SMD84 - Switch Machine Driver Application Information

Solenoid Type Switch Machines:
The SMD84 will drive the following switch machines:

  • Atlas HO snap
  • NJI
  • Peco PL-10 "black"
  • Peco PL-11
  • Rix Twin Coil
  • Hammat & Morgan Twin Coil
The SMD84 will not drive two wire Kato switch machines.

There are several factors that can contribute to poor "sluggish" performance. A few include electrical connections at the driver and the machine, size and length of wire used for connection and mechanical linkage from machine to switch. If you are having problems check these areas.

In some cases the SMD84 may be able to drive two machines connected in parallel for a cross over application. Experimentation is required to determine if it will work. It depends on the type of machine and the linkage.

The Rix twin coil machine requires tension on the swing arm to keep the internal weight from bouncing off its end stop when the pulse of power is applied. Operating the machine without tension on the arm gives the impression that it is not working correctly.

Wiring:
The common on a board should not be connected to another boards common. Commons of a single board can be connected together but not between boards. Doing so may cause a problem.

Wire size recommendations are as follows: If you use the 26 gauge wire try to keep the wire length to each switch machine to under 12 feet. With 24 gauge you should stay under 18 feet. With larger size wire you can have longer wire lengths.

Current Budget:
Current numbers based on a track voltage of 14.5 volts. They are typical values and will vary with track voltage and between SMD84.

Solenoid operation:
Static state or idle:  13 to 15 ma
Solenoid activated: Pulse to change CDU starts  at 300 ma and rapidly (about 3 seconds) reduces to static level.

Tortoise™ operation:
Static state or idle: Output configuration (1) with 8 tortoise  320 ma
Tortoise activated: Output configuration (1) with 8 tortoise, slightly less than 320 ma while tortoise is moving
Static state or idle: Output configuration (2) with 8 tortoise  13 to 15 ma
Tortoise activated: Output configuration (2) with 8 tortoise  50 to 52 ma

Slow Motion "Stall" Type Switch Machines:
The SMD84 will drive the following switch machines:
  • Tortoise™
The SMD84 will not drive SwitchMaster, Scale Shops, Switch Tender, Cobalt, Hoffmann or Fulgurex motors. This is due to the internal impedance of the SMD84 output driver when configured for stall motor. Note: 1/22/15 the Cobalt iP Analog has a much lower current requirement and should work oK.

Caution: Slow motion does not necessarily mean stall. A stall motor means it can stall (stop moving with power applied) and not draw a lot of current. The Tortoise™ is sort of the "standard". The Cobalt requires ~ twice as much current as the Tortoise™.

Turnout state indication and frog power:
Sometimes it is desirable to show switch state and route power to a turnout frog. The SMD84 has no provision for this since it adds extra cost for features that are best implemented elsewhere. Switch machines that have contacts can be used to control LED indicators and/or route power to a turnout frog. Examples of this are Tortoise™, NJE and Altas deluxe under table. Peco has an accessory switch that mounts to the switch machine.

Known issues:
Version 1 (V1) of the manual in section 3 "Smart" Programming and 6.1 Example of "Smart" Programming incorrectly state that if using section 1 of the table to program the output configurations are unchanged. In fact, the output configuration is programmed based on the close or throw command. Version 2 (V2) of the manual corrects this error and can be downloaded from the SMD84 product page.