Can you get electrocuted by your phone’s charger?

A week or so ago, there was a very sad story about a woman in China who’s father has alleged that she was electrocuted by using her iPhone while it was charging.  This is very alarming to many of the 600 Million iPhone users, not to mention the iPad, Android and other smart phones and tablets.  The question to ask is whether this is really possible and if so, what might cause it?

Image: apple.com

Image: apple.com

Before starting, it’s important to realize that it is still unclear what really happened with this poor woman.  The Chinese authorities, as well as Apple are investigating and until there is more information, its only speculation that it really was caused by the charging phone.  Also, its a good time to mention that I’m NOT an electrical engineer, so my knowledge in this field isn’t deep.

Phone chargers usually have two main components: A transformer to convert wall power to low voltage/amperage power for the phone and a cord that connects to the phone.  The transformer is a marvel of engineering in that it can connect to 110-120 or 220-240 volt power at either 50 or 60 hertz AC (alternating power) and convert it to some small amperage,  low voltage DC (direct current) stream required by the phone (or any other electronic device, like your printer or laptop).    This means that potentially dangerous power enters the transformer, but what comes out the other end should be benign low voltage power.

This conversion is done electromagnetically by two coils of wire near each other.  One coil has the high voltage, while the other is the converted low voltage.  The important point is that these coils do not touch.  Also, there is some “waste” during the conversion process, which manifests itself in heat.  You’ll notice that a working transformer is warm to the touch (which is OK).    If a transformer is overwhelmed by the conversion, say by a short, it will “pop”, usually with trace smoke and stop working.  A poorly made transformer might catch fire.

So, the question remains: Can one really get electrocuted by using one’s phone while its charging?  This would imply that dangerous higher voltage power somehow jumped from the high voltage coil to the low voltage coil.  This is possible, but (and this is a big but) the low voltage coil is not strong enough to withstand contact with high voltage.  It would burn out very quickly, thereby disconnecting the circuit.    So, let’s assume that it DID jump the gap between coils and the low voltage side didn’t burn out quick enough.  The current would then have to move up the wire, through the connector into the phone, again crossing over components not equipped to handle high voltage.  At multiple points along the way, it should short out, disconnecting the circuit.  Assuming that doesn’t happen, then it’s possible that the circuit could connect to the metal ring around the iPhone (it’s an antenna after all).  If you don’t have a case on your phone that could act as an insulator, then it could be a shocking experience.

So, theoretically it is possible but highly unlikely.  There are several points along the path that should burn out long before reaching the case of the phone itself and if you have a protective case around the phone, you should be insulated (unless you’re taking a bath while on the phone, which generally is a bad idea).

I think the bigger issue and a possible cause of the problem in China is whether one is using the proper charger for the device.  I suspect that like me, you have a pile of various chargers somewhere that you’ve kept for possible use in the future.  You might also have purchased a 3rd party charger which might be of questionable quality.  The charger needs to be appropriate for the device.  In needs to be able to handle the input current as well as output the appropriate voltage and amperage (which might be specified in wattage) for the device.  The latter is a problem with chargers using micro-USB connectors as they aren’t all the same.  So, here are a couple examples (which are marked on the transformer):

  • Motorola micro-USB charger:
    • Input: 100-240 V~ 50/60Hz 0.2A – The input can be 100 volts up to 240 volts at 50 or 60Hz and pulls 0.2 amps or 200 millii-amps (mA) of current
    • Output: 5.0V 550mA — The output is 5 volts at .55 amps of current  Do not assume if the connector fits, it will be correct!
  • Apple iPad/iPhone Charger:
    • Input: 100-240 V~ 50/60Hz 0.45A – Same as the Motorola charger, but able to handle over twice the current
    • Output: 5.1V 2.1A (10 watts) – The output is roughly 4x the Motorola charger.  Note that the iPhone specific charger is a 5 watt charger and shouldn’t be used with the iPad.

So, what’s the best practice around chargers:

  • Use the charger that came with the device.  If you do use a 3rd party charger, be sure it’s the correct input/output, has the appropriate connector and is certified by UL in the US or your local certification lab in other countries.
  • Stay away from knockoffs.  The quality is potentially poor and could be hazardous.
  • Be sure to check the input when traveling to other countries.  Chargers with input rated at 100-240V ~ 50/60Hz only need an adapter.  Do not use a converter.
  • For larger chargers/power supplies like those for laptops, be sure to use the 3-prong plug if available since the third prong is a ground that will bleed off current in the event of a short.
  • If the charger gets damaged or worn out in any manner, throw it out and replace it.  It’s not worth a fire to squeeze another hour or so out of it.
  • If you dispose of the device, toss the charger also unless you know its a proper charger for another device (e.g., I have several iPad chargers I use with all our iPads and iPhones).

Lifehacker.com has a good article entitled Does it Matter Which Charger I use? which provides additional information.

5 Comments

  1. Adam

    My baby put a plugged in charger cable in her mouth and unfortunately zapped her and made her mouth bleed. Obviously this was my fault and feel terrible, however surely this shouldn’t happen? Can we go to magnetic charging as many devices are already?

    • Ouch! I hope she’s OK. Magnetic charging is an interesting topic, which I’ll take a look at in a future post. It’s starting to become more common for phones and other small devices (like the Apple Watch). It will be interesting to see about changing larger devices (i.e., laptops) in this manner. Also, what are the challenges that is preventing more rapid use.

  2. Kiminari

    I have an original Asus charger which when inserted one way gives 110V AC potential between house ground and output ground! So touching the device chasis and anything grounded in the house is dangerous. I am tempting to disassemble it and try figure out why the input live wire goes to the output. It’s 240V in the socket where I live so it suggests lowered ‘universal’ 110 voltage leaks to the output. Reason unknown. So yeah it is possible to get killed by using a faulty chrger.

    • What you say is true, the charger itself can be dangerous if not properly engineered, built, maintained and appropriate for the device. However, the issue that the post was discussing was getting electrocuted via the phone.

      In the end, there wasn’t any corroborating evidence that this incident actually occurred. Also, this has not been shown to be a real problem.

      Now, Lithium-Ion batteries catching on fire …

      Thanks for the comment.

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