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I was just messing around with a very small permanent magnet (round) stuck to a piece of metal.

The magnet is round, ~6 mm in diameter. I guess 1 mm thick. (I lack precision tools where I am at the moment) The metal is about 5.5 cm long, 0.5 cm wide and almost exactly half as thick as the magnet.

I detected a bit of a sting from it (don't ask me how), so I went to check it with a voltage meter.

There's a very noticeable jump to ~0.6 V, declining very slowly. After I take the voltage meter off, wait a few seconds, and then re-attach it, it has jumped up to 0.6 V again.

What makes this happen? Am I just very stupid and missing some obvious thing here?

This is my setup (sorry for blurriness, seriously bad lighting):

Overview of setup

Close-up

The "metal strip" is a tool from an old lock-picking set. The black plastic is the handle.

After making these pictures, it's now counting up. Over 0.54 V now. (Update after 3 minutes: It's going down again, no sign of stopping)

(Update) I now notice that when I pour water over the part where the probe, the magnet and the metal strip collide, the voltage climbs up again, and after reaching a peak, slowly starts falling again.

(Update on setup with multimeter) As a user in the answers pointed out, my multimeter setup is incorrect. The plugs are plugged in wrong, causing one of the leads to float. I now plugged them in correctly, and it shows the same, if not higher voltage.

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    \$\begingroup\$ I detected a bit of a sting from it ... either an electrostatic discharge from your body or a metal sliver from the piece of metal \$\endgroup\$
    – jsotola
    Commented Apr 11, 2020 at 18:53
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    \$\begingroup\$ @jsotola I detected the sting with my tongue... And it now gives continuous .587v, slightly going up. With no load, of course. \$\endgroup\$
    – Jeff Huijsmans
    Commented Apr 11, 2020 at 18:56
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    \$\begingroup\$ it isnt some galvanic current is it? \$\endgroup\$
    – DKNguyen
    Commented Apr 11, 2020 at 19:05
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    \$\begingroup\$ Please do not lick uncovered super magnets. They are made with nasty metals. I support the galvanic theory. \$\endgroup\$
    – skvery
    Commented Apr 11, 2020 at 19:19
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    \$\begingroup\$ The measurement is bogus - negative black lead is stuck into multimeter current measurement input, and positive red lead is stuck into multimeter voltage measurement input. The multimeter common ground is floating. It is also so bad picture it is impossible to read the symbols on display - most likely you are measuring DC. \$\endgroup\$
    – Justme
    Commented Apr 11, 2020 at 20:26

2 Answers 2

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My guess is it's a Galvanic cell. One electrode is your metal strip (maybe nickel), the other is your magnet whatever it's made of (or coated). The electrolyte is probably sweat or saliva (you used your tongue as a probe). When your electrolyte dried up, voltage went down.

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  • \$\begingroup\$ That sounds pretty in-line with what I experience: when I pour water over it, it becomes a very steady voltage source, declining with 0.001v every 20 seconds or so. I'm pretty sure there is no usable current here, even if I keep it under water, right? I haven't tried it yet, but I expect voltage to drop to 0 when I attach something like a booster. Maybe a joule thief? \$\endgroup\$
    – Jeff Huijsmans
    Commented Apr 11, 2020 at 19:09
  • \$\begingroup\$ Forget it! The current is more-or-less proportional to the area, and the internal resistance depends on the electrolyte's conductivity and the arrangement of all these. You won't get much current from them. A joule thief needs current as well (works as a voltage booster using even more current). \$\endgroup\$
    – Nyos
    Commented Apr 11, 2020 at 19:14
  • \$\begingroup\$ Alright, thank you for answering! I just find it very fascinating that using so little and (in the end) pouring a little water over it generates a voltage difference between the two sides. \$\endgroup\$
    – Jeff Huijsmans
    Commented Apr 11, 2020 at 19:22
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    \$\begingroup\$ The measurement is bogus - negative black lead is stuck into multimeter current measurement input, and positive red lead is stuck into multimeter voltage measurement input. The multimeter common ground is floating. \$\endgroup\$
    – Justme
    Commented Apr 11, 2020 at 20:26
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    \$\begingroup\$ @Justme in the configuration you suggest in your answer, measurements are around the same. Leaving the plugs unplugged shows 0.000v. It's VERY obviously coming from the setup, not some fault in the setup (tried all the different configurations). \$\endgroup\$
    – Jeff Huijsmans
    Commented Apr 12, 2020 at 17:04
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You are not actually measuring anything about the circuit because the leads are plugged in incorrectly.

The negative black lead is stuck into multimeter current measurement input, and positive red lead is stuck into multimeter voltage measurement input. The multimeter common ground is floating, so the multimeter is not able to actually measure voltage with the meter leads.

It is just the multimeter picking up some fluctuations because it's common terminal is not connected to anything. It might show similar readings with the meter leads unplugged.

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    \$\begingroup\$ I think there is validity to the galvanic cell theory, but until OP is measuring correctly, all other conclusions are suspect. \$\endgroup\$
    – notloc
    Commented Apr 11, 2020 at 20:52
  • \$\begingroup\$ Great observation. +1 I posted a followup question electronics.stackexchange.com/questions/492597/… \$\endgroup\$
    – Spacy
    Commented Apr 12, 2020 at 13:08
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    \$\begingroup\$ Nice catch. However, using the configuration you suggest provides the same results. \$\endgroup\$
    – Jeff Huijsmans
    Commented Apr 12, 2020 at 17:02
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    \$\begingroup\$ Also, leaving the leads unplugged shows a steady 0.000v. I would've catched that sooner, if it were like you suggest. I know this might be a beginner question, but I'm not THAT stupid, hah. \$\endgroup\$
    – Jeff Huijsmans
    Commented Apr 12, 2020 at 17:03
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    \$\begingroup\$ "You are not actually measuring anything about the circuit because the leads are plugged in incorrectly." - The 10A jack though is connected through a low-resistance shunt to common. Assuming the fuse is intact, it shouldn't make a huge difference in this case... \$\endgroup\$
    – marcelm
    Commented Apr 12, 2020 at 17:07

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