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Electromagnet that plug into wall outlet?

  1. May 13, 2008 #1
    electromagnet that plug into wall outlet???

    I am working on a project for science and and trying to make an electromagnet that will plug in a normal wall outlet (120v ac).
    I have been searching the internet for a way to do this and have found out very little. I am on a lower budget and want to make the strongest magnet i can for the money. A electromagnet is a short so i can't just attach wires to a outlet plug or it will pull to much current and trip the circuit breaker. I was thinking that i could use a series of high current diodes or a full wave rectifier to wave a pulsating dc current but i am still not positive that will work or where to find a full wave rectifier. I this will still be a short and need to find out how to make a working strong electromagnet without shorting a house or school circuit. I think the house circuit is 15 amps but i am not sure about a school classroom circuit.

    I would really appreciate any information about how to make a electromagnet be able to work in a household/ school ac wall outlet power supply or what parts- wire gauge, type of rectifier or any other things. I am a little new to this electronics thing being in only my first year of electronics but would really appreciate any help i could get. Thanks
     
    Last edited: May 13, 2008
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  3. May 13, 2008 #2

    chemisttree

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    Why not use a transformer (that plugs into the wall outlet) and has a more modest DC output?
     
  4. May 13, 2008 #3

    Redbelly98

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    The easiest, and safest, thing to do is buy a DC plug-in "wall wart" at Radio Shack. Then all of your wiring and handling is at a safe low voltage level.

    Since the requirement is low voltage and high current (an Amp maybe?), something like this might work (about $20)
    http://www.radioshack.com/product/i...pply&x=9&s=A-StorePrice-RSK&parentPage=search
    I know I've seen other supplies in their stores that are not showing up on a search at their website for some reason.

    You may also want to wire a resistor in series with the magnet, as a means of adjusting the current. Radio Shack has 10W resistors, you could try 1 to 10 ohms depending on what current you end up needing:

    http://www.radioshack.com/product/i...esistor+10W&kw=resistor+10w&parentPage=search
    http://www.radioshack.com/product/i...esistor+10W&kw=resistor+10w&parentPage=search

    Note, you would probably fry the small 1/2-Watt resistors that are typically used in simple circuits.

    p.s. Does anybody know a typical current requirement for home-built electromagnets? I've seen several threads in here about this now and am curious myself.
     
  5. May 13, 2008 #4
    yeah i thought about using that but would it still not be a short? and Do u have any idea how much weight it could hold... i want to make it as strong as possible and just wondering if it is possible to do it this way. thx though

    to your question i don't know sorry.
     
  6. May 13, 2008 #5

    Redbelly98

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    It would probably be a short, yes, hence my suggestion of adding a resistor so that it is not a short.

    I just did a test with a 3V 1A supply (from Radio Shack) that I have at home. Connected an ammeter to it (equivalent to a 0.3 ohm resistor), and get 0.84A.

    So shorting these things will give you nearly max current at nearly zero voltage. As long as the magnet wiring can handle that current, you're okay.

    > "Do u have any idea how much weight it could hold"
    No, sorry. I'm hoping somebody else will answer that though.

    You might also search for other threads on electromagnets and see what other people have done.
     
  7. May 13, 2008 #6
    what size resistor would i need? yeah i have been but none seem to be about using an ac wall supply. I just wan to know if it is possible to use ac power from the wall and try to do that.
     
  8. May 13, 2008 #7

    Redbelly98

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    To get 1A through the magnet (and I'm not even sure if that's enough current but let's try it for argument's sake) you would need a 120 ohm, 120 Watt resistor. The wattage rating is every bit as important as the resistance. Those 1/2 Watt or even 10 Watt resistors available at Radio Shack will not work.

    Have you ever done any 120V wiring before?
     
  9. May 13, 2008 #8
    no it's all sorta new to me.
     
  10. May 13, 2008 #9
    Is there any maybe ac to dc converter that goes from 120v ac to like 25v dc?
     
  11. May 14, 2008 #10

    Redbelly98

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    You really, really, really should have somebody with experience look at any 120V circuit you build before trying it out. Making good connections that will never ever loosen or short out is an art, and the help of someone with a trained eye is invaluable for somebody just starting out.

    Probably, but I don't recall seeing any at Radio Shack as high as 25V. But you might as well try one at whatever lower voltage is available. At 25V, you would just use a larger series resistor than with a lower voltage converter, to get the same current through the magnet wire.

    Current capacity is what is important here. How many volts ultimately will there be across the magnet wire? Answer: very little!

    Good luck, it does sound like a fun project.

    p.s. for experimenting purposes, you might try a D cell battery, just to get something working more quickly.
     
  12. May 14, 2008 #11
    Are you suggesting he run straight from AC through a 120 ohm resistor the size of a brick and through his coil of wire? I have to assume that is what you mean since you are suggesting a 120W resistor. 1A @ 120V = 120W.
    AC source as a magnet would not work as the voltage alternates polarity.

    Surely I am misunderstanding you.

    I think the best bet for a electromagnet is to use an old 6V Lantern battery. Big amps, but do not last very long. For magnets, you want lots of current straight through your coil. No current limiting resistors. If you use a PS, you want one with a constant current source. A standard wall wart will not do the job. Perhaps an old PC power supply will have the amps you want.
     
  13. May 15, 2008 #12

    Redbelly98

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    I was suggesting that it is too much trouble to be worth doing it this way.

    Wouldn't it still attract iron or common steel objects that are not themselves permanently magnetized?
     
  14. May 15, 2008 #13
    Yes your right, I guess it would. My major concern here was safety, but I think my point is moot since you suggested it was not worth doing.
     
  15. May 15, 2008 #14

    Redbelly98

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    Yes, safety is definitely the most important.
     
  16. Oct 7, 2009 #15
    Re: electromagnet that plug into wall outlet???

    This is totally possible and really not that hard at all. I saw a demonstration of one of these electromagnets that plug right in to a wall outlet and work flawless, no problems, so I decided to make one for myself.

    1: I took the power cord from an old lamp, the kind that has the box somewhere in the middle with the round clicker to turn it on and off, and used this as my power source.

    2: I used 100-150 ft. of 18 gauge speaker wire, not bothering to separate the two, this just made it easier to wrap, and doubled the number of copper coils (you want a lot).

    3: I wrapped the speaker wires around a pvc tightening coupling, like here (keep the wires between the nuts, you want to be able to actually tighten it around the iron core you will make):
    http://www.personal.psu.edu/u0y/nanoreef/diy/skimmer/compression%20coupling%20p.jpg

    4: Once I got the wire all wrapped around, I wrapped them up in electrical tape to keep it tight to the coupling.

    5: Connect one wire from the power source to the beginning of the speaker wire.

    6: Connect the other wire from the power source to the end of the speaker wire, which I fed back through the coupling so both of the connections were on the same side.

    7: Then I made an iron core out of several 1 ft. sections of ReBar. holding them in a tight circle and wrapping them up in electric tape.

    8: Stick the core inside the coupling, tighten it up, plug it in, and turn it on. Works like a charm.

    -If you continue to flip the breaker with this, add some more wire coils. (These coils of wire are like a big resistor, so NO SHORT)

    -The copper coils get warm fast, so I'd recommend not leaving it on for long...

    Best of luck with your project!
     
  17. Dec 12, 2009 #16
    Re: electromagnet that plug into wall outlet???

    Yeah that will work if you are going to have it on a few seconds at a time, listen the best way to do powerfull magnets is DC power. I would get a transformer for 100 DCV, pick up a bridge rectifier, and get some pretty decent cables to hook it up like 10 awg or better. Get a soldering gun if you dont' have one, if you are wanting to build electromagnets its a must have because you are going to burn your house down if you don't put some resistors in that setup. Unless you are completely comforable working with electricty don't even try that straigt 120 ac with no resistors. No offense to ol chap above I routinely do the same thing, but I also have seen my friends try to repeat it and light themselves up good lol.

    Be carefull
     
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