Our Shrinking Economy

Posted by rob on 30 March 2009

Coin Shrinking from Jeremy Ruhland on Vimeo.

Turn half dollars into quarters! Turn quarters into dimes! Turn dimes into little semi-molten balls of metal! All this is possible with the proper application of insanely high electrical current at very high voltage.

"God made the quarters. It's up to us to make them shrink." --anon.

The coins don't just shrink; they keep their identity and fine details. But do they keep their value?


Hackerbot Labs is proud to contribute to America's economic downsizing.

How does it work?

A high voltage DC supply charges the big 300 µF capacitor to 10 kV, or about 15,000 J of stored energy.

The rig.

This energy is released as quickly as possible into a small copper coil wrapped around a coin.


The fast changing current creates a very powerful magnetic field in the coil, which creates a very powerful magnetic field in the coin itself. The strong opposition between the two fields causes the material of the coin to contract, while at the same time the copper coil expands. A few dozens of microseconds later, the coil has violently exploded inside a specially built blast chamber. And the coin itself is much smaller!

spark gap trigger

Where does the coin go?

No material is lost from the original coin: the weight and volume are the same as the original. But the coin now has a smaller diameter and is thicker, while retaining much of its surface detail. It's also extremely hot just after firing!

Isn't this dangerous?

Oh yes. An average automated defibrillator (AED) provides a jolt of about 150 joules. The energy stored in the big cap is about 100 times that much.


There's also the tremendously loud noise, a very bright flash of UV when the spark gap switch closes, the possibility of fire and toxic gas when stuff in the chamber burns or pyrolyzes, and bits of copper shrapnel moving with enough energy to blast clean through six-ply blocks of plywood. And somebody always burns themselves when they try to pick up the newly shrunken quarter.


To contain and prevent much of that danger, we have designed a custom-built blast chamber out of very thick high density plastic. It contains the shrapnel and covers most of the electrodes, and provides a solid platform to hold the mechanical spark gap trigger. The trigger is engaged by yanking a very long rope: simple but effective.

ready to fire

Who invented this thing?

It wasn't us. We just built one. It's an actual industrial process called electromagnetic forming. See some of these links for more coin shrinking madness:

14 Responses

  1. zach "freakybatiki" green Said,

    i love you guys.
    please send my sacajawea to
    931 madison st
    hoboken, nj, 07030

    Posted on April 8th, 2009 at 3:42 pm

  2. The Cool Tech Stuff Blog » » Hackerbot Labs Resizes Quarters into Dimes Said,

    [...] To see more of the process including photos, check out their blog. [...]

    Posted on May 31st, 2009 at 12:06 pm

  3. AllanD Said,

    Would love to buy one of those shrunken quarters

    Posted on June 1st, 2009 at 8:35 am

  4. Rich Said,

    I was thinking it might be cool to try this with a canadian "toonie" (2-dollar coin).

    they have an outer ring of nickel - buy their core is 92% copper.

    Good hanging with you guys at maker faire.


    Posted on June 1st, 2009 at 2:34 pm

  5. Intellectual Ventures Lab » Quarter Shrinker Said,

    [...] Rob Flickenger was kind enough to bring over his device and allow us to film it. What is presented below has likely never been seen by the human eye. [...]

    Posted on June 11th, 2009 at 3:40 pm

  6. Hackerbot Labs » Blog Archive » High Speed Coin Shrinking Said,

    [...] to work with the fine folks at Intellectual Ventures to quantify some of what goes on with our coin shrinker. Using a bunch of neat gear (including an extremely high speed camera), we were able to learn all [...]

    Posted on June 12th, 2009 at 12:10 am

  7. Bill Beaty Said,

    "Who invented this thing?" Gary Hawkins did: the guy who sold you those three capacitors. (also Dale Travous; they were both sharing a lab in 1991) They published details in 1993, in the Tesla-coiler hobby magazine EXTRAORDINARY SCIENCE, Volume 5 No.3, summer 1993, p10. Bert Hickman's site has some of my partial recollections at

    Posted on June 12th, 2009 at 12:43 am

  8. Becky Stern Said,

    Is 300 microfarads really the right spec on those capacitors?

    Posted on June 17th, 2009 at 7:26 am

  9. Dominic Muren Said,

    Have y'all tried this contraption on a more homogeneous coin -- say a pre 1964 silver quarter, or half dollar? The lower melting point, and lack of cladding might give you a much smoother finished product.

    Posted on August 22nd, 2009 at 10:42 pm

  10. Ric Said,

    Can you please contact me in regards to a parts list or (even better) a kit?
    I would LOVE to see an instructibles for creating this with explicit directions.
    Or if you are done with yours, i am willing to buy your quter shrinker


    Posted on September 25th, 2009 at 9:09 am

  11. dɸ/dt » Blog Archive » Gigantic resistors Said,

    [...] a high voltage voltmeter and oscilloscope lately. Using a gigohm resistor (just like we use for the quarter shrinker) I can make a voltage divider, which will let me use my regular bench tools for testing. It looks [...]

    Posted on February 2nd, 2010 at 5:18 pm

  12. High Voltage Hacks: shrinking coins - Hack a Day Said,

    [...] if doesn’t pay.” Some men just want to watch the world burn, so Hackerbot Labs posted a great walkthrough about shrinking coins and in the process making our pocket change worth just a little bit [...]

    Posted on August 20th, 2011 at 5:59 am

  13. Simon Said,

    Would be nice to see one of these coins sawed in half...

    Posted on August 20th, 2011 at 7:17 am

  14. High Voltage Hacks: shrinking coins | You've been blogged! Said,

    [...] if doesn’t pay.” Some men just want to watch the world burn, so Hackerbot Labs posted a great walkthrough about shrinking coins and in the process making our pocket change worth just a little bit [...]

    Posted on August 20th, 2011 at 2:21 pm

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