Re: FW: FW: Fwd: Wall switch dimmers work with12v halogen?

[Nigel Orr <nigel.orr@xxxxxxx>]

At 17:42 17/03/99 -0000, you wrote:
>Nigel, I've received a reply from X10. This seems to make sense, I
think the
>thing to do is try it with the transformers, and if it doesn't work
swap
>them out for 240V bulbs, care to  comment?

I've read it twice, and it still doesn't seem to make much sense, but I'll
try to follow what it says...

In summary, your plan seems quite sensible, but I would still say that
dimming halogens might not be what you want to do... unless you run them at
full power occasionally- have a look at :
http://www.sylvania.com/lighting/educate/know/tungsten.htm
to see how they work normally... if they are run at lower power, the
tungsten apparently condensed on the glass instead of being recombined.
Have a look at www.dejanews.com and search for "dimmer halogen",
and you'll
probably see some informative postings, maybe on some of the sci.* groups.

>in my earlier message, I normally do not deal with international
products,

I assume (as I said, I'm not a fan of X-10) that the UK product is
different because it is redesigned to use only live & switched live
connections, and not need a neutral?

>has stated that this switch is a dimmer and I can tell you that if it
is
>merely called a dimmer that means that it is an Incandescent or
Resistive
>load dimmer.

That is absolutely true- at this point, I did try to explain how dimmers
work, and what inductive loads do, but it got too complex so I've deleted
it- if you need more details, ask!

> What you have with a TRANSFORMER IS AN INDUCTIVE LOAD.

Hmmm, sortta, but not really... A transformer on its own is an inductive
load (a coil of wire round a core), and so it wouldn't dim very well (which
doesn't matter, as there are no lights attached)... however, once you
connect a resistive load to the transformer secondary winding (the 12V
side), it 'looks' like a resistive load.  This holds true for real genuine,
lumps of ferrite with wire wound around, transformers, but is a bit more
complex for electronic controllers which are often used instead- if it's
big and heavy, it's probably a real transformer, if it's small and flat,
it's probably an electronic controller- there are dimmable varieties of
both types...

>Inductive loads
>do not use resistance to the AC wave form to cause heat which in turn
causes
>light (as resistive loads do), they actually change the wave form
through
>the
>transformer to a different wave form (stepping down). This stepped down
wave
>is much less than the original, thus running your low voltage lights.

Sort of, but obviously not written by someone with much of a technical
grasp of things... he's really saying 2 things:

1) Transformers are not light bulbs (I hope that didn't surprise you too
much)
2) Transformers take in a higher voltage (mains) and convert it to a lower
one (12V) (that probably didn't surprise you much either)

>But the lights are not the problem, the inductive load transformer is.
Our
>switch is designed to use the wave form in it's original form. Any
variation
>from that will cause the switch to act erratic. So you must use an
inductive
>dimmer, please do not ask me to recommend one, I am not familiar with
the
>international products.

This is where it all degenerates... for your purposes, you can assume that
a transformer marked as 'suitable for dimmers', with a halogen light
attached to its secondary, will look almost exactly like a 240V halogen
light as far as a dimmer is concerned.  The switch will see the waveform
just as the electricity supply company sent it to you, and the dimmer
should work just fine- in the unlikely even that it doesn't, then you
should take the transformer back to where you bought it, with the dimmer,
and get your money back!

There can be a big problem using conventional dimmers with inductive loads
(eg fluorescent lights, motors), but a lighting transformer with lights
attached is _not_ an inductive load.

Hope that helps, if you need more detail, feel free to ask, on or off this
list (as I may be wandering off-topic for ukha- again!)

Nigel
--
Nigel Orr                  Research Associate   O   ______
Underwater Acoustics Group,              o / o    \_/(
Dept of Electrical and Electronic Engineering     (_   <   _ (
University of Newcastle Upon Tyne             \______/ \(

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