LED fixtures and inrush current

BillConnerFASTC

Well-Known Member
On another board it was suggested that ETC LED fixtures have more inrush than "equivalent" fixtures by other manufacturers and stress the electrical systems more. The statement was " As someone who works mostly in ‘found spaces’, where I have to pull extension cords from outlets with less than stable power, I’ve found ETC LED fixtures to be less then forgiving. (Something about the inrush current causing a voltage differential between neutral and hot that is more than the fixture allows." And the poster suggested "Elation Opti-Tri-Par and Opti-Tri-30 fixtures". I know there are questions - like which ETC LED fixtures - but is there any basis for this? I suspect that ETC may be much more thorough and conservative in their research, design, measurement, and documentation, but maybe there is a design issue/feature that does make the inrush on ETC units greater.
 
I'm no electronics expert but my understanding is that inrush is from 'charging' capacitors and inductors. Since these are important in the regulation of power supplies I can see a link. A more conservative approach would have larger/higher rated components for power quality and durability. I think I'll ask around about that theory.

More than anything, I'm happy I've started seeing inrush listed in spec sheets, from ETC and others.
 
I wonder what issues the OP is running into. I would be much more likely to believe that the ETC fixture would go into safety shutdown to prevent damage from wonky power in a situation that the cheaper fixtures might not. Also I have questions about if we're comparing apples to oranges. Are we looking at the power draw of a low to medium power Elation fixture vs a relatively high power ETC fixture?
 
While there is a brief inrush spike when powering up the fixtures, it's hard to imagine it being a problem unless many fixtures are crammed on a single circuit. If the fixtures are in DMX mode, there is no additional inrush when you take them from 0 to 100 like there would be with an incandescent load. In other words, the problems would show up during set up as compared to during the show. I can't imagine that there would be a lot of difference between manufacturers if the fixtures are of similar power capacity.
The new line of ETC LED caps for existing Source 4s can be run without DMX, much like a conventional load on a dimmer. I have not had or used any, but I suspect the inrush is even less of an issue as the caps would partially charge off the idle leakage.
 
While there is a brief inrush spike when powering up the fixtures, it's hard to imagine it being a problem unless many fixtures are crammed on a single circuit. If the fixtures are in DMX mode, there is no additional inrush when you take them from 0 to 100 like there would be with an incandescent load. In other words, the problems would show up during set up as compared to during the show. I can't imagine that there would be a lot of difference between manufacturers if the fixtures are of similar power capacity.
The new line of ETC LED caps for existing Source 4s can be run without DMX, much like a conventional load on a dimmer. I have not had or used any, but I suspect the inrush is even less of an issue as the caps would partially charge off the idle leakage.

It's a big problem for the new ETC LED caps. In their datasheet they list the inrush current at 30 amps when a dimmer. They call for only 2 of them to be used on a D20 module. On the other hand you can put 14 of them on a non-dim circuit with DMX control.
 
It wouldn't be too surprising if ETC's power supplies had more circuit components than cheaper competitors (e.g. active power factor correction), and simply energizing everything takes more current up-front. That said, I would also think part of that circuitry would be assigned specifically to limiting in-rush current....
 

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