CLINIC - Points (turnouts) variations
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The ultimate points, block & reverse loop wiring. |
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The simple set of points, one that you might make by soldering the rails to PCB sleepers,
will have these components:- Stock rails on the outsides. Moving Blade rails, hinged to the Closure rails and joined by the Tie-bar, which is insulated from the Stock rails and the Blade rails. A Frog, the sharp point, where the sets of rails cross over and Frog rails at the exit (heel) end. Guard rails to guide the wheels away from the point of the Frog and prevent derailing. The Closure and Frog rails are electrically joined, so the track power from the blades through the hinges is present on both Frog rails. |  |
| Points or Turnouts or Switches |
The simple point (from Shinohara and typical of a handmade point) is called a power switching point.
It does not supply power to the unselected track but puts a short circuit across the rails.
Can be identified by having no insulation across the frog area. It needs a
large gap at the blade rail to stop the wheel backs shorting on the unused
blade which has the opposite voltage on it.
This point is of most use in Yards or on a siding where the power needs to be controlled and loco's can be parked, unpowered.
Power at the red arrow can flow through all the joined rails and through to the frog,
the oppposing track's rails are both at the same voltage
When the blades are in the other position power (red) can only flow in the stock
rail and all the other rails are at the black arrow power level.
The danger point is at the unused blade rail where the wheel back or a
derailment can short out one power source to the other.
There is another problem that can develope with time. Dirt getting between the blade and the stock rail it should contact prevents power from getting along it to the frog. Also the hinge, which is usually a rubbing contact, can also stop or impede the power flow.
The all live point is used on a main line. It maintains power to all tracks.
Insulated at the frog and throw-bar, it has internal jumpers
round the frog to direct the power. An actuating switch or relay is needed to
route power to the frog. In the diagram the wire jumpers are shown in red and
black. Note that the open blade is at the same power level as the stock rail next to it now.
What is available over the counter. Most are a variation of the above.
Click here to see Electrical connections of various points.
Peco (English) Insulfrog type has a completely insulated (plastic) frog area and internal jumpers to route the power to the frog rails. Trains can stop over the frog and not be able to get power (an 0-4-0 is bad) if their pickups are not clean or the track uneven. The blade to stock rail is a wiping contact although springs in the tie-bar hold it firmly against the rail in either position. Blade to stock shorts can occur as it is the 'Simple' type of blade connection.
Bachmann Insulfrog has an insulated (plastic) frog and frog rail jumpers but also includes the stock rail to blade electrical tie so it wont short out the power. This makes it an 'All Alive' type without the need for a switch to supply the frog's power.
Peco's Electrofrog are a power switching type with an all powered frog, it is better as it gives more reliable slow speed pickup through the points area. The blade to stock rail is asisted by springs in the tie-bar and blade to stock shorts can occur as it is the 'Simple' type.
Peco Streamline Electrofrog points have powered frogs and the frog rail jumpers. The latest set of these I received has a different jumper that joins all closures and frog rails. The earlier one has three sets of jumpers but it is not possible to convert to an 'All Live' type by rewiring as the frog rails are connected internally at the point.
DCC safe points.
These have to be similar to the 'All Live' type with adjacent blade and stock rail at the same power. Peco points can be modified readily with some cutting and soldering to make them DCC safe.
To
modify, cut the closure rails about 20mm forward from the frog point but do not
cut through the plastic underneath (use a cut-off wheel) Solder a flexible wire
on the underside of the rails from the blade to the closure (across the hinge) and
out to the stock rail. Some plastic sleepers can be cut to get easier access to the rail
undersides. The frog has to be
power switched by a switch (physically connected to the tie-bar) or a relay that would also operate
the points motor. Switching is normally done at the same time as the points are
moved.
Click here for photos of a modified Peco point.
Precautions. Short circuits can damage your points, current flows can quickly heat up the wires, hinges etc. Some 'Switch Machines' do not have electrical contacts that can withstand the full short circuit current...check. Use a 21 or 35 watt car light bulb in the power lead to the frog to limit the current. This wont protect 'light' electrical contacts but it sure shows you where the short is. Driving onto a reversed point is the usual way a short is generated, when the first set of wheels crosses the gap, this puts the full short current through the loco power pickups and can cook these too so they lose their spring.
To be double safe on the DCC layout I have used a double pole switch/relay to also cut power to the stock rail past the points so that a wrong-way entry will stop the loco before the power shorts.
3 Way Peco Electrofrog are not power switching types and will require switches actuated by the throwbars to direct the correct power to the frog rails.
The Ultimate Points and Reverse-loop wiring.
Points wired as described will give you:-
- Assured power to the Blade rail
- Good contact across the blade hinge point
- Correct power to the frog
- Blade rails at a safe polarity
- Power control if you enter a reversed point
- A controlled slow down and stop
- Reverse loop control without special boosters etc.
Most points motors (except Peco) provide a two pole change-over switch. This can be used for the simple DC Safe power routing. If you have Peco actuators or hand made points you will need to have a relay actuated by the tie-bar position (or Tortoise switches) to give you the two pole change-over contacts. If a reverse section is also included then a three pole change-over relay will be needed.
You could of course be using a manually actuated slide switch connected to the tie bar and so would have the necessary two or three switch poles in the slide switch..
The Ultimate-Ultimate DCC electrical operation would have a relay for each point plus a change over relay for each signalling block so thay if a train is required to be stopped for a Red signal then the track power can be switched from DCC to a DC voltage that will allow the train to coast to a halt. CV 29 and the decoder would need to implement analog control and the DC be at a low voltage to allow the Deceleration to a stop.
If you also have signalling then at least one change-over switch is required for this.
So what do you get for all this? A DCC (and DC) safe layout with minumal possibilities of short circuits through accidental derailments, reversed points etc causing a power cut to all your locos. And of course you would not get the Dong from the Digitrax controller because of a short.