Controlling Single Coil And Twin Coil Switch Machines

With SPST And DPDT Toggle Switches

Using Capacitor Discharge Type Supplies

  The circuits on this page allow single coil and twin coil switch machines to be controlled using SPST and DPDT toggle switches.

  The handle of the toggle switch and LEDs can be used to indicate the lined route of the turnout.

  The circuit uses a power supply that is capable of supplying most of the current needed for the switch machine as well as large capacitor. There is as little restriction as possible on how quickly C2 can be charged to the supply voltage.

  A 12 or 15 volt supply that can deliver 1 to 2 amps is used. The supply does not need to be regulated but its unloaded output voltage should not be greater than 15 volts.

  The voltage needed will depend on the power needed for reliable operation of a particular type and make of switch machine.

  The circuit uses one capacitor that common to all of the switch machines and a capacitor at each machine. The common capacitor is at least twice the value of the capacitor at the individual machines.

  The common capacitor arrangement makes economical use of the capacitors as only N+1 (or 2) capacitors are required. Any number of machines can be connected to the common capacitor and power supply.

  The capacitors only draw current when they are being charged. If indicator LEDs are added to the circuits they will create a constant load on the supply that may require the use of a larger power supply.

  The time of maximum current draw is when power is applied to the circuit. Because there can be many thousands of microfarads on a large layout, the power supply must be able to handle the current surge when power is applied to the circuit.

  There are two versions of the circuit; The first circuits are for single coil machines such as KATO and Rapido, The second group of circuits are for a twin coil switch machines.


Diodes In Toggle Switch Leads

  There are diodes in the leads going to the top terminals of the toggle switches in some schematics. These diodes may not be needed but have been included until this has been determined for certain.

  These diodes prevent the 2,200uF capacitors of machines that are in the NORMAL position from discharging backwards through their coils when another machine is changed from REVERSE to NORMAL. This could possibly throw or displace the machine that is not being thrown. LEDs connected directly to the coil circuit could also be damaged.


Single Coil Switch Machines

  Using DPDT switches allows the second pole to be used for frog power control or route indicator LEDs.


Single Coil Switch Machines - Multiple Locations

  The diode in the upper leg of the toggle switch prevents the 2,200uf capacitors from discharging and possibly throwing the machine when any other machine is set to the NORMAL position.

  Crossovers could have their coils connected in series.

With Indicator LEDs

  Route indicating LEDs can be added directly to the switch machine's coil circuit. This could be convenient for multiple location controls because it does not require using a SPST toggle switch pole.

  If many LEDs are used, their power consumption will have to be factored into the capacity of the power supply.




Twin Coil Switch Machines

  The diodes in series with the coils determine which coil receives current depending on the position of the toggle switch.

  The diode in the upper leg of the toggle switch prevents the 2,200uf capacitors from discharging and possibly throwing the machine when any other machine is set to the NORMAL position.

  Using DPDT switches allows the second pole to be used for frog power control or route indicator LEDs.

  Crossovers could have their coils connected in series.

Twin Coil Switch Machines - Multiple Locations

  The diode in the upper leg of the toggle switch prevents the 2,200uf capacitors from discharging and possibly throwing the machine when any other machine is set to the NORMAL position.

  With multiple location controls, the handle of the switch is no longer an accurate indication of the route selected. Also, a second set of contacts on the SPST switch cannot be used for signals or frog power.

  If many LEDs are used, their power consumption will have to be factored into the capacity of the power supply.



Multiple Locations With Realys

  Control from multiple locations prevents the use of extra toggle switch poles from being used to control frog power. This can be overcome buy adding a relay to the circuit.

  The relay is connected so that it is off when the turnout is in the positon that it is in most of the time. This is so that the relay uses the least power.

  The power supply voltage shown for these circuits is 15 volts, this will not harm a 12 volt relay.

  If many relays are used, their power consumption will have to be factored into the capacity of the power supply.


Capacitor Values

  The value of the capacitors in the circuits suggested values. Smaller values may work equally well for a particular switch motor. Turnouts for crossovers may need larger capacitors.

  Kato switch machines will throw reliably using 1,000uF capacitors at the machines.

  RailCrew and Atlas switch machines will throw reliably using 2,200uF capacitors at the machines.

  The schematics show 4,400 and 4,700 microfarad capacitor values. Two - 2,200uF capacitors in parallel can be used in place of both of these values.


Possible PCB Schematic

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Please Read Before Using These Circuit Ideas

  The explanations for the circuits on these pages cannot hope to cover every situation on every layout. For this reason be prepared to do some experimenting to get the results you want. This is especially true of circuits such as the "Across Track Infrared Detection" circuits and any other circuit that relies on other than direct electronic inputs, such as switches.

  If you use any of these circuit ideas, ask your parts supplier for a copy of the manufacturers data sheets for any components that you have not used before. These sheets contain a wealth of data and circuit design information that no electronic or print article could approach and will save time and perhaps damage to the components themselves. These data sheets can often be found on the web site of the device manufacturers.

  Although the circuits are functional the pages are not meant to be full descriptions of each circuit but rather as guides for adapting them for use by others. If you have any questions or comments please send them to the email address on the Circuit Index page.

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03 April, 2018