Mains Halogen Lights - Face Switch Warm

[tnarg999]

In our kitchen we have 12 X 50 Watt mains halogen downlighters recessed into the ceiling (GU10's). They are connected by 1.5MM T&E on the same circuit as all of the downstairs lights (16A Fuse I recall) . The light switch is a 1000 Watt dimmer unit.

1) When turned on, the dimmer face plate gets warm.

2) When turned on, there is a "buzzing" from the Consumer Unit. When off, there is no buzzing. (So I know it's not in my head..!)

Are both of the above common or should I be concerned?

Thanks

 

[oharaf]

The dimmer switch will/ can become warm as it contains a rheostat.

As for the 'buzzing' from the consumer unit, that has me stumped and slightly worried, are you sure it is not the dimmer switch buzzing?

 

[tnarg999]

Hi oharaf,
Yep I'm sure it's not the dimmer making the buzzing. The dimmer is in the kitchen, the CU is in the garage...

We do have a cheap dimmer in out lounge that does "buzz" so I guess you've come across them before. Our lounge ones are cheapo's from Trago Mills - note to self, buy some better quality ones..

The 1000W kitchen dimmer wasn't cheap IIRC, bit concerned about it making the CU buzz.

 

[BS3036]

I would have thought that a rheostat was unlikely. A rheostat is a 2 terminal variable resistor, and would have to be wired in series with the lighting load, and drop large amounts of power, which would be completely wasted. For the last 40 years or so, dimmers have usually been made using a thyristor or a triac; a semiconductor switch which is either on or off. Typically these devices switch off automatically when low current flows (at the crossover point of the mains cycle), and turn on when current is injected into the gate. A potentiometer will control a timing circuit to control the point in the mains cycle where the device is switched on.
This has the advantage that in theory no power is lost in the dimmer, as it is either on or off. However no circuit is perfect so there will still be some power lost, which probably accounts for the heating you are experiencing. Of course if the switch is uncomfortably hot there could be a problem with it.

Now the nature of switching during dimming is to switch current on and off during every mains cycle and this change in current will cause a change in magnetic field in the mcb which can cause it to vibrate (or buzz). This happens at 100Hz. You will hopefully find that the buzzing is loudest when halfway dimmed, and quieter when not dimmed at all.

 

[oharaf]

BS3036, bow done before your magnificence!!!!

By the way the part about the 100Hz, was really new to me thanks, i'll remember that now.

I talked about rheostat because that is how i think of them, for i am at the moment but a simple maffs teacher.

 

[BS3036]

Well it's a common misconception. You just have to think though; if you dimmed the lights half way using a series rheostat, then there would be the same power heating the rheostat as was being disipated in the lamps. Just imagine how hot they are and then imagine the switch getting that hot!

 

[tnarg999]

err over my head.... So no need to worry about the buzzing at the CU, but keep an eye on the temp of the dimmer switch.

Thanks both

 

[binguk]

hi,

thanks for the quick reply

the humming is rather on the loudish side and is noticeable.

the terminals are tight so i think they can be ruled out.

not much can be done then apart from going back to mains power?

.......and the government tells us to save energy!

would re-wiring half of them into a new circuit solve it?

although im wondering if its worth the bother!

bing

 

[securespark]

Two points here::

1. 16A fuse???

2. 600W of TH lighting - are you sure the dimmer can handle it without derating?

If it needs derating, then it should be a dimmer that can handle 1200W.

 

[TicklyT]

.......not much can be done then apart from going back to mains power?

.......and the government tells us to save energy! ..........
bing

Tungsten halogen lighting may be low voltage lights, but they certainly could not be called low energy or efficient lights. IIRC over 90% of the input energy is wasted as heat, even more if they are dimmed.
If you want to save energy, then you need to look at alternatives to any forms incandescent lamps.

600 watts of efficient lighting would be enough to give you quite a suntan!