Home made solenoid

  1. I wound 4 layers on a piece of 3/4 conduit. The wire is 20 gauge (.032) and the coil length is 7 inches. I put 5 amperes into the coil and a bolt that fits the conduit didn't move. It stuck to one side of the conduit but it didn't snap in as I expected. What do I do to make this solenoid work?
  2. jcsd
  3. Never having designed a solenoid I will make a wild guess and suggest that you might want to wind the coil on a non-magnetic material such as a piece of PVC. When it is wound on a steel pipe where is the magnetic field concentrated?
  4. I think it needs iron on the outside. All the solenoids I look at enclose the wire.
  5. Danger

    Danger 9,663
    Gold Member

    If you're messing about with 5 amps when you're not sure what you're doing, I fear for your safety.
  6. berkeman

    Staff: Mentor

    The conduit needs to be non-ferrous as Dario says. (non-conducting would be even better)

    What material is the conduit? What voltage are you applying to the coil to get the 5 Amps? What is your power source?
  7. Perhaps my reply was not detailed enough, chuckle. You want the magnetic field to be concentrated in the moveable center piece. You do not want the field to be concentrated in the ferrous pipe (conduit implies steel house wiring pipe.)
    The PVC pipe I recommended is a type of plastic, not metal. Plastic is good in this application.

    Let me say it again, the device depends on the strong magnetizing of the moving piece in the center of the coil. If it is magnetized it will center itself in the coil.

    The outside steel you speak of probably concentrates the field where you want it, but isn't necessary for the basic device to work.

    Next thing we will hear is that you are launching projectiles across the room. Ho Ho.
    Last edited: Apr 30, 2013
  8. Let's be honest here, are we building an electromagnet or a Gauss gun? I can help with either :D
    Also, I wouldn't worry about him running 5 amps through it; you can do that easily with a few 9V batteries in series. Heck, I can, and have, taught a 6 year old how to operate one of my coil guns @ 20V; the small stuff is pretty safe.
  9. berkeman

    Staff: Mentor

    We can discuss optimizing solenoids here, but we do not discuss coilguns.

    I want to understand more about his power supply -- so far he does not seem to have much electrical knowledge, and I need to make a safety determination in order to let this thread progress...
  10. Do I want to know what happened that we aren't allowed to discuss that particular application of solenoids? I looked over the rules and didn't see anything relevant. (Just curious/somewhat interested; hope it's not too off topic)
  11. berkeman

    Staff: Mentor

    It falls under the prohibition against discussing dangerous activities.
  12. I see... Irritating, but I guess there are other places to discuss my "dangerous" hobbies.

    Anyways, derail over until you OK his power supply.
  13. It is not a coil gun. The power at the moment is a line operated variable power supply. It is a solenoid "hammer"
  14. You switch more than a hundred amps to start your car. Voltage is the sharp teeth unless you are thinking high current getting hot enough to burn.
  15. Danger

    Danger 9,663
    Gold Member

    As mentioned in another thread, my car draws over 900 amps to start; I'm familiar with the concept. I also know that less than 1/2 amp can kill you. OP made no mention of what voltage he was using.
  16. I got some half inch thinwall PVC at the hardware store. The 3/4 PVC was crazy. The inside diameter was 15/16
  17. I am building this. http://www.amazon.com/dp/B00BXWNG96

    How important is the iron on the outside of the solenoid?
  18. Danger

    Danger 9,663
    Gold Member

    An "impulse drive" using a solenoid is a mass driver; ie: a rail gun. The neighbours probably won't appreciate any serious experimentation with it.
  19. berkeman

    Staff: Mentor

    That Impulse Drive thing looks to be crackpot. The only way to get net thrust is to eject the "billiard ball) or whatever you are accelerating. The book appears to imply that you can capture and re-use the ball. Am I missing something?
  20. It ejects nothing. You are jumping to conclusions.
  21. The sum of the moments is made asymmetric by an elastic collision. I'll be finished building soon. No one has answered my question regarding the iron on the outside of the coil. I am assuming I need it.
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