RE: Re: DMX Controller

["Keith Doxey" <ukha@xxxxxxxxxxx>]

Hi All,

Just one small point to mention regarding the use of DMX dimmer packs
designed for theatrical/nightclub use.

Because in use it is normal for the lamps to be switched on and off fairly
rapidly, many of the DMX dimmer pack feature "pre-heat" which is
where the
output never actually goes off completely, instead a small voltage is
output
all the time to keep the lamp filaments warm to prevent the switch on surge
that happens with a cold filament and also extends the life of the lamps.

Some dimmer packs allow this to be disabled but some dont.

Although only a small amount of power is fed to the load which is not
enough
to light the lamps, it is there all the time and this small but constant
power consumption could cause quite an increase in the old electricity bill
:-(

Fortunately there is a way round it *IF* you design your own DMX interface
board or an additional board that reacts either to DMX or xPL messages.
Connect a relay in series with the output of the dimmer pack that is off
whenever no light is needed for any significant time. This also has the
advatage of stopping any leakage current from the triac snubber getting to
the load.

Lutron do this on their dimmer packs. They have a level of 0-100% and they
also have OFF. Lutrons wiring is slightly different from what I descibed
above in that the relay is BEFORE the dimmer and they also output a
switched
live eg

LIVE----RelayContact----Dimmer---- Dimmed Live
------------Switched Live

This is particularly useful for dimming flourescent loads which have
special
ballasts that preheat the tube ends to allow dimming. The switched live
feeds the ballast pre-heat and the dimmed live drives the tube. It can then
be dimmed 0-100% but whenever it is turned OFF, the pre-heat is also turned
off prolonging the life of the tube heaters.

Anyway, enough waffling. got things to do :-)

Keep up the good work

Keith