Dodgey Fleabay USB + 13A Sockets

What do yee professionals make of this? I'm just after getting a nice little zap in the ear from a metal cased phone. I've installed three of these in different rooms on two different MCB's and the two I've tested are both misbehaving.

27VAC off a spurious 5V wall wart and 25VAC off an official Apple model.
AC earth -> DC Ground.

Righto 100V is the floating earth then? The low voltage side is isolated from the mains, no continuity on any connection.
Had another go and can't seem to reproduce the shocking ear symptom no matter how well earthed I am, tried three phones now.

2011

Sir Liamalot wrote: »

Righto 100V is the floating earth then

Yes, I would expect that it is floating. Funnily enough I am working on some 3 phase equipment at the moment that has no earth reference.

The low voltage side is isolated from the mains, no continuity on any connection.
Had another go and can't seem to reproduce the shocking ear symptom no matter how well earthed I am, tried three phones now.

I can't say that I know what caused this but even if the USB socket had an earth reference I would not expect it to be connected to the metal case.

Do you wear a hearing aid??:D:D

DublinDilbert

Put a small load resistor (1K or 10K) in parallel with the multimeter and see if there is actually 100V there. DMMs can give funny readings as their input impedance/resistance is so high. If your really concerned take one of the sockets off completely and do a continuity check between earth and the 5V, it would have to be isolated.

2011

2011 wrote: »

I can't say that I know what caused this but even if the USB socket had an earth reference I would not expect it to be connected to the metal case.

Correct. 0v ref. on the brick is not connected to the case. Tested at the battery contacts.

2011 wrote: »

Do you wear a hearing aid??

Nope. Spider maybe..

DublinDilbert wrote: »

Put a small load resistor (1K or 10K) in parallel with the multimeter and see if there is actually 100V there. DMMs can give funny readings as their input impedance/resistance is so high.

Yeah, it drops to mV, ports are parallel it's reading 3V Earth to Ground with the other port in use.

DublinDilbert wrote: »

...do a continuity check between earth and the 5V, it would have to be isolated.

Out of Limit


Nice do-fer so.
0.0095W idle consumption.
2A current limited @ 5V.

Bruthal

DublinDilbert wrote: »

. DMMs can give funny readings as their input impedance/resistance is so high.

Yea I posted that same thing a few times. They actually do give a true reading for the condition of the circuit with such high impedance as part of the circuit.

Adding the 1k resistor is changing the circuit. It will probably display 0v or close with that added in parallel to the meter.

whizbang

But the 100v will still be there without any load, so you shouldn't ignore it.

Its quite a common occurrence, due to the switchmode power supplies in use, the output always tends to float at around half the mains voltage.

Manyy 2pin mains switchmode adapters will have this issue.
Virtually all laptop Power supplies sold now have 3pin mains connectors, so the output can have ref to earth.

So, No excuse in the case of a hardwired device.

2011

whizbang wrote: »

But the 100v will still be there without any load, so you shouldn't ignore it.

I disagree, I think that it should be ignored because it is not there.

whizbang

Sorry, Bad choice of words.. Might as well ignore it, unless you care to do something about it...

I wouldn't see this particular one causing any real trouble, but the whole issue can cause hassle in interconnected equipment.

DublinDilbert

2011 wrote: »

I disagree, I think that it should be ignored because it is not there.

Well it is there, but its probably got a series impedance of > 2M Ohms (pure guess), so as soon as you try draw any current from it, the voltage will drop right off to nothing.

whizbang

Just measured a few i have lying around. Seems to average around 80uA
most are less, but a big Dell Laptop psu gets to 105uA

2011

DublinDilbert wrote: »

Well it is there, but its probably got a series impedance of > 2M Ohms (pure guess), so as soon as you try draw any current from it, the voltage will drop right off to nothing.

Ok, so effectively it is not there.

Bruthal

DublinDilbert wrote: »

Well it is there, but its probably got a series impedance of > 2M Ohms (pure guess), so as soon as you try draw any current from it, the voltage will drop right off to nothing.

The voltage will still exist. If we assume the 2M ohms, the open circuit is way higher so all voltage appears across that.

Multi meter impedance also higher than 2M ohms. So it reads high percentage of voltage.

Add 1k resistor and almost all voltage appears across the 2M ohm part of circuit.

Bruthal

2011 wrote: »

Ok, so effectively it is not there.

It is. The meter gives a true reading because it's impedance is of a magnitude as high or likely much higher than the circuit in series with it. The 1k resistor shifts the voltage to the high impedance part of circuit.

A person touching the open circuit will perceive little or nothing because their resistance/impedance is also a tiny fraction of the high impedance part of circuit. Which means almost zero voltage across the person, and a tiny current through the high impedance.

If a person barely touches the open circuit points, the resistance at point of contactors can present enough voltage to be perceived. Fingers not usually sensitive enough for that though, because again the overall circuit is still high impedance.

2011

Bruthal wrote: »

A person touching the open circuit will perceive little or nothing because their resistance/impedance is also a tiny fraction of the high impedance part of circuit. Which means almost zero voltage across the person, and a tiny current through the high impedance.

Agreed which is why I said "Ok, so effectively it is not there" in my last post.

Bruthal

2011 wrote: »

Agreed which is why I said "Ok, so effectively it is not there" in my last post.

Yes but no harm discussing the likely reasons for the op scenario.

For all intents and purposes it's nothing alright. I think it is something noticed before on set top boxes and such items as well.

2011

+1

ted1

Aldi are selling them this week. 2.1A output, quite a high rating compared to most of the cheaper USB Chargers out there.

https://www.aldi.ie/en/specialbuys/thursday-22-jan/products-detail-page/ps/p/double-wall-socket-with-usb/

hexosan

ted1 wrote: »

Aldi are selling them this week. 2.1A output, quite a high rating compared to most of the cheaper USB Chargers out there.

https://www.aldi.ie/en/specialbuys/thursday-22-jan/products-detail-page/ps/p/double-wall-socket-with-usb/

Are these good value at €17.99 I'm wiring my house shortly and was considering picking up a few. When you factor out the couple of having to purchase a double socket anyway

Same as the cheapest I could find on ebay.

I don't know how healthy fast charging tiny batteries is for their longevity. 2A is 4 times the standard wallwart output.

Suppose lithium cells are cheap as chips anyways and they have temp sensors on the charger.

Stoner

Sir Liamalot wrote: »

Same as the cheapest I could find on ebay.

I don't know how healthy fast charging tiny batteries is for their longevity. 2A is 4 times the standard wallwart output.

Suppose lithium cells are cheap as chips anyways and they have temp sensors on the charger.

True, its handy for tablets though, many of which wont charge from empty unless there is 2 Amps behind the charger.

imitation

whizbang wrote: »

Sorry, Bad choice of words.. Might as well ignore it, unless you care to do something about it...

I wouldn't see this particular one causing any real trouble, but the whole issue can cause hassle in interconnected equipment.

I'd be pretty worried about this setup as these days interconnecting stuff is getting common. If I was using a chromecast connected to a tv, Would it get fried by the tv's hdmi ground when using this adapter ?