Film-Tech Forum ARCHIVE: LED Dimmer pack?

This is topic LED Dimmer pack? in forum Digital Cinema Forum at Film-Tech Forum ARCHIVE.

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Posted by Dave Macaulay (Member # 813) on 09-14-2013, 02:24 PM:

A cinema has decided to save electrical cost by installing LED replacement lamps in all house lighting fixtures. After that they discovered the existing dimmers won't dim them, they are "dimmable" lamps but the dimmer is not compatible. The dimmer manufacturer agrees and says the unit can not be made compatible.
Has anyone found a dimmer pack that works with these lamps? We need dry contact, serial, or ethernet control with 3 presets (feature off, trailer/credits dim, exit full). Load power is about 300W with the LED lamps but having a higher load rating won't hurt.
Thanks in advance!

Posted by Steve Moore (Member # 4753) on 09-14-2013, 02:46 PM:

If anyone has I'd love to know too, been looking for this for ages. Currently I use 20 x 100w lamps over my screen curtains and am struggling to find LEDs with a long enough throw too. I have looked into getting a DMX controller for them then buying a analog 0-10v interface and borrowing a couple of the channel feeds that come from the dimmer controls to the dimmer pack as a method, thus still the same controls in the projection room. (something like one of these http://northlightdmx.com/dmx512decoder.htm )

Posted by Mark Gulbrandsen (Member # 72) on 09-14-2013, 06:14 PM:

LED fixtures are quickly taking over in the live theater world and many of those dimmer racks are compatible with LED so it's probably just a short time till theater light dimmers make the required changes to bring compatability around.

Posted by Harold Hallikainen (Member # 5405) on 09-14-2013, 11:56 PM:

I wonder if these would work if one of the lamps remained incandescent. Triac and SCR dimmers have trouble with nonlinear loads.

Harold
Used to design dimmers for http://www.dovesystems.com .

Posted by Steve Guttag (Member # 268) on 09-15-2013, 01:41 PM:

Harold...at the AFI/Silver, they have Lutron dimmers. And yes, by leaving one incandescent in the load of each bank...LED dimming seems to work perfectly.

-Steve

Posted by Mark Hajducki (Member # 1732) on 09-15-2013, 03:33 PM:

I have seen theatre lighting dimmers dislike low loads (such as filament Christmas lights) once a traditional lantern was connected in parallel there was no problem.

Posted by Mark Gulbrandsen (Member # 72) on 09-15-2013, 04:32 PM:

I believe you will find that most any dimmer that utilizes a solid state relay instead of a triac or dual scr will work. So checking which dimmers utilize this sort of load transfer device should be easy to find out.

This link may also help you out...
Phillips LED Lamp Dimmer Reccomendations
This article may also be helpful Understanding Dimmer Compatability & Wiring Issues

Posted by Brad Miller (Member # 2) on 09-15-2013, 08:29 PM:

Steve, what happens when that incandescent bulb dies? Does it cause any damage to the dimmer? I would assume the LEDs no longer dim properly.

Posted by Steve Guttag (Member # 268) on 09-16-2013, 06:09 AM:

The load seems like it doesn't dim....and then just goes out. It is like having a delayed switch rather than a dimmer.

Posted by Gordon McLeod (Member # 33) on 09-16-2013, 12:06 PM:

A triac SCR or SSR block all exhibit one issue in that the current and voltage must be in phase with each other or it will not be stable
Inductive loads or capacitance loads often cause them to either not have a suitable dimming range or that they flicker
Some transformer loads the transformer will fail to saturate on turn on at low levels and damage the thyristor
We usually put a large power resistor in serries with transformer LV lamps to minamize inrush and put a snubbing cap across the load to correct power factor
Some LED lights use a solidstate powersupply and they will dislike any chopped wave form