R20 vs CC20 for LEDs: Best practice vs cost benefit?

RonK

Member
This is not another "can I power my LEDs through a D20 dimmer" question.
This is a question about constant power versus relayed power that stems from a discussion with a colleague.

What is your opinion of best practice, and the cost benefit of using a CC20 Constant Current module to power LEDs vs an R20 relay module.
The scenario is a school with an active theater program (9-months, no summer use), with just shy of 80 ColourSource (mix of par/spot/cyc), powered through a Sensor rack (Classic, not yet upgraded, so Thru Power modules are not an option). There will be up to 10 fixtures per circuit (4 modules/8 circuits).

Is there a significant enough loss of life expectancy or other risks from leaving LEDs powered 24/7 through the school year (via CC20) that warrants paying twice as much for the R20 relay module? Is it okay for LED fixtures to remain powered (but no output) for extended periods of time? (Presume module breakers are not being used to switch power, after all a breaker should not be used for a switch).

I have my opinion, but curious what the hive mind thinks.

Thanks!
 
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after all a breaker should not be used for a switch).

Maybe someone from ETC will come along and confirm this is right, but CC20s are rated for switching duty, so a cycle per day or less ought to be okay. Whether the inconvenience is worth the savings, or whether people will get lazy and not switch off, or whether there are other safety concerns with frequently accessing the racks in a school setting are all good reasons to go with relays though. I've rented/borrowed CC20s for cost reasons in temporary uses, but wouldn't want to buy them to go with a house LED inventory.
 
There are a whole lot of LED's used as houselights these days that have 24/7 hot power and data for control. There's also some benefit in the CC20's not causing rack fans to run, while R20's do. That being said, there's also benefits of being able to reset your devices remotely if things go weird.

I think if this was an installation where I felt confident that there were enough skilled operators to relay on the relays acutally being turned on/off as appropriate, I'd stick with them. That being said, if this were an install in a church/high school where either a) the relays would remain parked on 24/7 anyways or b) I foresaw a regular "why don't these lights work" phone calls, I wouldn't feel bad about putting CC20's in.
 
In my mind, the "50,000hr LED Life" claim has more to do with the power supply than the diodes themselves. I'd rather that clock only tick during a show and not while I'm asleep at 3am.
 
In my mind, the "50,000hr LED Life" claim has more to do with the power supply than the diodes themselves. I'd rather that clock only tick during a show and not while I'm asleep at 3am.

That is the life of the LED, if measured correctly it's to the point that they are putting out 70% of their original output. In my experience the power supply usually dies long before that though.
 
That is the life of the LED, if measured correctly it's to the point that they are putting out 70% of their original output. In my experience the power supply usually dies long before that though.

True. Capacitors do have a lifespan measured in hours as well. They can live quite a while in cool temperatures, but their life expectancy drops exponentially as temperatures rise. I wish I could find the datasheet but it seemed like every 10° rise cut the life of electrolytics by some crazy number - like 20% or somesuch.
 
Just to clarify from the datasheets for both the Relay and Constant Current Modules, the switch breakers are switch rated.
Per the Circuit Breaker section:
Relay Modules: https://www.etcconnect.com/WorkArea/DownloadAsset.aspx?id=10737460559
Constant Current Modules: https://www.etcconnect.com/WorkArea/DownloadAsset.aspx?id=10737460662


Thanks for noting this! I was generalizing with the 'don't use breakers as switches' but you are absolutely right.

Given this info, which module would You prefer in this scenario? Assuming racks are reasonably accessible.
 
Who will be the primary people using the system?
Short answer, go Relays as you can automate power on/off with the powering on/off of your console.

Long answer:
At a local high school I frequent, there is a full time Director who is also the TD/Set Designer & constructor for all high school productions.
Because he is there ~40hrs each week all year, it could very easily be put on his daily to do list to turn on/off the CC modules. During tech weeks I would and have left gear plugged in and on for the entire week.
During off periods the Director would not even turn the gear on unless needed.
However at this local high school, the dimmer racks are in 2 separate locations thus making it an annoyance if we were to us CC modules. The Director has specifically said he wants Relay modules when they finally get some LEDs.

Another look at this:
You have thousands of dollars in quality LED gear. Do you really want to leave them on 24/7/365.25?
Do you leave your car running 24/7/365.25? Do you leave your computer running 24/7/365.25?
My personal answer to all the above is nope and will push/require relay modules whenever I can.

Lastly, the high school I frequent currently only has 2x S4 Revolutions. Because of the low number of 'intelligent' fixtures, we follow the suggestions in this ETC article:
http://www.etcconnect.com/Support/A...and-Moving-Lights-Powered-by-ETC-Dimmers.aspx

As you have a large amount of fixtures, I would go for Relay modules and automate the start up/down process on your light board so they turn on when the board turns on and turn off when the board turns off.
 
I use the R20 for LEDs and movers. When the board is off, the fixture is off. When someone hits a house preset station button, only those relays that are needed for that preset come on. I do not want to
a: waste energy
b: have those fixtures with fans kill the life of the fans
c: have lights I don't need on, on when there is a work call or a rehearsal

That being said, I do try and include a light that will come on immediately when a preset is hit, be it house lights or conventional or one theater a couple of dedicated LED works that are always powered.
 
"Vampire loads" are a thing, and if the school is factoring in ROI for their purchase decision than ensuring that handful of milliwats doesn't add up over time can be helpful. Also, if the fixtures have fans, turning them off preserves the motors and bearings and keeps them from sucking dust into the innards unnecessarily. It seems pretty unanimous for the R20, and I'll add to the chorus.

Plus, what technical service department isn't going say "Have you turned it off and back on?"
 

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