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Electromagnet for telegraph

  1. Jun 21, 2009 #1
    I'm trying to build a telegraph key and sounder. The sounder that I have designed (well, saw online) is a metal nail (which is ferromagnetic) with at least several dozen (maybe 200+) turns of wire around it. When a current is on the wire, the nail should become an electromagnet, and then pull down some kind of ferromagnetic metal strip, creating a sound. Upon being released, the strip bounces back up (maybe using a rubber band) to clang against something else.

    My issue: Using either two AA batteries or two D batteries, I can't get the nail to attract much of anything, not even close to making a sound. I haven't found a good metal strip yet, but even paper clips barely get attracted to the nail. If a compass is close enough, it will detect the magnetic field. Any suggestions? Is it possible that the nail isn't very ferromagnetic, or is there something better to use? Thanks for any help.
  2. jcsd
  3. Jun 21, 2009 #2


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    You need either more turns or more current. Try a 6V lantern battery or a 12 V Pb-acid alarm battery.
  4. Jun 21, 2009 #3


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    You might increase the diameter of your core. Try a screw, for example, maybe 1/4-20 x 2", wrapped with 1 layer of electrical tape so the threads don't bite into the wire. Are you using small gauge (around 24 AWG) magnet wire? (Magnet wire has a clear coating instead of thick plastic insulation, so you can wind many turns in a small radius.) Two dozen turns won't do the job--try hundreds. You should get action!
  5. Jun 21, 2009 #4
    I probably have 100-200 turns of 28 AWG, insulated. Does the length of the nail matter? It's about 0.5 cm diameter, 6cm length.
  6. Jun 21, 2009 #5
    Here is a nice telegraph sounder design:
    http://www.sfu.ca/~achanne/projects/Telegraph%20Sounder/ [Broken]
    There are two solenoid coils wound around small bolts, with a piece of iron connecting the bottoms of the two bolts, to create a horseshoe electromagnet. This horseshoe magnet design with two coils is a much better magnetic circuit than a single nail.
    Last edited by a moderator: May 4, 2017
  7. Jun 21, 2009 #6
    Wow, that's a great guide. I'll go ahead and try that out then.
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