• rotopenguin@infosec.pub
    link
    fedilink
    English
    arrow-up
    62
    ·
    edit-2
    1 year ago

    An AAAA cell has 200-350 mohms internal resistance. A 9v battery has 6 of them in series (many of them are literally that, others have their cells as a stack of plastic buckets). The nose ring is a short run of wire, it’s idunno a 0.2 ohm heater?

    I think the septum is going to get pretty toasty.

    https://data.energizer.com/pdfs/e96.pdf

    • enkers@sh.itjust.works
      link
      fedilink
      arrow-up
      53
      ·
      edit-2
      1 year ago

      I just tested this (for science!) with a 9V battery and an iron nail of roughly nose-ring diameter. Both the nail and the battery get unpleasantly hot after several seconds. I don’t think they’d get hot enough to burn you, though. (Don’t take my word, though, please!) I believe the internal resistance of the battery does also increase with the temperature, so it effectively somewhat self regulates itself.

      Common nose ring materials like Titanium and Stainless Steel are 4× and 7× more resistant than iron, which means they should dissipate more power than the nail, and thus get hotter. I was calculating something around 3 milliohms for a titanium 16 gauge 10mm wire, and 0.7 milliohms for an iron wire.

      Regardless of material, at 1000 milliohms internal resistance, i think the battery itself is doing most of the heat dissipation. (But also over a much bigger surface area!)

        • enkers@sh.itjust.works
          link
          fedilink
          arrow-up
          8
          ·
          edit-2
          1 year ago

          About 10-20s, I left it on until it didn’t seem to be getting much hotter. I also didn’t want the battery to overheat and fail catastrophically. I think because the “wire” is such a high gauge, there’s not enough current for it to get seriously hot. In a foam cutter, you’re passing all that current through a much smaller cross-sectional area.

          Edit: just to confirm, I did a little math. A 10cm steel wire with a tenth of the diameter would have a resistance of 5 ohms. That means that instead of 1% of the total heat dissipating in the thick wire, 80% of the heat is dissipating in the wire in foam cutter’s case, and there’s more total resistance, so more heat dissipation as well.

          This is because:

          A = π r²

          R = ρ × L / A

          So resistance is proportional to the material resistivity (ρ), the length (L), and the inverse square of the radius (r⁻²). That is to say, decreasing the radius by a factor of 10 increases resistance by a factor of 100.

  • Dave@lemmy.nz
    link
    fedilink
    arrow-up
    23
    arrow-down
    1
    ·
    1 year ago

    Would the person feel anything? Presumably the electricity would flow through the metal as path of least resistance?

      • 0ops@lemm.ee
        link
        fedilink
        arrow-up
        14
        ·
        1 year ago

        I used to burn paper with a 9 volt and a paperclip. Good times

        • TrickDacy@lemmy.world
          link
          fedilink
          arrow-up
          10
          ·
          1 year ago

          Why would you spread incorrect information so confidently? You’re absolutely wrong. A 9 volt will get hot in a few seconds when shorted.

          • Agent641@lemmy.world
            link
            fedilink
            arrow-up
            3
            ·
            1 year ago

            I used to put small coins on the terminals til they got super hot, then drop the coin on the desk in front of them. When they go to pick it up, it burns them. Peak comedy.

        • Melkath@kbin.social
          link
          fedilink
          arrow-up
          4
          ·
          1 year ago

          I mean, someone with a septum piercing could confirm this pretty fast.

          Pretty sure it would be nice and toasty inside 30 seconds.

    • SaltyIceteaMaker@lemmy.ml
      link
      fedilink
      arrow-up
      6
      arrow-down
      1
      ·
      1 year ago

      They prob wouldn’t get shocked but the ring and battery will get very hot very quick as there i pretty much no resistance wich means there is a lot of current flowing.

      Someone else in the comments claimed to have calculated a resistance of 0.2 ohms.

      I=U÷R

      9V ÷ 0.2Ω = 45A

      45 amps is a lot of current to flow through a nose ring. I don’t know how much that is in heat but i’d expect you to get burned from it

      • XTL@sopuli.xyz
        link
        fedilink
        arrow-up
        8
        arrow-down
        1
        ·
        edit-2
        1 year ago

        You won’t get more than a few mA out of an alkaline, but heat does build up. (Internal resistance)

        A NiMH on the other and can give over 10 amps. They’re a seriously risky thing to leave around loose metal bits. Or attached to thin wires.