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Harvesting Capacitors for Backyard Munitions
Diabolus writes "This is the tale of a man, a bunch of disposable cameras, and his techniques for harvesting lots of capacitors to build a gauss gun. Insane..." A basic capacitor tutorial is probably in order.
And I bet it still won't work....
"The best argument against democracy is a five minute chat with the average voter."
--Winston Churchill
Actually, it's not the size of the capacitor that really matters. I own several capacitors that are over 6 inches in diameter, and they are far from my most powerfull. In fact, the capacitors in camera flashes are more powerfull. You can even get capacitors the size of garbage cans (they're about 3 feet high and 2 feet across). My friend and I we're concidering buying one just for the shock factor (no pun intended). However, the most powerfull capacitor I have seen is actually no biger around than a quarter and about 1 cm high. It's capacitance ... 1 Farad (a massive amount if you know anything about capacitors, maybe it's time for better units, see prev article).
There's no sig like SIGSEG
Dude, check the voltages on those "powerful" "quarter-sized" capacitors before you go and build one of these based on capacitance alone. I bet if you add it up, they turn out to have the same energy-density as the other ones.
"I assumed blithely that there were no elves out there in the darkness"
Reading. You shold try it some time.
If you had, for instance, you would know he is not done collecting enough capacitors yet.
Moon Macrosystems. Sun's biggest competitor.
>Am I missing something, or is his time worth nothing?
.1 F.
Yes, you are missing something.
Car audio capacitor: 16-20 volts @
Camera flash capacitor: 330 volts @ 120 uF.
Now lets see, using the formula E = 1/2 * U^2 * C, how many joules are in each capacitor.
Car audio capacitor: E = 20 Joules
Flash capacitor: E = 6.534 Joules
Car Cap: $40 or $2 per joule.
Disposable camera: $5 or $0.76 per joule.
Camera caps are far cheaper, and this guy got them for free.
If you could be told what you can see or read, then it follows that you could be told what to say or think - BoC
Yes, you are missing the fact that most 'car audio' capacitors are 'rubbish' (to be polite) and are simply a method or removing money from peoples pockets.
For his purposes he requires an actual high capacity, high discharge rate capacitor, not an easy thing to create.
The challenge is having a VERY low ESR (effective series resistance), as well as a low inductance, and using a massive number of parallel capacitors is certainly one of the only economical ways of doing this. a LOT of care is also needed in how they are connected up to keep the inductance down.
You can, for example, by multi-farad 'supercaps', but these have charge/discharge rates in the milliamps and are used for memory backup and other purposes, you can also get kilovolt rated caps with very low capacitance, but it is very hard to get medium voltage very low ESR high energy caps, primarily because they are lethal. They are used in radar installations and a few other high energy 'toys'.
So, given the inclination and funds, I could, as an american, obtain things like rocket launchers, and RPGs?
.50 cal is a no-no.
What's the stance in the U.S. on privately owned nuclear ICBM's?
As long as they are non-functional as weapons, yes. You may NOT own a functional WMD.
Many private citizen vet organizations own tanks, old rocket launchers, etc. There are a number of non-weapons capable fighter aircraft in private hands, all the way from WWI biplanes to a guy restoring an early model F-16. And I believe there is a privately owned MiG-29.
"Demilitarize" it, and you're ok. Basically, the BATF says anything over
This is "Importation of arms, ammunition, and implements of war", but the same rules probably hold for domestic products.
Surface area determines the "charge" (which you measure in coulombs) a capacitor can hold. The maximum voltage (which is the difference in energy between the electrons on one plate and the other plate) is a function of the dielectric between the plates (how good an insulator it is -- ceramic is better than vacuum which is better than air, etc.)
How big a spark you get is a function of the latter. How long that spark might last is a function of the former. The voltage you get out of a capacitor is always the voltage you put in (minus resistance losses). Capacitors are voltage rated because a high enough voltage will break down the dielectric and spark inside the capcitor. Some chemical capacitors, like many electrolytic capacitors, will break down with a rewarding explosion. Some, like ceramics, will maybe make a bit of a "pop" and then either become shorts or open.
I've probably made things clear as mud...
I don't know anything about car capacitors, so perhaps this is a useless answer, but.... capacitor banks, rather than single large capacitors, are used in high-current circuits because they can crank out a whole lot more current a lot quicker when you have lots of small ones in parallel. This is frequently done even on small bypass capacitors in circuits -- rather than putting a few thousand microfarads on a motor, you might put several 470uF caps, for instance. The response is much quicker. So not surprisingly, this is the way you always do experiments that require frightening amounts of juice.
The streets shall flow with the blood of the Guberminky.
No pictures/videos at the site mentioned in the article, but here's a different site with videos of a capacitor-powered gauss gun in action:
First of all, there are no pictures of a gauss gun, because it doesn't exist yet. I have the parts for an inverter to charge it, but have not yet assembled it. Not having had much experience with switch mode power supplies, I'm just hoping it doesn't burn down.
For someone else's (working) effort, check out powerlabs.org
As to those who think car capacitors, etc might be better, they have a very low voltage rating (eg 15V). E=0.5*C*V^2, so even with a farad the energy isn't that great. Secondly, they are made from *thin* foil and have crappy current ratings, not much good for generating 10kA for 1ms. These are photoflash-rated caps, intended for 1ms discharge times - thick foil, good dielectric and some actual quality control.
Lastly, the capacitors will have to discharge through an inductor, even if it is only a couple of turns. Lack of voltage means the current rise is too slow (dI/dt = V/L) and so a low voltage, high capacitance bank will not discharge fast enough. Slow discharge means the ring has moved away before it receives much energy.
I'm also missing large silicon devices to actually discharge the thing. SCRs that can handle 10 or 20kA are not common and seem to cost many hundred of dollars. If anyone's got a spare one, please tell me! Otherwise I will have to make do with lots of smaller devices from surplus shops and build it multi-stage with messy triggering.
As for energy, consider 0.5*m*V^2. Given about 3 to 5kJ and about 2g of mass, you figure it out. It will be lucky to get 1% efficiency, but still. If it works well, I might have to look into firearms licensing. Big deal.
To those who say "you're a dickhead, that's lame", well, fair enough. Its not for everyone, and this page wasn't put up for the express of having it critiqued by /. bottom-feeders. I guess you could say "that's just sad", but if you're not an eleceng then you're not going to get what's interesting about this stuff.
Grandparent correct, As the owner of a few car audio shops, nothing made my day more than selling stuff to kids who thought they needed it. The sales pitch was always based on some fragment of truth then a wild jump to a $200 solution. In the case of the caps, the fragment of truth was that the voltage at the back of the car dropped when the amp sucked some current. The REAL answer is both of the following: 1: thats how electricity works 2: the effect can be minimized by making sure your connections are solid (the drop is caused by resistance, NOT the fact that your battery cant keep up to the demand.. the battery can run your starter at a couple hundred amps)
The real answers arent all that profitable, nor are they very cool, so we sell you big caps, and your friends drool with envy at your new equipment while you pretend to hear a big difference in the sound. The same principle drives the music/clothing/other industries... 'the dumbest buy the mostest'
Have you ever played with a car amp that needs 1000 watts?
No, and neither have you. 1K watts is about 1.5 HORSEPOWER. In recent years, many manufacturers of car audio equipment have been competing for your money by putting really large numbers on the cases of thier devices just because it makes kids buy them. Take the average radio.. a good one claims to do 40 watts per channel, on a 12 volt powersupply and a 4 ohm load, the maximum possible output wattage is 36.. and thats assuming a 100% efficient amplifier (which doesnt exist)
According to the ATF it is not illegal to make your own gun provided it is not a semi automatic and the person is not making it for sale and the person is allowed to possess a firearm.
A7) Does the GCA prohibit anyone from making a handgun, shotgun or rifle?
With certain exceptions a firearm may be made by a nonlicensee provided it is not for sale and the maker is not prohibited from possessing firearms. However, a person is prohibited from making a semiautomatic assault weapon or assembling a nonsporting semiautomatic rifle or nonsporting shotgun from imported parts. In addition, the making of an NFA firearm requires a tax payment and approval by ATF. An application to make a machinegun will not be approved unless documentation is submitted showing that the firearm is being made for a federal or state agency. [18 U. S. C. 922( o), (r), (v), and 923, 27 CFR 178.39, 178.40, 178.41 and
Article X: The powers not delegated... by the Constitution...are reserved...to the people
actually, the vacuum tubes weren't just "technology ten years out of date" at all. they were parts of backup systems which would operate under conditions which would render transistors useless (e.g. EMPs generated by nuclear explosions, i think). so that design actually was an advantage.
I know with the military issue guns, they aren't banned. You can still buy a tommy gun if you really want, but you have to pay an extremely high tax on fully automatic weapons, and register a certificate with the ATF.
Degaussing scares the bad magnetism out of the monitor and fills it with good karma.
1) The prefatory clause does not limit the application of the main clause.
2) "Militia" meant simply all male citizens of age and condition to be fit for military service. It wasn't necessary to be in any sort of organization, if you could potentially fight you were a member of the unorganized militia. "Well regulated", in 18th century military terms, meant "well equipped".
So the "militia" clause expressed a hope (not a law) that the citizenry would arm themselves suitably for military operations, just in case it became necessary to call on them. (And many indian wars, as well as the successful defense of New Orleans against British regulars in the War of 1812, were conducted primarily by men who joined up for just a few months.) The binding main clause says simply that the federal government should not interfere with individuals obtaining and owning "arms".
However, the US Supreme Court has always dodged cases that would require directly defining the limits (if any) on "the right to bear arms". It came closest in "Miller vs. US", where it decided that there is no right to own a sawed-off shotgun - confusingly, this decision went a ways down the road of misinterpreting the first clause, but then finally decided that the weapon in question was not covered since the military doesn't use shotguns. By the same logic, "Saturday night specials" (the cheapest, lowest quality handguns) wouldn't qualify either, because real military forces prefer weapons that don't blow up in your hand when properly used. The real problem at this point is that this reasoning seems to imply that you should have the right to buy and keep in your home a standard infantry weapon - nowadays, that's an assault rifle that can empty a 30 round clip in under 3 seconds. But we have laws not only forbidding these, but forbidding anything that even looks like them...
By the way, in Switzerland every able-bodied man is a member of the military reserve, and the government GIVES him a military weapon to take home. And the Swiss don't use them to massacre their neighbors. Is it because the Swiss are that much better behaved than Americans, or because they know the neighbors are equally well armed???
Umm, minor detail I cap of hat size wouldn't have a very high voltage rating, 500V if you're lucky. Above that, and it'll likely arc across the dielectric letting out the "magic smoke".
You can hit a million volts by placing lots of 'em in series to build up the voltage withstand. Of course, you reduce the capacitance with each series connection, so you make a string long enough to withstand the voltage and then parallel strings to get your capacitance up.
At 1MV, 5F is one *whack* of charge. Wow my mind hurts just thinking about it.
Well, you are right about the 36 watts. But many car audio amplifiers use inverters these days, allowing them to increase the voltage manyfold. Thus they may have fifty plus volts to play with (no pun intended) and can output many watts... but usually these are not RMS (continuous) watts, but PMPO or some crap like that.
there is no spoon
Take the average radio.. a good one claims to do 40 watts per channel, on a 12 volt powersupply and a 4 ohm load, the maximum possible output wattage is 36
The radio you describe is the same bridge output amplifier that a few years ago was rated at 12.5 watts per channel, or 25 watts for 2 channel or 50 watts for 4 channel. It's the same voltage into the same load. Nothing has changed but the numbers.
Because people tend to by things by comparing the fancy numbers on a spec sheet, lots creative writing has been done to seprate fools from their money.
#1 Rate peak power instead of RMS average watts.
Explaination; Music is not DC heating power. If you take the maximum DC voltage and figure the power based on load resistance, you can get a high number. In the example given, 40 watts was tossed out. It was pointed out that that number refuted with a supply of 12 volts. It wasn't figured at 12 volts. The charging system provides about 14 or more volts. Redo the math with this number.
An audio waveform is not a sine wave. The peak possible voltage is not provided to the speakers 100% of the time. In the '70's some good stuff was rated at RMS power at a specified distortion level. In the above case, 40 watts is only possible with the engine running and the speaker voltage never leaving peak values. In short a very distorted square wave output. Not pleasant music in my book. A 6 Watt RMS rated amplifer at 0.1 THD is a much more powerful amplifier. My favorite amplifier is rated 25 watts RMS per channel at 0.04% THD into a 4 ohm load. Some amplifiers are rated to provide their rated output only a very low speaker impedances. 2 and one ohm are common. Almost half the power rating for these as they can not provide the voltage needed to properly drive rated power into a 4 ohm speaker. Needless to say, that rating will misslead most newbies in the audio field. The don't understand why my 50 watt amplifier uses 8 AWG wire with a 20 amp fuse. They are also supprised when I connect a scope and show it provides more unclipped peak to peak voltage to the 4 ohm speaker than most amplifiers rated 200 watts. Yes the honestly rated 25 watt amplifer is a bigger and higher power amp. That rating is not a peak power rating. Learn to compare apples with apples. Is the spec peak or RMS? Is that rated into 4 ohm, 2 ohm, 1 ohm? Is that rating guaranteed at 11 volt supply, or does the amp need to be under the hood getting 14 volts direct with no power distribution system to provide voltage loss due to resistance and distance? If you have a 200 Watt RMS into 4 ohms rated amplifier, I'll be looking for serious hearing protection! The car audio market is "let the buyer beware". The specs on paper are deliberately missleading. Borrow a scope and a dummy load. Find out how much Peak to Peak voltage the amplifier will deliver before before clipping occures. Don't buy anything that will not put out at least 40 volts for a small amp and 80 volts for the super thumpers. Half these values for brige mode amps. I have seen stuff rated at 120 watts that are powered by an 8 amp fuse. 12 X 8 is only 96 DC watts in at the point the fuse will blow. (commenly spouted spec for cheap underdash EQ-boosters) Some power is lost to heat in the audio conversion from DC. How much is left for each speaker? How are they expecting to get 120 watts out with only 96 watts maximum in? That rating is not RMS average music power! There is some honest stuff out there. However bring your pocketbook. It isn't cheap!
Now onto the function of caps. Music has it's peaks and valleys. The resistance of the electrical distribution system is finite. It includes the wire, battery internal resistance and alternator internal resistance. Current draw over a finite resitance provides a voltage drop over the resistance. This is well defined in ohm's law. The current drawn by an amplifier is not constant. It varies. Simply the more the current draw over a fixed resistance the more the voltage drop. Because of this the voltage drop varies as the current drawn varies. The wiring can have it's resistance reduced by using bigger wire, battery resistance can be reduced by adding more batteries (and placing one close to the amp to shorten the wire from battery and amp).
To provide the maximum voltage to the amplifier at a music peak, the loss in DC voltage at the peak current draw can be acheived by providing the peak current from a local capicitor instead of through a long wire to the trunk. A big capacitor can provide the short duration high current the amplifier demands on a music peak, preventing the high current peak on the DC distribution system and it's associated peak voltage drop. A good scope will tell you in short order if the money is worth it. Watch the voltage drops on high power music at the amplifier with and without the cap. Saving a 1/2 volt peak drop may make a diffrence in a competition, but most people won't need it. Don't even consider adding a cap if your music peaks drop the supply voltage at the amplifier less than 1/4 volt. You don't need it.
The truth shall set you free!