Low-voltage lighting equipment noise

I've had C-Bus installed at my home in beginning of 2006 (new home, and Yes, by a qualified electrician) in NSW, AUS.

There are quite a few low voltage light fittings; some use manufacturer's magnetic transformers, and others have had them replaced with Possums (the green-yellow plastic ones). They are all connected to Dimmer modules like the L5508D1A.

Here's the problem:

• Light fittings with both electronic and magnetic transformers buzz terribly when dimmed to anything but 100% (loudest noise at ~10%-90% brightness). Oh, I'm quite certain that it is the transformers that generate the noise, not the 12V globes. And by terrible I mean almost the equivalent of, say, a pair of speakers connected to an amp with volume set near Maximum while nothing is being played: bzzzzzzz....
  
• Furthermore, noise from some lights can be heard when they're switched OFF. It IS very quiet and can only be heard either with one's ear right next to the light fitting, or on a quiet night (I feel this necessary: I've had my ears checked AND the noise had been heard by another sane person).

My electrician explained during installation that the Dimmers have Triacs in them and therefore there's always a potential in the wiring, and that nothing can be done about it. At that time I had no idea that I'd be able to hear light fittings buzz at night when they're switched off.

I recently came across a good document on different types of low voltage dimmers (http://www.lutron.com/applicationnotes/362219b.pdf), and my suspicions have grown.

I will be grateful if someone could authoritatively answer these few questions:
- Noise = energy, so if the transformer of my downlight buzzes at night then I'm paying for that noise, right? And if I can hear some, then the others are draining current too, 24/7/365?
- Are the L5508D1A Dimmers suitable for low-voltage lights (with magnetic or electronic transformers)?
- If Yes, then should the light fittings have been connected in series through a similar DIN-style relay?
- Should a different Dimmer module have been used, such as the Universal Dimmer? Have these Universal ones been on the market since December 2005?

 

As Mr Ashleigh said,

The light globes themselves (LV-Dichroic) act as a speaker for noise in the circuit. I have had a situaton was noise was an issue, - L5508D1A's and Tridonic iron core LV transformers, changed the globes to high quality units and got rid of 80% of the buzz. Electronics creates the noise cheap globes act as speakers in some instances

BTW where you say "AND the noise had been heard by another sane person" are you implying you are sane ?

 

More questions

Thank you for the replies posted so quickly.

I have another question regarding the noise, prospective rather than retrospective this time: what should be done to remove (at least partially) the noise generated by light fittings when they are On and Off (these are 2 different problems, correct?)?

The globes are all German-made 25W and 30W Osram HALOPINs (AC Mains) and HALOSTARs (12V DC). Light fittings with HALOPINs are very much silent at all times, so no complaints here.

One wall light (that uses Osram 12V HALOSTAR globes) that hisses very quietly when Off (therefore noise must be coming from the magnetic transformer) is pretty much directly above a child's bed, and it just doesn't feel right to have it buzzing away at night. (Note, I'm not concerned with safety implications here, the light is more than reasonably high).

Another light fitting, a downlight that also uses an Osram 12V HALOSTAR globe (with the light fitting's own reflector) can also be heard when switched Off. On this one, though, the transformer is the locally purchased Possum. I'm quite certain that it's the Possum that is generating the noise.

 

Well, not as much as I was BEFORE construction/electrical works!

 

Apologies for repetitive posting, but I made a mistake describing the transformer in the above post. The wall light has an electronic transformer as can be seen on this image.

It can therefore be concluded that the C-Bus Dimmer modules and the electrical transformers don't like each other very much... How typical of technology .

 

If that transformer has metal parts or is mounted on a metal back plate (not sure from the pic) I would be putting a lug on that earth conductor and slipping it over the threaded metal post for safety reasons. You never know it might even help your noise issues. That transformer setup looks like trouble to me - just a gut feel...

 

I?d have to agree with Phil.H the metal base plate in the pic should be earthed. There are single insulated conductors coming through a non-bushed cable entry, which could lead to some ?shocking experiences?.

What is the lamp loading on the 105va transformer? I have seen some very erratic behavior on 2 x 50 watt up/down wall lights with 105va integral transformers when being dimmed. Dropping the lamps down to 35 or 20 watts has fixed the problem.

 

Removing the light fitting showed this:

• All transformers seem to generate noise when light is Off. Without the fitting around it, I can hear a quiet buzz coming off it, (a different light fitting this time).
• Only the transformer generates noise; the globes, and the whole fitting assembly are silent at all times.
• Most of these light fittings ARE grounded, that one must be an 'oversight' by my electrician (I think he cut the cable too short and then couldn't be bothered).

This transformer drives 4x 12V 20W Osram globes. Removing 1x globe does not remove the noise when light fitting is dimmed. Could the transformer be underloaded...?

Any ideas on how to get rid of the noise when:

1. Light fitting is Off
2. Light fitting is dimmed

Thanks for the help so far.

 

"He couldn't be bothered - that's ok then. I just hope a dangerous fault only ever happens on a unit that is earthed.

 

I am not going to leave it like this, I will get someone to fix it - you don't want me doing the work? Because I might be tempted to do the work without switching off any circuit breakers - too adventerous I am .