Transformers

[Gyn_Paul]

This is one for those whose grasp of electricity theory is firmer than mine...

I'm installing a rope of LED's  under kitchen cupboards. It's 12v, fed from a brick which would be familiar to anyone who had a laptop a few years ago! turfs out 10A.

The rope is controlled with a little remote control whose entire life seems to be devoted to hiding from me (and it's not even installed yet!).

That's enough plot, on to the Question -

With the brick connected to the mains, but the actual LED's switched off with the remote, is it drawing any power?

Judging by the weight, it contains a real transformer with pri & sec windings, rather than some sort of chopper power supply.

My first thought was to hard-wire it into the lighting circuit, but if it's going to be humming its was through a quiescent 15w (or so ??) then I'll probably think again!

p

[andyh4]

Paul

I cannot claim to be anything of an expert in these matters, but isn't the simple thing to do, to fit a plug, plug in the transformer without the lights and if it buzzes or slowly warms up, you have your answer.

[Pierre ZFP]

It depends (that's not helpful is it?)

I will attempt to explain.

Modern chargers/power supplies tend to be 'switched mode' which means they turn themselves off when the thing connected to them is charged (ie not taking any more current) or not connected.

Older bricks, especially ones with a transformer are not like this and so will consume a watt or 2 all the time and therefore will warm up as Andyh4 says

[AnOther]

Even in the more efficient toroidal form 10A would be a substantial transformer, for example:

http://www.ges.cz/en/toroidal-transformer-tst-120-124-GES07506945.html

10A is also a substantial string of LEDs ! 

[dave21478]

If they can be switched on and off by remote then there must be a receiver that is always powered up even when the lights are off.

[Gyn_Paul]

You're right: 10A does sound a lot... (puts proper glasses on and reads the small print again) actually it's 6A@12v - it's supplying 2x5 metres of 5050 RGB LED's - I make that 7.2w/metre.

It's currently sitting on the window-sill connected to the mains with nothing on the other end. so I'll see what its temperature (change, if any) is in the morning.

p