Posted By Les on 22 Aug 2009 06:09 PM
2 questions: Does it really take that many relays for a common reversing loop? I'm tired, not grasping exacty what I'm seeing. And it's automatic? (For DC track).
Why is this screen so huge I've got to horizontal scroll like, 3 feet to see all of it? That's kinda hard, y'know?
Lizard Bash Loop Control
The included diagram uses five relays to automatically control the polarity of both the loop and main line. While all relays are shown as 4pole double throw (4pdt), not all of the poles are used on every relay. Furthermore, Relay 4 is redundant to Relay 3, but is necessary for a fifth pole on that relay. If a 5pdt (or more) relay is obtained, Relay 3 may be replaced and the pole contacts on Relay 4 may be shifted to Relay 3 alleviating the need for Relay 4.
As illustrated, the relays use 6 volts. But any voltage relays may be used, so long as the proper voltage is used to trigger them. The voltage connections that power the relay coils are shown in red while the current that goes to the tracks is in black. The Power Pack represents the power supply that actually runs the trains. The two Reed Switches are Normally Open (N/O). The Turn Out Toggle (TOT) represents the toggle switch that would be on the control panel used to activate an LGB turnout motor (or equivalent). We’ll use a double pole double throw (dpdt) switch that is off in the center position and spring loaded to return to the center. We’ll use one half of the switch (left blank in the diagram) to activate the turnout (assuming a common ground). The other half of the dpdt switch will activate the Lizard Bash Loop Control (LBLC).
Follow along the diagram as you take a ride through the loop and see what happens.
On our first trip, we’ll proceed from left to right (clockwise) going through the “straight section” of the turnout.
Current flows from the power pack through Relay 1, Pole 3 and 4 (counting up from the bottom of the diagram) (R1P3 and R1P4) to the main line so the train has power. It then flows from the track (would actually be from R1P3 and R1P4 but this is more intuitive and serves for illustration purposes), through R3P3 and R3P4 to the loop so the train has power when it enters the loop.
The operator toggles the turnout pushing the switch down. Voltage is applied to Relay 5 pulling down the armature. R5P1 is pulled down. Because no voltage is flowing to pole 1, nothing happens. (That’s OK at this point.) The train proceeds and first encounters Reed Switch 1 (RS1). The magnet closes the reed and voltage flows to R3P2. Because the circuit is open at this point, nothing happens and the reed switch is ignored.
The train continues on and encounters RS2. The magnet closes the reed and voltage flows to R3P2. From there it continues on to R1P2, firing Relay 1. When Relay 1 fires, it reverses the current to the main line. But that then reverses the current to the loop and if left like this, the train would go backward before it reaches the main line again. (More on this in a moment.) When Relay 1 fires it also completes the circuit so that voltage flows through R1P1. This voltage continues on through R2P1, and back to the Relay 1 coil. This then makes Relay 1 stay “fired” (keeping the current to the main line reversed) even after the train clears the Reed Switch.
As noted, when the current to the main line is reversed, it also reverses the current to the loop and the train would go backward when triggering RS2. As such, when the train passes over RS2 firing Relay 1, it also fires Relays 3 and 4 through R4P1. Relay 3 then reverses the current to the loop at the same time Relay 1 reverses the current to the main line. So the current to the loop is reversed and reversed again and stays as it was before the train passed over the reed switch. When Relay 3 fires it pulls R3P1 completing that circuit. Voltage flows thought R3P1, then though R5P1 keeping Relays 3 and 4 fired after the train clears the reed switch.
At this point, the control of the turnout points can be accommodated though this circuitry (with some modification), can be controlled using the typical LGB circuitry (adding the appropriate reed switch to activate the turnout) but without the bother of polarity control), or the train can simply “push the points” into position as the train transitions out of the loop onto the main line and pulls away.
So the train pulls away and takes care of business later to return to the loop. The turnout points are still where they were when the train left, either because they were fired by circuitry or because the wheels simply pushed them over. If left unattended, the train proceeds through the loop, this time in a counter clockwise direction through the curved leg of the turnout and first encounters RS2. Voltage flows though the reed switch to R3P2. But the relay is still in its active state and the voltage comes to an unconnected relay contact, and the Reed Switch is ignored. The train proceeds on and encounters RS1. Voltage flows again to R3P2 and this time passes through the relay on to R1P2. Relay 1 is also still energized, and the voltage passes through R1P2 and fires Relay 2. When Relay 2 fires, R2P1 opens interrupting the voltage that has been holding Relay 1 open and Relay 1 closes. This then reverses the current to the mainline.
Again, the mainline feeds the loop and to keep the train from going backward before reaching the main line, the voltage from RS2 passes through R3P2 to R4P1 (that is still in a fired position along with Relay 3) to the coil on Relay 5. This fires Relay 5 that removes the voltage that holds Relays 3 and 4 open. Relays 3 and 4 then reverse simultaneous with the main line and the current from the main line and loop are again in sync.
This will go on repeatedly with trains alternating clockwise/counterclockwise as infinitum without intervention. If the user decides to alter this natural rhythm, he can do so by toggling the turnout. This resets the relays to whatever “state” is selected through the Turn Out Toggle (TOT) also used to activate the turnout. When the TOT is pushed down it sends voltage to the Relay 5 coil pulling the armature that breaks the circuit through R5P1 holding Relays 3 and 4 open and they revert to the original clockwise direction relative to the main line. When the TOT is pushed up, it fires Relays 3 and 4 to the counterclockwise direction relative to the main line and they will latch in that position by sending voltage through R3P1 followed by R5P1.
That’s it in a nutshell. Enjoy.