Re: Re: C-Bus and Wire-wound transformers - HELP

["Jon Payne" <jgpayne@xxxxxxx>]

Or an IGBT based dimmer which tackles the rise-time problem...

jon
----- Original Message -----
From: "David Buckley" <db@xxxxxxx>
To: <ukha_d@xxxxxxx>
Sent: Thursday, July 31, 2003 1:23 AM
Subject: [ukha_d] Re: C-Bus and Wire-wound transformers - HELP


> --- In ukha_d@xxxxxxx, Bruno Prior <bruno@r...> wrote:
> > I'm using C-Bus for control and have gone for the 2A per circuit
> > dimmers, so they ought to be able to handle a 300VA load just
> fine. But
> > the wire-wound transformers make the most god-awful racket when
> the
> > circuit is dimmed
>
> Yes, they will.  With standard dimmers (ie triac based) there is a
> nasty inrush current at the point when the triac turns on at 100
> times a second, and thats where the buzz comes from.  Its the
> mechanical components of the transformer getting a mechanical shock.
>
> The only guaranteed way to reduce transformer buzz (and harmonic
> nasties introduced into the phones and hi-fi at the same time) with
> conventional triac dimmers is effective control of risetime.
>
> The way this is usually achieved is by using an inductor (a choke)
> in the dimmer.  The risetime of a dimmer is almost a quality
> measure; the very best dimmers have many hundreds of microseconds of
> risetime.  Lesser dimmers have very short risetimes.  Laws of
> physics come into play here; a long ristime needs a big
> (electrically) choke, which is (physically) large and heavy.  This
> is why "professional" dimmers are big and heavy.  Have a
butchers at
> http://www.mode-lighting.co.uk/Products/Architectural.htm
for a
> compromise example.
>
> Some companies (such as Lutron, with their Lamp Debuzzing Coil, see
> http://www.ylighting.com/ln-ldc-10-tcp.html,
dont know if there is
> 240v version) sell an add-on gizmo which is effectively a choke in a
> box.  The choke increases the risetime, which is good.  But what
> this will do is to transfer the noise from the transformer (which
> will be quieter) to the choke (which will now make the racket)
>
> Not good.
>
> There are only a small number of solutions to this problem.
>
> a) an appropriate electronic transformer.  But I would caution that
> having two six meter antennas a few inches apart with the best part
> of 20A flowing being switched through them at something over 20KHz
> may cause interference to sensitive electonics...
>
> b) Use different dimnming technology. Sinewave dimming.  s'not
> cheap, but is silent.  Will also need to be integrated into your
> CBus system, which may or may not prove a challenge.
>
> c) Go DIY - for the adventurous only - even better than sine wave
> dimming for genuine magnetic transformers is to use a variac.  The
> motor driven variac and controller will set you back about $1000 new
> (www.variac.com), but this stuff often apears on the s/h market for
> very little money.....   When I was a kid I had variac dimmed lights
> in my bedroom, using meccano components to add the control
> capability!