Author Topic: Phone charger gives electric shocks, How to measure voltage.  (Read 18708 times)

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Offline Simon

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Re: Phone charger gives electric shocks, How to measure voltage.
« Reply #25 on: January 06, 2016, 07:05:39 pm »
It is not normal to get shocks or tingles from mains devices. If you do it means you are either misusing the product or it was designed badly and dangerously.
 

Online IanB

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Re: Phone charger gives electric shocks, How to measure voltage.
« Reply #26 on: January 06, 2016, 07:20:00 pm »
Mine's a 4th gen iPad, but it is connected to a genuine Apple charger, the one it came with. I keep one permanently set up at my desk to charge both the iPad and iPhone, and I have another in my travel case in case I need to charge away from home. Never tried a non-Apple AC mains charger, though I did have a random one in my car. But yeah, never felt so much as a tingle while touching the metal back of the iPad connected to the charger and some other device connected to earth ground. Now I am curious since everyone seems to think this is pretty much normal, when I get home I plan to give it a test and see if there is measurable voltage there at all. I don't think there should be any difference other than line voltage, since I'm in the US it's 120V. My house is new enough that all outlets are equipped for a ground pin, and at least for the outlet when my computer and the phone charger are connected, one of those basic line testers shows the line, neutral, and ground all properly wired.
 Anyway, just curious for my own sake now, since I have never experienced an obvious shock of this sort, whereas the OP is getting what sounds like a rather nasty shock which to me just sounds dangerous and not merely an annoyance.

My Apple chargers make a non-contact volt stick light up and beep. If I plug my phone in to charge the whole case of the phone activates the voltage detector. So there is a definitely a mains electric field getting through the USB output cable. I don't feel anything when I touch it though.
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Online IanB

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Re: Phone charger gives electric shocks, How to measure voltage.
« Reply #27 on: January 06, 2016, 07:21:30 pm »
It is not normal to get shocks or tingles from mains devices. If you do it means you are either misusing the product or it was designed badly and dangerously.

Many actual products disprove this assertion. Just because it tingles doesn't mean it is dangerous.
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Offline electr_peter

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Re: Phone charger gives electric shocks, How to measure voltage.
« Reply #28 on: January 06, 2016, 07:39:17 pm »
The output is isolated, if there is leakage then it makes sense to connect the negative of the output to earth, It's fairly simple actually.
Proper earth pin can be a solution, I agree. Other mentioned solutions with higher insulation can work as well.
Grounding works only when it is properly implemented in systematic approach and no errors are made in the wiring (I guess 99.9% of population and many electricians do not have a clue how earthing/grounding should work and be wired. Have you seen examples of professionally :palm: wired sockets? I make no assumptions for a while now.). One wire snap in wrong place can be a complete disaster for grounded approach depending on circumstances.

My point is that isolated means high resistance path to AC mains and grounded means your are holding one side of the transformer ;) while thinking your are 100% safe. I think neither approach is inherently 100% safe - it depends on many factors and system level considerations.

---

Leakage current itself exists because "isolated" device is floating at ~half the mains AC voltage - this unavoidable by default with ungrounded items (all most all voltage sticks/pens and many multimeters can illustrate this). Small parasitic capacitances act as a current limiter which results in small varying non-harmful current. So people are very sensitive to this, so are not. And it depends on circumstances a lot (humidity, skin resistance, etc.).

If I recall correctly, sensitivity limits of human senses are measured when ~50% of population starts to see/feel an effect. With huge variation in human sensitivity levels, some are very sensitive to this particular effect.
« Last Edit: January 06, 2016, 07:50:23 pm by electr_peter »
 

Offline Nerull

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Re: Phone charger gives electric shocks, How to measure voltage.
« Reply #29 on: January 06, 2016, 07:56:52 pm »
I've felt it with an iPod using included charger.

A device CANNOT be both double insulated class II and have a grounded chassis. They're mutually exclusive. Demanding that a class II charger ground reference its output is demanding people violate electrical standards. Just sticking a ground wire on does not make it safe, and class II is generally considered safer than class I, as a wiring fault cannot make it dangerous.
« Last Edit: January 06, 2016, 08:03:58 pm by Nerull »
 

Offline mikerj

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Re: Phone charger gives electric shocks, How to measure voltage.
« Reply #30 on: January 06, 2016, 10:26:15 pm »
It is not normal to get shocks or tingles from mains devices. If you do it means you are either misusing the product or it was designed badly and dangerously.

It's quite normal on double insulated switch mode supplies.  The manufacturers could leave out the EMI suppression cap to reduce the leakage, but then it almost certainly wouldn't meet any conducted emissions standards.  How do you propose to fix this and maintain compliance to the various standards?
 

Offline aljowen

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Re: Phone charger gives electric shocks, How to measure voltage.
« Reply #31 on: January 06, 2016, 10:42:33 pm »
Couldn't they add a ground pin to the plug, then connect the ground connections on the usb port to that rather than connecting the ground connections on the usb port to something emitting ac current?

I would better understand if i was touching powered terminals on the usb cables. Even if they hadn't of connected the ground pins to anything i would have thought that would prevent this issue (although perhaps cause some for connected usb devices that intend to use the ground connection.

Out of interest would putting a diode and resistor on the ground to allow current to only flow from the connected devices to the charger itself have helped?


Just tested this ZTE wall wart out of interest and it was only putting out 0.3v AC on the ground connector, it also has no ground pin on the plug socket. So there must be ways of not electrocuting people on cheap chargers.
« Last Edit: January 06, 2016, 11:44:54 pm by aljowen »
 

Offline pmbrunelle

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Re: Phone charger gives electric shocks, How to measure voltage.
« Reply #32 on: January 07, 2016, 04:34:51 am »
It is not normal to get shocks or tingles from mains devices. If you do it means you are either misusing the product or it was designed badly and dangerously.

It's quite normal on double insulated switch mode supplies.  The manufacturers could leave out the EMI suppression cap to reduce the leakage, but then it almost certainly wouldn't meet any conducted emissions standards.  How do you propose to fix this and maintain compliance to the various standards?

We have had the solution for over a century: mains frequency transformers.

Funny how this 21st century stuff can give you an electric shock(while the old wall warts did not), yet this is considered progress |O

If your device has exposed metal parts that are connected to the internal circuitry(USB, audio jack, whatever), it's not really double-insulated.
 

Offline Brumby

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Re: Phone charger gives electric shocks, How to measure voltage.
« Reply #33 on: January 07, 2016, 04:44:39 am »

We have had the solution for over a century: mains frequency transformers.


That thought had crossed my mind as well.

The trouble is that SMPS are cheaper, lighter and usually smaller.  All the manufacturers have to do is build them to meet the relevant standards - and that's what tends to happen.
 

Offline Jeroen3

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Re: Phone charger gives electric shocks, How to measure voltage.
« Reply #34 on: January 07, 2016, 07:35:59 am »
Out of interest would putting a diode and resistor on the ground to allow current to only flow from the connected devices to the charger itself have helped?
I don't think you understand what is happening. Draw up a schematic first. From the transformer in your street/house, up to you being the (capacitor to) ground.
 

Offline aljowen

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Re: Phone charger gives electric shocks, How to measure voltage.
« Reply #35 on: January 07, 2016, 01:44:54 pm »
The cost is, either higher BOM cost,
To be honest that is probably the reasoning in full.
 

Online Zero999

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Re: Phone charger gives electric shocks, How to measure voltage.
« Reply #36 on: January 07, 2016, 02:10:51 pm »
It is not normal to get shocks or tingles from mains devices. If you do it means you are either misusing the product or it was designed badly and dangerously.

It's quite normal on double insulated switch mode supplies.  The manufacturers could leave out the EMI suppression cap to reduce the leakage, but then it almost certainly wouldn't meet any conducted emissions standards.  How do you propose to fix this and maintain compliance to the various standards?
Add a screen between the primary and secondary and connect the Y capacitor to it.


We have had the solution for over a century: mains frequency transformers.

Unfortunately mains frequency transformers don't comply with the minimum efficiency regulations, especially at very light loads such as standby

Quote
Funny how this 21st century stuff can give you an electric shock(while the old wall warts did not), yet this is considered progress |O

If your device has exposed metal parts that are connected to the internal circuitry(USB, audio jack, whatever), it's not really double-insulated.
.
Exposed metal parts, connected to internal circuitry, still need to have double or reinforced insulation from the mains. Fortunately Y1 capacitors provide reinforced insulation and comply with the regulations, even if the tiny leakage current is enough to give someone a tingle.

The real problem is when many appliances which use unearthed switched mode power supplies are connected together. The leakage currents add together and can exceed the regulatory requirements.
« Last Edit: January 08, 2016, 08:35:14 am by Hero999 »
 

Offline pmbrunelle

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Re: Phone charger gives electric shocks, How to measure voltage.
« Reply #37 on: January 07, 2016, 05:49:19 pm »
Perhaps by regulatory definitions a few nF counts as isolation, but I think a few (tens maybe) pF is more reasonable.

As for standby losses, the real problem is that very few products come equipped with power switches anymore.

Mostly, consumers are to blame for this whole mess.
 

Offline Monkeh

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Re: Phone charger gives electric shocks, How to measure voltage.
« Reply #38 on: January 07, 2016, 06:19:01 pm »
Just tried it with my iPad and my PC sitting next to my desk, all metal - also touched the slightly exposed metal ground of a USB cable plugged in to the desktop just in case somehow the case wasn't grounded, which is highly unlikely. No shock. Took my iPhone out of its case as well so I could touch the metal of it while plugged in to the charger, and also touched my computer case - also no shock. Don't have a meter handy to see if there is a potential there but too low to shock me - but I still say if it's great enough to feel a shock it isn't right.

You'd get at most around 60VAC. Which you most likely would never feel.

It is not normal to get shocks or tingles from mains devices. If you do it means you are either misusing the product or it was designed badly and dangerously.

Yes, it is. A HUGE number of devices are double insulated, and seeing potentially painful leakage currents on them is quite normal. Many if not most TVs, Bluray players, satellite tuners, and so on, have no earth connection, and unless they pick one up through external cabling (cable TV will provide one, some satellite installations, and often you sink enough through the boxes buried in the walls with terrestrial), they will bite you.

I dealt with a >$3000 TV recently which was quite happy to give me a tingle and any analogue audio a very impressive hum.
« Last Edit: January 07, 2016, 06:20:36 pm by Monkeh »
 


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