Re: Fwd: Wall switch dimmers work with 12v halogen?

[Nigel Orr <nigel.orr@xxxxxxx>]

At 14:18 18/03/99 -0000, you wrote:
>wire. The DC resistance of a transformer primary is
>normally only a few ohms and thus causes a massive current
>to flow through the dimmer until something goes POP :-((
>
>A properly designed dimmer will handle highly inductive
>loads with no problem as can be seen by all the neon
>lighting used in nightclubs and TV shows etc.

During an installation I worked on a couple of years ago, at a new
nightclub, the lighting designer was fitting low voltage lights (each one
with a built-in transformer) everywhere, about 1000 in all.  2 days before
opening night, he finished, smiled a big happy smile, pointed out to
everyone else how great it was that he had finished early, wandered off,
powered up the dimmers, faded up the lights, and everyone else in the
building got to watch and hear 1000 transformers going POP one after the
other... not a pretty sight, but not half as bad as the look on his face
when he realised... there followed a day of panic as he waited for
replacement transformers to be couriered to him, and a day of frantic
activity replacing the transformers... with 'dimmable' spec ones... in time
for opening!

I'm not sure what the difference is in the dimmable ones- maybe higher DC
resistance (so they would get warmer) or different core design to stop it
saturating?  I guess the latter?  And presumably the 'dimmable' controllers
are switch mode ones, so they rectify the incoming signal first, so it
doesn't matter whether it's DC or AC?

Thanks for the further detail Keith- I didn't realise that asymmetry was
the reason- I assumed it was just the phase angle between voltage and
current, so the switching point might be 10% in the voltage waveform, but
50% in the current one.

Nigel

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