Dimming 12V dichroics

[PigPOg]

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.

 

[Tim Mitchell]

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?

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.

 

[Phil Allison]

"PigPOg"

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.

** 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

 

[John Woodgate]

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?

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.

 

[Adrian Tuddenham]

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.

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.

 

[PigPOg]

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.

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.

 

[Phil Allison]

"Adrian Tuddenham"

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.

** 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