4 ms·

How is 12 volts high voltage? 12 volts would take a long time to heat up a ring or a watch, not millisseconds.

lights0123 5y ago
Those are going to be mostly solid metal, so they're going to have very low resistance. Worst case scenario, you have a silver ring, which has the lowest resistance of any common metal at normal temperatures. Even at a high value of 0.1 ohms (it's sure to be much lower than that), you're looking at 1440 watts, around the heat produced by many plug-in heaters in the US.
bacheaul 5y ago
It's not high voltage, that's the point. I suggest looking for videos [1] on welding steel with a 12v car battery to see how fast metal can heat up with enough current behind it. [1] eg. https://m.youtube.com/watch?v=2TtwrqIDnxg https://m.youtube.com/watch?v=2TtwrqIDnxg
neckardt 5y ago
You are correct that 12 volts is not high voltage. However it can still heat up a ring or watch in milliseconds if the power supply can supply the needed amperage. Using the equation V (volts) * I (Amps) = P (watts) we could calculate the power of putting a car battery through a ring: 12 volts * 100 amps[1] = 1200 watts. That's more than your average microwave. The reason you don't heat up when you touch a car battery is that at 12 volts your skin (mostly an insulator) won't conduct the needed amps. Metal (a conductor) will however transfer close to the full 100 amps of the battery. Here's an example of the effect[2] [1]: https://www.bestpowerbattery.com/how-many-amps-is-a-car-battery/ https://www.bestpowerbattery.com/how-many-amps-is-a-car-batt... [2]: https://www.youtube.com/watch?v=8Wx6-ysokJU https://www.youtube.com/watch?v=8Wx6-ysokJU
- littlestymaar 5y ago
  With 110/220V AC, you only need to touch the phase to be in trouble. With 12V, your body will basically block all current from flowing, so to get in trouble you'll need to accidentally make the metal part to connect both electrodes of the battery (short circuit). This is much, much less likely than with other low voltage system (btw, 12V is Extra-low voltage).
  - MayeulC 5y ago
    One of the elecrodes of the battery (-) is generally connected to the metal body. You only need a cable touching your ring while your hand rests on the frame to cause a short, which can happen. Or a loose cable touching the car frame. It's generally immediately obvious, and can be remediated by pulling the cable away before it welds. But dropping a screwdriver in the wrong place can and will (statistically, thanks murphy) happen, so better use insulated screwdrivers and gloves, to reduce the likeliness of it happening.
    - littlestymaar 5y ago
      > One of the elecrodes of the battery (-) is generally connected to the metal body. You only need a cable touching your ring while your hand rests on the frame to cause a short The current won't flow through your hand, 12V is too low to pass your skin with a significant current. The only way the ring can have raise to a significant heat is if the ring itself touches both sides of the circuit (anode -> car frame -> ring -> wire -> cathode). Anode -> car frame -> hand -> ring -> wire -> cathode won't cause any short, because your hand acts as a big resistance in that circuit.
      - MayeulC 5y ago
        > current won't flow through your hand Of course not, I didn't mean to imply that. > if the ring itself touches [the car frame] That's what I meant. > 12V is too low to pass your skin with a significant current Now of course the human body has a complex impedance, with cell membranes acting as capacitors: higher frequencies let more current flow. And that also depends on how much skin there is (single finger vs arm to foot), if it is wet, etc. I remember trying a (discharged) 9 V battery on my tongue as a kid... that was literally quite a shock, even with continuous current. In the end, I wouldn't bet that an electrocution is impossible using a mere 12V of electric potential.
        littlestymaar 5y ago
        We weren't talking about electrocution here, but about heating a ring quickly enough to burn you, which requires a much higher amperage than what's needed to kill you. Anyway, given that 12V is considered safety voltage for submerged swimming pool material in France, I'm pretty confident it is be extremely unlikely to kill anyone.
userbinator 5y ago
It's the amps, not the volts. A 12V car battery can supply hundreds of amps if you give it a low enough resistance to go through.
techdragon 5y ago
12V is high compared to a lot of <5V electronics that do "the thinking" for 12V & 24V power systems that do "the work" in a lot electric systems around the world. As for the heating up... https://www.youtube.com/watch?v=nbGcSjRAyxs https://www.youtube.com/watch?v=nbGcSjRAyxs is a good demo of how fast 12V can heat up a small hunk of metal given enough amperage (in the case of that video 12V at 100A) . There are a surprising amount of 12V and 24V DC power systems (like in that video) can push in well over a kilowatt (12V at >100A or 24V at >50A) of power in a dead short situation. My father had a paperweight in his shed that looked like someone used a spanner as a fork for lava, drooped away from its normal shape like a Salvador Dali clock, one end barely recognisable with blackened carbonisation marks and a ragged but lightly polished place where it was cut clean from something with an angle grinder. 24V at 150A for just a few seconds before the batteries were discharged, big marine batteries for lots of current to kick start an old heavy duty engine, lots of Amps but not many Amp Hours, still enough to destroy the spanner.

Those are going to be mostly solid metal, so they're going to have very low resistance. Worst case scenario, you have a silver ring, which has the lowest resistance of any common metal at normal temperatures. Even at a high value of 0.1 ohms (it's sure to be much lower than that), you're looking at 1440 watts, around the heat produced by many plug-in heaters in the US.

bacheaul 5y ago

It's not high voltage, that's the point. I suggest looking for videos [1] on welding steel with a 12v car battery to see how fast metal can heat up with enough current behind it. [1] eg. https://m.youtube.com/watch?v=2TtwrqIDnxg https://m.youtube.com/watch?v=2TtwrqIDnxg

neckardt 5y ago

You are correct that 12 volts is not high voltage. However it can still heat up a ring or watch in milliseconds if the power supply can supply the needed amperage. Using the equation V (volts) * I (Amps) = P (watts) we could calculate the power of putting a car battery through a ring: 12 volts * 100 amps[1] = 1200 watts. That's more than your average microwave. The reason you don't heat up when you touch a car battery is that at 12 volts your skin (mostly an insulator) won't conduct the needed amps. Metal (a conductor) will however transfer close to the full 100 amps of the battery. Here's an example of the effect[2] [1]: https://www.bestpowerbattery.com/how-many-amps-is-a-car-battery/ https://www.bestpowerbattery.com/how-many-amps-is-a-car-batt... [2]: https://www.youtube.com/watch?v=8Wx6-ysokJU https://www.youtube.com/watch?v=8Wx6-ysokJU

littlestymaar 5y ago
With 110/220V AC, you only need to touch the phase to be in trouble. With 12V, your body will basically block all current from flowing, so to get in trouble you'll need to accidentally make the metal part to connect both electrodes of the battery (short circuit). This is much, much less likely than with other low voltage system (btw, 12V is Extra-low voltage).
- MayeulC 5y ago
  One of the elecrodes of the battery (-) is generally connected to the metal body. You only need a cable touching your ring while your hand rests on the frame to cause a short, which can happen. Or a loose cable touching the car frame. It's generally immediately obvious, and can be remediated by pulling the cable away before it welds. But dropping a screwdriver in the wrong place can and will (statistically, thanks murphy) happen, so better use insulated screwdrivers and gloves, to reduce the likeliness of it happening.
  - littlestymaar 5y ago
    > One of the elecrodes of the battery (-) is generally connected to the metal body. You only need a cable touching your ring while your hand rests on the frame to cause a short The current won't flow through your hand, 12V is too low to pass your skin with a significant current. The only way the ring can have raise to a significant heat is if the ring itself touches both sides of the circuit (anode -> car frame -> ring -> wire -> cathode). Anode -> car frame -> hand -> ring -> wire -> cathode won't cause any short, because your hand acts as a big resistance in that circuit.
    - MayeulC 5y ago
      > current won't flow through your hand Of course not, I didn't mean to imply that. > if the ring itself touches [the car frame] That's what I meant. > 12V is too low to pass your skin with a significant current Now of course the human body has a complex impedance, with cell membranes acting as capacitors: higher frequencies let more current flow. And that also depends on how much skin there is (single finger vs arm to foot), if it is wet, etc. I remember trying a (discharged) 9 V battery on my tongue as a kid... that was literally quite a shock, even with continuous current. In the end, I wouldn't bet that an electrocution is impossible using a mere 12V of electric potential.
      - littlestymaar 5y ago
        We weren't talking about electrocution here, but about heating a ring quickly enough to burn you, which requires a much higher amperage than what's needed to kill you. Anyway, given that 12V is considered safety voltage for submerged swimming pool material in France, I'm pretty confident it is be extremely unlikely to kill anyone.

userbinator 5y ago

It's the amps, not the volts. A 12V car battery can supply hundreds of amps if you give it a low enough resistance to go through.

techdragon 5y ago

12V is high compared to a lot of <5V electronics that do "the thinking" for 12V & 24V power systems that do "the work" in a lot electric systems around the world. As for the heating up... https://www.youtube.com/watch?v=nbGcSjRAyxs https://www.youtube.com/watch?v=nbGcSjRAyxs is a good demo of how fast 12V can heat up a small hunk of metal given enough amperage (in the case of that video 12V at 100A) . There are a surprising amount of 12V and 24V DC power systems (like in that video) can push in well over a kilowatt (12V at >100A or 24V at >50A) of power in a dead short situation. My father had a paperweight in his shed that looked like someone used a spanner as a fork for lava, drooped away from its normal shape like a Salvador Dali clock, one end barely recognisable with blackened carbonisation marks and a ragged but lightly polished place where it was cut clean from something with an angle grinder. 24V at 150A for just a few seconds before the batteries were discharged, big marine batteries for lots of current to kick start an old heavy duty engine, lots of Amps but not many Amp Hours, still enough to destroy the spanner.