SOLENOID POINT MOTORS, SWITCHES, WIRING AND INFORMATION
|Solenoid point motors such as Hornby, Peco and Seep consist of two coils of wire (which form solenoids or electromagnets). When one solenoid is momentarily powered the point moves to the left. Powering the other solenoid moves the point to the right. The two coils result in four wires at the point motor, but as two of these go directly to the point motors' power supply they are sometimes connected within the point motor by the manufacturer to give 3 wires.|
|Solenoid point motors need a large current for a short time. If the current continuously flowed through the solenoid there is a danger of either the point motor or the power supply overheating and being damaged. For this reason normal on/off or changeover switches should not be used to change the points as they would continuously energise the point motor.|
|Suitable ways of switching the point motor are to use either push button (push to make contact) switches, or studs and probe, or momentary action toggle switches.|
|Push button switches.|
|These have 2 solder tag terminations on the back of the switch. The tags are electrically joined when the switch is pressed (the push button is spring loaded). Two switches are required for each point motor. They can be arranged on a control diagram showing the track layout, with one pushbutton on each branch of the point. The back of the switch is threaded and bolts into a hole in the control panel.|
|Studs and probe.|
|This is very similar to push button system. A metal stud is connected on the control panel diagram at each branch of the point. To change the point a probe is touched against the appropriate stud. Only a single probe is required.|
|Momentary action switch.|
looks identical to a normal toggle switch. The switch however has built- in
springs which cause the lever to rest in the centre position where no
contact is made. To operate the switch the lever needs to be temporarily
pushed one side according to the direction that the point is to be switched.
If the lever is pushed to position "1"then "c" and "b" are connected.
If the lever is pushed to position "2" then "c" and "a" are connected.
"c" is the common contact wired back to one of the power supply terminals.
The diagram shows the usual wiring to operate points. Note that in some types of point motors the two coils have separate connections on the point motor, others have two of the coils connected together within the point motor.
|Kato Unitrak Points click here|
|Point motors will work from either AC or DC. A minimum voltage of 12 volts is required but 16 to 24 volts may give more reliable operation. Also a current of about 2 amps is required for each point motor. Point motors can be powered from the auxiliary 16 volts output of a controller but the large current taken when switching the points may affect the output to the track and temporarily affect the trains speed.|
|Because a large current is required to switch the point motor it is preferable that wires capable of 3amps current capacity (or more) are used. This is particularly important if the wires are long (because the point motors are a long way from the switches) or one switch operates more than one point motor. As the current normally flows in a short burst there is no danger of a one amp capacity wire being melted by 2 amps flowing and for a short length it will probably work well; but 1 amp wire has a larger resistance than 3 amp wire and so over a long distance a greater volt drop will occur resulting in less power to switch the point motors|
|Some people find it simplifies wiring to solder short wires to the point motor and connect these to the longer wires from the switches with a terminal block.|
|Using a capacitor discharge unit (CDU)|
|A CDU stores electrical energy. It charges up with a small current and releases this energy as a large current when the point motor is switched. This has the advantage that it saves having to use a very large and expensive transformer to switch the points. This is particularly important when it is desired to switch a number of points at once. A second advantage is that once the electricity stored in the CDU is discharged it will not charge up or release any more electricity until the switch is opened. In other words it protects the point motors from being damaged by a faulty switch etc. A third reason for using a CDU is that it gives a DC output, this allows a diode matrix to be used.|
|Indication of point setting|
|It may be impossible to see which way the points are set if they are some distance away. LEDs can be fitted at the control panel to show the points setting. These may be switched by either a contact built into the point motor, an accessory switch, a micro switch or our Point Indicator Board.|
|Route setting with a Diode Matrix|
|As it is possible to use a single switch to change a number of points it may be desirable to have switches which set certain routes. If there are a number of routes it is possible that two different routes switch the same point. This would result in the wiring for each route becoming unintentionally connected together; so that operating route 1 would also cause route 2's points to change.|
|The following example shows how a diode matrix can overcome this problem.|
|When switch 1 is operated point motor coils B and C are
energised. When switch 2 is operated point motor coils A and B are
energised. The diodes act as one way valves for electricity so that
current can flow to point motor B but cannot flow out to the other point
For simplicity only one of the two coils of each point motor is drawn and only one of the 2 switch contacts.
|This arrangement can be used for much more complex situations, remembering that when more than one switch or IRDOT-P connects to a single point motor coil a diode is used for each feed.|
|The 3amp diodes we supply are suitable for this purpose|
|3 way point|
|The diode matrix idea can be used when operating a 3-way point. If studs and probe or push button switching is used then there are three contacts to operate the two point motors of a 3-way point. Routes may require both point motors to operate. For clarity the diagram has omitted the two common connections to the point motors from the "-" terminal of the CDU.|
|Automatic switching of points|
|Some of our SA boards automatically switch points for example SA5 automatic passing loop. The IRDOT-P and the Automatic Route Selector also switch points automatically.|
|Using Micro Switches with Points|
|Both Peco and Seep point motors are manufactured in such a way that the rod which fits into the points' tie-bar also extends below the point motor. By fixing a micro switch onto a block of wood beneath the baseboard this rod can be used to move the micro switch. The micro switch's built-in spring keeps the arm in contact with the rod. There are 2 holes in the micro switch for attaching it to the wooden block. Initially just use one woodscrew allowing the micro switch to be rotated until the position is found where the contacts have just switched over when the point has travelled to its' furthest position. A faint click cn be heard as the contacts change. Once this position is found insert the second screw.|
|Fixing LED's to Control Panels|
|Drill a 3mm or 5mm diameter hole for the LED and insert the LED. Solder wires to the LED legs, then bend the legs 90degees so they are flush with the back of the control panel. Secure the LED by putting a blob of epoxy glue over each leg. This has the advantage of preventing the LED's legs moving and cause a short-circuit.|
|Cable Ties and Bases|
|The photographs show how our cable ties are used to fasten wires to the underside of baseboards. The tie bases, which are 2 cm. square, are self adhesive and have slots through which the ties are threaded. The cable ties have a locking action to prevent them becoming unfastened. A pack contains 50 Cable Ties and 30 Bases.|
|See Electrical Components on the Ordering and Prices page for details of availability of switches, diodes etc.|