d7j2.pdf

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OriginallyCompiled by:

Updated by:

Updated:

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John A. Dorsamand John P. Seehaver

George Sevier, MMR

October 1999

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NATIONAL MODEL RAILROAD ASSOCIATION

DATA SHEET

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Title:

First Issued:

D7j.2

SWITCH MACHINECONTROL

October 1961 (D7c.551)

DATA SHEET

INTRODUCTION

Various methods of controlling electrically operatedswitch machines are covered in this group of sheets.Included in the first are basic circuits and in the othersthe applications of these circuits. All circuits have been selected on the basis of provenpracticality., Low cost, flexibility and relative simplicity. Consult Data Sheet D7j as to mechanicalfeatures and general characteristics of the switch machines discussed in this sheet.

A word used for circuits in which one device operates the next in sequence.

An electrical control device for opening and closing circuits.

Any motor, coil device, relay (or rotary relay) used to move the points of aturnout. For these sheets, divided into the following classes:

One having a rotating armature and requiring continuouscurrent flow through the motor coil to hold it in the operatedposition.

One having two opposed coils or solenoids, designed to beoperated by momentary current flow. (Most twin-coil machinesare likely to overheat or burn out if subjected to more than amomentary current.)

The trackwork element which separates one set of rails into two or more tracks.See Data Sheet D3c and Recommended Practices RP12.

(Normal Position)- of turnout: position of switch points as assigned by the track plan designer;

usually the main or most used route.- of switch: position which operates the turnout to the N position.- of switch machine: position in which coil of relay, either type, is

de-energized. In a twin-coil machine, position which holds turnout in N

position.

(Reverse position, operated position)- of all devices mentioned: Opposite of N position.

DEFINITIONS

C A S C A D E :

SWIT C H :

SWIT C H M AC H IN E:

S TA L L M O T O R M A C H I N E :

T WIN C O IL M AC H IN E:

TURNOUT:

N PO SIT IO N :

R PO SIT IO N :

Return to index

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SYMBOLS

NMRA graphical circuit symbols (RP41.1-.6) are used with these additions:

POWER SUPPLY AND WIRING

Twin-coil machines are generally operated by AC, although DC may be used. A 4 amp transformeof 18 VAC will operate at least two twin-coil machines simultaneously.

It is imperative that push button switches are used for this application for instantaneous activationContinuous power to twin-coil machines will result in non-operational burned out machines.

Motorized Switch Machines require DC power supply of 1 amps at 12 volts. These motors aredesigned to have power applied to them and not turned off. This is called the stall feature. Some

motorized switch machines feature auxiliary contacts. A micro switch can be used for the auxiliarycontact. It is placed in the path of the throw bar or wire and is tripped as the machine changesposition.

No. 18 wire is adequate for most switch machine control needs. Smaller, more flexible wire ispermissible within control panels. No. 14 wire, properly fused, is suggested for power supply to thpanel. Refer to Sheet D7p for discussion of the common power return system, which has importabearings on this phase of layout wiring.

N R Twin-coil switch machine. When not essential to the circuit,cut-off contacts will not be represented in diagrams.

Motor switch machine. This machine has a rotating armature thatchanges the position of the track switch from normal to reverse.The motor has a stall feature.

Any switch machine.

Detection.

M

SM

DR

DATA SHEET DATA SHEET

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SWITCHES

BASIC CONTROL CIRCUITS

In general, twin-coil machines require momentary-contact controls. With proper circuitry, howevercontrol devices are interchangeable for these machines. Refer to circuit diagrams in sheet D7l.

All momentary-contact devices are shown in the diagrams as push buttons, but their electricalequivalents, such as spring-return toggles, may be used. Locking-contact devices include toggleswitches, keys, rotary selectors and push-button selectors. The latter are useful because they fitwell into some track diagram boards, but it may be difficult to obtain the correct number of buttonsand proper circuitry.

Motorized switch machines can be controlled with a double pole double throw toggle switch withcenter off or no center off. Leaving the switch in the on position will not burn out a motorized switcmachine.

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Figure 1 shows the wiring of a twin coil switchmachine utilizing two push button normally openswitches. The coils will not heat or burn upbecause the power to the coils is momentarywhen either of the push button switches isdepressed or closed.

Figure 2 shows the wiring of atwin coil switch machineutilizing a single pole doublethrow switch without a springreturn. This is where the

auxiliary contacts on the sideof the switch machine areused. If the contactarrangement is not used, thecoils will heat and burn out.Be sure to note how theauxiliary contacts areconnected (the closed contactis always opposite theposition of the single poledouble throw switch).


N

R

+-

Figure 1

Figure 2

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MOTORIZED SWITCH MACHINES

There are two basic wiring diagrams for this type of switch machine. Figures 3 and 4 show the twwiring methods.

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Figure 3

Figure 4

Figure 3 uses a DPDT toggle switch and a resistor to complete the circuit. The DPDT toggle switcis wired in the same manner that a directional control switch would be wired. Note the two crossewires that go to the four outside terminals.

Figure 4 uses a split power supply ( or two power supplies wired in series ) system with a commonreturn. The split system is more economical and takes less wiring than the wiring displayed infigure 3. An SPDT toggle switch is used in this circuit instead of the DPDT toggle switch.


Figure 3

Figure 4

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It is important to size the power supply correctly. The instruction sheet, that comes with the switc

machines, suggests the correct power supply. If a different voltage power supply is used, theresistor or resistors will have to be resized.

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Figure 5 shows how auxiliary wiring or indication is accomplished with the motorized switchmachine. Today most model railroaders use the Light Emitting Diodes or LEDs. Some still uselamps. Both methods are shown in this wiring diagram. By adding lights using this method , it willlimit the number of switch machines that can be put on a power supply. To avoid this situation itwould be wise to use a micro switch or switches for auxiliary contacts that would run the circuits folamp or other track control.

The simplest indication system is the positioning of control devices on a track diagram that hasbeen drawn on the control panel. These switches should be located in such a way that theyindicate the direction that the turnout has been thrown. A multi-contact selector switch or rotaryswitch with a two position throw does an excellent job of handling indications. On all but thesmallest layout it is important to have indicator lights for each turnout. This is especially true if aturnout is controlled from more than one location. Large layouts utilize many of these sametechniques. Twin coil machines come with a number of contacts mounted on the side of themachine. These contacts are utilized for indicator lights , frog power wiring, or other wiring

requirements. Light omitting diodes make excellent indicators. They come in a variety of sizes anshapes to fit your control panel.

There are many different configurations for wiring switch machines and their controls. Thesedepend on the situation on the layout, the desire to have the operation as true to life as possibleyet simple to operate. Finally, the wiring is easy to maintain and trouble shoot. These data sheetare not intended to provide the model railroader with all the technical wiring and circuitry that mighbe wanted. Shown on the following pages are basic circuits and diagrams. These can beexpanded and combined to address a particular layout design or situation.

INDICATIONS


MOTORIZED SWITCH MACHINES - continued

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CONTROL OF LADDER TRACKSWITCHES

There are several circuits that willoperate a ladder track switch system.The trick to these systems are to figureout all of the configurations for the switchmachines that are involved. This can getquite complex depending on the modelrailroader and the ladder system. Theladder yard or system can be wired withindividual switch machine controls. Thisis great except that every machine mustbe thrown correctly in order to get thetrain to its destination. With the use ofthese ladder diagrams it is possible topush one button or throw one switch andthe route you want the train to take isdone in one or two throws of toggleswitches or push button switches.

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Figure 6 shows a simple ladder yard. Note there are seven different routes the train can take.These are listed as A through G. As was mentioned previously one can wire each machineseparately which results in a total of 6 toggle switches to control 6 machines.

Take a look at Figure 7. This diagram shows how to wire twin coil machines so that when a desirebutton is pressed it operates all the necessary switch machines. Note that all push buttons excepfor A and G have one normally closed set of contacts and two normally open sets of contacts. Aperson should shop around to obtain these switches. The wiring is straight forward. Follow onewire at a time when hooking up this circuit. Note the normal and return positions of each of theseswitch machines. This is important to get these right for the correct track designation.


Figure 6

Figure 7

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Figure 8

Figure 8 is a diagram of what is called a diode matrix. This wiring is much simpler than the circuitin Figure 7 and does the same thing. The matrix can be done on a plain piece of paper or if youprefer a sheet of graph paper. Across the top of the paper each line represents the normal orreverse coil of a twin coil switch machine. Along the left side of the matrix are the various routesthrough the ladder yard or system. Diagonal lines designate the energized switch machine coils feach row.

In the sample on the next page (Figure 9) we will have two switch machines and three tracks. RoA has one diagonal line going to coil 1N. Row B has two diagonal lines, one to coil 1R and theother to coil 2R. Row C has two diagonal lines, one to coil 1R and one to coil 2N. The trick to thiscircuit is that a diode must be inserted in every switch machine coil that contains two or morediagonal lines. In this sample two diodes are required. These two diodes are both in the wire thaleads to coil 1R. If we want the train to travel on route A coil 1N must be thrown. If we want thetrain to travel route B, coils 1R and 2R must be thrown. To travel route C, coils 1R and 2N must bthrown etc. As more tracks are added the matrix becomes larger and more diodes are required.The neat thing about this circuit is only three push buttons are required and two diodes.

1N 1R 2N 2R 3N 3R 4N 4R 5N 5R 6N 6R

A

B

C

D

E

F

Total

coils

thrown

3

2

5

5

3

4

Diagonal lines show the energized switch machine coils for each row.

Route Individual coils


CONTROL OF LADDER TRACK SWITCHES - continued

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A

A

B

B

C

C


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Figure 10 is another way of wiring a ladder yard or ladder system. This is done using 4 pole multwafer rotary switches. The rotary switch or switches are rotated to the desired track and then apush button switch is activated to set up the desired route. Make sure to purchase the correctrotary switch or switches. Use the non-shorting type.

Figure 9

1N 1R 2N 2R

A

B

C

+

+

+

1N 1R 2N 2R


CONTROL OF LADDER TRACK SWITCHES - continued

Figure 10

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INDICATOR CIRCUITS

Figure 11 is suitable for any type switch machine equipped with contacts or micro switches. Anypower source compatible with the lamp or LED rating may be used because it is not part of theswitch machine operating circuit. If a normally dark circuit is preferred, use only the upper portionof the circuit. Figure 12 utilized one contact to operate one indicator light. In the normal positionthe lamp or LED would be dark. In the reverse position the lamp or LED would be lit. Figure 13 isa simple wiring circuit using one LED. Remember that a resistor must be placed in series with theLED to keep it from burning out. The resistor is sized according to the voltage output of the powesupply. If switch machine indication is desired from multiple locations the lamps or LED are wiredin parallel. This will allow all locations to be lit.

TURNOUT POLARITY CONTROL CIRCUITS


The purpose of circuits depicted in Figures 14 and 15 is what is called a power frog. These circuiinsure that there is always power to the track in the direction that the turnout is thrown. In somecases the turnout relies on the spring tension of the point rails against the stock rails to completethe electrical circuit. This is not reliable when the points and the stock rails get dirty. They cancause some real maintenance headaches. These two circuits eliminate this. Polarity must becorrect with the way the turnout is thrown or a short circuit will result. Fig. 15 is similar to Fig. 14but with an additional feature that eliminates possible short circuits between long thin points andstock rails by metal wheels, since the open point rail is of the same polarity as the nearby stockrail. Note the four insulated joints isolating the frog and the jumpers from the points to the stockrails.

Figure 11 Figure 12 Figure 13

Figure 14 Figure 15

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SWITCH MACHINECONTROLDATA SHEET DATA SHEET

TURNOUT POLARITY CONTROL CIRCUITS - continued

Fig. 16 shows a circuit that combines the advantages of Fig. 15 with completely short-free stoppinsection, but at the expense of two sets of contacts rather than the single set required with eitherFig. 14 or Fig 15. Fig. 17 shows an unaltered Custom-Line or Snap-Track turnout with short-free stopping sections.

Detector locking is a term used for circuitry which prevents the turnout from being thrown under atrain. Some form of detection is required. There are many systems on the market that will servethe purpose. They are not covered in this Data Sheet. Your local hobby shop most likely will be

able to assist you with these circuits. When a train enters a track section equipped with adetection unit or units, a relay operates to lock the switch machine control circuit as they thenstand. The turnout may not be thrown until the train has cleared the detection section. Groups ofturnouts can be locked out in this manner using one relay. It really depends on the trackconfiguration. The figures below show some simple detection circuits from the point they connectinto the switch machine circuit. The internal detection circuits are beyond the scope of these datesheets. It is important to spend some time thinking out your layout operation and train movementpossibilities prior to incorporating these circuits into your layout.

DETECTOR LOCKING CIRCUITS

Figure 16 Figure 17

Figure 18

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SWITCH MACHINECONTROLDATA SHEET DATA SHEET

DETECTOR LOCKING CIRCUITS - continued

Figure 18 is suitable with any twin coil switch machine controlled by momentary contact devices(push buttons). Remember not to connect any other power return wires ahead of the detectionrelay contact except for additional switch machines that will be locked out at the same time.

Motorized switch machines detection circuits are pictured in Figures 20 and 21. These two circuitare very basic. Any more elaborate circuitry would be beyond the scope of these Data Sheets.These diagrams are straight forward using a double throw switch. Just remember that thedetection device relay contact must be placed ahead of the control switch for the switch machine.

Figure 19 Figure 20

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