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Comment by ajross | Hacker News Reader

OK, even granting the crazy notion that the charger put line voltage (which google tells me is 220V@50Hz in Vietnam) into the charger cable:

How do you electrocute yourself in bed with such a setup? That cable is going to short through the electronics easily. The tiny conductors in the connectors on both ends are going to melt and break. And even assuming you get unlucky enough to have them fail closed so you have the phone case energized... where is the ground in a bedroom situation to complete the circuit? Rolling onto a phone case at 220V is going to hurt like hell, but it won't kill you unless you can get a current across your heart.

I don't buy it.

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It only takes 100 or 200 mA to kill. This is probably not enough current to melt or break any conductors, the chargers are typically designed to deliver 1,000 mA or more. Off-brand chargers are known electrocution hazards and this is not the first case of injury, not even remotely.

Remember that heating follows P = I^2 R law, so it is entirely reasonable that the conductors wouldn't melt before the attached person dies. Current across the heart is not the only way to die from electricity, but it's not really that hard to accidentally get current across the heart anyway. For example, if your arm touches the energized phone case and your leg brushes against a metal pipe in the house, that could easily complete a lethal circuit.

>It only takes 100 or 200 mA to kill

yes, but the actual amount of current that your organs are exposed to depends on the the resistance and voltage. that's why you can't electrocute yourself by putting your fingers on a 9v battery even though it's well over 200mA.

This isn't an iPhone we're talking about, this is the charger which is connected to 220V AC power. The chargers are build very small, and cheap off-brand chargers have insufficient clearance between the LV and the HV side. This is dangerous, and can cause the 220V mains to go through to the USB port. This is also a very well-known property of cheap phone chargers, and you can find many teardowns online that show what I'm talking about.

https://www.youtube.com/watch?v=wi-b9k-0KfE

https://www.youtube.com/watch?v=dfJ3Ui8IS04

http://www.epanorama.net/newepa/2016/10/25/cheap-usb-charger...

I have also seen a few videos of teardowns of actual faulty chargers. For example, there was one where some of the insulation in the transformer windings were damaged, and you would get a continuous shock just by touching the LV side of any devices that are plugged in.

> that's why you can't electrocute yourself by putting your fingers on a 9v battery even though it's well over 200mA.

If you break the skin a 9v battery can kill.

http://www.darwinawards.com/darwin/darwin1999-50.html

Exactly. If you create a 9v voltage between an artery and a vein (though 0.1v is plenty) and you generate more than around 160mA current (any battery and static electricity can do that).

Essentially you'd have to get a conductor into an artery and one into a vein, and if there is a millisecond where both are in there but not touching the skin your heart will stop. It can be restarted for a minute or so afterwards, but it won't restart on it's own.

Your skin has a "safe" (more or less) conductive layer to prevent this from occurring, with another layer with enormous insulation below that. That's why humans usually survive getting hit by lightning, yet succumb to such a stupid tiny amount of current if it gets past the skin.

> It only takes 100 or 200 mA to kill.

Only if it reaches your heart.

I don't buy it either, the charger cable would melt instantly or the usb port would explode.

I'm reminded of an article I read way back about a teenage boy who had committed suicide. Except it wasn't suicide - he died of auto-erotic asphyxiation. But no family will let that be written in the papers (at least, not immediately) so they went with the story that he hung himself and was depressed.

There was another story recently of a girl who electrocuted herself in the bath when she dropped her phone into the water while it was plugged in. I was skeptical of that as well - who wants to tell people their child committed suicide by taking a toaster in the bath? Best just say it was the cellphone.

I don't blame the parents if this is their cover up.

Why would the charger cable melt? Is this your intuitive guess here, or are you basing this on your understanding of electrical engineering?

It takes 100 to 200 mA to kill someone. A typical charger would put out 1,000 mA in normal operation. Heating follows P = I^2 R law, so it should be obvious that you can kill someone without melting your USB cable. The problem here is with putting a high voltage through the USB cable, which might damage the cable since it's not designed for such a high voltage, but even the small amount of insulation in a USB cable can be enough that the attached person will die before the cable fails.

Amperage kills you, but it takes voltage to get to your heart first. 5VDC across your body's resistance (somewhere around 1MΩ in normal conditions) is nowhere near enough current to feel, let alone harm you.

Right, and the charger is plugged into the wall which provides 220VAC. The cheap chargers are unsafe because they don't have enough clearance between the high voltage and low voltage sides of the circuit, so the isolation can fail and energize the USB port with 220VAC, for example. This is a well-known failure mode of cheap phone chargers, and it should be obvious why these shortcuts are illegal in most countries.

Teardowns of cheap USB chargers online explain what I'm talking about, for example, https://www.youtube.com/watch?v=wi-b9k-0KfE

The story about the girl in the bathtub was filled with a lot of rumors. In the end, the girl may have touched a frayed electrical cord after she dropped the phone in the tub. Electroboom has a video of him explaining this likely cause on his Youtube. I would link it but Youtube is blocked at work.

She was using a non-standard Apple charger. I have seen two of those blow up myself (as in the internal components were literally blown up, and the case was blackened). Assuming the cable was fried and the charger was in her bed, she would have been using an extension cord, which could itself electrocute her. There shouldn't be 220v output on the 5v output line, but those chargers are so crappy that anything is possible.

The only thing I don't get is why didn't the fuse blow?

The "crazy notion" is old news: http://www.righto.com/2014/05/a-look-inside-ipad-chargers-pr...

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