Lighting a rocker switch

[glsummers]

Question for Jim Banner.
I have several 12v rocker switches that are lighted. Jim I want to use them for the tracks around the round house to indicate if that track is on or off. There are three prongs on the rocker switch and one is brass. How do I wire these. Remember you are helping someone who needs "Wiring for Dummy's". Thanks Jim you have helped me and many others. Larry

[Len]

If there are 3 contacts, it's most likely a single-pole double-throw (SPDT) switch. The off color contact is probably the common contact. You'll actually only use two contacts for a roundhouse stall track "On/Off" switch.

There's a simple way to find out which contacts bring the switch light on. Connect one side to a power supply to the center contact of the switch. Connect the other side of the power supply to either side of the switch. Set the power supply for somewhere around 10 volts. If the switch light comes on in either switch position, those are the contacts to use for turning the roundhouse track on.

If not, move the outside wire to the other side, and flip the switch again. The light should come on in one position or the other. Use the contacts where it comes on for your roundhouse track "On/Off" control.

Len

[glsummers]

Len,
I am running DCC so what you are saying is run two wires from my bus wire to two of the  contacts that work the light and then take two wires to the track on the roundhouse?

[Len]

Not exactly. You said the switches have three contacts, which would normally make them SPDT type switches. To use a SPDT as an On/Off switch you usually use the center contact and one of the end contacts. With a lighted SPDT switch, the light only comes on when a specific end contact is used, it's off in the other position.

I was just describing a method for determining which 2 of the 3 contacts to use for the light to come on. Once you have that, the switch goes in line with the wire from the power source to one side of you roundhouse stall track. This lets you turn it On/Off. The wire for the other rail would go direct from the power source.

One thing to check on is whether the switch light is a bulb or LED. LEDs normally operate off standard DC, and will not be too happy with a DCC signal.

Len

[glsummers]

Len what will happen using DCC; I found on the two prongs that light up the rocker switch. What problem will I have with DCC?

[Jim Banner]

Larry,

It looks like Len has been helping you out with this.  But maybe I can add a couple of things.  Switches that are designed to serve both as on-off switches and as pilot lights usually have 3 connections or prongs, but only two of those go to switch contacts internally.  The third prong is the return connection for the internal light.  And that prong is usually identified in some way - set at a right angle to the other two, raised relative to the other two, or by colour, as with yours.  I would expect the one brass prong to be the return for the internal light and the other two prongs to be for the switch contacts.

The power side of the internal light is usually connected internally to one side of the switch.  (There are also lighted switches with no connection between the light and the switch but they have 4 or more prongs.)  The three prong lighted switches can either use the internal light as a pilot light or by reversing the connections to the switch contacts, can have the internal light on all the time to help find the switch in the dark.

When used as a pilot light, which is what you want to do, the power is fed into the switch via the prong that does not go to the internal light.  So when the switch is off, the power does not go the the load (one of the roundhouse tracks in your case) and does not go to the internal light either.  When the switch is closed, power from the source (one connection of your command station) can go to the internal light and also to one rail of that roundhouse track.  After passing through the internal light, the power flows out through the marked contact and back to the second connection of the command station.  At the roundhouse track, the power flows through the locomotive (if there is one on the track), out the other rail, and back to the return connection of the command station.

Which connection of the command station is the "source" where the power comes out and which connection is the "return" where the power goes back to the command station?  It does not matter.  They are identical.  But it is convenient when repeating a circuit multiple times (such as having multiple roundhouse track switches) to designate one connection as "supply" and the other as "return." 

Which switch connection is which?  If you add a couple of wires to a good 9 volt battery, you can test the switch to find out.  Connect one wire to the identified prong (the one that is different than the other two.)  Connect the other wire to one of the switch prongs.  Flip the switch on and off a few times.  If the light goes on and off, you have the input prong.  If it stays on, you have the output prong.  Confirm that you have it correct by shifting the last wire you hooked up to the other switch prong and see if it does the reverse when you flip the switch (stay on or go on and off.)  If the internal light never lights, most likely you either have a bad battery or you selected the wrong prong as the internal light return connection.

I had planned to add a diagram and am still willing to if this is not clear enough.  Please let me know.

As far as DCC hurting an internal LED in the switch, take a look and see if there are any polarities marked on the switch.  If not, you can assume the switch and its internal light are suitable for both dc and ac at the voltages marked on the switch, unless it says otherwise.  Unless the switch is designed for a particular niche market, a smart manufacturer has already considered that problem and applied one of several possible solutions.

Jim

[glsummers]

Jim and Len, thanks for trying to help; A diagram would really help. Let me share with you what I have done so far and the result.

My bus wires are black and red. I ran a red wire from the bus to the brass terminal and a black wire from the bus to the center terminal. This lighted up the light when I turned it on and off. Then I took a black wire from the center terminal and went to one side of the track in the roundhouse and a red wire from the brass terminal to the other side of the track in the roundhouse. What happen is the light would turn on and off but the power to the track never went on or off; it just stayed on even if the light was on or off. I am not sure how to switch the wires around; I tried some but then the light would not work and caused some shorts.
Thank you so much for the help. Larry

[Len]

Larry,

Check out http://www.bcae1.com/switches.htm

There are diagrams for wiring a number of different switch types. About 3/4 of the way down the page is a diagram for a lighted rocker switch that explains things pretty clearly. You can even operate the switch on line!

Apparently these are actually SPST switchs (normally two contacts) and the third contact is the return path for the internal light. The picture is pretty self explanatory.

The '+' side of the power source would be one side of your DCC bus, the bottom of the bulb being controlled would be one of your stall rails. The '-' side of the power supply connects directly to the other rail (shell of the bulb base in the picture).

Len

[glsummers]

Len I am trying to understand that illustration; I love model railroading but electrical part of the hobby is not my strong suit. What would be helpful for me would be a diagram that showed how and where the wires from the bus or main power supply went and then how they went to the track from the lighted rocker switch. I am trying to picture that and make application to the railroad; but for me it is a little difficult. Please be patient. I copied off the diagrams and all the conversations from you and Jim to try and study it and figure it out. Thanks for trying. Larry

[mabloodhound]

Larry,
I know where you're coming from.   But this is similar to house wiring so you only have to turn one 'leg' of your power on or off.
From your main bus wires, one of the bus's will go to one side off all the roundhouse tracks.
Then from the other bus, that will go to your switch and from the switch to the track that you want to control.
So you see, both bus wires DO NOT connect to the switch.    This is the same as a household light switch.
Hope this helps.

[glsummers]

mabloodhound,
That is what I did the first time I hooked one up. The only problem was that the Light did not work. I had push on and push off switches wired and they worked fine but I wanted to light them so when we start operating we can easily see if the track is hot or not by the light. Does that make sense? Thanks

[glsummers]

Just one more question please,
Can one of you knowledgeable men draw me a illustration that takes me from my black and red wire bus to the rocker switch and then to the roundhouse track. I would sure appreciate it very much. Thanks Larry

[mabloodhound]

You're right.   You would have to bring the other bus leg over to the switch just to power the light.   But that should still work out OK.    See, now you've got me confused LOL.

[Joe Satnik]

Dear GL,

It's good that you are getting the lamp to light.

SwI = Switch Input
SwO = Switch Output
LG = Lamp Ground

SwI______ \_________SwO
                       l
                       l
                    Lamp
                       l
                       l
                      LG

I have no idea which of three terminals is which.  You have to figure that out yourself with an Ohm-meter set to lowest setting:

Touch Ohm-meter red lead to one switch terminal, and touch Ohm-meter black lead to the other switch terminal.
   

Test           Switch on             Switch off
SwI-SwO   Near zero ohms   No connection (no change in meter face from when meter leads don't touch anything.)

SwI-LG      Lamp resistance  No connection

SwO-LG     Lamp resistance  Lamp resistance

Lamp resistance (cold) might be in the neighborhood of 20 ohms. 

Once you have ID'd your switch terminals, connect as follows:


DCC bus red  -----SwI______ \_________SwO--------one rail of round house track
                                               l
                                               l
                                           Lamp
                                               l
                                               l
DCC bus black  ----------------- LG ----------------other rail of round house track

You may have to swap rails to get the proper bus polarity. 

Hope this helps.

Sincerely,

Joe Satnik

[Jim Banner]

Thanks, Joe.

I promised GL a diagram and never quite got to it yesterday.  Your diagram is perfect.  Worth at least 1000 words!

Jim