Odd one. Using an iPod in our travel speaker dock on holiday, powered by i ts own wallwart as usual (9v IIRC), via an extension cable. Working perfec tly, at the end of the evening I removed the ipod from the dock, and receiv ed a mild but distinct belt from the metal casing of the iPod as I did so.
Haven't used the extension cable again (wasn't mine, looked perfectly OK, d on't know if it was to blame) but both iPod and dock still work fine.
What gives!?
David
its own wallwart as usual (9v IIRC), via an extension cable. Working perf ectly, at the end of the evening I removed the ipod from the dock, and rece ived a mild but distinct belt from the metal casing of the iPod as I did so .
don't know if it was to blame) but both iPod and dock still work fine.
Were the conditions right for you to have picked up a static charge and the n discharged it to the iPod? I'd have thought most of these things were dou ble insulated rather than earthed but maybe that's an exception?
by its own wallwart as usual (9v IIRC), via an extension cable. Working pe rfectly, at the end of the evening I removed the ipod from the dock, and re ceived a mild but distinct belt from the metal casing of the iPod as I did so.
K, don't know if it was to blame) but both iPod and dock still work fine.
hen discharged it to the iPod? I'd have thought most of these things were d ouble insulated rather than earthed but maybe that's an exception?
Last year I kept getting minor shock ffrom my iMac keybord, I know it was s tatic as I noticed I only got a shock if I dragged my feet and wore my safe ty shoes. It never had any adverse effect on the iMac (that I noticed) it's still working.
I get this in the lab I work in at times, why they put carpet in a computer room is another matter :)
It won't be the extension cable as the wallwart will 99% certainly be double insulated.
Could it have been a build up of static on yourself that discharged into a metal object (iPod)? Were you standing on a carpet?
Although static discharge is one possibility, it seems more likely to be a "Half mains voltage" shock due to the use of the delta capacitor circuitry in the mains EMC filter. Typically a 100nF across Live and Neutral with a couple of 50nF caps connecting the earth pin to the L & N connections.
On its own when the 'earth connection' isn't required for safety reasons due to the use of double insulation, this presents a very high impedance half mains voltage on the 'earthed' casing which can be felt by most as a mild tingling sensation.
There's no real need for the zero volt line on a wallwart's smpsu output to be earthed other than perhaps "RF Earthed", usually achieved with another 50nF cap connecting to the common 'earthing point' in the delta connected EMC filter caps.
The problem only becomes aggravated when two or more such double insulated gadgets are linked together via a common earth connection such as USB ground/0v or ground return on unbalanced audio interconnects (typically Line In /Line Out via phono sockets or 3.5mm stereo jacks) _and_ all such gadgets eschew an actual mains earth connection (or the mains extension lead has an open circuit earth).
You still see only half mains voltage but the effective paralleling up of all those 50nF caps lowers the effective impedance to the 50Hz mains supply which increases the intensity of this otherwise mild shock current to an unpleasant or even hazardous level when the count of such interconnected devices goes beyond two or three.
Otoh, it could simply be a fault in a counterfeit Apple wallwart or charging pod (or WHY). :-(
There are loads of fake wall warts around. I opened one which looked real, only to find the creepage distance between the live input and the output was less than 1mm, along a length of 30mm of parallel tracks.
Wouldn't surprise me if the hidden transformer internal insulation was just as deficient too, if not worse.
Clearly a far bigger problem than the domain of Part P.
And yet nothing is done...
On an aside, I took apart a control module from a metal touch-lamp where you touch the lamp's casing to trigger on/off/dimming.
This worked as the map was Class II but the metal body had an "earth wire" that connected into the control module.
The final connection was by a low value solid capacitor and the capacitor had a 2mm wide slot cut between it's legs in the PCB to prevent tracking. I was actually impressed.
The module died however, so I wired the lamp up as a Class I appliance and stuck the plug straight on the business end of the flex. Figured it was better to do than than leave the metal case plus the earth connection floating.
Quite normal, I get a regular tickle from my metal chassis laptop (dell with genuine Dell PSU) when I'm wearing shorts or no shirt in the summer. It is a small leakage path to half mains voltage via the emc filter in the power supply.
The joys one one man band importers selling on ebay, along with the typically Chinese wholesalers strict adherence to product safety. Some quite good tear downs on youtube showing the internal construction you've noticed
Martin
"powered by its own wallwart as usual "
What earth pin?
I've noticed this on a Macbook. The difference is that it happens when using a travel adaptor, where the power brick is not earthed, but not when the brick is connected to a European (Schuko) plug with a proper cable with earth.
Theo
Agreed - depends on earthing of power supply - happens with some supplies but not others. Also agree a very slight tingle is sometimes noticeable on a first-gen iPad - don't know about later ones.
Much discussion on Apple forums.
I also have a dell (which has only 2 pins on the input to the PSU, so doesn't care whether it has an earth or not) I notice the tingle from the metal chassis where e.g. it's sitting on a metal cabinet, and my bare arms are also resting across the metal cabinet then touching the laptop.
But if it happens with an un-earthed supply and doesn't happen with an earthed adapter, the user can be said to be to blame for using the wrong type of travel adapter.
I suspect that's most likely, if its not static. Bad transformers have no bobbin, just enamel wire wound directly on top of mains voltage enamel wire. High v insulation test it if you can. And stop using it.
NT
Electrostatic charging by the sound of it. I've noticed this with things not earthed when you yourself are a good earth.
As an aside, a Sony Cassette deck with a mega fast rewind used to regularly generate sparks between the hub and its spindle, some sparkes over a quarter inch long. It only happened on some tiapes, a Kind of static generator by the rubbing. However, in your case I'd imagine the metal case was actually connected to the wall wart and the electrostatic coupling over time built up the charge via the transformer in the supply. I've noticed it much more on switch modes the than the four older analogue supplies though. maybe its the higher frequencies used. Brian
Virtually all switched mode supplies will have a small cap (Y-rated for safety) between the mains side and the low voltage side to reduce common mode interference. Although the value is low it does provide a path for a small leakage current through the user if the case of the item is connected to the low voltage supply at any point.
In message , Lobster writes
Sounds similar to my recent experience. I repaired a laptop for a local shopkeeper. When I plugged it in I got a belt from the metal sleeve of one of the USB sockets. I used a mains tester which reported live and neutral reversed, though probably not the only problem as I got a second belt from the head of one of the faceplate retaining screws when I plugged the tester in. We decided she'd stop using that socket and report it to the landlord.
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