Lamping S4s at 550W

[Charc]

Is this even possible?

(Please reference the March, 2008 issue of Live Design; page 34.)

[icewolf08]

Originally Posted by charcoaldabs

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.
Link

[Charc]

My god! I never knew.

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?

[icewolf08]

Originally Posted by charcoaldabs

My god! I never knew.
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.

[derekleffew]

The lamp 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.

[porkchop]

Derek hit it on the spot, when you do this you're not really worried about the difference between 575 and 550 watts. The idea is if you have say 48 dimmers and you could really use 60 you could use 12 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.

[icewolf08]

The most interesting thing to me is the fact that you get better luminous efficiency from lower 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.

[SteveB]

Originally Posted by derekleffew

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. .

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.

Steve B.

[DarSax]

Still not knowing too too much about the physics of electricity, but what does that do for 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?

[derekleffew]

The Dimmer Doubler Datasheet at www.etcconnect.com explains everything pretty well.