Coil gun HELP

[happyp]

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

[Enthalpy]

Hi Happyp!

 

The copper pipe is definitely inadequate, Pvc was the right choice.

I did rather similar games with a comparable capacitor energy and did see a mechanical effect - but just on a shorted loop of copper wire, not too heavy, close to my flat coils, and it was repelled to few cm height.

 

So depending on what a bb is (foreign language, sorry) it's very possible that the energy doesn't suffice. You might try the lightweight copper loop first.

 

Your coil isn't ridiculous (what's the diameter?), as is discharges the capacitors with 3ms half-period (I suppose the inductance is measured!). Damping is rather low so you should check if the switching circuitry or the rectifier protects your capacitors against inverse polarisation.

 

An SCR can handle some 10* the rated current for such a half-sine pulse, but be prepared to replace it occasionally - this depends on the precise waveforms in your circuit.

 

If you increase the energy (I had once 1m3 capacitors and 20kA to make magnets) be prepared to hold all wires firmly and check all contacts, as bad contacts detonate. And with 250V DC, please use appropriate care.