On Wed, 24 Nov 2004 15:25:33 +0000 (UTC), "Dave Jennings"
wrote:

Any ideas what either I've done wrong,

You've mixed halogens and dimmers. Don't do this.

For an easy life, don't dim them.

For good lighting, don't dim them. Halogens don't like running at half
power. Switch 50W bulbs to 20W, turn them on and off in banks, but
don't run them dimmed.

Don't try and dim them unless you have some reasonable understanding
of electronics.

Some types of transformer (both transformers and electronic PSUs) just
can't be dimmed. If you do try it, these probably work at either full
or zero output, but could do anything in the middle, including some
really bad letting-the-smoke-out type failures.

Many electronic PSUs can be dimmed, and dimmed easily by attaching a
low-voltage variable resistor to them. If you're doing furniture or
desklamps, this can be the best and simplest way of getting dimming.

_Some_ PSUs, mainly transformers, but a few of the electronics too,
can be dimmed by a standard light dimmer. If it's not marked as such,
it can't.

Of the few PSUs that permit it, some still don't like being dimmed
(mainly the smaller transformers). They'll object by buzzing noisily.
If you do have a "buzzer", try swapping the dimmer. A more modern
dimmer with better output suppression may use zero voltage switching
(look for a CE or FCC mark). This reduces the output harmonics that
may cause buzzing.

If you're planning a dimmed installation, breadboard it first. It's
easier to find that it buzzes and needs redesign _before_ you've
buried the transformer in a ceiling void.
--
Smert' spamionam