rating. 
 

Andi