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.

Comments

Anti-slashdotting....

[billbaggins]

Yes, the bandwidth is horrific, so I've shrunk all the images to a much smaller size (160 wide) instead of their usual 640 and 320. If you want to see this and actually make out the pictures (and read the text in them), come back in a week or so when the traffic has dropped and I've put the full-res ones back. Assuming I don't get firewalled off first :)

And I bet it still won't work....

some other cool things to do w/ capacitors

[lingqi]

fry a diode, for example

Flux?

[jcsehak]

No info on flux capacitors? Damn, guess I'll never get back to the 2030's...

Re:Flux?

[Cyno01]

if you call radio shack and ask if they have flux capacitors in stock, they'll tell you they're out, but they should be getting some in about two weeks

Re:Flux?

[Tablizer]

(* Actually, I work at Radio Shack... we'll tell you that because its easier then explaining why They don't exist. I mean come on, if your coming to *me* for parts, thinking a flux capacitor exists is the least of your problems... *)

Dude, make one up quickly in the back room and sell it to them for 300 bucks. When they come back complaining, ask them if they have a degree in nuclear physics. When they say, "no", then politely take it back, minus a 95 dollar restocking and time-diffusion recharge fee, which you pocket.

In unison, "Nothing"...

[MarkusQ]

Be careful if you try this; those capacitors hold a fair amount of charge.

My brothers and I played with some of them in the kitchen at a family gathering a few years back. One of them is in the biz, and had more used, disposable cameras then he knew what to do with. We were bored and trying to rig up something ad-hoc (as I recall, we were using whatever we could find in the kitchen--rubber bands, tupperware, etc.) Our wives were in the dining room with the everyone else, and we weren't being very structured about it.

Things were going fairly well until we accidentally shorted something. There was a loud bang, a flash, and one of us jumped back, knocking over a pile of pie tins.

All conversation in the dining room stopped, and after a moment our mother's voice called calmly: "What are you boys doing in there?"

Without missing a beat we all replied, in unison, "Nothing!"

It was like old times.

-- MarkusQ

Terrorist threat from cameras

[Random Bystander]

Does this mean we won't be able to take disposable cameras on to planes any more?

Imagine the memo to baggage scanning technicians:
"WARNING: Any passengers attempting to take large numbers of disposable cameras on board any flight is a terrorist. These cameras can be used as a weapon by assembling a gauss gun from their parts. Call your appropriate superviser IMMEDIATELY if you have any suspicions"

Re:Terrorist threat from cameras

[Tablizer]

(* Imagine the memo to baggage scanning technicians: "WARNING: Any passengers attempting to take large numbers of disposable cameras on board any flight is a terrorist. *)

Imagine all the things they would start banning if McGyvor worked for Al Quieda.

Re:cheap yes, but practical?

[shepd]

>Am I missing something, or is his time worth nothing?

Yes, you are missing something.

Car audio capacitor: 16-20 volts @ .1 F.
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.

Re:cheap yes, but practical?

[thesupraman]

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'.

Horrible Story Time

[Monkelectric]

Ok, when I was 17 (long ago, but not too long) I went on a band trip to Hawaii (you laugh now, but did you school send you to hawaii?:). The school gave us packs of junk, chewing gum, deck of cards, and disposable cameras as a goodwill gesture (I gather). I was the section leader for the tenor sax players -- if you've ever met any tenor sax players you know they are the bigest screwoffs in the world (I've often wondered -- does being a screwoff make you choose the tenor sax as an instrument, or do you become a screwoff after choosing it?).

Anyways, I was responsible for 4 complete goobers and one gorgeous blonde (who really dosent have anyhting to with the story, but I just want to mention her), which was not an enviable task. They got bored on the plane to hawaii and took apart their disposable camera ... well low and behold they figured out about the only thing you can do with a broken disposable camera is shock shit or get shocked. After some dumb luck (getting shocked in the first place) and some trial and error, they figure out if you touched these leads and pressed that button youd get shocked ... so the next step was to walk around the plane getting people to hold the leads so they could shock them (someday Id like to know why you would hold two leads a 14 year old asked you to).

So one afternoon our scheduled activity was to hang out in this park because thats damn cheap :) and well now you have to know about the director ... he was this big fat, raunchy, disgusting fat fuck who happened to be one of the best directors in the nation, and he had this even fatter and even rauncher wife their two skinny (but soon to be fat kids). The wife was horrible annoying and the kids were even worse, the whole band was sick of them. Meanwhile in the park, the band was getting pretty restless, shocking eachother with cameras actually became entertainment :) So these guys I am responsible for are shocking eathother, Im hitting on the blonde (amy hays if you're out there... ;-) ), and oie of the directors sons walks up and he says "Hey what are you guys doing?" (the kid couldn't have been more then 6 or 7) One of the worst jerkoffs in my section gets this HUGE grin on his face and he says, "I'll show you. you touch this and this, and then press this button" Meanwhile I look over and see whats going on, as Im screaming "nooooooooooooooooooooo!!" in slow motion like the matrix, the kid shocks the crap out of himself and I swear he almost pissed his pants as he took off running. We never got in trouble so I dont suppose he told his father :) but we were paranoid the whole rest of the trip.

on an unrelated topic, couldn't this guy just buy a couple 1 farad capacitors? Those are pretty popular with car audio buffs, they run maybe between 100 - 200$ a piece, I think that would be so much easier then getting UV burns like this guy is describing :D

a reply to some comments

[Anonymous Coward]

Hi, slashdottee here.

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.

Re:a reply to some comments

[Anonymous Coward]

I would not recommend fooling around with microwave ovens in any form, as someone suggested. There is a 4,000V power supply in there which *will* kill you, quite reliably, if you get across it. Much more reliably than standard AC mains power, in fact, because unlike, say, the 30,000V found in a colour TV set, the current from a microwave oven power supply is MUCH higher.

If you want some high-voltage capacitors, some of the electronic junk shops should still have them from the days of valve electronics, when they were exceedingly common. I recall as a teenager connecting up something like 3,000 microfarads at 600V and charging this up to 380VDC from a 230VAC mains supply.

This, when discharged, produced especially satisfying results when the target was a small piece of magnesium ribbon, placed under water in a plastic cup.

The high current vaporised the magnesium which explosively reacted with the water to destroy the cup in a most satisfying way. I imagine that aluminium wire would also work quite well.

Alas, the innocent experiments of youth would probably today have me rounded up as a terrorist, since amongst other things we also made gunpowder and nitroglycerin (which we never detonated because we were too scared to!).

Anyone planning on fooling with high voltages and high energies should be aware that even modest voltage and energy levels can cause fatal heart arhythmia if the shock coincides with a vulnerable point in the heart's electrical cycle. I would strongly recommend that you wear insulating gloves while working on any circuitry and be exceedingly careful. Also be aware that capacitors which have been abruptly discharged can then spontaneously recharge without being reconnected to a power source. This could cause a potentially fatal shock, so you should always connect the capacitor terminals together when working on any circuitry.

Re:Rubbish huh? (flamebait)

[bcrawford]

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)

Completed gauss gun projects

[gerardrj]

Here's a site that goes in to the math, theory and formulas of a gauss gun. At the bottom of the page there are some links to completed projects. There's an image of a completed gun on the top of the front page.