Deceitful_Frank Posted January 29, 2009 Posted January 29, 2009 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!
mike_au Posted January 30, 2009 Posted January 30, 2009 I assume your cryptic comments are a reference to the group you are in, in which case, sorry but I can't see this working. It would make a hell of an e-match, but I can't see it having enough oomph to do what you are talking about. The wire exploders I have read about run at several kV. If the cap bank has 450V in it *after* being fired it is considered practically empty. As well as that the wire exploders I have seen run some pretty heavy cabling, 2" busbar or heavy copper tubing is quite common and even then they try to keep it as short as possible, I don't see 100m of speaker wire doing the job. Having said that, give it a go the worst that could happen is that you have an extremely powerful ematch firing box. Your camera circuit may work but I wouldn't count on it, 330v -> 500v is a fair jump. How about a 555 putting out a square wave, into a transistor or two feeding a small transformer (say up to 20-30V) and then a cockroft/walten ladder to boost up to 450v and into a rectifier to feed the cap? Should be a relatively simple circuit and shouldn't cost more than about $30 to put together. The charged cap is relatively safe (although not pleasant) as long as it doesn't go across your chest. If you stick two fingers (from the same hand) onto the terminals you will get one hell of a kick and a couple of nasty little burns, but it is fairly unlikely to kill you. If you stick one finger from each hand onto the terminals that is a different story, although the combination of it being an incredibly short pulse combined with skin effect would be in your favour. There is an old rule about keeping your left hand in your pocket which it might be a good idea for you to follow. 409V into the resistor by my calculations, using the 100 + 10ohm values. As I mentioned before, no I don't think it would be suitably violent. I would suggest a fairly short time period for your bleed resistor so you can make it safe as quickly as possible (30sec - 1min sounds good to me), but you will be limited by the power ratings. I have had some difficulty finding resistors > 10w for a reasonable price. At 450v, I don't think you will have too much trouble with the wire acting as a capacitor, if speaker wire does cause problems then simply upgrading to something slightly heavier (which should have thicker insulation) should fix it. However 100m of wire, even fairly thick fig8 may well act as a cap once you get into the kV range which I think you will have to do to achieve your goals. All of the above is theory, so I would be interested to see how it goes in practice. Keep up posted.
Mindphreak Posted January 30, 2009 Posted January 30, 2009 I've fed nine volts into the capacitor charging circuit of a camera without blowing it, but thats right about the tolerance. Any higher and something will become faulty.About the resister... You might want to try replacing it with a diode (facing backwards). I've blown these before, the pieces go flying, but I'm not sure if you'll get any good heat/flame out of it. It's probably not a big enough charge but I'd give it a try. Transisters pop too and get hot.
Boomer Posted January 30, 2009 Posted January 30, 2009 "Quick Question, If I were to arrange for a fully charged 330V 230uF photo flash capacitor to be discharged across a 100 ohm 1/4 watt carbon film resister on the end of 100 meters of speaker wire ..... " This was your own post btw Frank, on page 2 here in "Electronics". Forgot? Its in "EBWs, capacitor discharge, wire blowing..." where I explained the theory in some length. And don't listen to mike regarding cap safety: "although the combination of it being an incredibly short pulse combined with skin effect would be in your favour." Nope, no skin effect here. The cap is charged with DC right? And if the arc blows holes in the skin (likely), your inner resistance of 100 Ohms will give you 0.1 second pulse length. With skin resistance, the discharge takes a minute.DC is less lethal than AC because it causes no fibrillation, but the discharge pulse can stop the heart. IIRC this takes 20 Joule (hand-hand), so the charge is definitely there (82 J).
Deceitful_Frank Posted January 30, 2009 Author Posted January 30, 2009 (edited) 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 January 30, 2009 by Deceitful_Frank
Richtee Posted January 30, 2009 Posted January 30, 2009 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! That's a LONG set of jumper cables, bud ;{) If it means that much, sacrifice a gel Cell 12 V 4 AH battery local and trip a relay right there. Bat's about 8 bux..my cost, and a relay about 10.
Deceitful_Frank Posted January 30, 2009 Author Posted January 30, 2009 That's a LONG set of jumper cables, bud ;{) If it means that much, sacrifice a gel Cell 12 V 4 AH battery local and trip a relay right there. Bat's about 8 bux..my cost, and a relay about 10. Sure this would work but do I really wanna sacrifice batteries and relays for every shot, and more importantly do I wanna be there with it all wired up...oh its ok I am perfectly safe 'cos the relay isn't switched yet... sounds like famous last words to me!
Richtee Posted January 30, 2009 Posted January 30, 2009 Sure this would work but do I really wanna sacrifice batteries and relays for every shot, and more importantly do I wanna be there with it all wired up...oh its ok I am perfectly safe 'cos the relay isn't switched yet... sounds like famous last words to me! Well.. I dunno how many shots ya planned. How bout an extension cord and run 110VAC out there..then it's only a relay. And don't plug the other end in til..well..you get it...
Deceitful_Frank Posted January 30, 2009 Author Posted January 30, 2009 There'#s an idea.... though I am not sure where I put that 8 mile roll of mains cable. I'll have a look for it and get back to ya!
Richtee Posted January 30, 2009 Posted January 30, 2009 There'#s an idea.... though I am not sure where I put that 8 mile roll of mains cable. I'll have a look for it and get back to ya! If you need to be 8 miles away, this is a divorce ;{)
Ralph Posted January 31, 2009 Posted January 31, 2009 (edited) you cant say that you want to use it as a primary (any one who hasnt worked out what it is for wont know what a primary is ) i am not sure it will be violent enough but i guess testing will tell i do know that capisitors are always used in demonstrations at uni so if you got a small capasitor and put that there (like a very small one) that would probably be more effective than a diode (if you have nover tired blowing up a cpacitor than i woudnt reomend it most capasitors contain an electorlite which normally end up really hot and could easily blind you these demonstartions are always carried out behind thick glass sheilds ) Edited January 31, 2009 by Ralph
Richtee Posted January 31, 2009 Posted January 31, 2009 There'#s an idea.... though I am not sure where I put that 8 mile roll of mains cable. I'll have a look for it and get back to ya! BTW, solid state dc/ac converters are fairly cheap.
Boomer Posted February 2, 2009 Posted February 2, 2009 Use some DC/AC from a CCFL backlight with a voltage doubler (2 x 2 UF4007 in series), and some foil caps, this does work with 2-3m of heavy cable (2x4mm), though being that close to 100g plastic is only for the hardcore.But the 2-3m are enough to protect a little firing box with a "relay". Relay here means a coil magnet moving a contact that doesn't fry at 1-2kA, think nail onto copper plate. You then only need 100 feet of cheap wire and a battery at the other end. This way it's not really "life" even if the cap bank is charged, as long as the battery stays in your pants.
EEguy Posted November 6, 2009 Posted November 6, 2009 I personally don't see the need to play with that much energy at that voltage. It is dangerous. An 80 joule, 300V shock would most likely be fatal if passed through the chest. To explode a resistor, you simply need to greatly over-power it, which could more safely be done with a lower voltage, lower resistance, higher current. I would definitely do this by lowering the voltage to below 60V and increasing the capacitance. A large, parallel, low ESR capacitor bank would provide a very high initial current capable of popping a 1/8 watt or 1/4 watt axial resistor no problem. Another issue I see with this design is a complete lack of pyrogen, which makes it unsuitable for reliable ignition of the rocket motors. Please be careful with high voltage charged capacitors. They are no joke, and can easily kill! I have a friend who built a Wimshurst machine to charge a high voltage, low capacitance, capacitor made from a plastic pitcher. When he accidentally touched the charged plate on the pitcher, he punched himself in the mouth and about knocked himself out. Even low voltage, high energy cap banks will cause severe burns if shorted to something you are touching. These issues are why most people go with a nichrome-based electric igniter or E-match. An output energy of 1/2 joule at 50V can easily overcome long connection wires to ignite many standard electric matches such as Starlight and Davey Fire. Examples of this can bee seen from the following links: http://www.youtube.com/watch?v=BYPo9RGVviM and http://www.youtube.com/watch?v=5nTYCGMO2MU
Purpley Posted July 7, 2010 Posted July 7, 2010 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!May I recommend using a high voltage transformer? I have a 15,000 volt 30 mA transformer and it has done the job for me.
Arthur Posted July 7, 2010 Posted July 7, 2010 A disposable flash camera will generate about 350v across a 150uF cap. Get several cameras and parallel the OP caps. HOWEVER the leakage in each cap will prevent the really tiny charger from achieving even nearly full voltage. In normal use the voltage regulation is simply the really tiny flashing neon lamp - once the neon strikes the volts stop rising because you've overloaded the driver cct!- I have a 100m reel of bell wire and it has a loop resistance in the order of 20 ohms. I have a 100m reel of better speaker wire and it's loop resistance is 12 ohms. Even if you pay silly money for cable 100m is going to seriously limit either the current in the wire, or your ability to carry the wire!
dagabu Posted July 29, 2010 Posted July 29, 2010 Just a couple times, they overcharge and you loose the circuit. PM EE guy, he has a CD box that you will love!!
madmandotcom Posted February 18, 2011 Posted February 18, 2011 have you tried using a paper capacitor?
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