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Deceitful_Frank
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Blowing up a resistor at the end of 100m of wire
Hello again guys.
Today my new toy arrived via eBay, an 820uF 450V radial capacitor with screw terminals, very cool!
My plan is to charge it to full energy (82J) and then dump all the juice in to an 1/8W resistor on the end of a length of thin cheap speaker wire up
to 100 metres long, with the hope that the resistor will EXPLODE. Not just overheat but disintegrate with great violence.
The rules of this board prevent me from saying why I want to achieve this but I am sure many of you could figure it out.
I have a few queries.
I plan to use the circuitry from a disposable camera to charge the capacitor. It kicks out 330V using a 1.5V AAA. Would the tolerances of the
circuitry allow me to feed in 2.4V (2 rechargable AAs) for a 500V+ output and simply moniter the voltage across the capacitor and simply charge untill
it reaches 450V?
Also, I have been shocked a few times by photoflash caps at 330V 150uF and didn't really enjoy the experience of 8J through my fingers. How would 82J
compare and how dangerous is this capacitor to a healthy adult male?
I figure that 100m wire there and back is around 10 ohms so if I use a 100 ohm resistor I can say that 400V will be across it yes?
...I guess that this will force the 1/8W resister to try to dissipate 1600W. Would its destruction be suitably violent?
Also I am considering a bleed resistor to go permanently across it and gather that after 5 time constants it will be safe eough to handle. I wont ask
to be spoon fed here as I can do the math but what do you guys feel is appropriate for one time constant for a bleed resisiter? 1 min, 5 mins.... ten?
Lastly would the 100m or speaker wire act enough like a capacitor to hinder the voltage rise across the resistor that I am hoping to destroy? If so
are there any solutions besides using thicker wire or just seperating the twin flex over the entire length?
I know these are a lot of questions but sensible guidance would be appreciated!
Thanks and regards!
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dann2
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Hello,
Googleing 'exploding wires' gets some info. which may be helpful.
There is a Thesis here on exploding wires (could you believe it), all 27mB of it.
http://etd.caltech.edu/etd/available/etd-08022006-104759/unr...
When attempting fast discharges the inductance of the wires (and even the capacitor construction methods) make a difference. Photo flash caps. have
low inductance to give fast discharge. Perhaps you already know that.
Dann2
Hope your not trying to blow up a car. A dude tried that over here and burned his lips on the exhaust pipe.............
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Xenoid
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Well, I have a variety of rocket motor ignition systems based on charging up photoflash capacitors and discharging them into resistors. My largest has
2 capacitor banks, each comprising 4 120uF 330V capacitors. I use one capacitor bank with a single 330 ohm 1/4 watt carbon resistor and both banks
(960uF) for 2 resistors in parallel for dual ignitions.
When the full 960uF is discharged into a 100 ohm 1/4 watt resistor (not sure if it is carbon or metal) there is a crackling noise, bright flashes and
the resistor bursts into flame for a few seconds. This is with the resistor connected directly across the output terminals of the ignition unit.
Contrary to expectations there is not a lot of difference between resistors in the range 1K to 100 ohms, they all burst into flame. I use 330 ohm
carbon resistors because they give a reliable hot flame with 480uF without resorting to pyrolytic coatings, the carbon and paint are sufficient.
In general the resistor tends to open circuit before the capacitor fully discharges and the 200V to 300V is not enough to bridge the gap. Metal
resistors are worse in this respect.
I haven't tried 1/8 watt resistors but I think you will be dissapointed if you are thinking of using them as detonators.
BTW I believe a single photoflash discharge across the chest is capable of killing someone with a weak heart, so a bank is certainly deadly! The
ON/OFF switch on my units is wired so in the OFF position a 3.3 K ohm (7 watt) resistor discharges the capacitors.
My earlier ignitors used photoflash components, rewired onto stripboard but later versions use components from old portable fluorescent lights. These
have more "grunt" and run off 6 volts (4AAs).
Edit: Forgot to mention I use a TYN816 (800V, 16A) SCR for triggering the discharges.
Edit: Added that 3.3K resistor is rated 7 watts - see Pantone's post below!
TAKE CARE WHEN EXPERIMENTING WITH THESE CAPACITORS - 
[Edited on 29-1-2009 by Xenoid]
[Edited on 30-1-2009 by Xenoid]
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Twospoons
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Photoflash caps are definitely capable of killing you. 82J cap discharge will definitely damage you severely, will most likely kill you. I've had 25J
arm to arm, and count myself lucky to still be here. It was extremely painful, left holes in my fingers, and I couldn't stop shaking for an hour. An
experience I plan never to repeat.
Bleed resistor is essential! Also put a 'tell-tale' across - an LED with series resistor and series 25V zener diode, which will glow down to 26V at
which point the cap can be considered safe.
Build yourself a 'chicken stick' too - a wood or plastic stick with a shorting bar or low value power resistor on the end for discharging the cap.
Again: the capacitor you have is extremely dangerous - treat it, and anything connected to it, with utmost respect.
Helicopter: "helico" -> spiral, "pter" -> with wings
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pantone159
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| Quote: | Originally posted by Xenoid
The ON/OFF switch on my units is wired so in the OFF position a 3.3 K ohm resistor discharges the capacitors. |
Is that number right? I didn't do any analysis, but a resistance only 3.3 times something that reliably bursts into flames sounds iffy for something
to slowly bleed power...
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Xenoid
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| Quote: | Originally posted by pantone159
Is that number right? I didn't do any analysis, but a resistance only 3.3 times something that reliably bursts into flames sounds iffy for something
to slowly bleed power... |
Well I can't be bothered with the maths either! It's not a bleed resistor permanently wired across the capacitors, but a DISCHARGE resistor which is
switched in when the switch is turned to OFF.
In practice the capacitor bank charges to 310 volts. The discharge resistor was just chosen by trial and error, it's actually 7 watts and discharges
the capacitors to 25 volts in about 10 seconds. I should have actually used a lower value resistor, for a faster discharge, but this was on hand and
it fitted into the cramped case nicely.
Remember the resistors bursting into flame are only 1/4 watt, the discharge resistor is 7 watts, 28 times the power handling, spread over about 10
seconds verses say about .1 seconds for the 1/4 watt ignitor resistor.
Incidentally, thinking about it, the reason the resistors don't explode is because they are not a solid resistance, but are very thin films around a
solid ceramic core. There is so little mass of resistance involved that it just vaporises harmlessly (bursts into flame).
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pantone159
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Ah, makes sense now. The OP talked of a bleed resistance but that isn't what you have. Thanks.
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chief
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450 Volts @ 10 Ohm cable gives lousy 45 A ; thats lousy, and far from violent !
Then the 100 Ohm-resistor: Alltogether only 4.5 A ... (peak); thats close to nothing ...
For violence at least maybe 1 kA is desirable, better much more ...
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hissingnoise
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Somehow, I don't think an exploding resistor would have the force to initiate anything less sensitive than a primary.
just my tuppence worth. . .
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Deceitful_Frank
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Thanks guys for your input. I have posted this thread on three forums and the general view seems to be that in order to get a real shock wave I need
KILOvolts across the resistor which is difficult to achieve let alone hundreds of feet away without putting myself in mortal danger. And lets not
forget the financial and time cost involved to realise this!
In my time I have conducted many amateur scientific experiments and have been a lapse of concentration away from instant death, even dismemberment a
few times but I always try to balance the risk involved against the gains.
This 820uF 450V cap is obviously not up to the task for which it was originally intended and would just in reality be great for firing an e-match... I
can do this with a photoflash cap holding a tenth the energy and I know that the penalty for failure is burnt fingers and extreme discomfort at worst.
If I fuck up with this big cap I am dead. It only cost me £6 so no great financial loss.
I know to many of you this may sound like a wimpy cop-out but the cemetry is full of heroes.
I will be scrapping the exploding resister idea in favour of heating a length of nichrome wire to dull red heat in the hope of "cooking it off to DDT"
Whether or not those five words mean anything to you will depend on which forum you are reading this post in but thats all academic really. I have
toyed with this Idea in the past with a view to igniting a simple mx of fuel and oxidiser but this is different.
All I need to do is select the right componants to build a device that will glow the 50mm length of coiled nichrome at 100 metres. The rest would be
in the lap of the gods!
[Edited on by Deceitful_Frank]
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chloric1
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What a cool thread! I will definately look into 'exploding wires" soon. I heard of this 10 years ago but never took the time to study up on it. I
love some of the catchy phrases on this thread.
| Quote: |
Hope your not trying to blow up a car. A dude tried that over here and burned his lips on the exhaust pipe.............
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LOL! priceless!
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I know to many of you this may sound like a wimpy cop-out but the cemetry is full of heroes.
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So true
When I went to school for electronics years ago, I used to blow up electrolytics buy deliberately switching the polarity. My Instructer loved
it(not). One day I brought in a cap from a television set about the size of a film canister and he said it would go off like a shotgun so I refrained
from doing so. I miss those carefree days of young bachelorhood.
Seriously though, take care and enjoy. Heck, come to think of it, there is enough fun to be had with high voltage without the chems. Just don't
build any EMP's
[Edited on 1/30/2009 by chloric1]
Fellow molecular manipulator
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hissingnoise
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| Quote: | Originally posted by Deceitful_Frank
The rules of this board prevent me from saying why I want to achieve this but I am sure many of you could figure it out.
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I assumed you simply wanted to detonate a secondary without having to use a (treacherous?) primary.
The filament of a low-wattage bub grossly overloaded by a capacitor-discharge is reputedly hot enough for milliseconds to bring to detonation several
(insensitive?) nitrates, e.g. EGDN and HNM.
Nobel himself said, IIRC, that this method was useful for nitro at around the time he developed the modern blasting cap.
[Edited on 30-1-2009 by hissingnoise]
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Deceitful_Frank
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Indeed, though 500mg of recrystalized ETN was more what I had in mind. Apparently it can cook off nicely to detonation if heated over 250 celcius.
This would need more than a short pulse of energy though I think.
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hissingnoise
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| Quote: | Originally posted by chloric1
| Quote: |
Hope your not trying to blow up a car. A dude tried that over here and burned his lips on the exhaust pipe.............
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LOL! priceless!
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I laughed too, chloric 1---that is, after the second reading.
It reminded me of the old joke about the hedonistic IRA "operative" and his visit to a UK brothel to practice the "fun" way of blowing up English
cunts.
But I digress---Deceitful_Frank, have you thought about stepping up cap discharge-voltage through a trans just enough so that a hot discharge ~1 mm
long could be made within a small quantity of finely powdered ETN or HNM using the detonator body as one terminal.
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hissingnoise
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| Quote: | Originally posted by Deceitful_Frank
Apparently it can cook off nicely to detonation if heated over 250 celcius. |
A fusing tungsten wire filament reaches nearly 3500*C, but I don't know what metal Nobel used; lightbulbs were but a gleam in Edison's eye at the
time.
Davis has described HNM as an almost primary explosive, since it can detonate by the heat of a match-flame.
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dann2
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Hello,
Check this out, good reading on exploding wires.
http://www.teledynerisi.com/0products/8td/page03.html
Patent here on exploding foil + 'flyer' as a detonator.
It uses a 'slapper' capacitor,,,,,,,, LOL
http://www.patentstorm.us/patents/6752083/description.html
and here:
http://en.wikipedia.org/wiki/Exploding-bridgewire_detonator
slapper detonator,,,,,,LOL
The guys working on can crushers etc are big into very fast discharge capacitors.
The need for 100 meters of cable in you application rules out fast discharge (at least fast in the sence that these guys speak of).
Can you consider putting the capacator at the business end of the wire? All the advantages of using fast discharge capacators and then running the
current pulse through 100m of wire gets lost because of the wire inductance (slows/spreads out the current pusle).
Can crusher stuff:
http://tesladownunder.com/CanCrushing.htm
+ capacitor banks:
http://www.amasci.com/amateur/capexpt.html
Dann2
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chief
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I have an idea for you, maybe its good:
==> put the to-be-exploded wire in place, and use 2 small 0.20$-capacitors (or less), rated for maybe 500 V;
==> each such capacitor withstands several kV, at least _once_, one is gonna fail first
==> these are paralleled, charged via 100kOhm resistors (on both connections, the resistors close to the capacitors (few cm))
==> so the paralleled capacitors are isolated (100 kOhm from the charging-circuit);
=============
Now: Since one of them is gonna fail first, it will provide path for the charge of the other one too; inside this path the to-be-exploded wire is
placed (a thin one, with these small capacitors), and voila: There you have the multi-kA-discharge; inspiration from the design of nitrogen-lasers ...
Of course it's understood that out of each such experiment you will have only one capacitor left of 2 ... ; also: Everything soldered, short and
relatively thick wires, everything compact ... for low inductance ...
Use NO electrolytics, because these don't stand much more than the rated voltage !
Maybe you want to use a small glass-diode instead of the wire - such a one may explode violently, because the housing provides some initial inclusion
for the plasma; maybe 2 diodes reverse-reverse, so that at least one is in reverse when the capacitor failes, might be more violent ...
Remeber: Energy of capacitor is (capacitance/2) * voltage(squared) ; this makes up for the low capacitance of non-electrolytics: Double voltage == 4
times the energy; but instead of 500 V you may charge such a one to 3 kV or more, before it failes; also the higher voltage provides a much faster
path through the circuit, contributing to a much higher peak-power of the discharge too ...
[Edited on 30-1-2009 by chief]
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Xenoid
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Hmmm... I just tried a few small diodes with my rocket motor ignition system, with little effect. Tests used all 8 capacitors and were through about
20 metres of cable about half of which was still on the spool.
A red LED produced a sharp "crack" sound and when examined was still intact but slightly blackened and fractured internally.
A small signal glass encapsulated Si diode (1N4148) produced no visible or audible effect, but when tested was found to be open circuited (needless to
say).
An old "point junction" signal diode (not sure if Ge or Si, but has wiggly wire inside and glass encapsulated) produced a bright flash but the glass
capsule remained intact.
These low voltages (300V) just don't cut it, I guess the initial current surge open circuits the diode, by which time the voltage has dropped to say
200 - 250 volts and is then incapable of bridging the gap and most of the capacitors energy goes unused!
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Mr. Wizard
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You won't get the sudden pop you are hoping for. The big advantage to a large cap is the sudden surge of current with almost no resistance in the
source (the cap). By putting 100 meters of wire in the circuit you add in lots of inductance which will slow down the sudden surge you want. The
normal DC resistance of the circuit will be significant too when you try to get that high amperage surge. In an ideal situation, your resistor or
exploding item will have the same impedance as the line circuit that is feeding it. If you recall the old 300 ohm TV antenna line, it works the same
way. If you imagined a pair of wires stretching to infinity and hooked a battery up to them, it would appear to flow current as if it had a 300 ohm
impedance. If you used a 300 ohm resistor and a 300 ohm source you would get maximum energy transfer. If you don't, the heat will be dissipated in
the mismatched items. You want a pulse, (bang) but what you'll end up with with all that stray inductance is drawn out surge.(whimper).
Maybe somebody that knows more about this than me can explain it better.
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woelen
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A real explosion cannot be obtained with just a few hundreds of volts. I use the following type of caps for that kind of experiments.
Having a capacitor in my hand:
A capacitor near a standard 300 ml bottle of beer:
This beasts can be charged up to 5000 V (they survive 7500 volts, but it is recommended not to go beyond 5000 V) and their capacity is 40 uF. This
makes up for 500 J per capacitor at 5000 V. I have three of them. One such capacitor has a weight of 5 kg.
I must say, that experimenting with these things is very scary, much more so than even the weirdest chemical experiments I have done. One mistake and
you're dead, so the last year I hardly did any experiments with high voltages anymore (my wife does not like it at all, actually she really dislikes
it and wants me to sell ALL of my HV-related stuff, she has no problems with my chemistry-related acitvities, even better she likes many aspects of
it).
Personally I think that very high voltage experimenting (kilovolts) is much more dangerous than chemistry, even when working with stuff like SOCl2,
oleum, conc. HNO3 etc. The only exception may be working with pyrotechnics in large quantities, but that is not something I do. Making mistakes in
HV-experimenting is fatal!
[Edited on 1-2-09 by woelen]
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Mr. Wizard
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woelen, I notice from the picture you don't have a shorting wire across those cap terminals. Short them out with a conductor and then leave them
stored with a nice wrap of wire around the terminals. These caps can 'reform' a charge after being discharged and when this size can pack a big
surprise. Short them out, and put a wire across the connectors when storing them. You may have taken the wire off for the photograph, but people
should realize the danger with 'uncharged caps'.
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chemoleo
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Well many years ago, I paralleled the big capacitors form several old discarded TVs - each had a 500V rating IIRC, and each was as about 3 cm thick
and 8 cm high. There were charged to that voltage or higher. I was only able to shortcircuit them a dozen times or so, then they died (no charging
possible anymore). But short-circuiting them caused the copper wire in the vicinity of the contact region to vaporise, in a loud bluewhite flash
In those care-free days I simply had two insulating pliers, gripped the wires and induced contact that way. But I knew the pliers were safe with 16 kV
too, so no fear of short-circuiting through the body
Never Stop to Begin, and Never Begin to Stop...
Tolerance is good. But not with the intolerant! (Wilhelm Busch)
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Sedit
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| Quote: | But I knew the pliers were safe with 16 kV too, so no fear of short-circuiting through the body
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If I had a nickle ever time I got zaped thinking that
Hell iv gotten so use to it Ill grab an OBIT on a bet now and not have it bother me at all.
Small amounts of RF will slowly degrade the insulation on the pliers and all it takes is a pin hole to ruin your whole day.
Always dischage with a sissy stick, just a nail or something conductive on the end of a stick or better yet a small pice of PVC. Sure beats the
alternative when working with a cap that big. You probly wont get a second chance to get it right.
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chief
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I have 2 capacitors of triple the size of above, each , sice they are for 3 phases. Label says: 40 kVar, isolation voltage 3/15 kV ...
I suspect the 15 kV is towards ground ; once I loaded one of these, don't know the voltage, but below 3 kV: When I shorted it (throwing) aluminum foil
onto it and quickly turning away, while the foil was still in the air, it gave such a loud bang, that my ears were ringing ... Probably the loudest
thing I ever heard, and I was glad my eardrums survived ...
Such a thing has an energy expressable in grams of TNT, and it unloads even faster ...
Wear ear-protection ! Also parts of metal (wire) may be accelerated to dangerous velocities, so eye-protection is a must too.
One idea: Maybe such capacitors could be used for shockwave-experimentation: One would get around the explosives, by just vaporizing calculated
amounts of stuff (1 drop of water-electrolyte, eg., some metal-powder ...) ; so it would be no legal offense (evidently such a capacitor is not a
terrorist threat)
Also these big ones, used for storing the energy of whole factories over a 50Hz-halfcycle, should withstand some abuse; within is oil as insulator, so
the dielectric is ever-fresh
[Edited on 1-2-2009 by chief]
[Edited on 1-2-2009 by chief]
[Edited on 1-2-2009 by chief]
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Mr. Wizard
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"One idea: Maybe such capacitors could be used for shockwave-experimentation: One would get around the explosives, by just vaporizing calculated
amounts of stuff (1 drop of water-electrolyte, eg., some metal-powder ...) ; so it would be no legal offense (evidently such a capacitor is not a
terrorist threat)
Also these big ones, used for storing the energy of whole factories over a 50Hz-halfcycle, should withstand some abuse; within is oil as insulator, so
the dielectric is ever-fresh"
The fact that the cap was used in a big plant to keep the phase angle correct and is oil filled (PCBs ?) is not a safe guide for using it in
capacitive discharge applications. The capacitor was made , according to your description, to adjust 50Hz the power factor, which means it would
take 1/100th of a second to charge or discharge it's current. This is an eternity compared to the microseconds it takes for some caps to discharge.
The faster the discharge, the higher the current, and the higher the magnetic field and mechanical stress. These currents can 'shrink' a conductive
coin by the induced magnetic field alone. Imagine the forces placed upon the conductors inside the can!!! Did the designer of the cap plan for this? I
seriously doubt they did, unless they were designing the cap for capacitive discharge applications. If they were planning for sudden discharges they
would build them a lot stronger and not in a flimsy metal can with oil that will spray over everything in the event of a failure.
I'm not saying not to do it, but realize the cap may decide to become 'the weakest link', and 'roll the darwinian dice' for you. Plan ahead, keep the
cap away from you during any discharges, separated by a solid barrier. Plan on how you would clean up an oily mess if the cap 'lets go'. Cat litter
does a great job of soaking up oil. Does the cap contain PCBs? You don't want to turn you lab, bedroom, or shop into a haz-mat situation. If you can
get to any of the oil in the cap, either through a leak or a hole drilled in the can, put some on a piece of copper wire that you have burned clean in
a blue flame of an alcohol or gas flame. A green flame is an indication of halogens when copper is in a flame. It is very sensitive, and will even
pick up freon or any halogenated organics. Halogenated oils = PCBs.
I don't mean to be a wet blanket to the fun, but just think ahead a bit and plan for the unintended.
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