5 ms·

>learn the safe way to discharge them According to one electronics professor (prefaced this with "do not do this at home") - all you have to do is short the le

>learn the safe way to discharge them According to one electronics professor (prefaced this with "do not do this at home") - all you have to do is short the leads with a screwdriver. Or really use a resistor and some alligator clips. Of course a screwdriver is easier to handle without touching the leads than those tiny alligator clips...

52-6F-62 8y ago
Similar experience in film/tv industrial lighting ballasts and heads. Had old techs evangelize that kind of thing. A lot of wacky people in that field. I wouldn’t trust a screwdriver to be safe enough in many of those cases. Some of the caps in those things are massive and hold a charge for ages. I almost killed myself on one thinking there’s no way there would be any charge left after years being stored in an old uninsulated tractor trailer outside. Boy was I wrong. We were demoing some old ballasts—essentially crumpling them before recycling to prevent raiders from seizing the equipment (it happened). Well one coincidentally-aligned swing of the sledge caved the steel chassis in just enough to short a monster cap. The thing exploded on contact. Thankfully those old steel ballasts were tanks and nothing happened. I was sure glad I was insulated at that moment. Kids, am I right? ;P Just want to second what others are saying: don’t toy with those things, and don’t make uninformed assumptions!
- xondono 8y ago
  It’s also good to remember soakage in this kind of applications. It’s irrelevant in low voltage electronics, but once you get over 1 kV and in the order of tens of mF, you can get some ugly scares.
  - 52-6F-62 8y ago
    Ugly scares, indeed. We did regular high-pot and soak testing. Some of those boxes would give us quite the light show when they went bad. And I mean without a lamp hooked up.
- trhway 8y ago
  >don’t toy with those things on a much smaller scale - in about 3rd grade at one point we had that game that took off like epidemic in our school and fortunately subsided quickly too - shocking each other (today you'd call it "tazering":), in an open fight kind of like 2 scorpions or sneaking upon, with the capacitors, wall socket charged (220v in USSR) and if i remember correctly of 10-200mkF (like an 1in thick cylinder or a block up to half Rubik cube size). The shock was profound to say the least and according to some literature seems to be crossing into accidentally deadly territory in unfortunate circumstances. Fortunately no injuries/deaths happened. Happy childhood in USSR :) - many things from our childhood one just cant do today anywhere.
  - bdamm 8y ago
    Doesn't the m and k cancel each other out, leaving just F? You must mean µkF == mF?
    - trhway 8y ago
      you're right, should have been "uF" (10e-6), thanks. My mistake - i transliterated Russian label "мкФ" ("mkF") which is abbreviation from the Russian word "mikrofarad".
  - MertsA 8y ago
    One thing that makes that capacitor prank significantly safer is that the terminals are so close together so the actual current path through the victim is very unlikely to send any significant current through their heart. Still possible if they touched one terminal to their hand and the other terminal landed on their body or if the victim got one terminal and the prankster accidentally touched the other.
    - trhway 8y ago
      yes. Never thought about it. Frequently there were wires attached so that the wires would stick out of your hand like 2-8in toward your opponent. Still usually both ends would touch about the same locality on the body.
- extrapickles 8y ago
  Big caps even if discharged are dangerous unless you keep them shorted (wrap some wire around the terminals). Thanks to dielectric absorption, a cap that has maintained a charge for a decent amount of time cannot be fully discharged easily, as it will recover 1-15% of its total voltage to zap you later.
HeyLaughingBoy 8y ago
I've had EE professors do more dangerous things, but I concur. Use a resistor! A big cap with a good charge comes into contact with a screwdriver and well, arc flash injuries (and death) are a real thing. https://www.youtube.com/watch?v=6hpE5LYj-CY https://www.youtube.com/watch?v=6hpE5LYj-CY
myself248 8y ago
A good old-fashioned incandescent lightbulb with alligator clips is lovely. It's self-indicating if there's still work being done. :)
jimnotgym 8y ago
I used to have a film canister with a big resistor in it, and crocodile clip leads for this job. Like I said though, make sure you are confident you know what you are doing. Some tricks, fit the clips entirely with one hand, and put your other hand in your pocket. You are trying to avoid a shock across your heart...

52-6F-62 8y ago

Similar experience in film/tv industrial lighting ballasts and heads. Had old techs evangelize that kind of thing. A lot of wacky people in that field. I wouldn’t trust a screwdriver to be safe enough in many of those cases. Some of the caps in those things are massive and hold a charge for ages. I almost killed myself on one thinking there’s no way there would be any charge left after years being stored in an old uninsulated tractor trailer outside. Boy was I wrong. We were demoing some old ballasts—essentially crumpling them before recycling to prevent raiders from seizing the equipment (it happened). Well one coincidentally-aligned swing of the sledge caved the steel chassis in just enough to short a monster cap. The thing exploded on contact. Thankfully those old steel ballasts were tanks and nothing happened. I was sure glad I was insulated at that moment. Kids, am I right? ;P Just want to second what others are saying: don’t toy with those things, and don’t make uninformed assumptions!

xondono 8y ago
It’s also good to remember soakage in this kind of applications. It’s irrelevant in low voltage electronics, but once you get over 1 kV and in the order of tens of mF, you can get some ugly scares.
- 52-6F-62 8y ago
  Ugly scares, indeed. We did regular high-pot and soak testing. Some of those boxes would give us quite the light show when they went bad. And I mean without a lamp hooked up.
trhway 8y ago
>don’t toy with those things on a much smaller scale - in about 3rd grade at one point we had that game that took off like epidemic in our school and fortunately subsided quickly too - shocking each other (today you'd call it "tazering":), in an open fight kind of like 2 scorpions or sneaking upon, with the capacitors, wall socket charged (220v in USSR) and if i remember correctly of 10-200mkF (like an 1in thick cylinder or a block up to half Rubik cube size). The shock was profound to say the least and according to some literature seems to be crossing into accidentally deadly territory in unfortunate circumstances. Fortunately no injuries/deaths happened. Happy childhood in USSR :) - many things from our childhood one just cant do today anywhere.
- bdamm 8y ago
  Doesn't the m and k cancel each other out, leaving just F? You must mean µkF == mF?
  - trhway 8y ago
    you're right, should have been "uF" (10e-6), thanks. My mistake - i transliterated Russian label "мкФ" ("mkF") which is abbreviation from the Russian word "mikrofarad".
- MertsA 8y ago
  One thing that makes that capacitor prank significantly safer is that the terminals are so close together so the actual current path through the victim is very unlikely to send any significant current through their heart. Still possible if they touched one terminal to their hand and the other terminal landed on their body or if the victim got one terminal and the prankster accidentally touched the other.
  - trhway 8y ago
    yes. Never thought about it. Frequently there were wires attached so that the wires would stick out of your hand like 2-8in toward your opponent. Still usually both ends would touch about the same locality on the body.
extrapickles 8y ago
Big caps even if discharged are dangerous unless you keep them shorted (wrap some wire around the terminals). Thanks to dielectric absorption, a cap that has maintained a charge for a decent amount of time cannot be fully discharged easily, as it will recover 1-15% of its total voltage to zap you later.

HeyLaughingBoy 8y ago

I've had EE professors do more dangerous things, but I concur. Use a resistor! A big cap with a good charge comes into contact with a screwdriver and well, arc flash injuries (and death) are a real thing. https://www.youtube.com/watch?v=6hpE5LYj-CY https://www.youtube.com/watch?v=6hpE5LYj-CY

myself248 8y ago

A good old-fashioned incandescent lightbulb with alligator clips is lovely. It's self-indicating if there's still work being done. :)

jimnotgym 8y ago

I used to have a film canister with a big resistor in it, and crocodile clip leads for this job. Like I said though, make sure you are confident you know what you are doing. Some tricks, fit the clips entirely with one hand, and put your other hand in your pocket. You are trying to avoid a shock across your heart...