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Coilgun design Help

  1. Apr 23, 2012 #1
    I am creating a coil gun using a capacitor bank consisting of 3 470uF capacitors rated for 500V. They charge to about 250V using a Cockroft -Walton voltage multiplier. A switch controls the amount the capacitors are charged and a voltmeter gives and accurate reading of the current voltage of across the capacitors. An SCR is in place to control the triggering of the gun, but is being shorted at the moment to test. The coil specs are Inductance = 0.673mH, Resistance=1.3 Ohms, 412 turns, 4 layers of 103 turns, 22 gauge magnet wire, turn density of 14.8 turns/cm, wrapped around a copper pipe. I tried firing a bb and it didn't even move. I'm assuming there isn't enough current flowing through the coil, and i tried using a pvc pipe instead and was still unsuccessful. Help please
  2. jcsd
  3. Apr 23, 2012 #2
    There are places more specialized than this one for coil guns. Anyhow I'll give it a shot.

    1) Why do you use a Cockroft-Walton design, are you running on batteries?
    2) How do you trigger the coils?
    3) I assume that you use steel BBs, can you convince one to move at all using a coil.
    4) The LC is heavily over-damped the pulse lasts for only 10 milliseconds (if it is going into one coil) Your capacitors are probably too small.
    5) The voltage seems very high. AWG 22 is rated for 7 amps continuous current -- maybe 100Amps in bursts, but you are trying to push 200 Amps through it, but maybe for a short amount of time it is ok.

    From what I found online you only need 15 Volts or so, but fairly high current, and you should be able to lift the bb with a magnet before you even think of assembly. This site seems to give a wealth of info: http://www.coilgun.info By the way I saw a neat design somewhere where the projectile pushed little sliders while going through the gun to turn the coils on and off.
  4. Apr 23, 2012 #3
    1) it isnt as expensive as a transformer and i am using a wall supply that is converted to dc through the multiplier

    2)I am using an SCR to trigger the coil and the scr is triggered by a 9V battery and a household switch as it is applied to the gate or the SCR

    3) i checked the ferromagnetic using a refrigerator magnet and it was attracted. ever tried and small screw and it still didn't work.

    4. I assumed it was over damped and doubled the wire to increase the inductance and reduce the resistance and was still unsuccessful.

    5. it is for a very short amount of time and has not given out yet. i found i was looking at the AC voltage on the voltmeter when in reality it i about 130V.

    I wanted to venture off and try my own form of design that was efficient in terms of cost for i am a college student and do not have much money to spend on such an experiment.
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