Will my waterproof iPod Shuffle electrocute me?
November 14, 2016 10:19 AM   Subscribe

I bought this waterproof iPod shuffle so I can listen to music while I swim laps. Sadly, I don't understand all the science involved. What is the likelihood this thing will electrocute me?

I realize I'm probably worrying needlessly. Could they legally sell this thing if it could kill people? Probably not. However, I'm having a hard time getting over the "electricity + water = death" thing. I'm hoping someone who understands this better than I can help me judge the risk I'm taking by using this thing. It will, after all, be awful close to my brain.
posted by when it rains it snows to Technology (11 answers total) 1 user marked this as a favorite
An ipod has a 3.65 volt li-ion battery. It's impossible (ok, very, very difficult) for such a small voltage to hurt you in any way. The shortest path if or when the battery shorts is directly between the battery terminals so there's nearly zero chance the current would flow through any part of your body.

Now, you might destroy the ipod. That's a risk.

Water-based electrocution occurs when there's a high voltage source, like a power line, that is conducting through the water to ground. In those cases the line is at 240V up to 68kV for distribution lines. (let's ignore really high voltage long-distance transmission lines since they tend not to be near people) That's dangerous voltage. And the other issue is path-to-ground. With batteries they're a closed system and the ground is right next to the positive electrode. With power lines ground is literally the ground and if you get between the power line and the earth you're going to have current flow through you. So there's a big difference between the two situations.
posted by GuyZero at 10:27 AM on November 14, 2016 [5 favorites]

In short, likelihood = zero.
posted by BurntHombre at 10:53 AM on November 14, 2016 [1 favorite]

Water is not actually a very good conductor of electricity. Therefore electricity + water is only bad when the voltage is high enough to overcome water's poor conductivity.
posted by kindall at 10:55 AM on November 14, 2016 [3 favorites]

Also, I know this probably doesn't make a difference, but I'm including it for completeness : the pool I'm swimming in is a salt water pool.
posted by when it rains it snows at 11:25 AM on November 14, 2016

Saltwater is more conductive but we're talking microohms vs milliohms - neither is very conductive.

Also note that the battery is current-limited - even at short circuit it will generate a limited current as it's only capable of supplying a few hundred milliamps, tops. An actual electrical transmission line is capable to supplying hundred to thousands of amps instantaneously.

You're far more likely to be injured by an exploding li-ion battery than electrocuted by one. And the odds of you having a battery explode on you are very low.
posted by GuyZero at 11:32 AM on November 14, 2016 [1 favorite]

Saltwater is more conductive but we're talking microohms vs milliohms - neither is very conductive.

this is misleading because both microohms and milliohms are very small resistances which mean that something is conductive. i guess guyzero means megaohms vs kiloohms. or is using conductance units (siemens). although when you're talking about a mass of stuff, like water, you generally use ohm metres and the resistance of sea water is about 0.2 ohm m, for what it's worth.

anyway, you're fine and worrying too much.
posted by andrewcooke at 11:50 AM on November 14, 2016 [2 favorites]

or is using conductance units (siemens)

oops, yeah, that's it. I looked up a reference and the units were mhos which I wrongly interpreted as ohms. Stupid Siemens. It is indeed megaohms to kiloohms of resistance.
posted by GuyZero at 12:12 PM on November 14, 2016 [1 favorite]

I have had two of those exact models over the years (I lost the first one). I have probably swam more than 100 miles while wearing them without any electrocution problems. Edit: oh, I have also taken them in the ocean once and had no problems there either.
posted by procrastination at 12:22 PM on November 14, 2016

"Saltwater is more conductive but we're talking microohms vs milliohms - neither is very conductive."
"Stupid Siemens. It is indeed megaohms to kiloohms of resistance."

Units fail, yeah - but also wrong in the magnitude of comparison. Bulk resistance of water varies considerably with soluble ionic impurities, and it doesn't take much to dramatically decrease the resistance. As a rough guide:
  • Ultra-pure water = ~2,000,000 ohm m.
  • Distilled water = ~200,000 ohm m.
  • Rain water = ~20,000 ohm m.
  • Tap water = ~2,000 ohm m.
  • Ground water = ~200 ohm m.
  • Brackish estuarine water = ~2-20 ohm m.
  • Salt (sea) water = ~0.2 ohm m.
But OP, you'll be fine. I won't say it's guaranteed - I can imagine a case where, say, the protective coating or seals fail & expose the battery positive and earphone ground to the water, some of the current passes through your skin between the two, and given the voltages & likely currents involved may be slightly irritating or unpleasant - but I personally would happily swim with one and wouldn't worry about it.
posted by Pinback at 4:22 PM on November 14, 2016

Get one of those rectangular 9V smoke alarm batteries. A nice new one. Now lick the terminals.

That slightly stinging tingle you just felt is what it's like to achieve the worst electrocution that a battery with about three times the punch of the one in your iPod can possibly deliver.
posted by flabdablet at 5:54 PM on November 14, 2016 [7 favorites]

Thank you all. I shall swim without fear.
posted by when it rains it snows at 9:19 AM on November 15, 2016

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