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Help Needed Wiring a Low-Volt switch for 110v circuit

  1. Jun 18, 2006 #1
    Hello there,

    I am working on a project in which I would like to place some "rope lighting" on a mechanic's creeper and rig it so that when the head-rest is in the up position the lights turn on. Its not so much a functionality project, but more of an experiment and learning experience in electronics. What I need to find out how to do is the following:

    I want to switch it using the body of the creeper as the two leads which operate the switch. (there is a part of the headrest mechanism which touches another part ONLY when in the up position and there is no continuity elsewhere).

    So my question is, is there a way that I can use a low-voltage relay/switch to do this? (i obiously do not want 110v of electricity running through the body of the creeper) I want to see if I can have a low-voltage flow through the body of the creeper which is harmless and that low-volt circuit/switch/relay activates or deactivates the 110v circuit.

    I would greatly appreciate anyone's help with this! I am really interested in electronics and looking to learn!

    Thank you in advanced for your comments and suggestions!

    Rody
     
  2. jcsd
  3. Jun 18, 2006 #2

    Integral

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    To me, it does not seem like a good idea to use the frame of the creeper as your main conductor. I would use a micro switch to sense the upright position. You could use a low voltage (12 or 24V dc ) to the micro switch then use that to control a relay, simple would be a standard contact relay, fancy would be to use a SSR (Solid State Relay). The trouble with the SSR would be cost. This would mean that you would need a DC power supply on the creeper, that could present some space issues, but then you will be plugged in some how any way. Maybe use a wall wart to get the DC to the creeper.... Just throwing out some ideas.

    Good luck.
     
  4. Jun 19, 2006 #3

    Danger

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    I agree with Integral about the trigger mechanism. While it's a clever idea at heart, using a switch would be far more practical. Although you didn't specify what kind of creeper it is, any that I've seen have been painted. You'd have to scrape that off to get decent conductivity. Also, it stands a good chance of becoming contaminated with grease, oil, etc. which could mess things up. For that reason, I would further recommend that you use a sealed switch as opposed to something like a mini-lever or pin type. My personal choice would be a magnetic reed switch such as the type used for doors and windows in an alarm system. A mercury tilt switch could also be used, but it will probably close sporadically just from the creeper being moved around and sloshing the mercury.
     
  5. Jun 19, 2006 #4
    Integral and Danger, I don't think you realize the beatings that these creepers take. Mercury switch is a bad idea. If I'm correctly imagining where these metal parts go together to complete the circuit, the paint is already long gone. It's most likely a wear point.
     
  6. Jun 19, 2006 #5

    Integral

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    The main problem with using the frame of the creeper as a conductor, is the likely hood of the user unintensionally closing the circiut with his body.

    Why would you suppose that Danger and I have never seen a creeper??? :rofl:

    I imagine Danger as having spend a fair portion of his life on one.
     
  7. Jun 19, 2006 #6

    Danger

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    Not as much as I would have liked, but yeah... I've got the requisite hours. Unfortunately, though, most of the time it was just a chunk of cardboard. (Just try getting a creeper under a Camaro on a gravel driveway without jackstands. :grumpy: )
     
  8. Jun 19, 2006 #7

    Integral

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    Hummm sounds like the same brand of "creeper" I use. The same goes for my Probe... I can barely get my head under it. One side on the curb helps a lot!
     
  9. Jun 19, 2006 #8

    Danger

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    No curb in my driveway, but the tracks are dug down almost a foot in some areas. Straddling one was almost like having a grease-pit. :biggrin:
     
  10. Jun 19, 2006 #9
    With low voltage that should be no different than handling 9 volt battery.

    I didn't say you had never seen one. Don't put words in my mouth. But, obviously you must not have a lot of real world experience with them otherwise you'd know the kind of beating they take and that a mercury switch will not stand up.



    How serious can either of you be about working under vehicles if you don't have the clearance to use a real creeper? Obviously you haven't invested in jack stands or ramps.
     
  11. Jun 20, 2006 #10

    Danger

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    I never really needed them, so why bother? The only times that I've had to be under a chassis rather than just under the hood were to change starters or U-joints, or rebuild the clutch linkage. If you check my member photo, you'll see that I don't need a lot of clearance. Besides, as I said, creepers don't roll properly on gravel so it's just a pain in the ass to try using one. Cardboard slides nicely. My time on a real creeper was put in helping friends in their own shops.
     
  12. Jun 20, 2006 #11
    thank you all for your comments and I myself am also the cardboard scrap type when it comes to working on my car... i need something that can quickly be moved and play it off since cops in my area give you citations for working on your car when parked in the sidewalk and i dont have a garage.

    anyway, the mercury switch sounded like a great idea but that is probably true that rocking it could make it go off and i sure wouldnt want that thing to break open anywhere near my skin...

    being a complete novice to electronics, I dont know what a micro switch is... can anyone give me a link or explain this to me? :)

    ive seen the magnetic sensors used on doors and windows before... how do these work? i imagine the circuit isnt completed by the magnets... the magnets must triger something like a relay would.

    my idea of using low voltage switching is exactly for the reason Integral pointed out... i dont want 110v of electricity using my body to close the circuit... but i figured 9-12v should be no problem at all. I was actually thinking of scraping some of the paint off for conductivity...but I am liking this magnet idea and im curious about the micro switch.

    how would i wire the magnet to this? I would probably put one magnet on the stationary frame and the other magnet on the support for the headrest which moves up and down so that when its closed the magnets are next to eachother and when its up the magnets are separated...

    thanks again to everyone for your input!
     
  13. Jun 20, 2006 #12

    berkeman

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  14. Jun 20, 2006 #13

    Danger

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    Rody, it's as Berkeman explained. The switch package is essentially just a relay with the parts separated. Rather than an electromagnet closing the contacts, a permanent magnet is brought into physical proximity and pulls the moveable reed into contact with the other one. Just epoxy the components into place after a few taped-in-place tests to make sure that the alignment is right. The parts are sealed, so you won't have to worry about contamination. Remember to solder the connections, and use shrink tubing rather than electrical tape to insulate them. It provides better mechanical strength to the joint, and won't crystallize over time.
     
  15. Jun 20, 2006 #14
    I would mount the reed switch, relay and small low power transformer in a plastic case. As Danger said, epoxy the reed switch into place. Place it on a wall of the case so a magnet can come close to it (through the wall of the case) when the headrest comes up.
     
    Last edited: Jun 20, 2006
  16. Jun 21, 2006 #15
    this magnetic reed switch sounds great!! i think im going to try this out...but what I am still having an issue with is how to switch the 110v source... from what I saw most reed switches are 20v max... and i really would like to stay away from 110v switching if at all possible.. so im wondering if anyone can tell me a way to do a low-voltage reed switch for a 110v circuit (in this case my rope lights)

    thank you!
     
  17. Jun 21, 2006 #16

    berkeman

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    One way to do it is to use the low-voltage reed switch circuit to energize a 110V relay circuit. So you'll need the LV magnetic reed relay, the HV relay, and a transformer to convert the 110Vac down to the 24Vac for the magnetic reed relay. Be careful wiring it all up!

    BTW, wouldn't it be easier to just use low-voltage lighting on your creeper? Aren't you going to be running over the power cord all the time? You could just use a 12V solid lead acid battery on the creeper, and plug it in for recharging when you aren't using it.
     
  18. Jun 21, 2006 #17

    Danger

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    Just use a simple SPST NO relay with a 6-12VDC primary coil and a 120VAC @ 2 amps or so rating on the secondary contacts. Run the primary circuit from a battery (or low-voltage transformer; might as well, since you'll have 120VAC on board anyhow) through the reed switch to the primary side of the relay. Mains power then gets switched through the secondary contacts to the lights. No need for a master switch, since you can just unplug the thing to disarm it.
    As a side-note, though, you could save a lot of hassle by just using 12VDC lights in ther first place.
     
    Last edited: Jun 21, 2006
  19. Jun 21, 2006 #18

    berkeman

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    BTW to the OP, if you do use 120Vac, be sure you know what you are doing, and make it safe. You want to design and build it like you were going to submit it to UL for safety approval, even if you don't. Like, definitely you will need a fuse in series with your power cord, and since it is for use working around the car in potentially wet conditions, you will need the power feed to be GFCI protected. All AC connections must be dressed correctly, and no contact with people should be possible. If you haven't worked with AC mains power much in the past, I'd recommend using the 12V lights as Danger and I are suggesting. It's just too easy to get hurt working with AC mains.
     
  20. Jun 21, 2006 #19

    Danger

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    Hey, Berkeman, I didn't realize that there was a second page to this thing already, so I didn't see your post #16 until after I submitted mine. I guess it's true that 2 great... naw, that can't be it.
     
  21. Jun 21, 2006 #20
    im going to take up your advice and just skip this project and do a new one with 12v lights...110v is just too much risk especially for a complete novice like myself. i think im going to look into something called LED-Flex which are pretty cool and are low-voltage andim going to give the magnetic reed switch a try.

    thanks to everyone for your input!
     
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