Coil Gun Help

[jnbrex]

Hello, I first discovered the coil gun about one week ago. After many failed attempts, I finally managed to fire a nail at a reasonable velocity. Now I have a few questions.

 

1) I am currently firing the gun by touching a lead of the capacitor bank to one lead of the coil itself. Would using an SCR (silicon controlled rectifier) switch result in more power, or just save the hassle of touching the wires together every time?

 

2) I used 30 gauge enameled wire to make the coil. The coil is probably 100 turns per layer, 4 layers, and 1 1/2 inches long. What is the optimum gauge wire to use, and the ideal coil length and thickness?

 

3) I bought a cheap voltage meter but am unsure where to connect it to measure the voltage stored in the capacitors. Do the capacitors store AC or DC current? Should I put the probes of the meter on the wires charging the capacitor bank, one of the capacitors itself, or the wires leading from the capacitor bank?

 

I am using six 330 volt/120 uF capacitors wired in parallel, for a combined 39.2 Joules. Thanks for all of the help in advance!

The attachment is a circuit layout that I drew.

 

Ignore the file text, failed attempt at adding a picture.

Edited May 11, 2011 by jnbrex

[Spyman]

1) If you make a fast and firm contact with the wires then an electronic switch will not yield more power but likely result in a tiny loss instead.

 

2) No idea, you need to experiment to find the optimum for your gun.

 

3) Capacitators stores DC, you can view them as very fast rechargeable/drainable batteries. If all capacitators are in parallel then it doesn't make any difference if you measure the voltage on the incoming wires, one of the capacitors or the outgoing wires.

[jnbrex]

I had my questions answered over chat by a person experienced in electricity. Now I have a new question, how can I make a charging circuit for my capacitor bank. I want to use a 9 volt battery for power. I know that capacitors are charged using inductors, but do not know how to make the circuit. Pictures and a step by step process would be appreciated. I am currently using a disposable camera flash capacitor charging circuit.

[Schrödinger's hat]

That's rather more complicated, for charging high voltage from DC you need a switched mode transformer or similar. It involves an oscillator of some kind, some transistors, some diodes, and an inductor.

There will probably be an off the shelf part which will do this, or if you do a bit of browsing online/in a suitable library (your local university may have a publically accessable library) you may find schematics.

Again I emphasize the importance of caution when dealing with high voltage electronics. Although a 9V battery is not dangerous on its own, it contains more than enough energy to kill you if you step up the voltage.