How to Fixing the Shorting Problem of a 3 way Shinohara Turnoutgreenspun.com : LUSENET : Wiring for DCC : One Thread
The article below references a diagram which I could not figure out how to attach. I hope you can figure out what I am saying without the diagram. If you want a copy of the diagram, let me know and I will send it to you.
The Shinohara 3-Way turnout is a mechanically beautiful turnout but a wiring nightmare. I wanted to use this turnout on my layout with two DPDT switches to control the direction of the points and two sets of bi-color LEDs on my control panel. Bi-color LEDs change from green to red depending on the direction of current flow through the LED. This provides a quick check on the direction of the switch which can be seen from across the room. Unfortunately, wiring the Shinohara 3-Way turnout so that it does short out and shut down the layout proved to be a challenge.
The turnout, as purchased, contains three gaps which are identified as A, B, and C on the attached diagram. Gaps A and B are easily located because they are black plastic about 1/8 long. Gap C is difficult to spot without a multi-meter. The gap is actually in the frog itself. The fourth gap D [across the inner points] does not exist in the turnout as purchased but is required to overcome shorting.
First, lets talk about gaps A, B, and C as the turnout is delivered. Gaps A and C are unnecessary since the polarity across these gaps never needs to change as will be shown in the attached diagrams. This will be explained later. Gap B is a false gap in that continuity across this gap can be traced through the frog to the right of gap B and the brass bar across the inner set of points. This brass bar is soldered to the two points and the attached to the throw-bar with a grommet.
Well, how do we solve this problem. Andy Sperandeos book, Easy Model Railroad Wiring has a wiring diagram of a 3-Way turnout (Figure 3-18) which states that only one gap is required. This is actually not true. Two gaps are required. The first gap is labeled B in my figure. The second is across the inner points, labeled D in my diagram. In fact, Andy shows this gap in his figure but does not discuss it or point it out. Since the polarity of the points is different across the inner points, a gap is required.
Now lets assume we cut the gap D across the inner points. I did this by drilling, taping and inserting a small screw through the brass bar across the points and into the plastic throwbar below. Next I cut a gap across the brass bar between the screw and the grommet, then glued in a piece of styrene to insure the gap never closed.
The best way to discuss why gap D is required is to review the four positions of the turnout. Please realize the two sets of points can create four sets of conditions, and wiring problems, for the turnout: 1. Down-Down, 2. Down-Up, 3. Up-Up, and 4. Up-Down. Wire the turnout as shown in the diagrams. Please realize the wire from the outer set of turnout points has to be wired to two blocks of track. This is due to the unneeded gap A.
1. Down-Down Route to Track 1: Every track but the upper (left) track is red in this condition. Prove this to yourself by tracing each wire or track until you hit a gap. 2. Down-Up Route to Track 2: This is where gaps B and D become important. The points across the gap D brass bar have opposite polarity. 3. Up-Up Route to Track 3: In this state, all the tracks are black except the bottom rail leading into Track 3. 4. Up-Down Route to Track 3 with Inner Points miss-thrown: This condition can easily happen if a train is coming in from Track 1, reverses and goes out through Track 3. If gap D was not in place, a short would occur. This fourth condition is the main reason for cutting the gap at D. If you never throw the points into this condition, it is possible to wire the turnout as purchased and never have a short. For instance, a 3-position rotary switch could be used which would never allow this condition to occur. Unfortunately, it is very difficult to find a rotary switch that will work.
Another approach is to use a set of diodes to control current flow and never allow the inner points to be thrown in the down position when the out points are in the upper position. Using diodes to control the color of the LEDs also started blowing my mind. This seemed like a very complicated, and expensive, approach to overcoming the short.
The cheapest and easiest approach was to cut the gap at D, use two DPDT switches to control the points, and wire in the LEDs as normal. The loose end of the brass bar connecting the points at D can be screwed down to the moving cross tie.
A few additional observations from these four conditions.
1. The polarity of the gaps A and C never change across the gaps. This means the gaps are unnecessary. 2. The wire feed from the outer points has to be soldered to two rails because of gap A. That is, the frog, surrounded by gaps A, B, and C needs to have a power lead as well as the frog in the lower right of the diagrams. 3. Gap B is useless unless gap D is cut.
Of course, Shinohara could easily solve this problem by redesigning the turnout as discussed.
-- Didrik Voss (firstname.lastname@example.org), June 16, 2003