Dear respectet electrical professionals.
I'm facing a problem that my mobile charger shocked me while charging. So I opened the case and checked for if there any faulty component I can find. But I couldn't found any visible faulty components. And I'd like to kindly request your help that how can I fix this problem or reason why.
Thank you so much.

 

What were you touching when you felt the shock?

 

The transformer may be bad. Does it charge batteries?

 

What were you touching when you felt the shock?

Tip of lightening cable Sir, I usually clean the tip before I charge my phone and this time I got electric shock

 

The transformer may be bad. Does it charge batteries?

I don’t know sir. As soon as I got electric shock while I’m cleaning the tip of my lightening cable before charging, I didn’t tried to charge my phone anymore.

 

The only components that actually cross from the high to low side are the transformer, the optoisolater and the blue capacitor (CY1).

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A fault in any of those might allow the mains current to pass through. The opto is an unlikely cause, so you are left with the transformer and the cap. The designed itself should not have the output referenced to the mains.

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The small capacitor marked CY1 is probably the culprit, it connects the Negative sides of the output to the bridge rectifier, try removing it and see if the fault goes, if so then you can replace it.

 

Poking the neon screwdriver into the USB socket won't have helped! The blade is wide enough to short-circuit the socket's internal connectors.

 

A double-insulated switched-mode will always have enough leakage to illuminate a neon screwdriver.
Measure the current from the USB case to mains earth. It legally may be as much as 750uA.

 

I think we all may be missing one crucial thing: Exactly what the shock was.

Was it an electrical shock where every time you touch it you get the shock, continuous and non-stop? Or was it a snap of a shock that went away just as quickly? It COULD have been an ESD (Electro Static Discharge) event.

Over the years I've found that many people don't fully understand terminology associated with electricity. For instance, a shock can be an ESD event, just like that shock when you grab the door knob on a cold dry morning, or when you get out of the car and as you get out you get hit with that static discharge as you brush by the door frame. Or a shock can be when you come in contact with an energized part of a circuit. Shocks of that nature can occur from voltages as low as around 60VAC to extremely high voltages, which can result in death. Some people call all electrical problems "Short" when in half the cases it's more appropriately an "Open" circuit. My neighbor talks about current when he's trying to relate a problem with the voltage of a battery. For a few years he had an issue where his car would drain the battery. When it wouldn't start he'd ask me to check his battery for him. So come Christmas I bought him a cheap meter, one that would show the voltage of the battery. However, he would set the meter to measure Current and then touch the battery terminals. The very first time he did that he blew the internal fuse, called me and said the meter didn't work. So not everybody fully understands electronic terminology.

So when you say you got a shock - first thing coming to my mind is static discharge. Is that the shock you felt? Or was it a shock that lasted as long as you touched the connector? If it was continuous then my suggestion would be to simply buy a new charger. They're cheap enough and you're not exposing yourself to other, potentially dangerous voltages inside the charger. Even a capacitor can hold a charge, then you touch that cap and SNAP! You get a shock. But it's not a continuous shock, it's a discharge. Capacitors can be dangerous if the voltage is high enough and you get hit directly across your heart. ESD can be as high as 50,000 volts static. But its discharge isn't likely going to cause any real harm to you. It can smart, can even hurt. But it's not likely going to be dangerous or life threatening.

While it may seem to some that 50KVS would be more dangerous than 240VAC, the truth is not in the voltage but in the amount of current. ESD is extremely high voltage but extremely low current whereas 240 volts can carry significant current that can do substantial harm to human tissue and muscle. So the question is - what kind of shock did you feel?

It legally may be as much as 750uA.

Just to be clear, 750µA is 0.000,75 amps. VERY not dangerous. Life threatening current can be as low as 6mA (0.006A). Or even a little lower, but that's substantially higher than 0.000,75 amps. 6mA versus 0.8mA

 

This is why you only buy such chargers that are actually UL, CE or otherwise certified by required country standards as SAFE.

 

Cheeep counterfeight product with counterfeight certification label.

My electricity provider bought and gave away for free compact fluorescent light bubs. They were all recalled because some dripped melting plastic.
The news said they were made in China and the manufacturer copied the certification number from an expensive manufacturer.

 

A charger for a cell phone is intended to only be used for that purpose and so there is no reason at all that the circuit needs to be isolated from the mains. So from some chargers, depending o which way they are plugged in, connecting with the 5 volt DC output could connect you with the hot side of the 220 volt mains. THAT is the reason that I never suggest using them for other than charging a phone.
But folks are welcome to ignore my advice , and let natural selection "do it's thing."

 

A charger for a cell phone is intended to only be used for that purpose and so there is no reason at all that the circuit needs to be isolated from the mains. So from some chargers, depending o which way they are plugged in, connecting with the 5 volt DC output could connect you with the hot side of the 220 volt mains.

I seriously doubt this is true for any cell phone charger and particularly ones made in this century. That would not pass any regulations which require isolation from any part a user could touch.

 

How would any user touch the electrical connections while charging a phone??The case is isolated, or plastic of some kind that might look metallic. And the charger may not even switch on until it communicates with the phone, at least that is how my Verizon charger functions.
And the probability that a knock-off charger made in China does not comply is quite likely. and how many of the cheap chargers ARE made in the USA??? I have not yet seen one of those units.

 

A cell phone "charger" is not a charger. Instead it is a 5VDC power supply with a USB output jack. The phone has a charger circuit inside it. Its USB jack must be isolated from the deadly mains. Cheap ones might have poor or no isolation.

I have 8 of these little 5V power supplies, one is for the charger for my hearing aids.

 

Given that the intended purpose of most of the devices used mostly for charging, mobile battery powered items that are isolated, there is no operational reason for them to be isolated from the mains supply connections. Thus it is reasonable to expect getting a shock when making contact.
Consider that the materials cost of a non-isolated switcher power supply is less than the materials cost for an isolated one.
Consider also that most people only use the things as battery chargers and have no shock problems at all.

 

Please see this post for an experiment identifying some fallacies in this thread.

 

How would any user touch the electrical connections while charging a phone?

By dropping it the bathtub. Don’t laugh, it has happened. m

 

Given that the intended purpose of most of the devices used mostly for charging, mobile battery powered items that are isolated, there is no operational reason for them to be isolated from the mains supply connections. Thus it is reasonable to expect getting a shock when making contact.
Consider that the materials cost of a non-isolated switcher power supply is less than the materials cost for an isolated one.
Consider also that most people only use the things as battery chargers and have no shock problems at all.

You don't seem to he accounting for the fact that the "charger", even if it offers proprietary fast charge modes, has a standard USB connector on its output.

This means the end user can plug in anything terminated in the mating connector, not just the supplied cable or the phone. Anything that uses such a connector must behave according to at least the minimum standards for USB, and not provide any unexpected voltages.

In addition, safety standard promulgated by organizations like CE and UL have specific requirements for mains isolation to prevent injury or even death. So there is every reason for such a supply to be isolated.

But, to go further, even if the charger was a charger dedicated to a particular device, with a captive output cord, and a proprietary and completely shielded connector, the integrity of the insulation on the cord cannot be guaranteed, nor can the behavior of the end user who might attempt to modify the charger by splicing on a different connector.

There really are chargers so poorly designed that they actually exposing mains at the port.

Consider this: