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johansen
Posted: February 09, 2012 05:40 am
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user posted image
user posted image

working on shrinking quarters...

more to come.

i estimate 20,000 amps rms through a 24 turn coil of 15 awg wire to make that copper shrink that far down.

the wire was stretched from .062 inches to .052 inches in diameter.
it was a two layer coil, each layer had about 5 layers of fiberglass packing tape wrapped around it.
24 turns total for about 2-3uH.

104uf, 4000 volts.


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9/11 was really a prototype steel smelter that runs on naturally aspirated jet fuel and phosphorus.
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johansen
Posted: February 09, 2012 07:52 am
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user posted image

Before:
user posted image
after:
user posted image

I neglected to get an after shot of this coil, its the one i described in the first post.
It probably took several thousand pounds to rip the fiberglass tape.
user posted image


Any ideas on how to contain the coil?
I'm going to try making some proper fiberglass sleeves with epoxy.
plaster of paris is another route, just cast it in a steel pipe for containment


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AwesomeMatt
Posted: February 09, 2012 08:52 am
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From what I've seen the last time I looked into this, probably a year or two ago when you mentioned it... the coils are a 1-shot thing. You can't get enough turn density if you use thick wires, so the coils are vaporized each time. Microseconds before they vaporize though, they do the crushing work.
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Geek
Posted: February 09, 2012 09:28 am
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Electromagnetic circumciser! blink.gif wacko.gif unsure.gif laugh.gif

Awesome!


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tekwiz
Posted: February 09, 2012 09:08 pm
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QUOTE (Geek @ February 09, 2012 12:28 am)
Electromagnetic circumciser! blink.gif wacko.gif unsure.gif laugh.gif

Awesome!

You try it first... bye2.gif

user posted image


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Geek
Posted: February 10, 2012 01:55 pm
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Spammers make better guinea pigs devil.gif


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johansen
Posted: February 11, 2012 11:12 am
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This time with real bus bars and about twice the capacitors.

192 uf at 4kv
15 turns of 15 awg.

user posted image


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johansen
Posted: February 11, 2012 11:18 am
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user posted image


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MikeGyver
Posted: February 11, 2012 11:58 am
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Badass.
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johansen
Posted: February 11, 2012 12:06 pm
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this is the video from the above copper pipe and its description
http://www.youtube.com/watch?v=zMdLxQf9nC4


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AwesomeMatt
Posted: February 11, 2012 01:47 pm
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*stamps*

APPROVED!
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CWB
Posted: February 11, 2012 02:37 pm
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coooolll ...


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AwesomeMatt
Posted: February 11, 2012 05:02 pm
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What's your rig consist of?

I see what appear to be a stack of microwave oven caps. I've got over a dozen myself now, and no use for them... yet.
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johansen
Posted: February 12, 2012 11:02 am
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http://www.youtube.com/watch?v=6i_55K2S_Io

wait till the end. i accidentally left the charger on.


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CWB
Posted: February 12, 2012 01:56 pm
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heh heh heh ... "safety first" ?

i would think that using a steel pipe as a sleeve over the copper coil would be a good idea .


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tekwiz
Posted: February 12, 2012 09:37 pm
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thumbsup.gif


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Trouble rather the tiger in his lair, than the sage among his books.
For to you, kings & armies are things mighty & enduring.
To him, mere toys of the moment, to be overturned at the flick of a finger.

Fortuna favet fortibus.
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johansen
Posted: February 12, 2012 09:53 pm
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yeah i'm no where near that thing when its charging or firing.

friend of mine got hit by a piece of wire. it flew three feet, through an 1/8th inch plexiglass window and another 10 feet.


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AwesomeMatt
Posted: February 12, 2012 10:16 pm
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So, reading up on this: http://205.243.100.155/frames/shrinkergallery.html

You're not going to be containing those coils. Fragments are ejected at 3,400 miles an hour. One guy blew apart his lab when his steel containment wasn't sufficiently large.

They're using 1/2" thick steel plate all the way around bulletproof lexan glass and the lexan regularly fails. One guy has 400 pounds of sandbags on top of his containment and the discharge still lifts the top off O.O .

Is this just a big capacitor bank discharging into a coil? Nothing else?

You're dumping 1,500 joules into it, which should be enough to already shrink dimes 10-20%. biggrin.gif
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johansen
Posted: February 12, 2012 11:09 pm
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the soda can above was shrunk with 768 joules BTW, the secret is in the proper coil geometry.

I am rebuilding the capacitor bank to parallel 40 capacitors in two banks, to allow 8kv if i feel i need the extra voltage. (2560 joules in any case)
Also, the aluminum flashing i used may have a higher resistance than I expected, and it is in fact useless for winding foil inductors, not sure why though, might have some thing to do with the fact that we used it at the time for the switch contacts.

20 turns of 1/2 inch wide 10 mil copper is probably the secret to shrinking a quarter with only 2.5 KJ. fiberglass tape seems to do a really good job of insulating the layers. not so much for round wire though, it seems to push right through the fiberglass.


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tekwiz
Posted: February 13, 2012 09:10 pm
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QUOTE (johansen @ February 12, 2012 02:09 pm)
the soda can above was shrunk with 768 joules BTW, the secret is in the proper coil geometry.

I am rebuilding the capacitor bank to parallel 40 capacitors in two banks, to allow 8kv if i feel i need the extra voltage. (2560 joules in any case)
Also, the aluminum flashing i used may have a higher resistance than I expected, and it is in fact useless for winding foil inductors, not sure why though, might have some thing to do with the fact that we used it at the time for the switch contacts.

20 turns of 1/2 inch wide 10 mil copper is probably the secret to shrinking a quarter with only 2.5 KJ. fiberglass tape seems to do a really good job of insulating the layers. not so much for round wire though, it seems to push right through the fiberglass.

Look into silver plating your coils. This will drastically increase conductivity of any metal used for a coil.
With that type of discharge profile, the skin effect is quite pronounced.

What are you using to switch the discharge?


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Trouble rather the tiger in his lair, than the sage among his books.
For to you, kings & armies are things mighty & enduring.
To him, mere toys of the moment, to be overturned at the flick of a finger.

Fortuna favet fortibus.
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AwesomeMatt
Posted: February 13, 2012 09:52 pm
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QUOTE
What are you using to switch the discharge?


From the video, it appears to be a broom handle with a coathanger poker on the end. Jabbed in the direction of another wire tongue.gif
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johansen
Posted: February 13, 2012 10:05 pm
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well, i'm rebuilding the switch.

in the first couple videos it was pretty crude.
in the later videos we used a magnet and a steel bolt with a copper washer soldered to the bolt, the magnet pulled the switch contacts closed, at a speed of about 100ft/sec.

i've got a few ideas up my sleeve for how to switch it. All the switches i've seen are pnumatic, heavy and retarded. contact ablation is actually negligible if you do it right, if you slam the switch contacts fast enough. at 4 kv it won't reliably arc until the air gap is less than 2 mm.

btw: 1mm/uS is 1Km/sec, or about as fast as a bullet.
If the switch only has to move 1mm within 10us, then it only has to be moving one tenth as fast as a bullet, or 300 feet per second, which is quite doable with proper design.

but this aint RF, its a a 7-20khz discharge. skin effect is actually negligible for exploding cans. exploding wires though, not so much

each capacitor has a capacitance of 8 uf, a resistance of about 125 m ohms, and an inductance of 300-400 nH
with all 40 in parallel the inductance would theoretically be 7.5 nH.

the best i can do is add 100-200 more nH for the bus bars.
due to the low voltage, the switch will add less than 10nH when i'm done building it.


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AwesomeMatt
Posted: February 13, 2012 10:19 pm
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Considering you're not switching all that often, you could just put a really beefy spring and a backstop for a lever. Cock the lever using your bodyweight, trap it with a shim block with a rope attached, and yank on the rope to release the lever driven by the spring.
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Sch3mat1c
Posted: February 14, 2012 03:17 am
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What really hurts is not skin effect, but proximity effect.

You know what regular skin effect is, right? Maybe a vague idea? Simply put, rapidly changing currents get forced to the outside of a conductor. Well, that's a special case solution -- it only applies when there are no external currents present.

Put another current near that wire you're looking at, and they pinch each other. If the currents are in the same direction (along a pair of parallel wires, say), they get forced apart, because they look like two skins of the same conductor. Current flows on the outer side of each wire. If the currents are opposite (like regular twin-lead), current flows on the innermost edge, inbetween the wires.

Inside a winding, the situation is even worse, because you have not just a pair of wires, but a huge bundle of them, piled up. The outermost turns aren't so bad, current flows along the inside edge of those conductors, but it's not too bad; the next layer down, it's forced more dramatically to the inner edge, and the bottom layers have basically no current flow in maybe 90% of the conductor area entirely!

Food for thought: a 28AWG wire might be suitable for ~100kHz AC alone, but Litz wire manufacturers recommend 38AWG strands for most cables at the same frequency. Why so much finer? Because when the strands duck inside the huge bundle of current, the current gets forced to the outside really hard, and the strands must be that much thinner to compensate.

I've seen some more graphic illustrations of this -- if you wind an induction coil from rectangular copper tubing (which is pretty easily available, I guess, and actually quite wonderful to actually work with, as long as you don't let it twist on you!). If you have a fairly coarse induction coil, wound with round tubing, the current mostly flows along the innermost edge, because the tube is pretty big at most any frequency (1/4" tubing isn't going to be nearly fully utilized until, like, a few kHz or less). But because it's round, it's a smooth effect, so when you pump 20kW or whatever into a slug of steel, you see the spiral reflected on the metal heats up more rapidly. Take the same coil, wound with rectangular tubing -- now the current is forced into only the very inside corners of the helix, and this leaves you with two sharp, distinct lines of heat on the workpiece. Maybe hard to describe, but it's an excellent illustration when seen in person.

As a consequence, if you want to spread out the current density, and reduce inductance, you need big, wide, flat transmission lines. I've seen quarter shrinkers before, which were mistakenly built with edge-parallel transmission lines. This is incorrect. Current will only flow on the inside edge of each conductor, wasting almost all of the, say, 2" wide strip the guy bought. Broadside facing bus bars are required, and though current will still tend to flow along their edges, the short distance between will ensure inductance is minimized.

For reference, a twisted pair of wires (regular hookup wire insulation size) might have a characteristic impedance of 70-100 ohms and an inductance of ~0.1uH/ft (or is that m^-1, I forget). In a 4-layer PCB, you can put a ground plane on layers 1 and 2 (which are typically laminated with only 10-15 mil thickness; layers 2-3 are laminated on a ~40 mil core), make a broadside transmission line with maybe 2" width, you'll get a characteristic impedance of a few ohms, and a few nanohenries inductance per inch.

I know of one cable manufacturer which uses a whole mess of separate twisted pairs inside one monster cable. You'll get as much ampacity as you ask for (say, a few hundred or thousand amperes, air or water cooling, however), and the inductance might be 0.1uH... for a ten foot run of the stuff!

Tim


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johansen
Posted: February 14, 2012 06:11 am
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QUOTE
For reference, a twisted pair of wires (regular hookup wire insulation size) might have a characteristic impedance of 70-100 ohms and an inductance of ~0.1uH/ft



I actually looked it up, when i was running into problems with my darlington transistor's reverse base current protection diode reflecting into the base drive.

ethernet cord is a whopping 500nH/meter for a single twisted pair.
I discharged 600j through a 6 foot length of it, and it stretched the wire 10% or so, leaving a 1/8th inch gap between the two helices of copper

thanks for mentioning the proximity effect,
i had forgotten about that.


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