Electronic – What did I feel testing a car battery

batteries

Was trying to test the voltage of my car battery but accidently had the multimeter set up for Amps (was using it for an old project and forgot to switch cables/turn the dial).

Turned my multimeter on. Connected the terminal to my car battery to test for a flat and while holding the multimeter probes thought i felt something travel through my fingers. No pain or anything. Just a very odd sensation.

It's a 12V battery. I know (from the sparks and 30 seconds on google) they pack a LOT of current but surely there isn't enough voltage to shock me through the (a) plastic handles of the multimeter, and (b) my skin.

So what did I feel? The multimeter is only rated for 10A. Any chance it could have 'failed dangerously' when I accidently overloaded it? Or was the sensation in the probes just the sudden surge of current inducing some sort of force in the wire?

Thanks for you help. Panicking a bit.

Best Answer

A multimeter in ampmeter mode is basically a short.

If you're lucky, the multimeter has a fuse that instantly burned when you connected the battery – a charged, a shorted car battery can easily source > 80 A, and that just vaporizes a lot of on-board conductor traces.

So, what you might have been feeling is

  1. the electromotive force due to wires with very high currents running in opposite direction being very close
  2. the thermal reaction of measurement leads most definitely not speced for shorting car batteries (compare your multimeter leads to car jumper wires. Assume that at least 70% of your lead's diameter is isolation.)
  3. something in your multimeter violently exploding and that mechanical shock being sent down the wires.
  4. your nervous system's shock response to seeing sparks and hearing something pop.
  5. Back-EMF: a fuse blowing has very high derivative of current over time, which means that the very little inductance of your wires might have caused a very high voltage for very shortly, think a couple kV. That might actually have shot through your isolation, but honestly, the resulting current would most likely have been low enough to not pose a danger
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