Outlets powered by dimmer rack-Problem?

[RedmonwantsEOS]

Hey guys,

I need some advice.
In our Auditorium, we have two duplex outlets in our control booth that are being fed from our dimmer rack via a constant module. The dimmer rack also houses all the dimmers for the stage and house lights. I personally do not feel that this is a good idea because SCR dimmers put noise and harmonics on the lines, correct? We are going to be getting a full sound system put in during January 2009, and I don't think the new equipment should be powered from these outlets because of the harmonics and voltage flucuations. Also, couldn't noise enter our sound system because of this as well?
The Power supply is 480 volt 3 phase before our transformer, then comes out as 208Y/120 into the dimmer rack.

I am going to present this problem to the school engineer, and I just need to know if there is anything else I should mention as to why this is (or isn't, if so) a problem.

Thanks!

[gafftaper]

What Brand and Model of Dimmers?

A constant module is essentially just a circuit breaker. So it is the safe way to run any sort of electronics off of a dimmer rack. There is no SCR in a constant module. The only problem with running a sound system off of there permanently is that the two systems will forever be tied together. You have lost that flexibility of those circuits forever.

There is a bigger problem however, How larger of a sound system are you getting? How many Amps and how larger are they? In my theater we have one circuit for each amp plus one for the rest of the gear. Unless they are small, multiple amps on a circuit is a bad idea. You need to do some research about how much amperage you sound system will draw before you can answer the question of how much power you need.

However I do not consider myself a dimmer or power expert so I yield the floor to those who are...

[waynehoskins]

If it's a non-dim module, that's not a problem in itself.

But more problematical is the notion of running all or part of your sound system off of dimmer-switched power, noise aside even. You don't want the PA keeping going to be dependent on the light board.

Also, a proper PA will take more than two circuits for power. I use three at the church, and we're a 300-seater. Our PA can also go to Eleven without tripping anything.

A proper PA most likely will have the amplifiers located offstage rather than in the booth, so you'd be plugging your console and drive rack into the switched power. If something goes stupid, as it undoubtedly will at some point, you'll likely get a big power-on or power-off thump if the amplifiers are on when the console and proc side turn on or turn off. Depending on what system processor is used and where it's installed, that can mean a huge nasty "pow!" that could damage the drivers in your loudspeakers.

So yes, don't do it. Try to get a dedicated unswitched always-on circuit in the booth for audio, ideally on an isolated-ground supply with the amps ("clean audio power").

[JD]

So, the concept here is that you are running sound off of breakers (no SCRs) on a dimmer rack, otherwise know as "constant on."

Although technically there is not a problem, I have a bad feeling about this one! Generally, you want to keep sound a world apart from lights as far as supply. It sounds like there is a dedicated transformer for the dimmer system. If this transformer has a harmonic filter on it (some do) the output under load can be pretty far from sign wave. Even without the filter, a transformer secondary can get pretty noisy looking when it is used to feed a dimmer rack. Transformers by nature are part choke and part resistor so those chop points where the other SCRs kick on can be pretty visible even on the supply side. Now we all know that all power comes through transformers, but the smaller transformers used for secondary distribution on a 480 system tend to be worse then their big pad-mounted counterparts.

Yea, try to nip this one in the bud. It will be a thankless task as they will never know the trouble they missed!

[Oobleck1441]

I'm not going to get into specifics, becuase I don't know them
Haha
But anyways, in my theater, our booth is hooked to regular building power, and is also hooked into the emergency generators just incase of a power outage, we can make annoucements and have a way to alert out building in an emergency.
Just some input

[RedmonwantsEOS]

Thanks for the replies so far.

I should have been more clear, the amps will not be on these outlets, just the booth equipment.
It is a Lehigh DX-120 Rack and the module is just a constant 15 amp circuit breaker model.
Actually, for some reason I do not think this the module that supplies these outlets can be switched off at the lighting console, only by cutting the power to the rack.
And yes, the trasformer is dedicated to the dimmer rack.
So even though the module itself does not contain an SCR, wouldn't the noise from the other dimmers affect the outlets in the booth?

Let me know if more info is needed.

Thank you so much!

[derekleffew]

Originally Posted by RedmonwantsEOS

...So even though the module itself does not contain an SCR, wouldn't the noise from the other dimmers affect the outlets in the booth?...

Absolutely. See JD's post. Doesn't even matter what kind or what manufacturer the dimmers are. Also, even if there were no dimmers in the system, the mixer needs to be on the same transformer as the amplifiers. This is why R&R audio companies run their own power, along with the mic and drive snakes, 300' from backstage to FOH, rather then just using lighting's power. It's also why 97% of the time for arena tours, Dimmer Beach is SR and Monitor World is SL.

[gafftaper]

Originally Posted by RedmonwantsEOS

Actually, for some reason I do not think this the module that supplies these outlets can be switched off at the lighting console, only by cutting the power to the rack.

A "constant" module can only be turned off at the rack. I believe "contactor" or "relay" module is the correct name for a module that is still a true non-dim but you can turn it on and off remotely from the board.

and AMEN! to what has been said about all your audio gear needing to be on the same transformer.

[TimMiller]

I was setting up for a show and the audio guys forgot their power distro, so they just came out of the edison plugs that were on my distro (the feeder was first connected to my dimmer rack, and then my moving light pd, which also had edison outs that they used). They had some really nasty buzzes and hums in their PA. Luckally they were just using it to get setup and tested, they brought in their distro the next day, but it was very nasty sounding, especially when we set all the dimmers at 50%

[RedmonwantsEOS]

Awesome guys, this has really helped me. Thanks!