Bi Directional Crossing Gate
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Dale H
Joined: Sep 25, 2010
Topics: 32 Replies: 39
Topics: 32
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Usually a single relay will work (see my relay for block detection post) but someone on the other Forum asked for a more precise solution. Here is a hand drawn diagram using 3 relays and the outside insulated rail method
Above is a diagram of a crossing approach,the crossing being placed by IR2 (outside insulated rail 2) using 3 relays and 5 insulated outside rails. You can click on it to enlarge. Relay A is DPDT,the other 2 are SPDT. A separate transformer is used to power the relay coils which does not share a common with the track. Instead the minus of the bridge rectifier does. If the relay power transformer shares a common you could use a small bridge on each relay,but this way only 1 is needed. The 470 uf capacitor is connected across the + and - of the bridge in proper polarity. Diodes across the relay coils remove voltage spikes.
Outside insulated rails IR A and IR B are at least 1 train length from insulated rails 1 and 3 respectively in the loop on approach to the crossing. Relay A is self latching in series with its own NO (normally open) contacts and through Relay B NC (normally closed) contacts.
A train moving clockwise crosses IR A,the circuit is completed by the train wheels and Relay A latches energized. The second set of contacts on relay A connects IR1 and IR2 together and disconnects IR2 from IR3. The crossing gate relay connected to IR 2 is then energized by occupancy of IR1 or IR2 by the train wheels. The contacts of relay 2 switches the crossing gate (not drawn here for clarity but shown on my previous link). When the train clears block 2 the gates go up as relay 2 is de energized.
A train moving counter clockwise crosses IR B, de energizing relay A if it is electrically latched. IR2 and IR3 are connected and the gates are down when IR2 or IR3 are occupied,the circuit again being completed by the train wheels.
You are looking at about $25 in parts, plus shipping to do it.
For 12 VDC coils 10VAC input will work. For 24VDC coils 18VAC input will work.
IR A and IR B need only be 1 track section long each. IR1,2,and 3 can be made to suit the operating characteristics desired.
Dale H
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