Can a usb charger kill a phones touchscreen?

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Fred99

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#1644513 3-Oct-2016 09:12

He is too. Circuit diagrams for a genuine charger do show the single Y-cap bridge between the high voltage DC and USB "earth" pin 4. I'm amazed that's allowed in a class II appliance, they'd more normally be used in an earthed class I appliance with a common ground, "safety" of the cap important in case the earth connection is lost/faulty and the cap short circuits - so there are two points of failure before the user gets a zap. That design does reduce it to one failure point - possibly not for the device itself - but when something which isn't insulated is plugged in.

allio

885 posts

Ultimate Geek

#1644536 3-Oct-2016 09:58

Only charger I've ever had that caused this symptom was a fake Apple charger.

Anyway, genuine or not - who cares? It's misbehaving. Chuck it out.

Fred99

13684 posts

Uber Geek

#1644558 3-Oct-2016 10:13

No don't chuck it out just yet if you've got the time - stop using it - but pull it apart and post some photos. Should be able to get a pretty good idea if it is "genuine" or not.

mb82

223 posts

Master Geek

#1644938 3-Oct-2016 21:15

I measured between the case of the phone while charging and the earth and neutral pins.

Apple charger I have been using which produces tingling feeling 80 VAC

Spare unused apple charger 65 VAC also produces tingling feeling

Different outlet = same result

Phone plugged into pc via usb = no tingling feeling.

I have an interest of know why it is not working rather than it is not working = throw it

MadEngineer

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#1645060 4-Oct-2016 09:39

Theres a bunch of reasons why it could have failed but one likely reason has already been discussed.

Also, you've asked how to measure the voltage yet you've gone and done it anyway. If your sockets or switchboard are wired incorrectly you could have smoked something or worse.

You're not on Atlantis anymore, Duncan Idaho.

Fred99

13684 posts

Uber Geek

#1645230 4-Oct-2016 13:30

Well - after participating in this thread, which motivated me to go and do some research on google university, I've come to the conclusion that either nobody knows anything or there's something wildly mysterious going on.

Plenty of reports of "tingling" out there.

No doubt that those fake chargers on the youtube link are potentially dangerous / don't meet standards.

I saw some fake Iphone chargers which looked so close to the genuine thing, that you'd really struggle to see any difference externally.

I read a blog by an electrical engineering tutor who stated that he used genuine i-phone wall warts in class to demonstrate voltage leakage, claiming that the 60-80v as measured by the OP was quite normal. I don't know how sure he is that the chargers are genuine, I have doubts.

I watched a youtube where someone tested some fake wall warts vs genuine, but the scale on his meter was set at 100mA or something, one of the fakes measured at a couple of mA but he couldn't get a reading from the genuine charger. I guess (and only a guess) that you might be able to feel that amount of leakage current as a tingle if voltage was also up there, but it's still only a fraction of the 30 mA which triggers a typical RCD.

I tested the two non-apple but genuine other brand USB wall warts I had here, and couldn't measure any leakage at all with my cheap digital multimeter. I don't know if either have noise suppression y-cap like the apple chargers, I'd expect some measurable leakage from them if they did, so I guess that they don't.

I tested a MBP charger (genuine) here, voltage leakage was about 0.25v, current 120 uA (IOW close to nothing). That charger isn't marked class II and has an earth lead. There's no continuity between mains power earth and ground on the macbook, I assume the case is anodised, I needed to put the multimeter on a screw on the case to get a reading.

I tested a Sony Vaio laptop charger, voltage leak was 0.1V, current about 10 uA - so small it might have been nothing (galvanic perhaps - and nothing to do with the charger at all). That charger is a class II (2 pin).

Because the current is so low the voltage readings I did get would depend on the impedance of the digital multimeter I used, but I don't know what it is, and I'm not feeling inclined to look it up.

I was wrong about use of Y-caps on class II devices with the circuitry used by apple, I found data confirming that it's okay if the caps are certified. Would people making fake chargers use certified caps? Even if they looked right, my guess is they'd be fakes.

I found comments from US users claiming to have genuine chargers, stating that if they reversed the polarity of how they plugged in the chargers then the "tingling" would stop. I don't think that should make one iota of difference if it was a genuine charger with bridge rectifier as per the circuit diagram for the charger I saw, but it would definitely make a difference with the circuit diagram for the "clone" charger shown in the youtube video linked to above in this thread, as it just used a single diode with the other mains line going directly to the transformer primary, then the (wrong type of) noise suppression cap connected from that end of the winding in the primary to the secondary.

TLDR - I suspect that many people who think they have "genuine" chargers don't, and it would be nice if someone with a certifiably genuine charger would measure leakage voltage and current.

richms

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#1645232 4-Oct-2016 13:56

Post about an aussie seller of unapproved chargers getting some pretty significant fines.

https://web.facebook.com/SupremeCourtNSW/posts/705174239631801

Perhaps that might stop the flood of them being sold here too?

Richard rich.ms

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Move to New Zealand's best fibre broadband service (affiliate link). Free setup code: R587125ERQ6VE. Note that to use Quic Broadband you must be comfortable with configuring your own router.

mb82

223 posts

Master Geek

#1645322 4-Oct-2016 17:10

MadEngineer: Theres a bunch of reasons why it could have failed but one likely reason has already been discussed.

Also, you've asked how to measure the voltage yet you've gone and done it anyway. If your sockets or switchboard are wired incorrectly you could have smoked something or worse.

I asked how as I was unsure the way I thought it should be done was 150% the correct way. I did not get an answer here so I looked it up online. Then when I was sure it was the correct method I tested it. I never 'play' with wall voltage.

Cheers Fred99 for the info

richms

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#1645336 4-Oct-2016 17:24

Tried my genuine samsung QC2.0 charger from my note 4, 28v to ground one way around in the socket, 36v the other way around.

No current at all, even on the uA scale on my fluke 15+.

Richard rich.ms

Aredwood

3885 posts

Uber Geek

#1645525 4-Oct-2016 23:50

Another possibility - Another appliance in the house causing lots of harmonic distortion on the mains. I have managed to get tingles from devices with switchmode supplies, when plugged into my inverter which outputs a modified square wave. Plug the same device into the national grid - no tingle.

Those Y caps are intended to behave as a short circuit at RF frequencies. Yet be open circuit at 50Hz. But if there is a whole ton of RF superimposed on top of the mains. Then some of it will flow straight through that Y capacitor.

Here is an article about Y capacitor problems (and switch mode supplies in general) http://sound.whsites.net/articles/external-psu.htm#kil

SepticSceptic

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#1646427 6-Oct-2016 10:33

Aredwood:

Here is an article about Y capacitor problems (and switch mode supplies in general) http://sound.whsites.net/articles/external-psu.htm#kil

That is quite an interesting article.

I'll be keeping my transformer-based DC wall-warts for a lot longer than I thought ...

I'd always kept a couple aside for for the very odd-times I needed to do some low-level audio electronics, but now I'll think about keeping (hoard) a few more iron-cored devices.

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