Electromagnetic chamber

Discussion in 'The Projects Forum' started by stevet47, Sep 30, 2010.

  1. stevet47

    Thread Starter New Member

    Sep 30, 2010
    I have built some small electromagnets previously, but I have come across the need for a "magnetic chamber" of some sort.
    Basically I want a cylinder about a 10" in diameter and 18"-24" tall. I want to be able to place steel objects inside the cylinder and magnetize them temporarily (they are magnetized while in the chamber, and not when they are removed).

    I am thinking this is far to complicated of a task, but I ask you how I would go about doing such a thing.

  2. Norfindel

    AAC Fanatic!

    Mar 6, 2008
    What about using the non-metallic chamber as the core of a big inductor?
  3. someonesdad

    Senior Member

    Jul 7, 2009
    What magnitude of magnetic field do you require? How uniform does it have to be? Creating a 100 gauss (0.01 T) field would be reasonably straightforward, but creating a 10,000 gauss (1 T) field would be a significant effort. You should also give us an idea of how much money you're willing to spend. The cylindrical size you indicated is fairly large and will contribute significantly to the cost as the required field size goes up.

    Three "classic" methods are a) a solenoid like Norfindel suggested, b) Helmholtz coils, and c) a typical lab electromagnet configuration (two solenoids with variable spacing between the pole pieces). Depending on the field needed and the uniformity required, it might also be possible to use permanent magnets.

    More importantly, give us an idea of what it is you're trying to accomplish. Often we get a notion in our head to solve a problem one way, yet there may be other ways to solve the problem in an easier fashion. You'll leverage the experience of a number of folks if you do so.
  4. stevet47

    Thread Starter New Member

    Sep 30, 2010
    Thanks for the replies guys.

    To answer the questions...
    I dont have to reach 1T gauss, but something like .6T or .7T would be nice.

    It doesn't have to be a cylinder like I described, technically I just need to be able to magnetize stuff. The cylinder is just what I pictured.

    As far as what I am trying to accomplish... it is for a sculptural experiment, I work for an architecture/design firm. This is definitely not the easiest way. I am going to start experiments with some permanent magnets tomorrow, but the principal of the firm wants to pursue this idea. I dont think spending a couple hundred bucks would be much of an issue.
  5. someonesdad

    Senior Member

    Jul 7, 2009
    If you're wanting fields on the order of 0.5 T over the dimensions you indicated, you're probably estimating 1.5 to three orders of magnitude too low on cost (perhaps more) if you're going to make the fields with electrical currents. You can get neodymium permanent magnets that have fields that approach that (you'd have to get a gaussmeter to actually measure their values), but that's going to be pretty close to the magnet itself.

    I've seen production tooling to magnetize magnets for disk drives that used pulsed currents and pretty heavy power supplies. This was 30 years ago and I'd estimate they spent $20k-$30k on the hardware and probably the same on the engineering and tech time to build it. However, the magnets had lower coercivities than what you're after; still, that may give you a feel for what you're wanting to do. OTOH, you might be able to accomplish what you want to do with some permanent magnets. They will be the simplest and cheapest to start some experimentation with.
  6. wayneh


    Sep 9, 2010
    Ummm... How could you tell they had ever been magnetized if they no longer are magnetized once removed? Do you merely mean that they will be exposed to a field inside the chamber and not outside of it?
  7. stevet47

    Thread Starter New Member

    Sep 30, 2010
    hmmm.... it sounds like just what I thought.... to complicated and expensive for what it's worth.

    If anyone else has ideas, keep them coming, but for now, I think I am going to stick with permanent magnets, or maybe an electro magnet from a motor or something.
  8. Ghar

    Active Member

    Mar 8, 2010
    I've used a Helmholtz coil with a 50 Gauss field, the field is a 7 inch cube and it's many pounds of copper and requires 10 amps to get that 50 Gauss.

    Most coils are very low field strength especially if make them large.

    Check out the Helmholtz equation...

    If you stick with 10 amps and use a 10" coil spacing with 20" diameter (0.254m radius) with a desired field of 0.01 Tesla requires 280 turns ... that's about 450 meters of wire per coil and for 10 amps tightly coiled you need 14 AWG or something like that. It'll actually be more length because as you go about winding it the radius gets larger and the field gets weaker.
    That's 20 pounds of copper per coil (you need a pair).

    It's a very simple construction but practically it isn't that easy.
  9. windoze killa

    AAC Fanatic!

    Feb 23, 2006
    Caution: Depending on how you make this cylinder you may end up creating a solenoid and when you energise it the object inside may be thrown out. I guess this would depend on the size of everything but I can just picture it.