Re: Awesome Quarter Shrinking Capacitors on EBAY

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Original poster: "Jim Lux" <jimlux-at-earthlink-dot-net> 

For that matter, the amount of energy needed to squash a quarter into any
arbitrary shape is a lot less than 10s of kJ... It's the dramatic, high peak
power aspect that makes it interesting, even if it's hideously inefficient
(after all, the quarter does get hot, so there's that loss there.)
I did actully figure this out once (but can't find my notes).. the amount of
force required to deform the metal is well known (probably somthing in the
10-20kpsi range (copper's not too strong), and you can figure out the
geometry, so you can calculate force times distance.
Here's a quick ballpark.. assume that the quarter is just under an inch in
diameter (i.e. 3 inches in circumference), and you squeeze it to half size
(i.e. the force acts over a distance of 1/4"). Further assume that the
quarter starts out 0.1" thick, and the yield strength of the metal is
20kpsi.  So, to get it moving takes 3x0.1*20k = 6000 pounds of force.  That
moves a distance of 1/(12*4) feet, call it 1/50th.. That's 120 ft pounds of
work.. 170 Joules  (120*4.54 N/lb * meters/3.28 ft)

Even if you're shrinking steel, with a yield of 60 kpsi, it's still only
about 600 Joules... And yes, there's a kinetic aspect, it takes some energy
to accelerate the metal flying in.

Another way to look at how (in)efficient the quarter shrinker is, is to look
at it thermodynamically. The quarter weighs, what, a few grams? (call it 5)g
Copper melts at about 1100 degreesC.. To melt the coin would require about
0.3*5*1100 =1650 (assuming specific heat of 0.3) calories, or about 6-8 kJ.
The quarter gets nowhere near molten (it doesn't even get to 100C), and
there's no real opportunity for it to dissipate the heat either by
conduction or radiation.

Imagine a big strong screw clamp type device that gradually squeezes the
quarter...


----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Saturday, October 11, 2003 1:39 PM
Subject: Re: Awesome Quarter Shrinking Capacitors on EBAY


 > Original poster: "Paul Marshall" <klugmann-at-hotmail-dot-com>
 >
 > One thing that I have noticed, in quarter shrinking is that total
available
 > energy does not always Guarantee success. It seems that the best results I
 > have gotten have been at higher voltages 30kv and above. Even when the
 > energy is equal. For instance, I had a 40kv 32 uf maxwell total energy 25
 > kj. I never went that far most of what I shot was between 8-12 kj. The
 > quarter was under .5". Later I used
 > a 45uf 30kV cap. Even at a full 20kJ I never reached the .5" mark. Now I
 > have a 330 uf 25kV cap which will give me 103 kJ. I will try this out
soon.
 > This cap is very low inductance.
 >
 >
 >
 > Paul S. Marshall
 >
 >
 >
 >
 >
 > >From: "Tesla list" <tesla-at-pupman-dot-com>
 > >To: tesla-at-pupman-dot-com
 > >Subject: Re: Awesome Quarter Shrinking Capacitors on EBAY
 > >Date: Thu, 09 Oct 2003 15:04:20 -0600
 > >
 > >Original poster: Ed Phillips <evp-at-pacbell-dot-net>
 > >
 > >"Original poster: Mark Broker <mbroker-at-thegeekgroup-dot-org>
 > >
 > >John, an "m" or an "M" always refers to micro.  The standard units for
 > >capacitors are Farad, microfarad, and picofarad.  Nano and especially
 > >milli
 > >are rarely, if ever, used.  I always wondered why cap manufacturers
 > >couldn't use "u" for micro - it looks close enough to Greek "mu" and is
 > >certainly much less ambiguous than "M".
 > >
 > >I think most of us have stories of EEs showing their ignorance in front
 > >of
 > >the AAS techs....  And I have no problems admitting that I've been on
 > >both
 > >ends more than once.  ;)
 > >
 > >Cheers,
 > >
 > >Mark Broker
 > >Chief Engineer, The Geek Group"
 > >
 > >         Unfortunately the SI unit nuts are taking over the world (at
 > > least that
 > >of technical magazine editors) and in that system no number is allowed
 > >to be less than 1 or over 1000!!!  As a result, nano and milli are
 > >coming into use in printed literature at least.  It's the "in" thing to
 > >do just like some rules of etiquette or placement of silverware at the
 > >dinner table; no practical value but separates those who "know" from
 > >those ignorant fools who don't!
 > >
 > >         By the way, a 38 millifarad LV tantalum capacitors sounds much
more
 > >reasonable than a 4 millifard 4 kV oil-filled capacitor!
 > >
 > >Ed
 > >
 >