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.
On Thursday, July 10, 2014 3:57:22 PM UTC+1, Lobster wrote:
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?
On Thursday, 10 July 2014 16:43:50 UTC+1, firstname.lastname@example.org wrote:
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
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
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
Could it have been a build up of static on yourself that discharged into
a metal object (iPod)? Were you standing on a carpet?
On Thu, 10 Jul 2014 08:43:50 -0700 (PDT), email@example.com
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 &
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.
[email address is not usable -- followup in the newsgroup]
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
On Thursday, July 10, 2014 6:11:33 PM UTC+1, Tim Watts wrote:
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
On Thursday, July 10, 2014 6:03:07 PM UTC+1, Andrew Gabriel wrote:
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.
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.
If it isnt the original Apple wallwart, have a look at some of the
charger teardowns on youtube and get a real Apple wallwart.
Much more expensive than the cheapest shit on ebay
or amazon, but well worth the higher price IMO.
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
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
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.
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
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
From the Sofa of Brian Gaff Reply address is active
"Lobster" < firstname.lastname@example.org> wrote in message
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.
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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