- Few parts.
- Huge parts (for posing purposes).
The internet is full of examples, this is a particularly well-made one: http://hackedgadgets.com/2009/05/07/mv-coilmaster-mark1-coil-gun/
This one comes with a lot of information on the snares: http://www.coilgun.info/mark4/home.htm
I wanted my build to be a single stage version (obviously – I had never done this before), but I went for mains voltage (which was not the best decision here).
Math said: If I charge 9.900 µF to peak voltage there would be 0.5 * 0.0099F * (325V)² = 522.8 Joule stored, about 9mm Parabellum engergy. If an efficiency of 1% could be achieved, the projectile would be at eye level with an airgun (7.5 J).
That the enormous current spike would kill almost every thyristor I threw at it was figured out the hard way later…
I cannot comprehend anymore which state of development this schematic resembles – look at the latest picutes below and read the values there. 😉
…and there went the first thyristor! Studying “Barry’s Coilguns” revealed to me, that I was too generous with the wire diameter for the coil – the current had to be tamed with more resistance later.
But first I wanted to make this a little more scoop-proof.
Testing this setup I realized what I had built – and how much 500 Joule are, if they can be instanly released…
I went for snubbers to solve my problems – to no avail.
There was no problem with inductive kickback – the inrush current killed the solid state switches. Fittingly hackaday.com pointed me to circuitlab.com, so I could simulate what was happening. (There was no way I would hook up an Oscilloscope to THAT circuit, obviously.)
An air coil calculator classified my coil as ~ 200µH. The capacitors were 3.3 mF “Ultra Ripple, Inverter Grade” types, 4 in parallel, so I just skipped the sideeffects.
So there was the problem: the last thyristor was rated 1200 V / 49 A (RMS) and could handle 300 A for 10 ms (half a sine-wave). The only way it could have survived was a lot more damping – the snubbers would be irrelevant then.
After the simulation I went for an IXYS “CLA 80 E 1200 HF”, rated 1200 V and 126 A with IFSM (“max. forward surge current” of 900 A. Damping resistance was set accordingly.
…and I wound a new coil. But then i didn’t have a smaller pipe at hand and zip tied a hose to a board.
Re-simulation (740 A peak) and test firing went well, so now I needed to build a 3D-printer and print a coil winder…
You guessed it: it ends here. For now. 😉
(Original posts starting February 13th 2012, e.g. http://www.metalforum-owl.de/viewtopic.php?f=21&t=138&start=140#p44674)