LED fixtures connected to dimmers

[sosayweall]

Good Morning guys,

So I worked at a theatre that plugged their fixtures into dimmers due to the lack of rely power, I had not control over the situation but expressed my concern as the longevity of the fixtures. I had always been told before "never plug leds into dimmers, it doesn't matter how the dimmer is curved!" I have had the technical argument explained to me a few times when time allowed, but after years I had forgotten it.

I would think that modern LED fixtures can filter their power much like a power conditioner, eliminating the dimmer sine wave.

So what do you guys do?

Cheers, TM.

 

[GreyWyvern]

I had always been told before "never plug leds into dimmers, it doesn't matter how the dimmer is curved!"

The first part of that is correct. However, it doesn't matter what the dimmer curve is set to. If the power is dimmed, that will damage the power supply module faster than it just being connected to the dimmer will.

I would think that modern LED fixtures can filter their power much like a power conditioner,

You are somewhat correct here. The power supply modules used in fixtures have gotten better over the years and are better able to deal with power coming from dimmers. Simply meaning they likely won't crap out as quickly.

eliminating the dimmer sine wave.

Dimmers by nature tend to "chop up" the nice clean sine wave of clean AC power.* The power supply modules are expecting a clean AC sine wave and the output of dimmers is not a perfect sine wave. That means, that it doesn't matter if the dimmer is parked on full or is set to a switched mode. The power is still passing through a dimmer module and is therefore corrupted. Air-gap relay modules or constant power modules are the options for powering units with circuits coming from a dimmer rack.

*There are sine wave dimmers that are better at reproducing a sine wave on their output, but due to cost and reliability, those really haven't made it here in the U.S.

 

[robmerow]

It's worth noting that some dimmer racks have modules available for just this purpose. ETC Sensor racks have relay modules that provide non-regulated power for electronic devices. They also have more versatile hybrid modules that can be set to "switched" to provide AC to moving lights when you have excess dimmers but are short on constant circuits.

 

[BillConnerFASTC]

Well, to be contrary, if the dimmers are auto-transformers, your probably fine.
While I would ALWAYS STRONGLY RECOMMEND not putting LEDs and movers and other things with solid state technology on phase control dimming circuits, I'm not sure if very, very careful you can't get away with it.

 

[sosayweall]

The power supply modules used in fixtures have gotten better over the years and are better able to deal with power coming from dimmers. Simply meaning they likely won't crap out as quickly.

The fixtures in this scenario are FIRST GENERATION 12" Chromaq Color Force's. With the issues they already have, I wouldn't entirely trust the power supply.

It's worth noting that some dimmer racks have modules available for just this purpose. ETC Sensor racks have relay modules that provide non-regulated power for electronic devices. They also have more versatile hybrid modules that can be set to "switched" to provide AC to moving lights when you have excess dimmers but are short on constant circuits.

Sadly this venue had a Rosco Intelligent Power System, which meant we couldn't have spent money to purchase modules like the ETC Sensor racks. One can dream.

I think I have found a solution however! I told them to purchase a power distro that could tap into an unused 3-Phase 240 circuit located above the grid. Giving enough power to their 12 fixtures.

 

[PeteEngel]

You know, being LED gear, you could do the wattage math and just run a few circuits from wall outlets... (of course I don't know your rig layout)

Just a thought.

 

[Les]

Might be cheapest to just have an electrician come in and add a few 20 amp circuits in the grid. Have them switched so they can be turned off every night since an LED fixture "at zero" isn't truly "off".

Sounds like a full distro would be overkill for the current rig of LEDs but of course might be a good idea if you're going to be adding a bunch of moving lights.

 

[BillConnerFASTC]

Parallel 1 to 3 outlets off the (usually) 20 amp 3 pole feed to each IPS strip. Should be very minimal work - maybe just close nippling a box to the job feeding the strip.

 

[FMEng]

I think I have found a solution however! I told them to purchase a power distro that could tap into an unused 3-Phase 240 circuit located above the grid. Giving enough power to their 12 fixtures.

Be careful there. 3-phase, 240 V is from a closed delta secondary. Two of the phases are 120 V to neutral, but the third is a "wild leg." The wild leg is 208 V to neutral!

If it is 3-phase 208 V, wye connected secondary, then all phases are 120 V to neutral.

 

[RickR]

Contact Phillips Strand. The Rosco IPS was IGBT from Entertainment Technologies that made it's way into the Phillips conglomerate. So they will have the details of what's possible.

If you really have IGBT type dimmers there is a relay setting that is better (less chopping) than most SCR dimmer non-dim curves. I believe Strand is now selling a relay module for their IPS type bars. Retrofitting is doubtful, but you can ask!

FWIW Sensor racks have a switched mode that does not do power regulation. Similar concept-different technology.

 

[JD]

Dry, clean power is only going to become more and more necessary as we move toward the future. Might as well deal with the issue now. I don't see us regressing and going back to the days of tons of conventional lights. There are plenty of big systems out there and they will be around for years, but looking forward, there will only be more and more DMX based lighting that only wants to see straight AC power from the mains.

 

[Ford]

While PSUs have definitely come a long way, unless they are specifically designed for running on a dimmer, the chopped waves will introduce harmonics that are likely to kill your fixtures...eventually.

We worked with our PSU manufacturer to develop a power supply that is specifically designed to run on a dimmed circuit for our Ovation E190, and F165. It took us 2 years to make it work properly... but much of that time was spent on fine tuning and rewriting the fixture software, as we designed the fixtures to dim via either DMX, or on the dimmer (the fixtures can actually sense if they are on a dimmer, and behave appropriately).

We have found that a bigger issue in terms of PSU longevity is the fact that many users are leaving the fixtures powered continuously. As Les implied, the fixtures are on whether the LEDs are emitting light, or not. And whenever a fixture is powered, the PSU is working.

In a recent study commissioned by the U.S. Department of Energy, it was noted that most theatrical LED fixtures draw between 5 and 27 watts when not in use. This is a lot of power being wasted, and a lot of unnecessary wear and tear on PSUs.

I attached the whitepaper, it makes for riveting reading... ok, that is an exaggeration, but there is some useful info in here.

So, in short, if you want for your fixtures to last, disconnect them from power when they're not in use.

 

[derekleffew]

In a recent study commissioned by the U.S. Department of Energy, it was noted that most theatrical LED fixtures draw between 5 and 27 watts when not in use. This is a lot of power being wasted, and a lot of unnecessary wear and tear on PSUs.

I believe the term is quiescent power draw, or as @STEVETERRY likes to call it: vampire power.

 

[JD]

This is a lot of power being wasted

Same could be said about conventional lights and the "idle set" of the dimmer. Usually, they are trimmed to about 5%, or 50 watts for a 1k load, along with a super-bad power factor rating.
General rule of thumb, shut the stuff down when not in use. That can be easier said then done on a large dimmer system.

 

[de27192]

It's worth noting that some dimmer racks have modules available for just this purpose. ETC Sensor racks have relay modules that provide non-regulated power for electronic devices. They also have more versatile hybrid modules that can be set to "switched" to provide AC to moving lights when you have excess dimmers but are short on constant circuits.

Not just modules but many dimmers do have a "hard" curve which are suitable for taking inductive loads - IE being used as relays. For example, the ETC Smart dimmers (SmartPack, SmartBar, etc) can be switched on the unit to provide relay power, the SGM PowerPack and the LSC GenIV can both do it too.

 

[SteveB]

Not just modules but many dimmers do have a "hard" curve which are suitable for taking inductive loads - IE being used as relays. For example, the ETC Smart dimmers (SmartPack, SmartBar, etc) can be switched on the unit to provide relay power, the SGM PowerPack and the LSC GenIV can both do it too.

It should be noted that this is a new feature on Smart systems to have the Thru-Power module, which is switchable to relay mode. It's not your older and more typical Smart dimmer system. To state "many dimmers" is inaccurate.

Bottom line is typical SCR dimmers do not provide clean power as you would get from a relay module, constant breaker module, or regular outlet.

 

[BillConnerFASTC]

Maybe somebody can post a couple of pictures of an ociliscope view of "clean" power in a typical building and the output of a dinner set to non-dim mode - still through the SCRs or IGBT.

 

[JD]

Although I cannot speak for the output of a pure sine IGBT dimmer, SSR/SCR/Triac dimmers all share the same limitation:
All these dimmer designs work by using an opto-cupler to isolate the control pulse from the device doing the power switching. On the power end of the circuit is the output of the opto-cupler, some type of current limiting resistor, and the gate of the SCR or Triac. (An SSR is simply this whole circuit in a potted module.) The important take-away is that this end of the circuit is powered by the voltage drop across the switching device which is in series between the line input and the load. In order for it to operate, there has to be a minimum voltage dropping across the device, usually about 12 volts although it can be more. What this means is that even when the dimmer is parked at 100% (relay mode), the first 12+ volts of the waveform will be missing before the device gates. The result is a sudden jump in voltage when the device fires. Thus, even in the best case, your sine wave starts off as a square wave. I would suspect as each generation of LED lighting is built, it will be more tolerant of this distortion, but there is no question that thrysistor based dimmers all have this distortion.