I have a bjiou promlem-ette with some Peco diamond crossings. The way they are built, there is an exposed rail-end of opposite polarity to the adjacent rail such that if the back of the wheel touches it, a short occurs. But the other end, where the adjacent rails are of the same polarity, is insulated! Two crossings (different angles) are both the same. Since the crossovers are nowhere near a point and I use DCC (so don't have isolated sections of track) this is a bit tedious.
Obviously I can fix it simply by filing back slightly and adding a thin insulating piece over the rail-end, but why is it done that way? Simply reversing the insulated and exposed ends would solve the problem completely.
Noticed the exact same thing on my crossovers. No idea why it is this way except maybe the wiring is simpler and there should only be a small short if any at all!! I'm gonna modify the wiring on mine and fit a relay so that any points facing the crossover will cause the two offending rails for each direction to be isolated when the trains are travelling in that direction. The wiring provided underneath the crossover should provide all the connection I need but I'll snip a few of the interconnections.
So just turn the crossing around - the angle will be a little larger, but who will notice? Slightly more seriously, you need to isolate both routes and apply one of those automatic revewrsing loop thingies they make for DCC or power both blocks from their nearest turnouts and utilize a diode matrix so that both routes can't be selected at the same time.
I'm sorry about getting heavy about this, but other people have been going on about correct railway terminology (see threads about "frogs") so :
Please do not use the word "crossover" to refer to a diamond crossing. A diamond crossing is not a crossover. A crossover is two points (turnouts, switches) in a double track arranged so as to cross the train over from one track to the other.
I've come to the conclusion that messrs. Peco have designed these on the assumption that the crossing lines will have opposite polarity (not unreasonable). I will be cutting back the exposed rail slightly and laying in an insulator, and painting the insulated section in the middle with conducting paint to reduce stalling on the crossing. I really don't want to get into special wiring just for a couple of crossings when the rest of the wiring is so simple.
I am not sure how well diode matrices work with DCC. I was under the impression that they tended to cause problems, is that not right?
I imagine that would be the way most (British) modellers would use them.
By simplifying wiring in that manner, you're restricting current collection in a fairly major manner, in that you will have; _dead frog, insulated rail join - insulated rail join - insulated frog in quick succession.
If you're driving turnout motors with DCC decoders that will not allow a separate power supply then diode matrixes probably will cause problems, but most accessory decoders now allow a separate supply. Otherwise there is no difference. I've had diode matrixes in use for 25 years using IN4001 diodes driving Peco and H&M motors and never had a failure.
I assume you mean a 'scissors cross-over? Pilz make a nice one, but all wired as a single unit. (it took ages to isolate the two main lines)^: (57mm spacing) The problem with a preassembled one is that not everyone uses the same track spacing, particularly in stations where platforms are likely to be involved.
Yes, maybe. All my track has the same polarity because it was wired for DCC from the outset.
Er, what? No insulated rail joins at all on my crossing. Cross porpoises? This is a diamond crossing (SL84), not a crossover as per the subject (as John picked me up on below).
No, my point motors are all supplied separately via passing-contact switches, I don't use DCC to drive them. Partly because of the cost and partly because it amuses me to build the faux frames. DCC is only on the track.
I do the same thing for analogue. I haven't yet used a diamond crossing where I've encountered a polarity problem.
Sure, but why power the conflicting track? You can't run two trains across a diamond crossing at once and unless your layout consists of two independent, overlapping circles you must have turnouts somewhere.
OK, so capacitor discharge units are indicated and why operate every point turnout individually when you could operate routes?
A simple example: With a three way turnout you have three possible routes but four solenoids - why provide four buttons/ passing contact switches which have to be pressed in the right order when three buttons will do the job without the complication of sequence? If you add another turnout beyond the three way you have six solenoids/six buttons but only four possible routes.
My layout has two loops and some branches, all connected by various points, and all permanently powered with the same polarity. There are no isolating sections anywhere, no relays, no microswitches, and the only insulating joiners are on electrofrog points. Oh, wait, there is one isolated section - the programming track. That can be switched in and out of the main circuit (so you can drive a loco in, switch a DPDT switch and program the decoder). It also acts as a loco siding.
The nearest points on one of the tracks are just under 8ft away and on the other there is a set 6ft away and another set 14ft away. In between is a station. If I isolated the crossing I could not run a train across the main line behind another train which was pulling out of the station away from it (or indeed move it within the station). Maybe that would be verboten on the prototype anyway, I don't know.
I never even considered doing it any other way. Maybe I should have, but I didn't. Every joiner (except the insulating ones) has a drop cable soldered to it, and they are all wired to one of a number of
2.5mm^2 busbars underneath, all of which are connected back to the Lenz DCC controller. There is no detectable volt drop anywhere on the layout, which was one of my key goals since my old layout (which used mainly the track to conduct the electrickery) was prone to volt drop in several places despite only being 12ft square. So there it is.
The two crossings are the only place where I have a problem thus far.
It's always possible to change wiring. My concern is that you will end up with a lot of non-conducting rail in a short length. Many short wheelbase locos get hung up on dead frogs, hence Peco offer the live variety, but two dead frogs and two dead sections of rail taken at slow speed in the station area is asking "what the limit is".
A track crossing the main line is going to be signalled - use the signals to switch the power from main-line to branch.
Phil: You are forgetting 2 things: 1: The Kiss principle - Keep it Simple 2: Not all layouts use physical signalling - for which the prototype is Radio Tokenloess Block Signalling or 1 engine in steam Just because its in this uk model rail group does not mean it is following BR Mainline (or Railtrack!) practices
Switching the supply ineccessarilly is introducing a possible point of failure - multiple current collection from locos is a better solution, and so would buying an alternative make of fcrossing with a slightly larger than Peco's - to no real detrimiment - only benefit.
Power should also be maintained on all sections to maintain coach lighting. REMEMBER that 'power o the 2 rail track' is NOT prototype practice - it is a modelling convenience.
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