The above Ad will no longer appear after you Sign Up for Free!
Discussion in 'Lighting and Electrics' started by Charc, Mar 22, 2008.
Is this even possible?
(Please reference the March, 2008 issue of Live Design; page 34.)
Indeed it is possible if you use dimmer doubling. You would then use the HPL550W/77V lamps.
I don't believe this has come up on CB before?
Does anyone here use dimmer doubling? I've read briefly about it, but am not positive about what the deal is with it. Can anyone shed some light on it? And why does dimmer doubling necessitate the move to a 550W lamp?
Dimmer doubling quick and dirty. Basically the dimmer doubling adapter splits the AC waveform so that the "positive" side goes to one fixture and the "negative" to the other. The SCRs (or SSRs) in the Sensor dimmers are capable of chopping the AC waveform in a non-symmetrical pattern. Meaning you could chop half of the positive and 75% of the negative at the same time. In normal SCR operation the same amount of both positive and negative gets chopped.
There are lots of complex electronics in there, and I have boiled it dow to a very simple answer. I am sure that Steve Terry or some of the other CB members from ETC could give much more detail.
Dimmer doubling does not necessitate moving to a 550W lamp, it necessitates moving to a 77V lamp. I know that there is a 77V 750W lamp, but it might only be in the QXL variety for the Revolution, but given that the only difference between the QXL and an HPL is the way the contacts are setup I would imagine you could have a 77V 750W HPL.
voltage of 77V is much more important than the wattage of 550W. Here is the propaganda from ETC. Although I can see some advantages, personally I've never used it, as I feel the cons (special "two-fers," lamps, and connectors) outweigh the benefits. But I work in places that bring in as many dimmers as are needed for each show. If I had a limited number of installed dimmers, I might consider it.
dimmer doublers to "split" 12 dimmers into two.
What happens though is (as Alex pointed out) your V drop goes from 60V to 0V and 0V to -60V respectively rather than 60V to -60V (using logic, half of 120 is 60, rms is fickle measurement, might a little be different in reality but you get the point). Since you have half the voltage drop you need a lamp rated for half the voltage. Power is proportional to voltage and current (P = V * I) so voltage goes does down current goes up and in the end the math works out to give you a 550W lamp. Unless you have a really good eye you're not likely to notice a difference of 25W's (haven't used them maybe physics causes noticeable differences) but there's going to get significant differences in the lamps. 575 is close to 550 but I'm pretty sure bad things would happen if you mixed them up and put the 77V lamp on a 120V dimmer.
If your interested further in the math PM me this is the kind of stuff I'm majoring in.
voltage lamps. I don't know offhand why that is, but for the HPL575/115V you get 28.73 Lumens per watt, while the HPL550/77V gets 29.4 lumens per watt. I know that we had this discussion when I was in school, but I don't remember why it works out this way.
Also, as I said, there is a reason you get 77V from the DD system, but I don't remember what that is either.
Dereks points are well spoken.
The control end - an ETC console of recent variety, has to be switched to DD. It splits a 512 DMX universe into 2.
Dimmer/Circuit 1 has a DD 2-fer, so the dimmer rack Control Module is told that dimmer 1 is now one 1A and controls one half of the sine wave, 1B is the other. The console assigns DMX address 1 to dimmer 1A and DMX address 257 to 1B, thus allowing separate channels.
If you have dimmers above 256, you need to re-think where those dimmers reside in the DMX addressing scheme (Not to mention circuit labeling issues, etc...) Thus a bit problematic to incorporate on a larger system.
DD is a great tool for a big theatrical tour, as you can put 12 lamps on a 6 circuit multi, ea. with it's own dimmer. The fixtures have to be an S4 of some variation with a 77 volt lamp. But a 50 ft truss full of 60 S4's only needs 5 multi's - which half is as many as non DD's. Plus half as many dimmers. The savings in cable and dimmer racks save's truck space.
FWIW, we recently explored adding this to a black box with 60 dimmers and and a need for more. We have a Sensor 96 rack that's not filled, but it looks to be cheaper to go DD, even though the DD 2-fers run about $100 ea. Still cheaper then adding dimmers and adding wiring, raceway and receptacles. Luckily the inventory is mostly S4's.
fixture hum, filament damage, all that? It kind of sounds like its cutting up the sine wave into pretty dirty parts, does that have an effect on the filament?
Dimmer Doubler Datasheet at www.etcconnect.com explains everything pretty well.
ETC console just fine, you just have to keep your numbers strait. Its great for places that you can not get more power up there, such as Loge, Beams, Box Booms etc... Its also used often for touring shows for the reasons above. You can halve your cable and dimmers, which is a good thing. The only real pain of it is most place do not purchase the extra base caps with twist connectors on them, instead they adapt the DD's to stagepin. You then have to label ever instrument that has a 77v lamp in it so you don't blow it on a standard circuit. Dimmer doubling can be very useful, and yes you can two-fer off a dimmer doubler.
The sine wave is chopped either way--that's the way SCR dimmers work.
Haven't not really spent much time with DD, I would be curious as to how the 60Hz hum is different between a DD and non-DD lamp.
fixture is only receiving half as many chopped wave forms. The way I understand wave chopping to work is at 50% half of the positive part of the wave from is chopped and half of the negative is. So if you're only receiving half that wave form, you will have more "resting" points from the magnetic field. I'm still thinking about this though because theres a few holes in it in my head still.
Lower voltage = smaller filament = more of a point source = more LPW in an ERS.
ETC Dimmer Doubling Data Sheet: "77V HPL lamps have an additional pin that prevents you from installing them into a non-Doubled fixture."
Does this mean that all the fixtures that you use on Dimmer Doublers need different lamp bases? It also says that the DD's use 15 amp twist-lok connectors. I can see the cost adding up quite quickly. How much are the doublers themselves? Anyone have a rough estimate?
dimmer doubles listed at $116.25
from the ETC "propoganda" there's s screw in the lamp base that must be removed to install the 77V Lamp. So no you don't need new bases, just modify the ones you have.
So yah twist-lock or you voild the UL listing, they do say that you can install them yourself though. NEMA doesn't actually list an L2-15P but the L1-15P seems to fit the 15A 125V two pole requirement. I found them for $9.00.
I found HPL 550/77X's online at ~$20. So could do the doubling for something like $200 per dimmer/fixture pair. That's a lot cheaper than more dimmers. Just an organizational pain.
One last note, ETC's info says that the dimmer doublers themselves have L5-15 connectors on the output side so that's a phone call to ETC before buying this system cause of the mis match.
"NEMA L2-15P" is a typo on the PDF. The 2 should be a 5.
NEMA vocabulary lesson for me. Does two pole, three wire describe an L1-15 or an L5-15? The words two pole makes is sound more like the L1 configuration.
Two Pole, 3-wire would be an L5-15. Two Pole, 3-wire implies a grounded connection: two poles=Hot + Neutral, the third wire being ground. Besides, in this case it has to be a grounded connector to comply with code.
wire" (grounding) may refer to NEMA configurations:
5, 6, 7, 8, 9, & 24.
Here's a great chart, courtesy of Pass & Seymour. I suggest EVERYONE in the US print it out as big as possible and post it on the electrics workshop wall.
Separate names with a comma.