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

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.

One of the reasons that the plastic earth pin is included, is that the line and neutral connectors in the wall socket are always shuttered. Sometimes, the shutter has shaped faces a bit like those on a security screw, such that when the plug pins are inserted, the shutter 'twists' out of the way, allowing the pins to pass by it. Many other sockets, however, have the shutter mechanically linked to the earth pin hole, so that as the (longer) earth pin goes into the hole, the shutter is pushed out of the way for the other two pins to follow into their holes. Hence the dummy plastic 'earth' pin is needed to work the mechanics, where no 'real' earth connection is needed.

Arfa

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.

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

Maybe 'inrush current'. Not unknown.

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

No.

Graham

CE safety regs should test for that.

Graham

In article , Doug Smith W9WI writes

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.

se

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!