Dimmable transfomers

I read in sci.electronics.design that "Rich, Under the Affluence" wrote (in ) about 'Dimmable transfomers', on Thu, 3 Nov 2005:

Not harmonics but sidebands of the supply frequency.

A 240 volt, 100 VA tranny has a primary resistance of 20 to 25 ohms.

So, the I squared R loss from 10 volts DC is only 4 or 5 watts.

For sake of clarity, I should have mentioned that the figures pertained to

......... Phil

The saturable reactor (General Electric?) came along before solid state switching. Highly reliable, and widely used for cinema or stage lighting control.

ACin---------//////////////--------+ +----------------+ | | | | DC----------|-//////////////-|--+ | control +----------------+ | | DC----------|----------------|--+ | | | | +----------------+ | ACout---------//////////////--------+

The dc control winding on the centre limb altered the incremental permeability of the outer limbs.

It not the most effecient way of doing this

Thanks everyone on this thread for your input. Certainly food for thought.

Simon

I read in sci.electronics.design that Phil Allison wrote (in ) about 'Dimmable transfomers', on Thu, 3 Nov 2005:

Don't you? (;-)

Incorrect. I'm going to contact a manufacturer (Phliex) of dimmable units to seek their advice. Satisfied?

"Rich Grise"

All of them running on dimmers.

They get enormous life out of them.

........ Phil

Oh. Of course. How duh.

But I'm still not going to _blame_ alcohol - it's my own fault that I _chose_ to impair my brain to that degree. ;-P

In fact, I've even _seen_ those sidebands on a spectrum analyzer looking at pulsed microwaves. (a la radar) They're kind of cool, actually

- especially watching their density and envelope change with PRF and pulse width. :-)

Cheers! Rich

"Reg Edwards"

Such chokes were operated remote control in large installs - the position of the core being determined by a 0 -10 volt DC input.

The 0 -10 volt control standard stuck when triad and SCR dimmers came along only replaced by a serial digital ( DAM ) code now.

........... Phil

"Phil Allison"

Corrected text:

........ Phil

"PigPOg"

Correct ?

........ Phil

I'm going to agree with Phil's advice on this subject. There is a difference in the type of dimmer which can be used with iron-core transformers as compared to "electronic" transformers.

See

In my own case I have Clipsal leading edge dimmers and iron core transformers and they work perfectly from zero to maximum brightness.

Ross Herbert

Before Phil jumps on me, I know he hasn't even mentioned "electronic" transformers in relation to low voltage lamp dimmers. The essential point I am making is that when using iron-core transformers you need to use a leading edge dimmer. You can't use any old triac dimmer.

I don't know if the use of other (eg. toroidal) than a low voltage transformer which is specified for domestic low voltage lighting would make any difference as long as the correct dimmer type is used.

I read in sci.electronics.design that Ross Herbert wrote (in ) about 'Dimmable transfomers', on Fri, 4 Nov 2005:

Please say why.

"Riscy"

........... Phil

"PigPOg"

......... Phil

I read in sci.electronics.design that Phil Allison wrote (in ) about 'Dimmable transfomers', on Fri, 4 Nov 2005:

I don't troll and I was asking the organ grinder...

I saw your explanation. I want to know what Ross' is.

Righto, let me have a go and see if this sounds right to you.... I don't have any expertise in the field of transformer design so I must bow to the experts in the field who have been designing these devices for donkeys ages.

According to Tridonic-Atco, who manufacture all types of lighting transformers, using a dimmer which employs asymetric switching can induce a DC offset waveform in the transformer thus leading to overheating and eventual failure. A properly designed leading edge dimmer will reduce high amplitude current spikes at the switching points so not all triac dimmers may be suitable. According to Tridonic-Atco (and other manfs such as Clipsal), leading edge dimmers are best suited to control resistive and inductive loads such as would be presented by an iron cored lighting transformer. Trailing edge dimmers are best suited to control capacitive loads and a snubber is used to minimise high amplitude spikes at the switching points.

On the subject of suitable transformers for elv lighting, Tridonic say that these have a higher impedance to reduce cold inrush current thus prolonging lamp life. Such an attribute is not common to standard toroidal transformers, so here is one reason against using them for elv lighting.

ELV transformers are approved devices and have higher specifications such as;

Class H insulation (180C IEC600) ie, Tridonic use vacuum impregnated polyester resin. Withstand a winding temp rise of 140C at 6% overvoltage. Good regulation. Thermal overload - self resetting Secondary protection against short circuit. Long life - for each 10C rise over 130C transformer life is halved according to Tridonic.

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