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Solenoid core material

  1. May 17, 2005 #1
    http://img16.imagevenue.com/img.php?loc=loc76&image=054_doorbell1.jpg

    I am building a circuit such as the one above. The only difference is that it will be running for long periods of time. So heat becomes an issue. To make the most efficient and strongest electromagnet I am wondering what I should be looking for in core material. The cores will be 5/16" x 1 1/4" wrapped with 22 or 24 ga. magnet wire. This will be a DC circuit with voltages between 3-8 volts at around 1 amp give or take. Operating frequency will be between 80-160 Hz for long periods of time...like 20 minutes or more. There can be between 228-304 turns per coil....Not sure about this as the permeability and saturation is different for each core material. Also I'm trying to keep the resistance under 1 ohm per coil. If it means anything I will be using a capacitor in parrallel to the coils to catch the spark...usually a 30v 47uf.(incidentally if anyong can explain to me why changing the cap. value has such a drastic effect on the htz it would be greatly appreciated...I mean the cap. must be doing something besides just catching the spark...)
     
  2. jcsd
  3. May 17, 2005 #2
    well, im probably not as experienced as other people on this forum, but ill give my 2 cents

    For the core, i think iron would be the best, it has the highest magnetic permeability, so you will get the strongest electromagnet possible, without using too much power in the coils. An ironm bol will work just fine and i find that the ones that are threaded just make winding the wire easier as it will give it some uniformity(not that it matters too much anyways)

    As for the capacitor, it will probably be essential in creating the desired frequency of ring because capacitors discharge at constant intervals, so having a cap that will discharge every 120hz for example will cause the dc current moving towards the magnet to pulsate at 120hz, now this could be completely wrong, as i have little experience with capacitors
     
  4. May 17, 2005 #3
    Iron is what I'm using now. I was wondering if there are better materials or alloys that would lend themselves better to this application...for lowest hysterysis...highest permeability...etc. Thanks for the reply.
     
  5. May 17, 2005 #4
    i dont know its exact composition, but it is used in the deflection of electrons on the back of a TV tube..
    it is a dark , kind of brittle material , which has outstanding magnetic properties.. maybe you could crush it up and form it to the shape that you want with some polyester resin..
     
  6. May 17, 2005 #5
    that seems a bit overkill just to make an electromagnet(unless u need it to be super powerful with the very least ammount of energy), anyways out of all the common materials you can easily get, iron is best
     
  7. May 18, 2005 #6
    I agree iron is the best overall as far as availability and cost go. But what if I wanted to increase the efficiency of the coil....more efficiency = less voltage=less heat. I've been researching and have come across powdered iron cores...nickel iron cores...etc. Cost is not an issue. What I am looking for is a lead on what would give me the greatest flux density and since this will be turned off and on about 100 times per second I need the least amount of hysteresis...the least amount of magnetic memory...etc.
    thanks
     
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