Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Electromagnet cores

  1. Oct 30, 2005 #1
    Hello all,

    I'm working on building a resonating electromagnet and I was curious to know what the best core material would be. I know soft iron is a good common one and I've also heard of using ferrite. A third thing I was thinking about was using a magnet as the core but I was cursious to know what that does to the coil. I've heard somewhere that if you pulse a coil wound around a magnet, the magnet does something to the frequency of the oscillations in the coil, (although I'm not sure what). Could anyone shed some light on this? Also, my first question, which is where would be a good place to get a core to wind a coil?

    Jason O
  2. jcsd
  3. Oct 30, 2005 #2
    The Softest pure Iron would probably be best for you, If you wanted the Magnetic perm to drop off suddenly then Ferrite would be better, Iron remains a little magnetic after the coil is shut off, This is one reason to use ferrite, Ferrite is lighter than Iron but isn't as influenced on the permability level, Hemitite can also substitute Ferrite.

    If you wanted to use permenant magnets as your core you can roll up NIB Magnets like coins in a coin roll, |N/S,S/N,N/S,S/N,N/S| then wind your coil wire around it, the only draw back is it will remain Magnetic after the coil is shut off.
  4. Oct 30, 2005 #3


    User Avatar

    Staff: Mentor


    Most steel companies offer "electrical steels", but I am not sure what the smallest size will be.


    See also - http://www.electronics-related.com/usenet/design/show/104938-1.php

    Perhaps an electrical engineering lab would have some cores, or know a supplier.

    Or make your own.
  5. Oct 30, 2005 #4
    Thanks for the insight there. Just curious, why should the magnets be placed together so that they repel eachother insetead of placed end to end attracting eachother? is this to get the fields to squeeze out more? Also, how does this affect the coil itself?

    Thanks again,
    Jason O
  6. Oct 30, 2005 #5

    Thanks for all the information. So if regular old steel could do the trick, how good of a core would ordinary bolts from the hardware store compare to soft iron or ferrite? I was thinking about getting some big long carrage or hex bolts from Home Depot or something to wind the wires around. Would that be a good core? also, any idea what kind of steel those are made of?

    Jason O
  7. Oct 30, 2005 #6


    User Avatar

    Staff: Mentor

  8. Oct 30, 2005 #7
    When you put magnets together |N/S,N/S,N/S| you lose exterior field potential because of field binding.

    When you put magnets together |N/S,S/N,N/S| the Field lobes extend out into space more and there is less field loss due to binding.

    This can also be exampled by breaking a complete magnet in half, the new broken edges repell each other, the assembly should be just like putting a broken Magnet back together the way it broke apart.

    I make scrap Magnets in the |N/S,S/N,N/S| formula and they are very strong compared to |N/S,N/S,N/S|.

    It can be difficult to work with |N/S,S/N,N/S| because they are always pushing each other away but it's worth it, Especially with NIB Magnets, Careful, a NIB Magnet is very Dangerous and destroys Monitors and Television screens from 5 feet away, Also, NIB Magnets can come together so quikly that they will shatter into pieces, Little fingers can get broken if the NIBs come together over a finger, They also require special shipment because they will erase a credit card from 5 feet away as well.
  9. Oct 30, 2005 #8

    Actually I'm working with a resonating AC current in the coil. And I need to be able to make a relatively large coil so I was hoping to find a core material that would be thicker than an average nail, thats why I asked about using hex bolts instead since I can buy large once for cheap.

    Jason O
  10. Oct 30, 2005 #9
    Hi Thanks for the tips. I actually have some Neo35 disks that I could stack together and use for the core. Would ceramic magnets work for this too? I know they are non-conductive but since the material is magnetized, would that do the trick?

    I found out where I heard about the magnets doubling the frequency of the coil. it was from some article I read about that spoke of early magnetic transformers for old radios.

    Jason O
  11. Oct 30, 2005 #10
    Ceramic Magnetics will work but try to avoid materials with edges like rectangle, Square, Magnets, Try to keep your winding as uniform as possible without sharp cornering, Sharp cornering leads to higher losses in induction do to heat.

    Also, another good experiment is using small diameter refrigerant copper tubing as your winding material and using a Beer cooler to refrigerate the tube winding so lots of current can be applied without frying your winding out, You can make some powerful electromagnetics this way. cooling your winding.

    Also, you can get some high grade Kaolin White bone Clay and mix Very fine powdered Iron into the Kaolin Clay, Mix the Clay very sludgy by adding a little more water than needed, you should now have a pourable mixture which looks like goopy wet cement, take your preferred winding and place it in a cardboard cup, but don't allow the winding to touch the Cup so when you pour your wet magnetic mixture into into the cup the mixture will engulf the winding completely, Allow to Air dry on a shelf slowly for up to a month, then, if you desire, you can place the new electromagnet in a kiln oven on low for a day or two, careful not to use high heat in your kiln. You don't have to put it in a kiln but it is recomended for hardening. GreenWare is very brittle. you may also use Glazes on your new ElectroMagnet, especially as an additional coating on presubmerged winding to add to potential insulating of windings from each other.

    after all this you will have a self contained Electromagnet that can be very strong, and fun to play with.

    You can also make cores this way with no internal winding.

    Regular Modeling Clay mabe a substute for Kaolin Clay with added super fine iron powder. 60% iron and 40% Kaolin wet clay suspension.
    Last edited: Oct 30, 2005
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook