In-Rush Currents

[Anonymous067]

At a facility I work at, a particular employee who is "in charge..." thinks it is a good idea to turn the "stage lights" (1kw lights) off and on every ten minutes. If something isn't going on for another ten minutes, he turns them off. He's trying to save money...

Myself and an electrical engineer are the people who program and run the lights (not much work, just architectural system). We both argue he's actually wasting it because the inrush is so great on a CD98 Strand rack (I THINK thats the name..it's the common strand one...I haven't looked at in in a few months...) (x2)...

Can anybody separate the myths from the facts here?

 

[JD]

The inrush can be 10 times the working current, but only lasts a few cycles. If electricity was the only concern, the on & off would be best. But it is not!

This inrush is stressful to every part of the system. The most damage is done to the lamps. Lamps usually base their lifespan on tests where the lamp is cycled on for several hours at a time. The more on-off cycles you have, the shorter the lifespan.

The dimmers also take a hit. Good dimmers are designed for the inrush, but each one causes a thermal surge inside the switching device. (SCR, Triac, SSR, or IGBT) Eventually, enough damage is done to the silicon junction and the device fails.

 

[kevinz]

It doesn't matter. Even if it does save money, frequently turning lights on and off rapidly heats and cools the filiments, although this is fine for a preformance, greatly increades the chance of a lamp buringing out. A 1kw lamp is pretty expencive, and I'm pretty sure electricity is, on average, like $0.50 per kilowatt/hour. You would have to run a light for at least 60 hours (I think most 1kw lamps are at least $30) to use up that much money in power. Also, inrush is a lot of power, and I'm pretty possitive that he's wasting money anyway. So all in all, your "boss" is an idiot.

 

[Chris15]

1k stage lights is a very broad description. Are you talking about PAR lamps or something more fragile?

What is the control method being used to turn them on and off?

How many of these 1k lights are there?

 

[David Ashton]

You might wear the dimmers out, in 40 years or so,you cannot remove the inrush current, only move it from one time to another, hence the preheat myth, turn the dimmer down when you want the lights off and fade them up when you want them on, you will not use much power unless they are on preheat setting which is a great way to use power for absolutely no return.Of course theatre lamps are designed for continuous fluctuating use, they would be of little value otherwise.

 

[Anonymous067]

The lights are a combo of ellipsoidal and pars, architectural versions of them.
We use Strand Premier Architectural system to control. Most of the 128 presets have , <5 seconds of fade time.

 

[Anonymous067]

So all in all, your "boss" is an idiot.

I discovered that quite some time ago...

That's why I don't offer my services to that "job" anymore...

(It was all volunteer work anyways...).