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Points & Crossings
Points are all electrofrog, with frogs powered by a switch in the point motor. The centre two rails from the frog need to be isolated with nylon fishplates.
All points are operated remotely using point motors driven by DCC accessory decoders. Initially, SEEP PM-1 point motors have been used. These are solenoid motors with an integral switch for frog polarity.
The N gauge point tie bar doesn't move far. With the point motor mounted directly behind the 13mm thick baseboard, the point motor switch didn't move far enough for the switch to operate reliably: although its operating rod has some "sprint" to it, it just wasn't bending over a long enough length. The solution I've adopted is to mount the PM-1 motors on 10mm timber battens elow the baseboard to space them away from the track - now approx 23mm behind the base of the point. The spring rod then bends, allowing the solenoid armature & switch to move over its full length. The battens are pre-drilled with a 13mm hole, then glued underneath before the point motors are mounted.
Wiring to the SEEP motors has caused major grief. Initially I used 2.8x0.8mm push fit "tab" connectors, with a tab soldered onto the motor. Unfortunately, the force needed tp push the spade connector onto it breaks the PCB track. The next approach has been to drill the PCI with a 1mm hole; the tab connector is then an interference fit into the hole. It can be solvered and the excess cut off. HOWEVER it is bad if there is any excess at all on the "baseboard" side of the PCB. The final approach is solder flying leads to the point motors, and to used crimp "bullet" connectors.
Crossovers (i.e. a diamond crossing) need to be wired carefully. The crossing itself will have four dropper wires: one for each outer rail, and one for the frog at each end. The way power is applied to these depends on which route a train will be taking. There appear to be two commonly used approaches:
Apply constant power to the outer rails, and use an autoreverser to feed the frogs;
- Use a relay to switch the power depending on the setting of the point feeding the junction.
In my case, the crossovers are always on 2 track main lines with an adjacent point connected to the "crossing" route. In a real railway, this point would only be set to the crossing direction when the signalling system was about to let a train run through the crossing route; otherwise the point would be set to "straight on". When the crossing route was selected, a signal would prevent traffic on the other line reaching the crossing. My railway will have all of those constructs; consequently it is practical to use the point state to determine how the crossing is powered.
The key changes needed are to isolate the frog from the closure (inner) rails, and to wire the closure rails to the stock (outer) rails. The frog area is then electrically separate, and needs to be fed with switched power: it will no longer collect power via the point blades. The only difference I've made is to isolate the closure rails a bit further back from the frog: this reduces the likelihood of "back to back" shorts.
The quickest way to explain this is with pictures:
With a DC controlled layout, the track is electrically broken into sections. If a train derails on a point frog, then the controller limits the maximum current at around 1A or so. If the back edge of a wheel contacts the "wrong" rail while going through a point, the the controller may remove power momentarily, or may not even notice. In either event, power loss is to one zone only and the remainder of the layout will continue uninterrupted.