Hello everyone, I'd like your thoughts please.
I'm going to design a garden lighting system that will control a number of 12V AC GU5.3 dichroic lamps. I want to fade up/down a number of these lamps and I'm trying to think of the best way to do it. At present, I'm thinking of using a microcontroller to drive a number of triacs by way of zero-crossing opto-isolators. Does anyone have any suggestions on a better way of controlling the lamps?
Any suggestions appreciated.
In article , PigPOg writes
That would work - but dimming the 12V means the current is quite high. Also if you are using "electronic" transformers to generate the 12V, some do not like their output being dimmed like that.
You could get a "dimmable" electronic transformer and dim the mains side.
You can get electronic transformers for LV ilghting with 0-10V control inputs.
-- Tim Mitchell
I read in sci.electronics.design that PigPOg wrote (in ) about 'Dimming 12V dichroics', on Thu, 29 Sep 2005:
A much simpler way is to use phase-controlled dimming, as in a simple wall-mounted dimmer for mains lamps. If you only want to fade up and down manually, that is simple and low-cost. If you want to program the dimming, then you are likely to find the microcontroller route better, but you can use hybrid digital/analogue techniques, with a DAC controlling a phase-control dimmer.
-- Regards, John Woodgate, OOO - Own Opinions Only. If everything has been designed, a god designed evolution by natural selection. http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk
If the bulbs are halogen types, don't cut the power down too much, especially outdoors or in a draughty place.
Lowering the operating temperature of the envelope will disrupt the tungsten recycling mechanism and result in blackening and premature filament burn-out.
-- ~ Adrian Tuddenham ~ (Remove the ".invalid"s and add ".co.uk" to reply) www.poppyrecords.co.uk
Thanks everyone for your input/suggestions. I'll try to source a dimmable transformer (UK) with some sort of control input - if I can. It'll certainly simplfy things. Failing that, I will probably follow John's suggestion as I intend to use a microcontroller for other control/timimg features anyway.
"PigPOg"
** Forget the "zero crossing" bit .Lamps need to be dimmed by phase control of the triac - not by dropping out whole cycles - unless you *really* want to see the light flickering madly.
This will mean using the triac/s on the mains voltage side of the stepdown transformer/s.
.......... Phil
"Adrian Tuddenham"
** I thought that myth had been thoroughly disproved donkey's years ago.Although the "halogen cycle " deposits metal back onto the filament - but sadly it is not in the same places that originally lost it.
Running the 12 volt dichroics dimmed will in fact extend lamp life very considerably - as with all tungsten lamps.
By the 12th power of the voltage reduction ratio IIRC.
.......... Phil
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