Mains Dimmer buzzing question

Hi, I wrote to the group a while ago about brands of dimmer switches and have now opted for an MK single plate 2 gang dimmer. It controls standard wall lights on one switch and mains halogen ceiling lights on the other. Unfortunately I could not find the cheap MK model that doesn't cope with LV halogen and had to go for the all singing all dancing model. Anyway, when I turn on and dim the wall lights (bog standard bulbs) there is no problem. However, when I turn on the mains halogens there is a buzzing noise coming from the switch + the lights themselves (I think it's also coming from the lights but I could be imagining this). I am used to LV halogen transformers buzzing as they did in the kitchen of my previous house but I did not expect mains halogens + dimmer switch to buzz. Is this because I've got an unnecessary transformer in the equation or am I stuck with it ? Can I buy a dimmer that will only cope with mains voltages and the buzzing will go away ?
Thanks for any help you can give, Keith
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LV
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The halogen lamps are not low voltage from a transformer in the fitting ?
What load is on the halogen lamps in total ?
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standard
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Hi BW, I'm a complete arse when it comes to knowing anything about electrics so I unfortunately can't answer any of your questions. These were fitted in my new build property and I don't even know what type of halogen bulbs they are or what the fitting is like - the electrician just mentioned that they were mains voltage on one of his many visits to fix stuff. I haven't had a need to change a bulb yet. I'm also so concerned about the quality of the fittings themselves that I don't want to go removing bulbs unless it absolutely necessary. I've already had the bathroom halogen fittings start falling out of the ceiling :-( As such I thought that they didn't need a transformer as they have been called 'mains voltage' but I am probably wrong. To install the dimmer I simply copied the wiring from the original 2 gang switch into the dimmer thinking it was as easy as that. Unfortunately I can't even recall if they buzzed before but I'm pretty sure that they didn't.
Apologies for being a bit dim .... gettit :-) Sorry.
Keith
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I've got mains halogen wall lights on a dimmer, and the dimmer buzzes quietly - I've not met one that didn't (ducks incoming), and the lights often sing quietly.
When I asked for advice the gist seemed to be "get used to it"
Maybe thinga are better now, but - you are not alone
mike r
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Cheers Mike, That is good to know in a weird kind of way :-) I'm not bothered if I can't improve it 'cos the benefit of dimming the spots far outweighs the slight buzzing. I've got a pet cockatiel that stayed awake (and sang at the TV) until the lights were turned off completely. Now we can dim them he seems far more laid back and quietly drifts off to sleep with the lights dimmed thank goodness.
Keith
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I haven't got a cockatiel, I just like watching old films last thing at night with the lights down low and a couple of tins - I don't know why the lights sing, but they do! and I get a much lower dim than using floor lamps or summat,
mike
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Keith D Pipex wrote:

from http://www.residential-landscape-lighting-design.com/light-dimmer-switches.h tm
"If we hook up a really cheap dimmer switch, we may notice a strange buzzing noise. This comes from vibrations in the bulb filament caused by the chopped-up current coming from the triac (triode alternating current switch)."
"Better dimmer switches have extra components to squelch the buzzing effect. Typically, the dimmer circuit includes an inductor choke, a length of wire wrapped around an iron core, and an additional interference capacitor. Both devices can temporarily store electrical charge and release it later. This "extra current" works to smooth out the sharp voltage jumps caused by the triac-switching to reduce buzzing and radio interference."
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Chris Spyrou wrote:

http://www.residential-landscape-lighting-design.com/light-dimmer-switches.h
In my experience it often the choke in the dimmer that buzzes esp. in the cheaper ones. Potting the choke in silicone or epoxy can alleviate this. I believe halogen bulbs buzz more than others because they can respond to the chopping action of the triac.
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<snipped>
were
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they
LOL !!!
Can you tell me if the fitting is deep, as in, about one and half inches (40mm) deep. If it is any thinner than this, then it more likely to have 240Vac halogen lamps in it.
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halogen
the
bulbs
been
BW, I'm afraid that I don't know... the bathroom fittings didn't make it all the way out of the ceiling before they got pushed back in. I'll have a check of one of the bulbs over the weekend if I get the chance.
Thanks, Keith
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<snipped>
have
all
Ah Ha !!! They're recessed lights ? Small fittings ? With small lamps inside them ? Fitted to a transformer ? If they are, then check that the transformer is really a dimmible type. The fact you say that both the dimmer and the lights are buzzing is getting to me. I've heard dimmers switches buzz, but not the lights as well.
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The fact you

Mine do, BW. An earlier answer makes me think I might look for a better dimmer, and it's some time since I looked, but my definitely mains halogens do sing, at quite a high pitch,somewhere round F (4 above middle C)
Does anyone know how I would know a better dimmer if I met it?
mike r
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halogens
You would normally get a whistling if halogens are fed from a DC supply, but never that high up the scale. :-))
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BigWallop wrote:

Correction. You wouldn't.
However 'electronic' transformers are actually thungs that take the mains, turn it into more or less high voltage DC, smoth it a bit, then chop it rather fast to apply it to a little ferrite transformer. That steps it down to 12vAC at a fairly high frequency. Its probably that which is audible.
Use a toroidal.
AFAIK LV light units do not use DC, ever.

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The actual fundamental frequency is of course 100Hz, so it must be harmonics you're hearing. The design of the fitting and lamp will make a difference.

I'm not sure it would make much difference.
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Keith D Pipex wrote:

All dimmers buzz to some extent. If you take one apart you will find one, or more, toroidally wound chokes inside. This is probably what is doing the buzzing. As the nasty sharp edged dimmer currents go through it the wires expand and contract in teh magnetic filed.
If you soak the windings in Epoxy that should help a bit.
The chokes stop the nasty edges getting into you radio, so don't short em out.
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