Can Crusher 3 uses 6 defibrillation capacitors to a total of 3 kJ

Can Crusher 3 is now boosted to 3 kJ and mounted into a microwave oven case.
“Continue reading” for more details and photos.
I have used 6 identical used defibrillator caps of about 34 uF 5.1 kV (500 J) each. Its features are: 1 Able to fit in a microwave oven with a top cut out so that caps are safely out of the way and there is some explosion protection in case one of the caps dies dramatically. 2 Tungsten contacts for the gap. Hopefully long lasting and non-stick. 3 Provision for solenoid activation of the gap. 4 A sturdy base for the coil connection. 5 Brass connectors used or planned. Potential problems are the slightly longer circuit path with a number of dissimilar metal junctions particularly the tungsten contacts as these can’t be soldered.

The capacitor bank, gap contacts and crushing coil next to a can crushed recently. The centre photo shows a close up of the tungsten contacts and the movable switch arm attached by heavy braid.

A through the middle shot with the connections to the capacitors.

The smaller coil setup to place inside a can. The coil mounted inside a can and the effects of it with expansion rather than crushing. This photo shows a can which had 3 turns wound lengthways but the power was inadequate to crush it. At this stage I had strong suspicions that the caps were failing.

The neat arrangement of the caps inside a cut out microwave oven case with an NST for charging. The defibrillator paddle that I use as a remote switch.

The functioning unit as set up for public display complete with signs and instructions. The can crusher has a flip open front which has the active HV covered. The coil can be angled to shoot an aluminium ring forwards as well. The switching is mechanical with tungsten contacts by a solenoid, triggered by the switch on one defibrillator paddle. There is a voltmeter and a red strobe to indicated charging obscured by the paddle in the pic. The 6 caps shown had died however so they were removed and 4 new ones were added to the original 2 larger defib caps to give a total of 3 kJ. I strongly suspect that these have now died too.

The cancrusher setup included in my public demo that I set up for the Physics Dept during the University of Western Australia open day on Sept 20, 2005. It was a popular display with both the can crusher and the Tesla coil generating large noises to bring the curious from afar. I did lots of demos crushing both light and standard strength beer cans with a good crowd response. Although it crushed the cans well it was probably only due to the original large defib caps at 1 kJ that were still functioning. The whole idea of using defib caps is flawed without correcting the voltage reversal.

So, time to move on but not before an autopsy of one of the caps. The opened can of a modern type small 35 uf 5.1 kV defib cap. The cap being unwound after one end was sawn off. What happened next was interesting… As I unwound more and more (about 10 feet) I started to get little shocks and these became stronger the further I went. These caps had just been tested to 5kv then discharged fully. Typically they can recover a couple of hundred volts to give a visible spark when shorted. Not to be deterred, I got rubber gardening gloves and continued unwinding and the zaps became audible and very visible in low light. Sensing a photo opportunity I set up the new camera in a dark place and started tearing off the dielectric. With each tear there was a row of faint sparks along the tear line which recurred with each tear of the dielectric. This is one of my most interesting photos despite how dull it looks. It is a 13 second photographic exposure with 2 or 3 tears of the capacitor dielectric showing rows of tiny blue sparks (roughly in line with the two wood screws seen here). My blue-green gardening gloves have a white cuff that can just be made out in the motion blur. This shows the dielectric is charged but not allowing the charge to flow elsewhere. Alternatively it is triboelectric generation (think van der Graaff generator). I haven’t seen this type of photo anywhere else. I wouldn’t have been able to take it without the Nikon D70S SLR digital which has much better low light ability.

This can crusher has now gone to the Physics Dept at the Uni of Western Australia. For details of the upgrade see the public display section. Next is tearing the can into strips with an internal coil. The setup is 4.5 helical turns of rectangular wire placed under the end of the can and a block of wood above it to provide some inertia. The left photo above shows the setup with the coil inside the can to explode rather than implode the can. The wooden block in the centre is not needed as the net forces are outward. The right photoshows the can torn into strips which were blown away on the free end and curled around the attached end like a large dead insect. The left photo above shows the setup with two cans in one coil. The centre photo shows the two cans crushed together. The right photo shows toucans.