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Help wiring 3-prong SPST illuminated rocker

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by Super Rad, Apr 6, 2009.

  1. Super Rad

    Super Rad New Member

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    I'm building an adjustable regulator (1.2-25V @ 5A) and want (if possible) an illuminated on/off switch. This switch will be connected to the mains, likely in between the fuse and transformer.

    I bought a 3-prong spst illuminated switch at radioshack, it's rated for 10A @125VAC. Prong #3 is "gold" (copper). The diagram on the packaging indicates prong 1 is for ac in and that prong 3 is for neutral, also indicating that prongs 1 and 2 are connected by the switch and that the lamp is between prongs 2 and 3 and that prong 3 is also tied to the switch.

    However I'm having trouble figuring out the right way to wire it. It seems like no matter what position the rocker is the connection between 1 and 3 and between 2 and 3 is "open." I figured that it probably has to do with the forward voltage of the LED in the switch, but I tried tripping this using a 12V battery with no luck.

    I just don't know if I'm supposed to assume that the connection between 1 and 3 will be made when the switch is hooked up to mains? Also, what is prong #2 for? Right now it's the only prong that's actually working as a switch but will it power the light? For clarification I want the light to be off when the power supply is off and on when the supply is on. The diagram doesn't name prong #2 at all, while prong #1 is receiving from mains, and prong 3 is going to load.

    Seeing as I'm making a thread I have another question, is a 2.5A fuse good enough to place between the transformer and mains to trip if the 5A 25vdc regulator circuit somehow shorts?
     
  2. blueroomelectronics

    blueroomelectronics Well-Known Member

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    It's a 120VAC switch so it probably uses a neon bulb. They don't work at 12V.

    You should put in a low voltage fuse across the supply output too. A better solution might be a current limiter in the design.
     
    Last edited: Apr 7, 2009
  3. Super Rad

    Super Rad New Member

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    There is a current limiter in the design, the LM338K. I just want a fuse on the a/c side if somehow the regulator circuit shorts.

    Anyhow I'm still confused by how I should wire it. I found this on radioshack's site:

    "This is a 125V AC switch with 3 terminals.

    Copper colored terminal is connected to one side of neon lamp. Connect
    to neutral to keep light on all the time. Center terminal is connected
    to the other side of the neon lamp and one side of the N. O. Switch.
    Connect this terminal to power. Tin colored outside terminal is
    connected to other side of the N. O. switch. Connect this terminal to
    the load."

    This is not the configuration I want.

    There's also another wiring diagram on radioshack's site:

    http://www.electro-tech-online.com/custompdfs/2009/04/51418.pdf

    Is this how I want to wire it??? Or should I should set prong 1 to hot and connect prong 3 to one side of the load, ignoring prong 2 completely?
     
  4. dave

    Dave New Member

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  5. blueroomelectronics

    blueroomelectronics Well-Known Member

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    Then you need a different switch.

    Pins two & three are the switch, the bulb is on pin one.
     
  6. Super Rad

    Super Rad New Member

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    Sorry, I wrote that post using the pin designations as they are written on the switch itself. I'll try writing this post without referencing pin numbers.

    One outside pin is connected to the lamp and inner pin. The other outside pin is connected to the inner pin by a switch. Since I just want the lamp to be on when the switch/load is on, what is wrong with connecting the non-bulb switch pin to hot, and connecting the bulb pin to the load? Won't there be a connection between these two outside when the switch is on? Or would this just overload the lamp?

    What about the wiring diagram on the radioshack site? It seems to imply that the status of the light can indeed depend on the switch.

    I'm sorry if I'm not "getting it," I'm still learning and it may take a simple explanation of what I'm overlooking.


    EDIT: The wiring diagram on the radioshack site is looking more and more like what I want, since it splits the lamp and load into parallel circuits that are switched by the connection between the other two pins. Can someone verify this for me?
     
    Last edited: Apr 7, 2009
  7. ccurtis

    ccurtis Active Member

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    Look at the diagram in the link you provided showing the switch wiring. Is it not true that the lamp and the load are connected in parallel? Yes, it is true. Therefore, when power is applied to the load, the lamp will be lit. What else could you want?
     
    Last edited: Apr 7, 2009
  8. Super Rad

    Super Rad New Member

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    Thanks! It's one of those things where I had to think about it one too many times to "get it" and I just needed some confirmation from those more knowledgeable than I. Thanks!
     
  9. ccurtis

    ccurtis Active Member

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    Don't mention it. It appears to be a good example of something drawn in a confusing manner.
     
  10. jcepeda

    jcepeda New Member

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    I was successful with wiring 3-prong SPST illuminated rocker

    connect wires from the battery to the two shorter prongs, then connect the positive led wire to the third prong and connect the negative led wire to the negative short prong...so one of the shorter prongs would have the negative wire to the battery connected as well as the negative LED wire connected to it. hope fully this will help!
     

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