Small Change, and Other Physics Fun

fishy jew writes "Ever want an easy way to make your 'small change' even smaller? Well, Bert Hickman has it - mix a home-brewed machine, 6.5 kiloJoules, and 100,000 Amps of current! On his website, he has descriptions and pictures of his many exploits with large quantities of electricity, notably including shrinking coins, building a Tesla coil, creating Lichtenberg figures (chaotic sculpture), and more! He has extensively outlined the equipment, procedure, and results for each of his experiments, and included many pretty pictures, too. Here are Google caches for when the site gets /.'ed: Main Page, Shrinking Coins, Tesla Coil, and Lichtenberg Figures."

Comments

Re:Google Cache?

[Anonymous Coward]

To see check out auctions by him:

Here, Here, Here, And Here

Tesla Coils and other cool stuff

[Temporal Outcast]

See Sam Barros' Powerlabs for similar stuff - the guy has got a lot of very cool and realy interesting stuff.

Especially interesting are his high-voltage stuff.

How shrinking a quarter works

[Anonymous Coward]

* Theory of Operation
* Results
* EM Field Theory and Wire Fragmentation?
* Isn't Defacing Money a Federal Crime?
* So Who Invented this Crazy Device?
* References

Theory of Operation:
The Quarter Shrinker uses a technique called high velocity electromagnetic metal forming, or "Magneforming". This technique was originally developed by the aerospace industry in conjunction with NASA, and has been popularized by Aerovox, Grumman, and Maxwell. It involves quickly discharging a high energy capacitor bank through a work coil to generate a very powerful and rapidly changing magnetic field which then "forms" the metal to be fabricated. While it works best with metals of relatively high electrical conductivity such as copper or aluminum alloys, it will work to a more limited extent with poorer conductors such as sheet steel.

In my current system, I charge up a large capacitor bank consisting of a number of large capacitors, each weighing about 165 pounds and about 30" high x 14" wide x 8" thick. A High Voltage relay is used to connect the caps either to a high voltage DC charging supply, or to a high power bleeder resistor chain. A 15 kV 60 mA transformer and a set of 40 kV rectifiers provide the DC charging voltage for the capacitor bank. The primary of the transformer can be overdriven to 140 volts via a variable autotransformer to speed up the charging process. The electrical energy stored in the capacitor bank is proportional to the square of the bank voltage, and the degree of "shrinking" force is directly proportional to the capacitor bank's energy.

The charged capacitor bank is quickly discharged through a single layer work coil made of heavy magnet wire. The coin is held firmly in the center of the coil by a pair of dowel rods so that it's axis of rotation is parallel to the centerline of the coil. This constrains the coin from twisting, and also helps balance the forces wanting to eject it from inside the coil. The two ends of the coil are stripped of insulation and firmly bolted to heavy copper bus bars. The high voltage "switch" that connects the capacitor bank to the work coil is actually a high power triggerable spark gap, called a "trigatron". The main gap electrodes are solid brass, 2.5" in diameter. One of the electrodes is drilled and tapped to hold the triggering electrode (actually a modified spark plug). A triggered spark gap is the only affordable device that can hold off the high voltage and then reliably and efficiently switch the high currents involved in the shrinking process (70,000 to over 100,000 amperes).

The trigatron is fired by applying a high voltage (~40 kV) pulse to the trigger electrode, which then causes the main gap in the trigatron to ionize and fire. Once the main gap fires, current rapidly climbs in the work coil, the rate of change (di/dt) being of the order of 4-5 billion amperes/second. The natural resonant frequency of the LC circuit formed by the capacitor bank and work coil is of the order of 8-12 kHz. Through transformer action, a huge circulating current is induced in the coin, but because of skin effect, this current is confined to the outermost rim of the coin, typically penetrating to a depth of less than 0.050". In clad coins more of this circulating current flows through the better conducting copper center of the clad sandwich than in the outer layers. The coin and work coil magnetic fields oppose each other (Lenz's Law), resulting in tremendous repulsion forces between the work coil and the rim of the coin. The circulating current in the rim of the coin actually prevents the rapidly increasing magnetic field of the work coil from penetrating the interior of the coin.

The large current that's induced into the outer rim of the coin can reach a million amperes or more! The initial bank energy is typically in the range of 3,500 - 8,500 Joules (or watt-seconds) but it is being discharged in microseconds. As a result, the instantaneous power is quite large, and for a brief instant is roughly

Re:Google Cache?

[Jonah Hex]

Check out these two posts on the topic of /.'ing small sites and why /. can't mirror sites, you may find them informative.

Jonah Hex

Re:Does the metal become more dense?

[eclectro]

What happens is the coin ends up _thicker_ than before. Because it is thicker, the coin in turn becomes smaller. The mass is indeed the same before and after.

There is no exotic atomic manipulation going on. Not that people have tried (aka alchemy).

Here are his ebay auctions

Since people are interested...

[Ironsides]

Here is a link to a site on Tesla Coils, since so many of you seem to be interested in them.

http://www.eskimo.com/~billb/