dimming 12v halogens

[Largemoo]

i've installed 6 12v 25w halogen downlighters in my study, each of them with their own transformer.
They all work perfectly well when using a normal switch.
I decided to replace the switch with a dimmer and again all fine.
the only problem is when I dim them to the lowest setting on the dimmer, the lights only dim to about half their full brightness and the dimmer switch emits quite a buzzing- I've tried different dimmer switches and get the same result?
I would like to dim them fairly low if possible to avoid glare on the PC screen.
Any idea's?
Thanks

 

[Qedelec]

Are the transformers dimmable? Did you check this when you bought them?

 

[Steve]

a few issues here

is the dimmer rated to as least 300w?

is the dimmer suitable for multiple transformers? and more specifically, this many? I think my varilight dimmer said its limit was 4.

Are the transformers wire-wound or electronic? electronic like dimming, wirewound dont (so i understand)

EDIT: was the dimmer expensive (£20+)? These usually have self-protective electronics so they cannot be damager when connected to unsuitable loads, this may be why it is only dimming half way. Varilight dimmers are full of this sort of stuff, its practically impossible to destroy them.

 

[ban-all-sheds]

You shouldn't dim halogen lamps too much anyway - it shortens their lives...

 

[plugwash]

wirewounds don't mind dimming its dimmers that mind wirewounds

electronic transformers should only be used with dimmers if they specifically say they are dimmable and i belive there is also a leading/trailing edge issue that must match.

 

[Largemoo]

thanks for the responses, answers as follows:

i've tried a dimmer rated at 400w and also one at 600w
The transformers say they can be dimmed
The dimmers say they work with transformers
No where does it say that there is a mximum number that can be dimmed
The transformers are rated at 60w and so presumably I could run two lamps off one transformer should the need apply.

still a mystery, in another room I have run a similar set up although only for two lamps - The answer could well be that 6 is too many? if that's the case how would i get round the problem?

Thanks again.

 

[ban-all-sheds]

There is a little known compatibility issue with dimming ELV lighting "transformers" (in quotes because they aren't actually transformers, which is why the problem arises)

Dimmers do not work by lowering the peak voltage, they reduce the RMS voltage by simply chopping out part of the waveform - they either turn on part way through each cycle (leading edge, or phase-delay) or turn off part way through (trailing edge, or phase cut), and what the dimmer does must match what the transformer needs.

So you might have a "transformer" that is labelled as suitable for dimming and you might have a dimmer switch that is suitable for use on ELV power supplies but you still need to match the leading/trailing edge characteristics of each.

Getting it wrong can create a serious buzzing noise.

http://www.google.co.uk/search?sour...n&q=+"leading+edge"++"trailing+edge"++dimmer*

 

[baldelectrician]

if the dimmer is suitable (ps I have varilight stuff and use GET or MK dimmers, with JCC trannys - suitable for leading edge & trailing edge dimmers), try increassing the lamps to 50 W each. As you are dimming them you will get a better range with the higher rated lamps.

MAKE SURE ALL THINGS ARE COMPATIBLE.
If in doubt get someone in to check things out.

 

[olly_k]

Just as an experiment try connecting (temperarily but SAFELY) a standard 60W bulb to the circuit then try dimming to see if all lights then dim properly. I wander if a purely resistive load will provide a better path to neutral than that of the electronic transformers?
Don't forget the dimmer itself is an electronic circuit that needs a usefull potential difference across its own internal circuit to work!

Also as Ban says, halogen bulbs are designed to be run at full wack to get a reasonable life expectancy out of them!

 

[Largemoo]

Finally got to the bottom of it - took one of the transformers back to the supplier complete with dimmer swith etc. They tested it and agreed there was a compatibility issue with the two. They supplied me with different transformers and BINGO - all OK

Thanks for all the advice / help

 

[breezer]

and it took you all of 6 months?

 

[reggie perrin]

Good God man, what's with the attitude?

Have you had a bad week?

Too much pop tonight?

How do you expect people to post if all they can expect is sarcastic and aggressive replies?

If you have the knowledge to help people then impart that knowledge with grace - not arrogance.

 

[breezer]

just seems a bit odd to wait 6 months to fix some lights

 

[securespark]

Breezer: I've been waiting 7 years to decorate my HS&L.......6 months is nothing in our house!

Reggie, he was not imparting any knowledge, he was asking a question...

 

[breezer]

I once waited 6 minutes to have a dump.

...................................................as i was ill at the time, i never made it