Coilgun KMWCBS562A1

I am building my own coilgun. On this page, I’ll keep you informed about what’s going on.

Last update: 21 may 2007

The beginning

My fascination on coilguns started quite a while ago, when I stumbled across an online discussion about shooting away a projectile with electromagnetic force. Since then, I’ve been searching the net for more information about the subject and I even constructed a small capacitor bank (about 200 joules) consisting of second-hand capacitors with the intention to build a small coilgun:

As you can see, this setup is far from ideal. The wires are too thin, the charger (rectified mains with a 60W light bulb in series) was very slow and would only charge to 300V instead of the intented 325 and some of the capacitors are pretty old. Because of this and the fact that I couldn’t find a suitable high current switch, I abandoned the project.

However, I still wanted to build a coilgun some day. And when I recently stumbled across a number of 1200 μF 400 V capacitors I couldn’t resist and bought six of them for a total of € 20,-. Although it are regular computer grade electrolytics (not pulse rated) and they were probably used (but still look pretty good) I think that’s a good price. The fact that it are computer grades doesn’t bother me too much because I won’t be using them for a very high power coilgun and won’t be firing it all day long.

Design goals

The design goals for this coilgun are as follows:

Capacitor bank: Six 1200 μF capacitors in parallel for 7200 μF at 400 V
Energy: 562 J (when charged to 395 V)
Peak current: 1000 A (roughly 167 A per capacitor)

Building the gun

25 may 2006

Today I bought the capacitors at a electronics flea market. I also bought a large diode (Semikron SKN 130, rated 165 A continuous and 2500 A peak at 400 V) for € 5,- that I will probably use to protect the capacitors from reverse voltages and currents.

A few days later

The construction of the capacitor bank is now completed.

The busbars are made from aluminium and are 20 mm wide and 2 mm thick which makes a surface of 40 mm².

I also found some BTY95-400R thyristors on the internet for € 5,- a piece and bought two of them. These thyristors are rated for 680 A peak so when I connect them in parallel, I should be able to swith a maximum of 1360 A. Hopefully they will arrive soon.

Building of the coilgun will contiune as soon as the thyristors have arrived.

2 june 2006

The thyristors (or SCR’s, how you want to call them) arrived today. I’ve tested them using a
simple SCR test circuit and they work fine.

The next thing to do is connecting the SCR’s.

17 june 2006

Long time no update, but I’m glad to tell you that I ordered the wire (20 meters of 1,5 mm enamelled wire) to wind the coil for this coilgun. Hopefully it’ll arrive soon.

22 june 2006

Today the wire arrived. Now I can start with winding the coil.

30 june 2006

Two days ago, I made a quick lashup and tested the gun at relatively low energies. With the bank charged to 200 V (approx. 144 joules) it can already shoot a nail clean through a can (i.e. it enters at one side and exits at the other) and almost through a piece of cardboard (the first part of the nail goes through, but then it gets stuck). The gun could also make a hole in the bottom of the can, but the nail didn’t go through.

Yesterday I started building an enclosure for the gun. When that’s finished, I will start testing it at higher energies. This is what it looks like so far:

In the middle picture it looks like the barrel isn’t straight: in reality, that’s luckily not the case. The code is the name for the coilgun, and can be read as: Kipmans Magnetic Weapons Coilgun, Bench mounted, SCR switched, 562 joules, first revision, single stage.

The switch that I wanted to use as a firing switch was obviously of very bad quality because its casing cracked while under normal use, ruining the switch. I’ll have to order a new one. In the picture showing the whole setup, you can also see the trigger circuitry. In fact, that’s only a 9 V battery, two resistors and a header to connect a switch. When the switch is on, a current of approximately 80 mA (the SCR’s max rating) flows through the gate of every SCR to its cathode.

The barrel is a piece of aluminium tubing with a outer diameter of 10 mm and an inner diameter of 8 mm. The walls are relatively thick: 1 mm. When the gun is fully working and I’ve done some measurements I will consider searching another tube with thinner walls. The barrel is slotted to prevent eddy currents.

The coil consists of 10 layers of 24 turns each. It’s wrapped in cellotape so it doesn’t look very good. Unfortunately, I didn’t have any nice looking, black electrical tape left so I didn’t have a choice…

7 july 2006

I mounted the new firing switch. This week I’m planning to do some extensive testing on the coilgun to determine the projectile velocity and the efficiency (I’m not expecting much – most first coilguns have efficiencies between 0,05 and 0,5%).

21 may 2007

Finally, an update containing the results of the aformentioned tests. I actually did these test in july ‘06 but never took the time to upload them to this site.

Highlights are:

• Highest velocity: 16,90 m/s (60,84 km/h) at different energies & with different projectiles;
• Highest kinetic energy: 2,29 J at both 300 and 200 V (144 and 324 J electrical energy respectively), with a projectile measuring 0,8*5,5 cm and weighing 16 g;
• Highest efficiency: 2,45% at 100 V (36 J electrical energy) and with a projectile measuring 0,8*3,7 cm and weighing 12 g.