Building a universal switch machine control
their original position with a spring when power is turned off; thus main- line turnouts are set for the main track when power is turned on at the begin- ning of each operating session. Standard diode matrix circuits using single-pole push buttons can be used to activate yard ladders or other complex routes.
The capacitor-discharge power sup- ply dependably operates many switch machines at once when required to set up a standard route or yard lead.
Stall motors Needless to say, the rotary relays I used to build my switch machines are no longer available, and if they were they would be prohibitively expensive. Commercial twin coil machines were rejected as replacements because they are maintenance intensive. Fortunate- ly, several brands of stall motor switch machines have come on the market in recent years.
Circuitron (Tortoise),
Switchmaster, Torquemaster, and Mi- cro-Mark all make such machines. They all work reliably and are reason- ably priced.
Stall motor machines are activated by reversing the polarity to the motors, and they can be controlled using cross- wired DPDT (double-pole,
double
throw) switches, a bipolar d.c. power supply, or an a.c. power supply with steering diodes. None of these control systems allow a switch to be controlled from more than one location without complex wiring, and none are compati- ble with control systems used with old- er twin coil or relay switch machines. For those modelers who use digital
PHOTOS BY BILL BOTKIN UNLESS NOTED Wiring diagram for universal switch machine control
12 V.D.C. Filtered Power Supply
+ –
Capacitor Discharge Power Supply
– + SPDT
Center Off Momentary or
Pushbuttons or
Control Circuit from Diode Matrix
Common return buss wire
SPST Relay
Normally Closed
Stall Motor Switch Machine
3PDT Relay
The universal switch machine control that the author developed can be assembled in two dif- ferent ways (below). The module on the left uses “ice cube” relays, while the one on the right uses PC board relays. Although built from different components, they provide identical results.
command control, stationary DCC de- coders can be used to operate stall mo- tor machines from multiple locations, but they are expensive ($25 - $40 each) and they use DCC power, which I pre- fer to reserve for running trains. My challenge was to find a way to control stall motor switch machines with my existing capacitor discharge control system.
Universal control system I used 24-volt “ice cube” relays for my circuit since I had lots of those on
hand and already had a 24-volt d.c. power supply installed for the rotary relay switch machines. Most modelers will prefer to use 12-volt relays so the control module relays can be operated from the same 12-volt d.c. power sup- ply that powers the stall motor switch machines. The relay contacts don’t handle
much current, so heavy duty relays are not necessary. One single pole normal- ly closed relay is needed (or use an SPDT), and one 3PDT (three-position double throw) relay is needed. If you
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