Phone charger gives electric shocks, How to measure voltage.

[aljowen]

-Backstory-
I have a phone charger that was purchased from Maplins (made by intertek) and it gives very painful electric shocks whenever touching the ground connectors on the usb ports, The charger itself has no ground connection on the plug socket. This is the second charger of this model with this issue since i returned the first. I am now also living in a different county to when I had the previous charger so I can probably rule out the buildings power. I did electronic products in school but its been a long time and we never did ac, only dc, so any limited electronics knowledge that I may have had is now fairly rusty.

-Issue-
I want to correctly measure the voltage that is being output on the ground connector. From what i know about dc you measure across the component you want to check. But in this case it is a flying wire and touching it will shock you without any ground connection, so i presume that means it is AC but i could be wrong in assuming that. It also means there is no component to measure across.

So I have tried a couple different methods all giving different results. I have no idea if any of them are correct.

-Images-
This is with the red connected and the black left flying.

This was with red connected to the charger and black grounded on my computers usb port.

This was with red on charger and the black grounded on my computer case.


Thanks, Any help would be appreciated

[Jeroen3]

Measure the USB Shield against mains earth in your socket. That can also be water pipe, assuming you have copper plumming.
Or literally a metal rod in the ground.
You are measuring AC voltage through the Y caps. Here you'll see why:
https://en.wikipedia.org/wiki/Film_capacitor#Safety_and_EMI.2FRFI_suppression_film_capacitors

Try to measure the AC current (mA range) to earth (not water pipe!) should be less than 1mA. If the RCD (or GFCI) trips or the multimeter fuse blows, return or bin the device. It's a death trap.

[rrinker]

 Wow, not sure how you get almost 5 volts with only 1 lead of the meter even connected to anything - that appears to be a battery powered portable multimeter, correct?

 That last one though - BAD! Your computer case is likely connected to the power line ground, so between the power line ground and the ground side of the USB port on the charger you have over 100 volts! No wonder you get a shock! One way I can think this would happen would be that the USB charger had the hot and neutral lines crossed up internally - is the plug polarized in any way? In the US it is common for one blade to be wider than the other and the sockets should match, so that you can only plug a device in one way to prevent issues like this (now if the wiring from the outlet back to the breaker is poorly done, that's another story...). If the plug on the charger can fit either way, test it with the plug reversed and the 102V reading should go down - it should be 0, or close to it. Even if it does - this would appear to be a rather dangerous device and I wouldn't want to fool around with it much other than to take it apart and see how badly the built it. I would definitely not be plugging any of my phones or tablets into that thing.

[wraper]

This kind of topic appears every few weeks here. You could try to search the forum for it.
https://www.eevblog.com/forum/beginners/switching-power-supply-y-capacitor-between-primary-and-secondary-ground/
https://www.eevblog.com/forum/beginners/ipad-electric-shock/
https://www.eevblog.com/forum/projects/minor-electric-shocks-from-equipment-with-smps/
https://www.eevblog.com/forum/beginners/ac-electrical-leakage-from-surface-pro-3!/

[wraper]

Wow, not sure how you get almost 5 volts with only 1 lead of the meter even connected to anything - that appears to be a battery powered portable multimeter, correct?

 That last one though - BAD! Your computer case is likely connected to the power line ground, so between the power line ground and the ground side of the USB port on the charger you have over 100 volts! No wonder you get a shock! One way I can think this would happen would be that the USB charger had the hot and neutral lines crossed up internally - is the plug polarized in any way? In the US it is common for one blade to be wider than the other and the sockets should match, so that you can only plug a device in one way to prevent issues like this (now if the wiring from the outlet back to the breaker is poorly done, that's another story...). If the plug on the charger can fit either way, test it with the plug reversed and the 102V reading should go down - it should be 0, or close to it. Even if it does - this would appear to be a rather dangerous device and I wouldn't want to fool around with it much other than to take it apart and see how badly the built it. I would definitely not be plugging any of my phones or tablets into that thing.

[rrinker]

 You can say it's low current leakage all you want, but I have NEVER EVER been shocked by any one of dozens of computers I have built, all with switchmode power supplies, of course, nor by any of my iPhones or iPads. Or any other small metal devices that have switchmode power supplies. Not once. If it's strong enough to feel it's not right, period. If you feel it with a so-so ground, how much current will flow if you were well and truly grounded, say worst case, barefoot on a wet concrete floor?

[wraper]

You can say it's low current leakage all you want, but I have NEVER EVER been shocked by any one of dozens of computers I have built, all with switchmode power supplies, of course, nor by any of my iPhones or iPads. Or any other small metal devices that have switchmode power supplies. Not once. If it's strong enough to feel it's not right, period. If you feel it with a so-so ground, how much current will flow if you were well and truly grounded, say worst case, barefoot on a wet concrete floor?

Then put one hand on exposed metal part of your grounded PC and second hand on the macbook which has a double insulated PSU and see what happens.
P.S. Some people can touch mains voltage and feel a small tickling at worst, others will receive a huge electric shock and pass out. There is a such thing as skin electric resistance and it's very dependent on particular person.

[rrinker]

 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.

[wraper]

I'm not sure if ipad chargers have  Y cap inside, small power chargers (<15-20W) often do not have them. Therefore I suggested macbook as I'm certain they do have them. Also, measuring voltage won't tell too much. Useful measurement would me measuring AC current from the GND from the output of the charger to the earth pin of the mains socket. If the current is more than about 0.5mA for low power equipment, it would be a serious concern.

[rrinker]

 I'll have to see what other sort of goodies I can check with, a MacBook is one thing I don't have - much as I love my iPad an iPhone, OSX just doesn't do it for me. And my Windows laptop has a grounded power supply. As does the external monitor connected to it (I'm now in my office and not at home).
 It's all relative, but I don't think I'm one of those high resistance people, I can get measurable readings with both a cheap crap multimeter and a Fluke, and while not exactly the same thing, I have no problem working capacitance touch devices. It's getting cold and dry here, and I can build up a quite substantial static charge in myself and get a good zap - bad time in my part of the US to work without a proper static strap, and the dogs and cats start avoiding people.

[aljowen]

I am in the uk. So our plug sockets can only go in one way. The phone charger has a plastic ground pin on the plug socket and as such is not grounded. Since this is the second one with the exact same issue (bought many months apart too, so not just a single batch) I presume it is a design flaw of the device. Its painful enough that i have to remove my finger from the connector as soon as i touch it since it feels like its burning my skin.

My computer case is screwed to the power supply which is a cooler master silent pro 80+ gold rated psu, the metal case of that power supply will be mains grounded within the power supply, so the computer case is mains grounded. The front usb hub that i used on the computer is a sata based hub i think but i cant remember, either way that will be grounded through my computers motherboard in some way or another i would presume. I have never received a shock from any of the computers ports.

The multimeter that i am using is this one: http://www.amazon.co.uk/Crenova%C2%AE-Multimeter-Detector-Portable-Backlight/dp/B014IZF7HI/ref=sr_1_4?ie=UTF8&qid=1452093046&sr=8-4&keywords=multimeter
It is powered using a 9v battery.

Thanks for the links to other articles. They did a good job of giving the gist as to what is going on.

I have measured the current and it is about 110 microamps AC. The frequency is about 0.65Khz.

[IanB]

If the current is in microamps then there should not be any danger. You are not normally expected to touch the metal parts of a USB plug or socket since they invariably have a plastic moulded outer shell. Make sure to hold the USB plugs by the plastic parts when you plug and unplug them.

[aljowen]

If the current is in microamps then there should not be any danger. You are not normally expected to touch the metal parts of a USB plug or socket since they invariably have a plastic moulded outer shell. Make sure to hold the USB plugs by the plastic parts when you plug and unplug them.

While it may not be dangerous it does hurt quite a lot, so I think I will return it on that basis and find a charger that wont zap me whenever I touch a connector on it. Also any devices plugged into it then receive the same ground current, so my tablet gives me shocks since it has docking connectors on its chassis.

The worst problem is if i am listening to music on my phone. My In Ear headphones have a metal chassis and are grounded to the phone through the 3.5mm jack. So if i connect my phone to the charger while listening to music it shocks me through my ears, which is incredibly painful and caused skin pain for a day or so after being shocked on the last charger i owned of the same model. At the time I had no idea what caused it. But was then immediately shocked through my hands when pulling them out of my ears too :p

[Tomorokoshi]

Would it be possible to open it up and get some pictures of the circuit board?

[aljowen]

Would it be possible to open it up and get some pictures of the circuit board?

Not the current one because i would like to be able to return it. The other old charger is at my parents house as well. I will see if I can get my dad to take it apart and send some photo's to me.

I did take the old one apart though after they gave me the new one. But all I can remember is that they had 2 separate pcb's inside, one for the I/O and one for everything else. The I/O had two wires leading to it for +ive and -ive and then all 4 usb ports attached onto that. So they were powering all ports from a single charging circuit and I presume they had resistors to manage the current output for each port individually since 1 port is 2.1A and the others are 1.0A.

[Simon]

Maplin sells garbage that make dodgy chinese product on ebay look like gems of quality technology..... Take it back or better contact trading standards (well consumer direct who will ignore you). I never buy from maplin, they just sell expensive garbage.

-Backstory-
I have a phone charger that was purchased from Maplins (made by intertek) and it gives very painful electric shocks whenever touching the ground connectors on the usb ports, The charger itself has no ground connection on the plug socket. This is the second charger of this model with this issue since i returned the first. I am now also living in a different county to when I had the previous charger so I can probably rule out the buildings power. I did electronic products in school but its been a long time and we never did ac, only dc, so any limited electronics knowledge that I may have had is now fairly rusty.

-Issue-
I want to correctly measure the voltage that is being output on the ground connector. From what i know about dc you measure across the component you want to check. But in this case it is a flying wire and touching it will shock you without any ground connection, so i presume that means it is AC but i could be wrong in assuming that. It also means there is no component to measure across.

So I have tried a couple different methods all giving different results. I have no idea if any of them are correct.

-Images-
This is with the red connected and the black left flying.

This was with red connected to the charger and black grounded on my computers usb port.

This was with red on charger and the black grounded on my computer case.


Thanks, Any help would be appreciated

[mikerj]

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.

This is very common on switch mode chargers, I'm surprised you've not felt this before.   My original iPod and iPhone, both with a genuine Apple chargers used to show about 110v AC w.r.t ground on the case and felt quite unpleasant to touch though it wasn't exactly a shock as such.

[_Andrew_]

I have come across this with Mac Books before where your touching the case of the laptop and also happen to touch something else that is connected to the protective earth of the mains supply. Not painful but noticeable.

If you look in the IFU that we all leave in the box and never look at for the phone there will be an instruction to say not to use the device while it is connected to a charger.


My Mega PAT-420 has the facility to perform differential leakage current testing and it is quite surprising how often I see new appliances that have leakage currents near the permitted limits. Surge arresting gang plugs ect often exceed the limits on differential testing.


Reference Page 109 of the IEE Code of Practice for In-service Inspection and Testing of Electrical Equipment ISBN 978-0-86341-833-4

“V.3.6 Earth leakage test
This test is carried out at the rated mains input voltage and the maximum leakage should not exceed the following.
> Class I products: 3.5mA (0.75mA for hand-held appliances)
> Class II products: 0.25mA”

[_Andrew_]

Should also say that differential leakage current testing should be done with test equipment designed for the purpose.

Don't go using a regular amp meter. If somthing is wrong things could go badly wrong.

[electr_peter]

While it may not be dangerous it does hurt quite a lot, so I think I will return it on that basis and find a charger that wont zap me whenever I touch a connector on it. Also any devices plugged into it then receive the same ground current, so my tablet gives me shocks since it has docking connectors on its chassis.

The worst problem is if i am listening to music on my phone. My In Ear headphones have a metal chassis and are grounded to the phone through the 3.5mm jack. So if i connect my phone to the charger while listening to music it shocks me through my ears, which is incredibly painful and caused skin pain for a day or so after being shocked on the last charger i owned of the same model. At the time I had no idea what caused it. But was then immediately shocked through my hands when pulling them out of my ears too :p

While it is not dangerous as it is, people sensitivity to small currents vary a lot - some people feel it as a sensation, some as a pain under identical conditions. If you know that sensation really well, you can find this sensation (meaning small AC current leakage) in many places.
That said, I still do not see anything that is really wrong with device function it self.

This is what happening in my opinion:

• when powered from AC-DC charger, headphones transmit small leakage current though primary-secondary noise suppression capacitors -> headphones with metal parts -> grounded body to ground. This will happen with any charger (to a bigger or smaller effect) which is not grounded or has only two pins in mains plug.
• person in question is very sensitive to small currents. Especially, because metal parts touch inside of his/her ears.

Again, described situation is pretty normal under circumstances, I see no real signs of failure. All symptoms are due to normal AC leakage through parasitic capacitances.

To remove the problem, use one of these methods:

• change headphones to other ones with no exposed metal parts (especially inside ear) OR
• do not listen to music while charging with ungrouded AC-DC adapter or one with two pin mains plug OR
• get grounded AC-DC adapter (with three pins mains plug) OR
• buy bigger battery pack so you can use item for longer between recharges

[Simon]

Err some men devised the earth pin for a fucking reason! lots of other men seem to think the laws of nature don't apply to them when designing this shit!

[wraper]

I have measured the current and it is about 110 microamps AC. The frequency is about 0.65Khz.

About an average of what you usually get from power supplies with similar power rating.

[electr_peter]

Err some men devised the earth pin for a fucking reason! lots of other men seem to think the laws of nature don't apply to them when designing this shit!

So... I hope you understand the reasons you say here and contribute to forum topics with meaningful posts.
Earthing/grounding is not trivial topic and not a holy grail by any means to put it shortly.

[Simon]

Err some men devised the earth pin for a fucking reason! lots of other men seem to think the laws of nature don't apply to them when designing this shit!

So... I hope you understand the reasons you say here and contribute to forum topics with meaningful posts.
Earthing/grounding is not trivial topic and not a holy grail by any means to put it shortly.

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.

[rrinker]

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.

This is very common on switch mode chargers, I'm surprised you've not felt this before.   My original iPod and iPhone, both with a genuine Apple chargers used to show about 110v AC w.r.t ground on the case and felt quite unpleasant to touch though it wasn't exactly a shock as such.

 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.