When I finished the “University of Applied Sciences” I thought a coilgun AKA Gauss rifle (not to be confused with a railgun) would be a gerat hobby project:

  1. Few parts.
  2. Huge parts (for posing purposes).

The internet is full of examples, this is a particularly well-made one:

This one comes with a lot of information on the snares:

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.

CIMG1948  DSCN6472

But first I wanted to make this a little more scoop-proof.

DSCN6477 DSCN6474 DSCN6473 DSCN6476  DSCN6478 DSCN6479 DSCN6480 DSCN6484 DSCN6530 CIMG5768


Testing this setup I realized what I had built – and how much 500 Joule are, if they can be instanly released…

CIMG5727 DSCN6591

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 pointed me to, 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.

50mohm_sc15u2j 50mohm_simdpuwp

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.

400mohm_scm6uwg 400mohm_sim6iuq1

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.

DSCN6618 DSCN6622 DSCN6616

…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.

IMG_20120301_202933 IMG_20120306_173728

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.

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