6 ms·
That device was a cheap wifi power plug, had cheap unisolated power supply, it was never intended to have user accessible electrical parts sticking out, so no n
by yetihehe 2y ago
That device was a cheap wifi power plug, had cheap unisolated power supply, it was never intended to have user accessible electrical parts sticking out, so no need for isolation. In such cases device has common ground with ac voltage. I don't know all specifics, but NEVER connect any single terminal of 220V plug to your computer ground (usb ground in this case). When it's properly grounded, most devices will survive this. But somehow monitor connected to that mac didn't survive it. And several milliseconds of full 220V before circuit breaker reacted, made very thin traces in debugger pretty much vaporise and explode.
- nuancebydefault 2y agoIf i remember correctly, a lot of power supplies of cheap electronics have AC-coupled the low voltage side with the mains side. There's no physical wire, just a capacitor. You can often feel the AC when touching the 'safe' side of the adaptor.
- amluto 2y agoForget “cheap”. As far as I can tell, many modern ungrounded power supplies, including Apple’s, have enough A/C coupling from the line to the output that you can feel a bit of tingling when you touch a metallic object connected to the output.
- spockz 2y agoHow is this even allowed? My tv had it. My MacBooks since time memorial have it. They all feel “spicy”.
- ChrisClark 2y agoMy Fold 5 has that feeling along the hinge when charging too, no matter the charger I use. I guess it's considered safe, but it's weird.
- wbl 2y agoThe Y capacitor is needed to allow the EMI to have a way to ground from the output rather than going out and getting radiated by the output lines.
- amluto 2y agoI don’t believe for a second that this is actually necessary in a way results in that spicy feeling. I do believe that it’s far cheaper to use a Y capacitor than to come up with a better filter network that works well, though.
- wbl 2y agoCommon mode noise filtering is either going to be purely inductive or need a Y-cap. No other way around it.
- amluto 2y agoOne can build lots of things out of inductors and capacitors. I bet it’s possible and even fairly straightforward to built a little network to allow high frequencies to pass from output to the two line inputs with low impedance but that has extremely high impedance at 50 and 60 Hz (and maybe even at the first few harmonics). It would add components, cost and volume. I bet this could be done at the output side, too. And a company like Apple that values the customer experience could try to build a filter on their laptop DC inputs to reduce touch currents experienced by the user when connected to a leaky power supply. Of course, the modern design where the charging port is part of a metallic case might make this rather challenging… (Seriously, IMO all the recent MacBook Air case designs are obnoxious. They have the touch current issue and they’re nasty feeling and sharp-edged.)
- wbl 2y agoThe capacitor has to see the common mode voltage. Where do you put the other end?
- 2y ago