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Comment by ideals | Hacker News Reader

This looks like what we used to do with electric lighters to turn them into weak tasers and zap each other at school.

Disposable cameras had a little more umph though.

My first lesson in "capacitors store electricity" when I was a kid was when I took the battery out of a disposable camera... and then managed to shock myself with the flash discharge anyways.

I shocked myself a few times with these too, in the process of disassembling the cameras. I needed components (capacitors and the flash circuit) for the ignition system for the rocket engines we were building with a friend, so I went to a local photo store and asked nicely for used cameras with flash. They gave me a bag with some 20 of them.

(The shocks I got were through carelessness; I used a kitchen knife to discharge the caps after ripping off the plastic shell of the camera, but sometimes I touched the wrong thing while disassembling. Roughly half the cameras I got had the caps charged to the point they'd spark brightly on discharge, and one of them damaged the knife.)

Context for those too young to remember: back before digital cameras were available and affordable, you could buy disposable cameras in kiosks and stores cheaply. These would come pre-loaded with a single roll of film, and after you used it up (~30 photos), you'd take the whole camera to a photo store. The photo store people would rip the roll out of the camera, develop your photos, and throw the camera away. Some models came with flash, so if you could get the used ones from the store (or their trash), you got a free source of high-voltage capacitors.)

I used to work at radio shack. The rug behind the counter was very efficient at providing static electricity and whenever we touched the barcode scanning wand - zap. So I got a package of 2kv high voltage capacitors and held one lead while touching the other lead to the wand while rubbing my shoes on the carpet, thereby charging the capacitor. I left the charged capacitor on the POS terminal keyboard for the asshole I worked with to discover. Of course he fell right into my trap and picked up the capacitor. It was pretty funny to me, but not to him. This jerk would often steal my sales and talk down to me, he had it coming.

I did it by sticking a screwdriver where I shouldn't have and touching the flyback cap on an old (CRT) TV that was only recently unplugged. Luckily I wasn't well-grounded and the part of the screwdriver shunted the current turned to slag.

TV repair shops use a special tool to discharge those caps, basically a high voltage rated resistor pack.

Largely a disappeared skill.

I believe if you are really lucky if you discharge with a screwdriver, the cap can explode, not just melt the screwdriver. Same with batteries, like auto batteries, extra points there with boiling acid and hunks of thick plastic flying around.

Pretty sure a car battery (at least the old school 12V lead acid type) wont explode from a short. I welded a spanner onto the terminals of one once by clumsily dropping it and having it land across the terminals.

Now I have to go look on youtube, to see if anyone's filmed themselves dropping a spanner across a Tesla's battery...

Growing up, my dad had a shirt with acid holes. My mother said he blew up a battery while working on it. My dad was a DYI guy, but didn't regularly work around anything caustic. This would have been early 1980's.

I have seen car batteries explode, always due to bad charging rather than shorting though. (Over charging generates hydrogen and oxygen inside the battery in precisely the correct stoichiometric ratio to go "BOOM!")

(I also had a friend wake up to about $500 worth of dead tropical fish, the morning after plugging a charger and car battery in on the shelf under his tank. Not entirely sure what the mechanism was, but the pH in the tank dropped enough to kill all the fish. )

Did you get shocked at all? I'm trying to understand what the return path for the current would be in this situation.

Through the screwdriver shank, as it's placed across the capacitor terminals. This creates a dead short through which the differing potentials on the capacitor plates can equalize - and if the capacitor is large enough, they do so quite enthusiastically.

I ruined a screwdriver of my own that way once, discharging a photoflash cap in a flash head whose control circuit had died with the cap at full charge. Didn't do my hearing any good, either, I'm sure - it took fully half an hour for the ringing to go away.

Did the same at a school trip, after taking off the film I thought I could tear the camera apart, thus exposing the cap connection. Left hand fingers would lean peeerfectly on these metallic parts when playing with the flash.

It became a game between kids. The shock was more intense than harmful, although I saw two white dots on my nail that I assumed was due to the shock.

Today I rip microwave ovens, but I carry gloves and remove caps before anything else.

We used a 5kV (DC) power supply for an A-Level physics experiment, and we quickly discovered that could give you a pretty unpleasant zap (peak current was ~3mA IIRC, so not particularly dangerous - one of our teachers initially insisted on us wearing latex gloves, until we demonstrated it arcing holes in them so it just gave you a false sense of safety). We also destroyed a fair number of multimeters that were allegedly rated for the voltage[1] - they started displayed obviously erroneous values.

I also discovered that accidentally holding a charged plate (thinking the supply was turned off) for a while could let you pick up tin foil just by holding your hand above it, which was pretty neat.

[1] IIRC we used a voltage divider to keep the maximum voltage around 500V, and the meters were rated for 1000VDC.

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