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Relay Types & Wiring

Relays are an important component of an LCOS layout. Relays are used for power management, such as for Master Power controls, cab selection on multi-cab DC layouts and for Reversing Loops. Relays are also used to run stall motor and coil motor turnouts. Relays are controlled by DNOU8 boards.

What is an LCOS Relay? #

In LCOS, a relay consists of an off-the-shelf 5 volt relay module, wired in a specific way.

The Physical Relay #

The physical relay, is a commonly available 5 volt “relay module” with an optocoupler circuit that allows a 5 volt microcontroller to control household current. This type of relay guarantees electrical isolation between the two sides of the circuit.

To use an off-the-shelf relay module, the trigger type must be set (by jumper on the relay) to LOW, and the IN trigger connections are attached to ports on DNOU8 boards. VCC and GROUND should be attached to layout +5volt and GND respectively. NC (Normally Closed), NO (Normally Open) and COM (Common) contacts are wired according to the application, as shown below.

single relay module
A typical single relay module. Inputs are +5v (DC+), GND (DC-) and IN. The jumper at the top determines if the relay is trigger by HIGH or LOW on IN. Move the jumper to set it to low trigger, then connect IN to a DNOU8 port.
A typical double relay module. The bottom left jumper is set correctly for LOW trigger. IN1 and IN2 connect to DNOU8 ports. This is the most common physical relay type used by LCOS.
5 volt relay modules also come in 4’s and 8’s, which you would generally use as “gangs” or “banks” of double relays. The connections are the same except there are more of them. Attach this module to a DNOU8 board for a high density relay solution.

Logical Relay Types and How They Are Wired #

LCOS uses physical relays, wiring and coding to synthesize several different relay types out of basic single and double relay modules. The available switching types are a mix of conventional and specialized relays:

1. Standard SPDT

SPDT Wiring
Two common ways to use an SPDT relay. Note that connection layouts can vary from relay module to relay module.

2. Standard DPDT

This is a DPDT relay wired as a reversing relay. This type of relay, wired for polarity reversal, is also used to control stall motor (Circuitron Tortoise; SwitchMaster) turnout motors.
Another common use for DPDT relays is for Cab control.

3. D3DT – This relay emulates a center off, DPDT momentary switch. It was specifically developed to control two-wire coil turnout motors (Kato, Atlas, etc.). The logical relay is composed of a double relay module, wired for tri-state (ON – OFF – ON) operation. The diagram below includes a recommended 1000μf capacitor when used for turnout control.

The NC contact on both relays is connected to Ground. Activating one relay, or the other, selects that relay’s output for VCC (leaving the other relay inactive and set to GROUND), activating the coil. The energy stored in the capacitor is enough to run the turnout motor when discharged.

4. SPDT BREAK-MAKE – This is a compound relay that breaks the circuit before switching between input poles. Use this relay to select one of two inputs, then energize the circuit. This type of relay can be linked to turnouts for providing a power feed to turnout frogs; the break before make feature prevents inadvertent short circuits.

5. SPDT SELECT-ENERGIZE – This is a compound relay similar to the SPDT BREAK-MAKE, except it has an output select instead of an input select. Use this relay to select one of two outputs then energize the circuit. This relay type is used to run 3-wire coil turnout motors (Atlas snap-track, Peco, etc.). NOTE: The common wire from each turnout motor should be connected to layout GROUND.

When using this relay for 3-wire turnout motor, include a 1000µf electrolytic capacitor on the INPUT side of the circuit.

Using Relays with Turnouts #

Relays are used to run coil motor and stall motor (Circuitron Tortoise; SwitchMaster) turnouts. Note that double relays require two DNOU8 ports. When setting up relays in the Configurator, “port 1” should be the port connected to IN1, or the bottom relay. “Port 2” should be the port connected to IN2, the top relay.

Below are the three most common wiring scenarios:

The Circuitron Tortoisetm is a popular turnout motor. It is easily controlled via a DPDT relay.
2 wire coil motors used in Kato Unitrack require a D3DT relay, which emulates a center-off, momentary DPDT switch. The capacitor buffers the current needed to run the motor.
Atlas 3-wire coil motors can be run with DC or AC current. This circuit is for DC use ONLY; the capacitor buffers the current needed to operate the coils.

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