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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
Registered Member #3888
Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649
Your circuit looks fine but you should include an antiparallel diode across your coil (the back emf generated when the coil's field collapses can damage your other components)
For your barrel you should use a thin walled, non conductive tube with an inner diameter as close as possible to the diameter of your projectile. non conductive prevents eddy current losses in the barrel, and thin walled allows the coil to be as close as possible to the projectile itself.
A BB is not a good projectile. Try a segment of a ferromagnetic nail that's about as long as your coil.
For more current in the coil, use fewer turns of a thicker wire. This will also give you a shorter pulse length. The inductor and RLC simulators here might help you. 10-15 turns per layer, 4 layers, 16-18awg wire is about what i'd suggest (should at least send a nail segment through the side of a can.)
The initial position of the projectile should be just outside the coil (varies with pulse length.) A few trials should help you narrow down the best initial position for a given coil, projectile, and energy level.
Good luck. I'll be happy to answer any more questions.
Registered Member #4237
Joined: Tue Nov 29 2011, 02:49PM
Location:
Posts: 117
Pretty much what forty said. You can also encapsule your coil in iron or another ferromagnetic material in order to gain efficiency. The main problem is still your projectile, though. Is it even magnetic, in other words, does it stick to a magnet? If not, then it's useless and won't move no matter how many amps you run through your coil.
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coilgun design help
