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Electromagnet questions

  1. Jun 25, 2007 #1
    I'm not too knowledgeable on electricity, but I'm constructing an electromagnet with aluminum strips as the coil and using a 120 volt household current. Proposing to solder an extension cord to the strip coil.

    1. When it is plugged into the outlet, will it automatically send juice through the coil? or does it have to be triggered someway like an appliance's on & off switch? If it DOES have to be triggered, how do I do that?

    2. I'm ordering some aluminum strips that are advertised to withstand up to 500 volts d.c.. The seller says he needs the minimum & maximum resistance (ohms) since the strip thickness depends on it. How would I determine the resistance based on 120 house hold volts? (I'd really like it to have a capability of withstanding up to 450 volts) Thanks.
  2. jcsd
  3. Jun 25, 2007 #2


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    Staff: Mentor

    Please be careful with whatever you are doing. I don't understand what you are trying to make (with aluminum strips?), and it doesn't sound like you've worked with AC mains power before. AC mains power is very dangerous, and you can start a fire or electrocute somebody pretty easily.

    What are you going to use the electromagnet for? Are you familiar at all with UL standards for safety in electrical appliances? Do you know how to fuse an appliance that is going to be plugged into an AC mains outlet? What are the UL regulations for insulation, grounding, etc., that apply to the electromagnet that you want to build?
  4. Jun 25, 2007 #3


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    Gold Member

    Just be careful when dealing with mains power with your lack of experience.

    (1) That depends on how you build your circuit. If there is a closed path i.e. no switch\closed switch; then current will flow through the coil.

    I hesitate to tell you more though as the mentors may get angry.

    edit: berkedude covered the safety issues pretty good. Listen to him; its in your best interest :)
  5. Jun 25, 2007 #4


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    I don't know too much about what you're trying to do, but please take every precaution as the others mentioned. You really should get familiar with low-power magnets run from batteries before you even think about plugging into the mains. What on Earth do you want this thing for, anyhow?
    I've never heard of aluminum strips being used. How are they insulated?
  6. Jun 25, 2007 #5


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    You're asking for all kinds of trouble experimenting with
    direct AC mains powered electromagnets and
    especially using aluminium strips for the coil!

    You can't easily (at all) solder to aluminium.
    The resistance will likely be very unstable due to
    temperature as well as possible short circuits that may
    be introduced in winding the thing.
    You'll very likely either blow the circuit breaker or fuse
    or will generate so much heat that the wires / strips will
    start to melt which probably *will* cause the thing to short
    out if it hadn't done so already.

    Electromagnets work best on high current, and usually
    don't require any kind of high voltage unless you have
    large lengths (hundreds of feet) of very thin wire.

    I'd suggest you get something like a 3V or 6V DC operated
    motor or relay or 12V solenoid,
    electromagnetic doorbell, or something like that
    that's already got an efficient low voltage electromagnet
    in it and tinker with that powered by a couple
    of rechargable batteries or maybe a 2 amp 6 Volt isolated
    DC power supply or so on. It'd be relatively a lot safer.

    You can only get something like 20 Amps out of a
    basic household AC circuit, so unless you had a 120V
    circuit and something like 600 feet of 20 gauge wire
    there'd be just no point whatsoever in using anywhere
    near mains level voltage.

    Even a common PC's power supply in the 500-600Watt
    range would give you around 20 to 30 amps at 5V
    which would be better suited to something like a
    200 foot or so long coil of 12 gague copper wire.

    That on an stout iron core would certainly be a fine
    modestly strong electromagnet using a much safer
    much lower voltage.

    Of course there are relatively inexpensive permanent
    magnets made from rare earth materials out there for
    just a few dollars each, and they're probably stronger
    than almost any electromagnet one could hope to build
    without a lot of engineering effort, and they don't need
    power at all, though one must be respectful of their
    strength and not get injured by their intense forces
    of attraction!

    Don't build any electromagnets that take more than
    a few watts of power or more than 12 Volts of voltage
    unless you've gotten solid information on how to be safe
    with the voltages, currents, and heat levels that will be
    produced by such a device!
  7. Jun 25, 2007 #6


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    Last edited by a moderator: May 2, 2017
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