Wednesday, November 13, 2013

Constructing Santa Rosalia – switch machines

As I’ve indicated in my previous post about the staging underneath Santa Rosalia, it is switched with twin-coil switch machines. (You can read that post at: .) I have powered these (and all my present and future twin-coils) with a capacitor discharge unit. These give very positive action and can power entire ladders with a single button push, a capability I used with success on my layout in Pittsburgh.
     The particular hardware I used is from Tri-Delt Electronics. It is basically a very large capacitor, married to a 24 V transformer. The Tri-Delt instructions below show how simple the circuit is, to power switch machines.

Here is how the equipment looks, as installed under my layout near Ballard. I follow their advice and use a single wire, usually orange or red, to be the positive “switch machine common” to all machines. Then the other, negative half of the circuit, which I often make a black wire, is the control side, connecting to the switch machines themselves through push buttons, SPDT switches, etc.

     Shown below is the way I usually arrange my controls, with this set-up for each switch machine. I like the SPDT switch to indicate how the turnout is thrown. Setting that switch is followed by pushing the button located next to the switch, giving a decisive action. An operator approaching a turnout can check the panel to see if the SPDT indicates the routing he wants, and can double-check by pushing the button, even if the indication looks right.

     This is, of course, analogous to the way CTC machines are arranged: the routing or signaling is set up with levers, then everything is activated at once with a push button. In staging yards, of which I had several on my Pittsburgh layout, I had arranged a diode matrix for each, so that you could select the track you wanted with a rotary switch, then throw all the needed turnouts by pushing one button. The Tri-Delt capacitor can easily throw five twin-coil machines at once.
     I made a simple panel to control the switches for Santa Rosalia staging, using the method I’ve used before: paint a Masonite panel yellow, then use tape to lay out the desired track diagram, and overspray flat black. With that completed, and the holes drilled for the switches and buttons, it looked like this.

With this part complete, I proceeded to install switches and buttons, and wire everything. The last preparation step was to add labels, using the same procedure I used with the previous control panel I discussed (see it at: ).
     I installed the panel on the Shumala side of the layout, from which mainline operations would normally be conducted. Additional pieces of Masonite fascia were applied to match adjoining layout areas. Here is how the completed installation looks. And by the way, everything worked as designed.

Note that the panel is recessed behind the plane of the general fascia. This avoids accidental switch or push-button activation (sometimes called “butt operating”).
     With this electrically-based work finished, the staging project is complete and I can proceed with construction of Santa Rosalia itself.
Tony Thompson


  1. It looks like the Tri-Delt package could also function as a defibrillator - I'm pretty sure I would not want that capacitor discharging into me if I grabbed the wrong end of things!
    Tri-Delt Sophisticated Electronics has not been in business for some time. Is there an alternative circuit and source available?

  2. Good question. I knew that Tri-Delt was no more, but really don't know what may be out there for capacitor-discharge setups. Mine has sure worked for me, including throwing all the machines on the ladder in a big staging yard.
    Tony Thompson