Coin deflation

By Phil Plait | June 23, 2009 2:05 pm

Via Built on Facts comes this slice of awesome from the Intellectual Ventures Lab site. They strap a scary big capacitor onto a U.S. quarter and zap it with 15,000 Joules, a truly terrifying amount of energy to pack into a few square centimeters. And what happens when they do?

Go watch the videos to find out. It’s pretty cool. Interestingly, in the high-speed video, you can see the affect on the coin before the materials get so hot they incandesce. That means the magnetic field is interacting with the quarter itself before it heats the air, which is not what I expected.

You can also clearly hear one of the guys telling people to look away when he trips one of the safety devices. That threw me for a moment. Why look away? Because it’s bright? And then I realized: they are creating a potential of 10,000 Volts, which means they get enough energy density to make X-rays ultraviolet light. Holy Haleakala. Anyway, watch the setup video as well.


CATEGORIZED UNDER: Cool stuff, Science

Comments (59)

Links to this Post

  1. Intellectual Ventures Lab » Quarter Shrinker | June 24, 2009
  1. BJN

    And how does looking away mitigate x-ray exposure? Where’s the lead foil for the gonads?

    Intellectual ventures, indeed. This could be named “Quarter Thickener” and be less misleading. The questions at their site indicate that some people think that the quarter really shrunk in volume as well as diameter.

  2. amstrad

    Isn’t this in violation of 18 USC Chapter 17 Sec. 333: Mutilation of national bank obligations

  3. Chris A.

    I’ll say it before someone else does: You mean “effect,” not “affect.”

    Cool video, nonetheless.

  4. Arnold Jamtart

    No, it’s affect. If you look really closely, you’ll see that the quarter is sad. Then angry.

    Did they ASK the quarter if it wanted to be shrunk? Scientists…

  5. Mike

    Yeah, I don’t think this contraption will make any significant number of x-rays.

  6. Jon B

    This is from a different company, but you can buy your own shrunken coins, too: (I’m not affiliated, I just think the end results are cool and wanted to share.)

  7. Guysmiley

    It does probably spit out a good deal of UV light though, so looking away from the actual explosion is a good idea.

    I’ve had my eyes singed by welding arcs before, it’s not fun.

  8. mus

    I once read somewhere that Richard Feynman (sp?) was able to look at the trinity atomic bomb test directly without going blind because he looked at the explosion through a windshield. The reasoning behind it was that bright light itself doesn’t cause any damage to your eyes, the only reason you go blind from staring at the sun is because of the UV rays. Since UV rays don’t pass through glass, it was perfectly safe to look at something that bright through a car’s windshield.

    Does anyone know if this is true? If so, does that mean that one could stare at the sun through a windshield if they wanted to? (personally, I have no desire to do that!)

  9. T.E.L.


    I worked for a while in the early ’90s at a place that did a lot of automated arc welding. The welding tips needed frequent adjustments by the maintenance department, and the (young) guys thought they’d streamline the labor by watching the tips in action with their bare eyes. I suppose they’re all having the cataracts removed right about now. :)

  10. Charlie Young

    Reminds me of some of the brilliant and lunatic minds in my high school and college physics and chem classes.

  11. There should be no X-rays produced by any part of the system. Rob said “look away” because the spark gap emits intense UV. We discovered this when we noticed that the HDPE around the spark gap glows blue for a few seconds after firing.

    Quoting Dan Heidel:
    [It’s] clear that we have a [preponderance] of UV and that UV induces molecular breakdown in the polyethylene, particularly in plasticizers, leftover [catalysts] and oxidation [breakdown] products. The luminescence observed tends to be associated with oxygen infiltration into the plastic and is probably a singlet oxygen forbidden triplet state transition which gives a very characteristic blue light emission with a long decay time. (most fluorescence [emission] decay times are in the pico or nanosecond timeframe)

  12. Charlie Young

    @#6 mus

    From what I know about visual photoreceptors in our eyes, it’s not just UV that burns them out. Radiation in the visual spectrum can also fry the neurochemical reaction to the point it can’t recover if there are enough photons.

  13. T.E.L.


    That’s a pretty good question. It’s true that window glass blocks a lot of the UV, and it’s true that Feynman looked and didn’t get blinded; but he also reflexively recoiled from the flash and didn’t get a lengthy exposure from the unfiltered emissions. In my estimation, if it’s bright enough to hurt, it’s probably not good for your eyes.

    Reminds me of when I was a theater booth operator way back in the 1970s. The projectors used 80-amp carbon arc lamps, which had to be manually trimmed after each reel. Once when I was doing this I didn’t realize that the current was still live. I touched the two carbon rods together (to check that they’d do so at the proper time), and they lit up right in my face. At that distance it was brighter than several suns, and my nervous system responded with some authentic puking. I was sick to my stomach the rest of the night.

  14. T_U_T

    Holy crap. I wonder how much energy it would be needed to compress the coin to density where nuclear fusion would start. ( provided the coin were hollow and filled with LiD )

  15. Mike

    I don’t see the mechanism for generating x-rays. It’s going to be hot, so I suppose there could be characteristic x-rays. What metals are in a quarter?

    Looks like it’s 90% Cu. Cu has a k-edge at 9 keV, so you could make 9 keV x-rays.

  16. Jason Dick

    That means the magnetic field is interacting with the quarter itself before it heats the air, which is not what I expected.

    I don’t know. Makes sense to me. I mean, the quarter is conductive, so it’s going to be absorbing energy from the electromagnetic field extremely rapidly. The air, being a very poor conductor, isn’t going to receive much. In fact, I would tend to expect that the heating of the air came indirectly from the heating of the electromagnet and the quarter.

  17. Torbjörn Larsson, OM

    Hmm. It’s probably the current through the coil that makes the most heating by resistive heating. It blows up from magnetic forces however. (Albeit I assume the circulating current of the coin should heat massively too despite the initially large cross sectional area. It certainly looks that way.)

    There’s two factors in play then.

    First, there are some thermal capacitances but poor couplings to, say, air in that system.

    Second, the magnetic field is induced by the current derivative di/dt. And this is hitting its maximum faster than the heating from the current amplitude.

    @ Guysmiley:

    On the UV light absolutely, electronics industry have UV lamps that are claimed to fry your eye faster than you can blink. (Funnily though, you can’t get anyone to test it. :-o) One shouldn’t dismiss the thermal load either when considering dumping lots of light into what is, after all, a poorly cooled optical system.

    And while you can recover from those welding accidents, you can also get material from explosions or arcs implanted in your cornea without safety goggles. It had happened to a guy I used to know at work, eventually he got serious trouble (infections, I think), and ended up having to have is loosened retinas spot welded back by laser, both eyes as I remember it.

  18. Torbjörn Larsson, OM

    Oh, update, update. I see Jason and I came to the same model for most of this.

    @ mus: Don’t try that with a quartz window, though. More UV will get through.

  19. Pieter Kok

    That means the magnetic field is interacting with the quarter itself before it heats the air, which is not what I expected.

    The change in the magnetic field propagates inwards with the speed of light, and the quarter reacts to that. The visible explosion is due to the dissipation of the current in the coil, which is a much slower process.

    Very cool video, though.

  20. Pete Gruett

    We looked into doing this for our public demos when I was an undergrad peon in plasma physics at the U of Wisconsin. We had plenty of capacitors (the main bank for our large experiment stored 3 megajoules at 10Kv) and ignitrons rather than those cheesy flip switches but we could never figure out a way to do it that didn’t blow the coil apart in a way that was really too dangerous for a public demo.

    The flash in this video appears to be entirely from the vaporization of the coil. It doesn’t look like the quarter ever incandesces. Also, when the guy tells people to look away, he appears to be dead-shorting the capacitors. Once the coil is destroyed, there’s no way for the capacitors to complete their discharge and, if I heard him right, they were still at about 400 volts, plenty of energy but not enough potential for x-rays. He was probably concerned about bright arcs between the carbide switch contacts.

  21. Codswallop

    Everybody’s comments on the physics of this are very interesting (wish I understood half of it), but mostly I have to say that the finished product is pretty damned awesome. I bought one of the quarters last week, and I can’t stop looking at it. I know some of your guys are rolling your eyes at the rube who literally plunked down good money for bad, but admit it–you want one too.

  22. Fallsroad

    These guys have been doing this for a long time. First read about it on a coin collector’s News group. I don’t know if any of the same people are involved.

  23. Kyle

    As an optician working with an ophthalmologist I can tell you UV bad for cataracts and x-ray even more so. Vet techs who have to hold animals still should wear a high lead content lens, really almost a lead crystal lens, for best protection. Only ever sold 1 pair, devilishly difficult to manufacture. Heavy too, 85 grams for a non prescription pair verses my high Rx at only 34g.

    I want to know how much data comes from capturing 100K frames per second. That’s gotta be a huge amount.

    Loved the vid, that was cool.

  24. mike

    Maybe I’m being dense (no pun intended), but I don’t find Lenz’s Law terribly surprising here.

    The “shrinker” physics is that an induced current heats the metal (the air is a side effect — this is a well known process known as “induction heating,” which is used for hardening steel, among other things). You melt the quarter, and confine the melt with a magnetic field, which must push to the center because of Lenz’s Law.

    People often assume that things glow before they melt. Steel certainly does. But many metals do not. I believe quarters are silver plated copper. Silver melts at less than 1000 C, copper around 1100 C. Not hot enough to glow visibly.

    The Other Mike, the potential for X-rays comes from breakdown. Zap electrons (via a spark, for instance) onto a conductor, and you convert most of its energy into X-rays. This is how X-ray machines work, conventionally. Given that conductors are exploding, it would seem likely that a breakdown would occur. And 10 keV is enough that these guys should be behind shielding. No idea if their box is enough.

    I *don’t* think this is why they look away, though. That’s brightness and/or residual risk of shrapnel.

  25. The guy in the gray shirt says “don’t look at this” when he discharges the capacitors after the shrinking is over. It’s just because of the bright spark. If there were any xrays, they would have been produced when the guy in the black shirt triggered the device and they would be trapped by the yellow box (if it’s shielded or thick/dense enough).

  26. Gary Ansorge

    Mike: it doesn’t appear to me that the quarter melted. All the details were retained and looked pretty near perfect.
    That application of Lenz LAw is also what is used to initiate fusion in the Tokamak, ie, big current running thru the gas(D-T), pushing against the induction coils mag field, compresses and heats the gas to a super hot plasma.

    Impressive demo. If they had just left the small container open, they could have launched it 50 miles. I sure wouldn’t want to be in the direct line of flight.

    GAry 7

  27. T.E.L.

    Gary Ansorge Says:

    “Mike: it doesn’t appear to me that the quarter melted. All the details were retained and looked pretty near perfect.”

    Yes. This is similar to a demo that physics departments sometimes do on a lesser scale. A soda can is clamped down with a solenoid around its waist and a buttload of current is discharged from a bank of capacitors. The can ends up shaped like an hourglass.

  28. X-ray machines make X-rays by accelerating free electrons and smacking them into a metal plate. The X-rays are produced by a process called bremsstrahlung (German for “braking radiation”) as the electrons decelerate extremely rapidly when they smack into the electrons in the metal surface, producing X-ray photons. Normal electron transitions in atoms aren’t energetic enough to produce X-rays and a thermal source would have to amazingly hot (hundreds of thousands of Kelvin?) to produce X-rays. Simply putting 10 KV across a conductor won’t produce X-rays, and I can’t imagine there’s any appreciable amount of X-radiation from the coil exploding.

    Most likely the guys are looking away because there’s a very bright flash when the coil blows up.

  29. A guy named Bert Hickman’s been doing this for years and selling the end result on eBay. I have one of his shrunk Sacagawea dollars (which I bought back in 2002). The preserved detail is amazing.

    Check out his main web site or his eBay page

  30. dre

    I remember seeing a write-up of this machine and examples of the shrunken quarters a couple of years ago somewhere. Don’t remember where, and there were no videos then. Hmmm…

  31. Joseph Blough

    Could you shrink a whole person using this method?

  32. Chip

    Gary Ansorge: “… it doesn’t appear to me that the quarter melted. All the details were retained and looked pretty near perfect.”

    Yes, but if you look closely you’ll see they turned a quarter into a nickel. They discovered the origin of inflation. 😉

    [total geek comment] BTW – this experiment reminded me of two 1950s Sci-Fi classics. “Forbidden Planet”, where Dr. Morbius tells the captain and doctor to look only at the reflection if the Krel power source, and “This Island Earth”, where the lab receives little beads – that hold a gazillion amps. [/total geek comment]

  33. Jon B

    @26: Possibly, if they were wearing a suit of armor.

  34. Very nice video.
    I see your shrinking quarter, and raise you Buzz Aldrin making a hip hop album.

  35. Mena

    Interesting, but this is my favorite use for high energy generating machinery:
    I just wish that the web site was better. No Archaeopteryx pictures, but the squid video at least explained how it works.

  36. MadScientist

    I’d make sure I had a face shield so I don’t get molten metal in my eyes and maybe really dark welding goggles to knock down the UV. I’m not sure if X-rays would be generated; they’re usually created by accelerating electrons at a target metal. In this case the electrons will lose a lot of energy in the air; I doubt they have enough energy left to knock out the inner electrons. Typical modern diagnostic X-rays will run 50 to 200 KV. I’d need to do calculations to see what voltage would be needed for the lower end of the X-ray spectrum. Looking away from X-rays will do absolutely no good except for the very low energy type which is easily absorbed by the body, not to mention if the event is fast enough by the time you react it’s too late anyway.

    @mus: Feynman was pretty far from the bomb and wouldn’t have received a large enough dose to instantly ruin his eyes. On top of that, people in the bunkers were told not to look directly at the initial flash of light (but you can use any number of tricks to view the initial flash). The car windscreen doesn’t really block all that much UV (well, it also depends on what frequency UV). You can still get a good UV sunburn while sitting in your car. I can’t remember which book Feynman describes the experience in, but he was a bit of a nut so I wouldn’t be surprised if he took risks. I do recall that he liked to say that others missed a lot because they were looking through such dark glasses, but I can’t remember if he dared to stare at that first flash.

  37. Hmmm, actually UV makes more sense to me. It’s what I thought originally, but then a back-of-the-envelope seemed to get me X-rays. I’ve corrected the text.

  38. Adrian Kleinbergen

    OK, so the volume of the coin is the same only the diameter is smaller and it’s thicker. There is _no_ compression of material here? Just a flash melting that preserves the surface detail?

  39. José

    Isn’t this in violation of 18 USC Chapter 17 Sec. 333: Mutilation of national bank obligations

    I don’t think so. The coin wasn’t fraudulently altered.

  40. It’s not a Sec. 333 violation — that one relates to bills, notes, etc. Coinage is addressed in Sec. 331. Like José said, the coins weren’t fraudulently altered: “Whoever fraudulently alters, defaces, mutilates, impairs, diminishes, falsifies, scales, or lightens any of the coins…” Obviously, they aren’t intending to roll them up and deposit them into anyone’s bank account.

    Either way — this is freakin’ cool. The sign on the front of the machine is pretty cool, too, as is the description of the power output. A one pound ball, two miles high? How far could it then send, say, a 1 ounce ball at a 45 degree angle (altitude) assuming no atmospheric drag?

  41. Stone Age Scientist

    Hmmm, so the coin shrunk in size… Is it still the same material as it was before the charge? What about the coin’s weight, volume and density in the aftermath?

    Looking at the video, it felt like I was looking at a star collapse.

  42. @Mike post #24: I’m a jeweler, I can assure you that silver does glow when heated. When soldering silver this is the way to tell when the solder is ready to flow… to note the color of the glow. Now, “glow” is a subjective term, so maybe we are talking about different things… but I don’t need to solder in a dark room. I can solder in full daylight, and still see the glow, a sort of dull red.

    Obviously if you keep heating it, it will melt. In my business, that would be a bad thing… :)

    Wouldn’t the metal compress? I don’t know, being a jeweler and not a scientist, but that seems likely to me. The copper center would surely compress… I’ve fired copper in a kiln to 2,000 F and it degrades and comes out with holes in it. Seems like there’s “room” in the metal.

  43. JB of Brisbane

    Dennis says: “The guy in the gray shirt says “don’t look at this” when he discharges the capacitors after the shrinking is over.”

    Alternate scenario: The guy in the black suit dons a pair of dark glasses and says, “Now watch this carefully…”

  44. 14. T_U_T Says: “I wonder how much energy it would be needed to compress the coin to density where nuclear fusion would start. ( provided the coin were hollow and filled with LiD )”

    A lot more than in those caps. We’ve got a machine here in Livermore to do that, about two miles down the road from me, that’s about to go online. It’s 30 m in diameter and consumes gigawatts for the nanoseconds that it’s turned on. Oh yeah, it uses lasers. They tried magnets, but it didn’t work.

    24. mike Says: “I believe quarters are silver plated copper. Silver melts at less than 1000 C, copper around 1100 C. Not hot enough to glow visibly.”

    Actually, I think they’re aluminum/copper, and it’s not just a plating. It’s three roughly equal sheets sandwiched before being punched and stamped. Aluminum also melts well before it starts to glow.

    For my own comment, I have to say I wasn’t terribly impressed with this. I’m sure these guys are very bright, but they’re a few tacos short of a combo plate when it comes to safety. They’re playing with some significant energies here (note the “risk of death” sign) but the equipment looks very crude. The primary switch is some SiC contacts in G10 brought together with a large rubber band? Oy! No one was wearing any sort of PPE (Personal Protective Equipment). At a minimum they should be wearing UV filtering lab goggles, but a face shield would be better. The people working around the high current pieces should have had insulating gloves. The guy who hollered “Look away!” didn’t wait very long before pulling the string. No one was confirming that they were looking away before the string was pulled.

    Cripes, even model rocketry has better safety procedures than this. We’re REQUIRED to use electrical ignition that can be stopped up to the last second if an unsafe condition pops up. We’re REQUIRED to make a loud announcement of impending launch and we’re REQUIRED to verify that everyone within the hazardous zone is aware of what’s about to happen before the button is pushed.

    Some people depend too much on luck.

    – Jack

  45. OK, I just watched the video again and my opinion hasn’t changed, but I noticed a few errors in my previous post. The contacts are tungsten carbide, not silicon carbide, and it looks like they’re held by nylon or Teflon or maybe white delrin, not G10. Outside of that, I still shuddered at the lack of safety procedures.

    Plus, does anyone know what that secondary string pull was? After the bang, the guy closest to the camera says something like “wait for this” then pulls some sort of yellow block out of the chamber.

    Also, the amount of energy stored in a capacitor, IIRC, is 1/2 CV^2. That agrees with their assertion of 15,000 J using a 300uF cap working at 10,000V. While that’s enough to kill you, I should note that our club’s launch equipment uses a 1 F capacitor (that right, one F, not “micro”) working at 12 volts. That works out to 72 MJ or nearly 5,000 times the energy in their setup. We verify that everyone is clear to a radius of about 100 feet before we start charging it.

    – Jack

  46. Stone Age Scientist

    Hi Jack Hagerty @ #45,

    David Barksdale’s (name) link may provide a clue to your question, “does anyone know what that secondary string pull was?…”

    Here is the link from Hackerbot Labs (my guess is it opens up the high-density plastic blast chamber):

    The link has answered my question as well @ #41.

    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!

    Hmmm, no wonder the coin appears puffy.

  47. Stone Age Scientist

    Jack @ #45,

    Hmmm, or maybe something that opens up the circuit (for precautions) like in thermal fuses. Though I have to admit, this is a bit far-fetched.

  48. Anne V

    Sorry, it really should be “effect.” It’s a noun. Affect is a verb, unless it refers to the psychological/emotional realm. And then it’s usually used as in “affective domain.” I don’t think the quarter has emotions here. Occasionally effect can be a verb, “to effect change” but not many people speak that way.

  49. eyesoars

    Jack @ 45:

    Your arithmetic needs repair. a 1F capacitor at 12V holds (1/2) * 1 * 12*12 = (1/2) * 144 = 72J.

    The capacitors in this demo held (1/2) * (300 * 10^-6) * (10^4) * (10^4) = (1/2) * (3 * 10^-4) * 10^8
    = (1/2) * 3 * 10^4 J = 1.5 * 10^4 J = 15,000J.

    This latter is clearly a few order of magnitudes more energy. Further, if you try to discharge your 1F
    capacitor through yourself, you won’t notice it — the voltage is insufficient to drive any current unless
    you short it with a low-impedance path. That’s definitely not true of the 300 microfarad setup.


  50. IVAN3MAN

    It appears that Phil Plait only listens when I point out his grammatical errors, so…

    effect –noun

    1. something that is produced by an agency or cause; result; consequence: Exposure to the sun had the effect of toughening his skin.
    2. power to produce results; efficacy; force; validity; influence: His protest had no effect.
    3. the state of being effective or operative; operation or execution; accomplishment or fulfillment: to bring a plan into effect.
    4. a mental or emotional impression produced, as by a painting or a speech.
    5. meaning or sense; purpose or intention: She disapproved of the proposal and wrote to that effect.
    6. the making of a desired impression: We had the feeling that the big, expensive car was only for effect.
    7. an illusory phenomenon: a three-dimensional effect.
    8. a real phenomenon (usually named for its discoverer): the Doppler effect.
    9. special effects.
    –verb (used with object)
    10. to produce as an effect; bring about; accomplish; make happen: The new machines finally effected the transition to computerized accounting last spring.

    affect –verb (used with object)

    1. to act on; produce an effect or change in: Cold weather affected the crops.
    2. to impress the mind or move the feelings of: The music affected him deeply.
    3. (of pain, disease, etc.) to attack or lay hold of.
    4. Psychology. feeling or emotion.
    5. Psychiatry. an expressed or observed emotional response: Restricted, flat, or blunted affect may be a symptom of mental illness, especially schizophrenia.
    6. Obsolete. affection; passion; sensation; inclination; inward disposition or feeling.

    Therefore, Phil, it should be “effect”, not “affect”.


  51. IVAN3MAN

    Minor correction; I neglected to italicize some words for the definition of affect in lines 4, 5, and 6:

    4. Psychology. feeling or emotion.
    5. Psychiatry. an expressed or observed emotional response: Restricted, flat, or blunted affect may be a symptom of mental illness, especially schizophrenia.
    6. Obsolete. affection; passion; sensation; inclination; inward disposition or feeling.

  52. Ken


    Where’s Adam and Jamie? I’d love to see Mythbusters lash together a setup like this.

    Can anyone formulate a “myth” around this for them to bust? :-)

  53. !astralProjectile

    Fascinating. And I agree that the coin couldn’t have melted- it would never have cooled fast enough to retain it’s shape.

    As far as X-rays go, just a reminder that Scotch tape peeled in a vacuum can create X-rays, Lightning also generates them.

  54. Some comments on safety:

    There are some non-obvious safety systems in place which don’t make it into the video.

    – Before operation, a safety perimeter is established keeping personnel at a safe distance.

    – The chamber which contains the coil has been tested hundreds of times. HDPE turns out to be one of the few materials which are up to the task of absorbing the shockwave and shrapnel. In addition, the walls are made out of nearly 2 inches of the stuff, and built way over spec. The shrapnel penetration depth is less than 1/4 inch into HDPE.

    – the 2ndary spark you see emits UV, however, all staff are wearing UV blocking safety glasses, in addition to earplugs. 132db is quite loud.

    – The operation of the chamber is as follows: Clear the area, Unsafe it, Charge it, discharge it, remove the balance of the charge (about 1kv normally), safe it. If any time during this cycle one of the spotters sees someone enter the danger zone, the operation is stopped. Keep in mind that after a charge is put into the cap bank, it is in a very dangerous state. The only way to safe it would be to discharge it.

    – Regarding the tubing in use on the trigger: Best practices require a simple explanation of safety. The mechanical triggers, while ‘crude’ can be easily inspected for proper operation, and their safety level and function can be determined at a glance. This was a design requirement which I believe we implemented very well.

    – Use of high voltage gloves – we are dealing with 10kv DC charge. high voltage gloves have many failure modes, and our safety policy demands that we simply do not interact with the device while it has a charge. Honestly, even if you had gloves, a bump of the elbow would likely cause death anyway, so they provide very limited protection.

    – The operators of this device have practiced handling failure modes – the only real tricky one is if the bank has a charge and we don’t have a way to discharge it. The yellow 2ndary switch, if it fails, still has exposed contacts. We have a method for manually safely discharging the bank remotely should our safety switch fail.

    If you have any further questions, please don’t hesitate to ask. you can email me at 3ricj ATTY hackerbotlabs DOTTY com

    As for mythbusters, I have not seen any of their work, but we built stuff for ourselves, not for TV. Thanks for watching. :)


  55. Jon B

    @52: Can anyone formulate a “myth” around this for them to bust?

    Well, the “does the coin melt?” question seems ripe for an episode.

  56. 49. eyesoars Says: “Jack @ 45: Your arithmetic needs repair. ”

    Thank you. I really shouldn’t try to do that in my head! I always drop an exponent somewhere. I had 1F equaling 1,000,000 uF (which is true), but I used the “million” instead of the “one” when multiplying out the energy.

    I was also going to point out that at 12V it didn’t pose a lethal hazard, although it can give you a nasty burn across your fingers. Plus we discharge it a lot slower. Our firing leads are 14 ga and they mention 12 ga, plus it’s about 15 feet of cable from the firing relay to the ignitor clips compared to a few inches for their setup. We probably have at least an order of magnitude more resistance in the discharge path (if you include the ~1 ohm in the ignitor itself).

    That still doesn’t excuse them for their shoddy safety practices.

    – Jack

  57. 54. 3ric Johanson Says: “There are some non-obvious safety systems in place which don’t make it into the video.”

    Thank you. After reading through that I’m much relieved. I’m sure that video was edited for maximum viewer impact and not as a documentation on your equipment and procedures, because none of that caution comes through on the video.

    As a little background on myself, I’ve spent the past 20 years or so on and off in the semiconductor equipment industry, including eight years at Applied Materials. I worked on etch chambers that not only had multi-kilowatt RF generators, but high pressure air operated devices and used some of the deadliest gasses known to science (silane, anyone?). It wasn’t enough to have safety pounded into us enough on a daily basis, we also had to take an annual “hazmat” training class to have the fear of death re-instilled in case we’d slacked off.

    In addition to that, I help run the largest model rocket club in the country, and have to oversee the safety of launches where we send 200 to 300 rockets skyward during a four hour launch. Procedure is everything.

    Thanks for the clarification,

    – Jack

  58. IVAN: I coined this sentence as a ‘nmemonic’ (and included it on my resume for ‘proofreader/editor’)

    They’re affecting their effect there.



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