Re: Low voltage dimmer

[Marc_F_Hult <MFHult@xxxxxxxxxxxxxxxxxxxxx>]

On Wed, 06 Jun 2007 04:57:01 -0000, DrK <drke51@xxxxxxxxx> wrote in
message  <1181105821.118926.196600@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>:

>I have a 600w magnetic 120V - 12V transformer that has 2 - 300 W 12V
>circuits that I plan to use for lighting.  I would like to control the
>2 load 12V sides independently.  Is there a comercial dimmer (X-10 or
>eqivalent) that will control the LV load side?  If not a dimmer, is
>there a remote switch that will do it?
>
>Thanks,

Please give us a few more specifics.

What's your application? One of the biggest advantages of low voltage is
that you can use DC power from batteries. Is that your intention? If so,
TRIAC-based dimmers like those used in most conventional dimmers won't
work. Like the X-10 signal itself, they need AC.

Or are you using low voltage for safety or other reasons?

Or a new-fashioned fixtures and lamps with (eg) exposed conductors that
have become fashionable. I think they'll be neato at least for a while ;-)

If it's just because you have the transformer, you might reconsider.

In the US, the National Electrical Code (NEC) allows for 'interesting'
configuration of low-voltage ( =<50volt) lighting circuits, but the
principal  section pertaininf to  low-voltage lighting requires that the
entire system -- transformer and all -- be UL listed as a system.
Presumably your transformer isn't so listed or you would already have
access to the dimmers. If you are in US and need to conform to NEC, this
might be a deal-breaker.

I have a distributed nominal 24VDC lighting system that uses nominal
24VDC-in to 0-12VDC out CE and RU-listed dimmers. The dimmers are in
commercial rack-mounted units from a surplused DMX512 lighting system that
previously powered 24 individual 12vdc lights in a floating exhibit in
Disneyland. These dimmers require DC, not AC and use 0-10vdc control
signal (which can be created by DMX512.

Note that the wire sizes required to carry low-voltage at high current can
get very large quickly. All else equal 24VDC requires half the copper of
12VDC. You two nominal 12VDC windings could be used to make  a
(2x12)*1.4)vdc  0.6 vdc = 33vdc supply.

But if you want a battery backed system, consider starting with a
UL-listed battery charger/supply (That's what I did. 'Course I think you
want to use the transformer ;-) My kids called this building a car because
you found a hood ornament when I did comparable things <joke intended>.

HTH .. Marc
Marc_F_Hult
www.EControl.org