UK plug/psu - faint whining noise until connected to device?

[151]

hi all,

I just bought a new gadget (a cheap IP camera) the plug/psu of which
makes a faint high pitched whining noise when connected to the wall
socket - UNTIL I connect the other end to the camera (camera works
fine by the way). Then the noise stops.

When I plugged it in at the socket, the wall the socket was already
switched "on" and there was a little bit of a spark I think... I have
seen this occasionally before (I have no idea if the psu was totally
silent before this or if its a factor)

Also I noted that the "top" prong of the plug (UK plug) was plastic?
I.e. no earth. Could this cause the small spark I saw?

What might this noise be and should I worry?

thanks guys!

 

[Doug Smith W9WI]

On Fri, 29 Aug 2008 06:20:28 -0700, 151 wrote:

Yeah it is indeed a switching PSU - at least it works at 100 - 240
volts...
The noise is not noticable unless I am pretty close, and then only
when the cable is dangling loose and not connected so its not really
an annoyance - it just made me a bit nervous

I can live with noise but I dont like fire!

I would be EXTREMELY surprised if running it without a load would result
in fire. (but there's always Murphy's Law!) Actually, I'd be pretty
surprised if it would result in failure of the PSU as well, but over time
it could happen.

 

[151]

On Aug 28, 3:42 pm, Doug Smith W9WI <w...@invalid.nospam> wrote:

On Thu, 28 Aug 2008 02:30:13 -0700, 151 wrote:
I just bought a new gadget (a cheap IP camera) the plug/psu of which
makes a faint high pitched whining noise when connected to the wall
socket - UNTIL I connect the other end to the camera (camera works
fine by the way). Then the noise stops.

When I plugged it in at the socket, the wall the socket was already
switched "on" and there was a little bit of a spark I think... I have
seen this occasionally before (I have no idea if the psu was totally
silent before this or if its a factor)

Also I noted that the "top" prong of the plug (UK plug) was plastic?
I.e. no earth. Could this cause the small spark I saw?

What might this noise be and should I worry?

Is this PSU relatively light in weight?  (I'll bet it is)

I'm betting this is a "switchmode" PSU.  There's a high-frequency
oscillator in there which, you could say, steps up the 50Hz mains
frequency to several thousand (/tens of thousands) Hz.  This allows the
use of a smaller & lighter transformer to step the voltage down from 240V
to whatever the camera wants.

The actual frequency the mains are stepped up to is not well regulated.
(and doesn't need to be)  I would not be surprised if it changes radically
with load - if it's much lower when the camera isn't connected and drawing
power.  With no load it might be dropping to a frequency low enough to
hear, while with the camera connected it may be above the range of your
hearing.

Or, it may be reaching the mechanical resonant frequency of some part of
the PSU, allowing that part to amplify the vibrations, and the sound.

Should you worry?  Good question.  I think the noise would probably bother
me to the point where I wouldn't operate it with the camera disconnected
for that reason alone.  

I know little or nothing about the way the UK power mains are wired so
can't really comment on the lack of an earth.  Here in the States, these
plug/PSUs almost never have an earth pin at all, plastic or metal.  It
would seem unnecessary if any part you can touch is isolated from the
mains by the transformer.

Yeah it is indeed a switching PSU - at least it works at 100 - 240
volts...
The noise is not noticable unless I am pretty close, and then only
when the cable is dangling loose and not connected so its not really
an annoyance - it just made me a bit nervous

I can live with noise but I dont like fire!

 

[Eeyore]

Doug Smith W9WI wrote:

151 wrote:
Yeah it is indeed a switching PSU - at least it works at 100 - 240
volts...
The noise is not noticable unless I am pretty close, and then only
when the cable is dangling loose and not connected so its not really
an annoyance - it just made me a bit nervous

I can live with noise but I dont like fire!

I would be EXTREMELY surprised if running it without a load would result
in fire. (but there's always Murphy's Law!) Actually, I'd be pretty
surprised if it would result in failure of the PSU as well, but over time
it could happen.

CE safety regs should test for that.

Graham

 

[Mike Tomlinson]

In article <pan.2008.08.28.14.42.22.849512@invalid.nospam>, Doug Smith
W9WI <w9wi@invalid.nospam> writes

I know little or nothing about the way the UK power mains are wired so
can't really comment on the lack of an earth. Here in the States, these
plug/PSUs almost never have an earth pin at all, plastic or metal.

UK power sockets are shuttered and a mechanical device physically
prevents you from plugging anything in unless an earth pin is present,
so even if an earth is not needed for the device, a pin is still
required. Obviously, it's cheaper to make it in plastic.

--
(\__/) Bunny says NO to Windows Vista!
(='.'=) http://www.cs.auckland.ac.nz/~pgut001/pubs/vista_cost.html
(")_(") http://www.cypherpunks.to/~peter/vista.pdf

 

[151]

On Aug 31, 9:47 am, Mike Tomlinson <m...@jasper.org.uk> wrote:

In article <pan.2008.08.28.14.42.22.849...@invalid.nospam>, Doug Smith
W9WI <w...@invalid.nospam> writes

I know little or nothing about the way the UK power mains are wired so
can't really comment on the lack of an earth.  Here in the States, these
plug/PSUs almost never have an earth pin at all, plastic or metal.

UK power sockets are shuttered and a mechanical device physically
prevents you from plugging anything in unless an earth pin is present,
so even if an earth is not needed for the device, a pin is still
required.  Obviously, it's cheaper to make it in plastic.

--
(\__/)   Bunny says NO to Windows Vista!
(='.'=)  http://www.cs.auckland.ac.nz/~pgut001/pubs/vista_cost.html
(")_(")  http://www.cypherpunks.to/~peter/vista.pdf

Thanks very much all for your help, really good info - so far the
thing seems fine so I feel more confident about leaving it switched
on

cheers!

 

[Doug Smith W9WI]

On Thu, 28 Aug 2008 02:30:13 -0700, 151 wrote:

I just bought a new gadget (a cheap IP camera) the plug/psu of which
makes a faint high pitched whining noise when connected to the wall
socket - UNTIL I connect the other end to the camera (camera works
fine by the way). Then the noise stops.

When I plugged it in at the socket, the wall the socket was already
switched "on" and there was a little bit of a spark I think... I have
seen this occasionally before (I have no idea if the psu was totally
silent before this or if its a factor)

Also I noted that the "top" prong of the plug (UK plug) was plastic?
I.e. no earth. Could this cause the small spark I saw?

What might this noise be and should I worry?

Is this PSU relatively light in weight? (I'll bet it is)

I'm betting this is a "switchmode" PSU. There's a high-frequency
oscillator in there which, you could say, steps up the 50Hz mains
frequency to several thousand (/tens of thousands) Hz. This allows the
use of a smaller & lighter transformer to step the voltage down from 240V
to whatever the camera wants.

The actual frequency the mains are stepped up to is not well regulated.
(and doesn't need to be) I would not be surprised if it changes radically
with load - if it's much lower when the camera isn't connected and drawing
power. With no load it might be dropping to a frequency low enough to
hear, while with the camera connected it may be above the range of your
hearing.

Or, it may be reaching the mechanical resonant frequency of some part of
the PSU, allowing that part to amplify the vibrations, and the sound.

Should you worry? Good question. I think the noise would probably bother
me to the point where I wouldn't operate it with the camera disconnected
for that reason alone.

I know little or nothing about the way the UK power mains are wired so
can't really comment on the lack of an earth. Here in the States, these
plug/PSUs almost never have an earth pin at all, plastic or metal. It
would seem unnecessary if any part you can touch is isolated from the
mains by the transformer.

 

[Eeyore]

151 wrote:

hi all,

I just bought a new gadget (a cheap IP camera) the plug/psu of which
makes a faint high pitched whining noise when connected to the wall
socket - UNTIL I connect the other end to the camera (camera works
fine by the way). Then the noise stops.

Obviously the no load on the PSU causes it to whistle. A side effect of
some switchmode designs.

When I plugged it in at the socket, the wall the socket was already
switched "on" and there was a little bit of a spark I think.

Maybe 'inrush current'. Not unknown.

I have
seen this occasionally before (I have no idea if the psu was totally
silent before this or if its a factor)

Also I noted that the "top" prong of the plug (UK plug) was plastic?
I.e. no earth. Could this cause the small spark I saw?

No. It just means the PSU is 'double insulated' and needs no earth.
Without the plastic earth pin the socket won't open.

What might this noise be and should I worry?

No.

Graham