5 ms·

Interestingly, working with low-voltage, high-current power supply has an uncommon danger: it won't kill you by giving an electric shock, but you may suffer fro

Interestingly, working with low-voltage, high-current power supply has an uncommon danger: it won't kill you by giving an electric shock, but you may suffer from serious injury due to joule heating. You would create a massive electric cooker if there's any accidental short from power to ground, especially, don't wear any jewel or ring.

AstralStorm 7y ago
Bonus points if high frequencies are used, as they are in this one I bet. Your things are antennas, and the transformer if any is an electromagnet too.
H8crilA 7y ago
You mean 12 volts at ~unlimited amps supply ran through my body may heat me up from the inside? Isn't the human body resistance too high for that, even if you go below the skin on both ends? At 10 ohm it would be just ~15 watts, hardly dangerous given that human bodies at rest produce ~100 watts of heat. Edit: fixed numbers.
- blauditore 7y ago
  You can also get burned without current flowing through your body, e.g. by accidentally shorting the circuit through some sweat on your skin.
  - H8crilA 7y ago
    Uh right. But still - my skin sweat having less than 10 ohm resistance sounds like a stretch. It is more salty than blood though (because of evaporation).
    - zaarn 7y ago
      If the droplet of sweat has a resistance of 10 Ohms, 1.2 Amps will be flowing at 12V. The droplet will be heated by 14 Watts of energy. Doesn't sound much. But it's enough to bring a droplet of sweat to the boiling point within 10 seconds. Your sweat starting to boil of your skin doesn't sound like a very pleasant way to pass the time.
      - H8crilA 7y ago
        I was thinking on a longer distance, like between left and right hand, or between a hand and a leg (which I still think is near impossible to cause any harm with 12 volts). But surely it can happen on a distance of less than few cm, when the + is in a very close proximity to the - (touch here to get your fingertip heated!).
        zaarn 7y ago
        Doesn't need to be a terminal, touching a broken wire with sweaty hands would be enough to induce flash evaporation of fluids on your skin.
        rlonn 7y ago
        not with 12V. 12V batteries are pretty safe for human skin contact. If you put your wet tongue across a 12V battery it will hurt, but not more than that (it's a good way to test 9V batteries actually)
        867-5309 7y ago
        only on HN..
        zaarn 7y ago
        Well, if you put your tongue on it, you'll obviously have a lot more distance to cover and a lot more fluid to handle the current. Batteries in general are fairly safe because their voltage breaks down at high loads. The chemistry can only react so fast internally and is controlled by various factors. Contrast this with capacitors, where there is always a general safety warning when handling them in live circuits. They have no limit based on chemistry. You don't want to test a capacitor with your tongue. A capacitor has no other current limit than it's internal resistance, with a modern sub10mOhm ISR a capacitor can, for the briefest of moments, discharge at up to 14 Kilowatts, quite the upgrade from the 14 measly watts that your spit will handle. A 100 Millifarad Low ISR Cap can sustain a kilowatt of output for almost 0.1 milliseconds, at which point you'll likely regret the choice of mishandling a cap. (It's only 14 Joules but these 14 Joules will be moving very fast)
- segfaultbuserr 7y ago
  > You mean 12 volts at ~unlimited amps supply ran through my body may heat me up from the inside? No. But you'll be injured if you short it with any metallic objects while touching it, like the wiring, the board, your probe, the ring on your finger, etc.
  - rlonn 7y ago
    Electric submarines have pretty large batteries with very low-voltage cells but where a cell is big enough to deliver huge amounts of current. Completely safe to touch with bare hands, even wet hands, but if you drop a metal tool that shorts a cell, the tool may be vaporized and the resulting metal fumes are very dangerous.
  - klingonopera 7y ago
    Yep. Imagine a ground plane and a positive +12V pole able to supply infinite amps. You can short circuit using your body and you'd probably feel a tingle (your body resistance is not high, but not too low either). But if the ring you're wearing on your finger is causing the short circuit, thousands of amps will flow through it, as it has an ultra-low resistance, and heat it up to temperatures that will quickly cause burns and whatnot. If the device does not have infinite amps, then this is the case where normally the power supply's fuse would blow, and thus the ring would never heat up and nobody would get hurt. To summarize: Low-voltage, high-current electricity is indirectly dangerous, whereas any high voltage electricity is inherently directly dangerous.
    - dreamcompiler 7y ago
      > Low-voltage, high-current electricity is indirectly dangerous, whereas any high voltage electricity is inherently directly dangerous. Very high voltage with very low current is not inherently dangerous. Static electricity is this case. The total energy (voltage x current x time) passing through the body is the critical determinant of harm.
- rlonn 7y ago
  Try measuring your resistance with a multimeter. You'll find that it is way more than 10 Ohm, which is why 12V is not dangerous to humans.
  - anoonmoose 7y ago
    Just do NOT stick the probes into your fingers, ie, don't break your skin. Depending on the multimeter this can be extremely dangerous. https://darwinawards.com/darwin/darwin1999-50.html https://darwinawards.com/darwin/darwin1999-50.html
    - carapace 7y ago
      Wow! You're not kidding... > As my electrical safety instructor said, "The reason we now have to teach the electrical safety course to all electricians at least twice per year is because some joe was bright enough to be the one person in the world who could figure out how to kill himself with a 9V battery."
- rstuart4133 7y ago
  > Isn't the human body resistance too high for that That must be true normally. But years ago I recall reading about someone who fixed an 12V underwater light in a pool. You would imagine that would be harmless, but he managed to create a circuit that ran across the pool. It was a salt water chlorinated pool, and after doing the job he dived in, and it killed him. I don't know how wide the pool was, but in any case the voltage across his body must have been less than 12V, and possibly a fraction of that.

AstralStorm 7y ago

Bonus points if high frequencies are used, as they are in this one I bet. Your things are antennas, and the transformer if any is an electromagnet too.

H8crilA 7y ago

You mean 12 volts at ~unlimited amps supply ran through my body may heat me up from the inside? Isn't the human body resistance too high for that, even if you go below the skin on both ends? At 10 ohm it would be just ~15 watts, hardly dangerous given that human bodies at rest produce ~100 watts of heat. Edit: fixed numbers.

blauditore 7y ago
You can also get burned without current flowing through your body, e.g. by accidentally shorting the circuit through some sweat on your skin.
- H8crilA 7y ago
  Uh right. But still - my skin sweat having less than 10 ohm resistance sounds like a stretch. It is more salty than blood though (because of evaporation).
  - zaarn 7y ago
    If the droplet of sweat has a resistance of 10 Ohms, 1.2 Amps will be flowing at 12V. The droplet will be heated by 14 Watts of energy. Doesn't sound much. But it's enough to bring a droplet of sweat to the boiling point within 10 seconds. Your sweat starting to boil of your skin doesn't sound like a very pleasant way to pass the time.
    - H8crilA 7y ago
      I was thinking on a longer distance, like between left and right hand, or between a hand and a leg (which I still think is near impossible to cause any harm with 12 volts). But surely it can happen on a distance of less than few cm, when the + is in a very close proximity to the - (touch here to get your fingertip heated!).
      - zaarn 7y ago
        Doesn't need to be a terminal, touching a broken wire with sweaty hands would be enough to induce flash evaporation of fluids on your skin.
        rlonn 7y ago
        not with 12V. 12V batteries are pretty safe for human skin contact. If you put your wet tongue across a 12V battery it will hurt, but not more than that (it's a good way to test 9V batteries actually)
        867-5309 7y ago
        only on HN..
        zaarn 7y ago
        Well, if you put your tongue on it, you'll obviously have a lot more distance to cover and a lot more fluid to handle the current. Batteries in general are fairly safe because their voltage breaks down at high loads. The chemistry can only react so fast internally and is controlled by various factors. Contrast this with capacitors, where there is always a general safety warning when handling them in live circuits. They have no limit based on chemistry. You don't want to test a capacitor with your tongue. A capacitor has no other current limit than it's internal resistance, with a modern sub10mOhm ISR a capacitor can, for the briefest of moments, discharge at up to 14 Kilowatts, quite the upgrade from the 14 measly watts that your spit will handle. A 100 Millifarad Low ISR Cap can sustain a kilowatt of output for almost 0.1 milliseconds, at which point you'll likely regret the choice of mishandling a cap. (It's only 14 Joules but these 14 Joules will be moving very fast)
segfaultbuserr 7y ago
> You mean 12 volts at ~unlimited amps supply ran through my body may heat me up from the inside? No. But you'll be injured if you short it with any metallic objects while touching it, like the wiring, the board, your probe, the ring on your finger, etc.
- rlonn 7y ago
  Electric submarines have pretty large batteries with very low-voltage cells but where a cell is big enough to deliver huge amounts of current. Completely safe to touch with bare hands, even wet hands, but if you drop a metal tool that shorts a cell, the tool may be vaporized and the resulting metal fumes are very dangerous.
- klingonopera 7y ago
  Yep. Imagine a ground plane and a positive +12V pole able to supply infinite amps. You can short circuit using your body and you'd probably feel a tingle (your body resistance is not high, but not too low either). But if the ring you're wearing on your finger is causing the short circuit, thousands of amps will flow through it, as it has an ultra-low resistance, and heat it up to temperatures that will quickly cause burns and whatnot. If the device does not have infinite amps, then this is the case where normally the power supply's fuse would blow, and thus the ring would never heat up and nobody would get hurt. To summarize: Low-voltage, high-current electricity is indirectly dangerous, whereas any high voltage electricity is inherently directly dangerous.
  - dreamcompiler 7y ago
    > Low-voltage, high-current electricity is indirectly dangerous, whereas any high voltage electricity is inherently directly dangerous. Very high voltage with very low current is not inherently dangerous. Static electricity is this case. The total energy (voltage x current x time) passing through the body is the critical determinant of harm.
rlonn 7y ago
Try measuring your resistance with a multimeter. You'll find that it is way more than 10 Ohm, which is why 12V is not dangerous to humans.
- anoonmoose 7y ago
  Just do NOT stick the probes into your fingers, ie, don't break your skin. Depending on the multimeter this can be extremely dangerous. https://darwinawards.com/darwin/darwin1999-50.html https://darwinawards.com/darwin/darwin1999-50.html
  - carapace 7y ago
    Wow! You're not kidding... > As my electrical safety instructor said, "The reason we now have to teach the electrical safety course to all electricians at least twice per year is because some joe was bright enough to be the one person in the world who could figure out how to kill himself with a 9V battery."
rstuart4133 7y ago
> Isn't the human body resistance too high for that That must be true normally. But years ago I recall reading about someone who fixed an 12V underwater light in a pool. You would imagine that would be harmless, but he managed to create a circuit that ran across the pool. It was a salt water chlorinated pool, and after doing the job he dived in, and it killed him. I don't know how wide the pool was, but in any case the voltage across his body must have been less than 12V, and possibly a fraction of that.