How to make an electromagnet?

Discussion in 'General Electronics Chat' started by Flaffen, Oct 1, 2009.

  1. Flaffen

    Thread Starter New Member

    Oct 1, 2009
    4
    0
    Hi. I've got a project going and I need to make an efficient electromagnet. The problem is that I'm pretty much a noob at this, so I could use some hints and tips at how to make it as efficient as possible.

    The electromagnets I'm building are supposed to repell eachother (when putting + next to + and vice versa). The electromagnets are supposed to only be turned on for a very short time and then turned off again, and I need them to be as powerful as possible for this short period of time. The shape of the electromagnets are supposed to be tubular.

    What metal should I use? Where can I get hold of this metal?
    What wire should I use to wrap around the rod? Does it need to be thick or thin? What metal is best used for this wire? What batteries should I use? Is there a ratio between the diameter of the wire and the rod that would make it more efficient?
    Should I make several layers of the wire wrapped around the rod or just one? Should I put insulation outside the wire? These types of basic facts is what I'm looking for, but I dont mind more advanced ideas either (tho I'm not that fluent in "electro-lingo" :p)

    At the moment I have an approx. 1cm diameter iron rod, and I use 0.6mm diameter copper wire to wrap around it (it has some lacquer around it as insulation). I dont know if its soft iron or not. I have tried paralell circuiting 5x 9v batteries to the magnet but it diddent seem to make it very powerful. So if any of you have any tips or hints on how to make this as powerful as possible for a short amount of time I would greatly appreciate it. I'm planning on using a high current and high voltage to make it more powerful (as high as possible from circuiting batteries). Also it would be preferrable if the magnetic field dissapated as quickly as possible after the current has stopped.
    And I'm also wondering how I can greatly increase the voltage of the current. As far as I have understood, I can make a tranformer to incfrease the voltage by wraping copper wire around two permanent magnets (facing in the opposite direction) and let the current flow throught this.

    If anyone has any hints or tips or any how-to's I'd greatly appreciate it.
     
  2. Wendy

    Moderator

    Mar 24, 2008
    20,765
    2,536
    Loose the 9V batteries, for a powerful magnet you're going to need real current. How short a duration are you thinking? You could use some of the tricks used by rail gun enthusiests.

    http://www.coilgun.info/about/home.htm
     
  3. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    The significant thing in an electromagnet is the permeability of the core and the current in the winding. Having a meter to measure current would be useful in experimenting.

    However, your thought -
    is not at all correct. Current is the result of the voltage divided by the resistance. So, upping the voltage will increase the current, but current does not have a voltage component, just that dependency. Be very careful about increasing the voltage applied to the coil, though. Too much current will make the wire hot and could start a fire. Past a certain level, the increase in current will not increase the magnetism - the core will be saturated.

    Turns of wire around a magnet's pole pieces will not increase anything. Transformers do not use magnets, and only work with continuously varying voltage.

    Here is a link into our Ebook about electromagnetism - http://www.allaboutcircuits.com/vol_1/chpt_14/2.html
     
    Last edited: Oct 1, 2009
  4. Flaffen

    Thread Starter New Member

    Oct 1, 2009
    4
    0
    Well I only want them to repell eachother for a short moment, like 0.5 secs or less. Also, cant I use 9v batteries even if I paralell couple them? I have like 30 of em (they were RLY cheap). And wont multiple layers of copper wire winding increase power? Or produce a better magnetic field? What do you mean by a real current? I need to be able to use this with batteries, should I use D cell batteries instead?
     
  5. hobbyist

    Distinguished Member

    Aug 10, 2008
    764
    56
    what he means is, 9 volt batteries do not have the current capacity, that your asking for, your coils of wire are a very low resistance to the battery circuit, so the battery is going to be almost shorted out, draining the battery very quickly.

    When we were kids we used to use dry cells, and wrapped wire around a nail and got a nice small electromagnet.
    Those were the big lantern batteries.

    A lead acid battery would probably work better for the kind of current your asking for.

    Probably a way to make it work, but not powerful, would be to calculate the amount of current your bank of batteries can put out, then using ohms law figure the amount of resistance against that battery voltage (nom.)7.5v. and then use a guage of wire, and length needed to give you the maximum ampount of turns possible, to have a resistance introduced into this circuit, about 10 times greater than calculated valuie, that your bank of batteries can withstand (current draw).

    Like I said before:
    A lead acid battery would probably work better for the kind of current your asking for.
    And there nice and compact nowadays, I bought a small 6v. and a 12v. to power some of my robot projects.
    Last a long time, and can be recharged with a car battery charger.
     
    Last edited: Oct 1, 2009
  6. rjenkins

    AAC Fanatic!

    Nov 6, 2005
    1,015
    69
    A simple, basic calculation for the strength of a solenoid / electromagnet coil is the Ampare-Turn rating.

    This is as it sounds, the number of turns x the current through the coil. The higher the ampere turns figure, the stronger the magnetic field.


    For example, a 1000 turn coil with 0.5A current gives 500 Ampere Turns.
    A 100 Turn coil running at 0.5A gives 50 A-T
    A 100 Turn coil running at 5A also gives 500 A-T.

    A core will change the effective strength, but for any given core (up to the point of saturation), the relative changes should still apply.

    For any particular wire size, adding turns will add resistance and reduce the current, so the ampere turns will roughly stay the same for a given supply voltage. Picking the wire size correctly is very important.

    To get a strong, short pulse, you could possibly use several batteries in series charging some high value capacitors. The capacitors could provide a short, high current pulse but you will probably need something in the tens of thousands of microfarads range.
     
  7. Flaffen

    Thread Starter New Member

    Oct 1, 2009
    4
    0
    Ok thanx for the info, it has helped a lot. But now I'm wondering if it is possible to "store" an electrical charge with higher current or voltage than what would flow from a bank of batteries? Kind of "charging up" and realeasing it, getting a very high current or voltage for a short moment. Or do I need to circuit a bunch of batteries to get a decent current?
     
  8. blueroomelectronics

    AAC Fanatic!

    Jul 22, 2007
    1,758
    98
    What are you trying to build?
     
  9. Duane P Wetick

    Active Member

    Apr 23, 2009
    408
    19
    I worked with electromagnets for many years. Here are some hints for design:
    The use of soft steel (1010 or 1020 alloy) makes the best electromagnet.
    DC amperes x # turns gives the magnetic strength figure. This applies to all electromagnets.
    Depending how you orient the poles, you can get a shallow or deep field.
    When you attach a piece of iron to a magnet, you effectively charge that piece of iron to the opposite polarity of the magnet's polarity; opposites attract.

    Regards, DPW
     
    Last edited: Oct 27, 2009
  10. Flaffen

    Thread Starter New Member

    Oct 1, 2009
    4
    0
    Well, my problem is that I dont really know where I could get the soft iron/steel for the electromagnets. Also does anyone know a good way to get the copper wire to stay put? Problem is that I wind it around the core, but it has a tendency to slide out to the sides, and that is especially a problem when I wind another layer ontop of that (the new layer of wire often slip between the copperwire beneath it, making it irregular). So if anyone knows a good place where I can buy magnets, that would be cool (I will save a lot of time and energy if I can just buy them, as I have tested the concept already and now I just have to build a prototype of the device).
    I need opposite pole magnets with a deep magnetic field, and I need to be able to reverse the poles quickly. They need to be very powerful, but only for a short moment.

    What am I trying to build? Well I have a lot of ideas I'm going to try out, the concepts themselves I will keep a secret for now.
     
  11. Duane P Wetick

    Active Member

    Apr 23, 2009
    408
    19
    Many electromagnets use a bobbin, just an insulating sleeve w/ ends and the wire is wound randomly; remember its the number of turns that are significant, not the parallelism of the turns. Putting the turns on neatly beside each other will make a smaller overall package however. A very strong electromagnet can be made by machining a cup out of a steel billet and leaving a center pole that accepts the bobbin w/ coil. Epoxy fill and you're done!

    Cheers! DPW
     
  12. BMorse

    Senior Member

    Sep 26, 2009
    2,675
    234
    After winding your first layer, wrap some masking tape around the first layer before wrapping the second layer, 1 layer of masking tape should do..... after the coils are completely made use some epoxy or hot glue on the ends to keep the coils from sliding off your core.....


    My .02
     
Loading...