• rotopenguin@infosec.pubEnglish
    58·
    8 months 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
      55·
      8 months 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
          9·
          8 months 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 large 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.

      • rotopenguin@infosec.pubEnglish
        51·
        8 months ago

        Do it with the piercing OUT OF YOUR BODY. You don’t want a hot piece of metal that you can’t get off of yourself fast enough.

  • Dave@lemmy.nz
    222·
    8 months ago

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

      • 0ops@lemm.ee
        16·
        8 months ago

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

    • SaltyIceteaMaker@lemmy.ml
      121·
      8 months 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
        101·
        7 months 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.

  • TimeSquirrel@kbin.social
    12·
    8 months ago

    You’re doing it wrong. You gotta place a metal sphere close to it connected to a Van de Graaff generator.