Dimmer Doublers and an MPE

[tayklor]

I did some searching and I couldn't find anything that answered my question.

I've been working with a small community theatre company for a while now, helping with lighting and electrics. This coming year we're looking to make some upgrades to our dimming system.

The space is a very small black box (30'x44' for the main room), seating around 60, and normally set up in a 3/4 thrust configuration.

Right now, we have a 24x2.4k Sensor system housed in a 12 space Sensor 1 install rack. It has an MPE for control, receiving DMX from an Insight 2. We want to increase our dimming capacity, as 24 is always a little short.

We were toying around with the idea of buying used dimmer doublers. We have 10 Source Four Jr. Zooms, 6 S4 PARs and a bunch of older fresnels and ellipsoidals. The intention would be to double all of the ETC fixtures and leave the others at 120v (because we have to). This would involve 8 doublers. Our dimmers are wired to pigtail boxes, which move around all the time (nearly every show). We rehang for every show.

This leads to the question: how does doubling work on an MPE control card? Would we be able to easily move doublers around, or would they be fixed to certain dimmers? I understand how doublers work, and have used them in another venue I occasionally work in, however, this space has CEM-controlled racks and a repertory plot.

[sk8rsdad]

If the manual is to be believed, the MPE uses DIP switch 4 to enable dimmer doubling for all the modules in the rack, rather than on any individual module. You should contact ETC support to get a definitive answer and discuss the options for an in-field upgrade from MPE to CEM.

[doctrjohn]

Hmm... This wouldn't happen to be Broom Street Theater, would it?

Best,
John

[JD]

If you switch the whole rack to Dimmer Doubling, you can still run conventional 120 volt fixtures, here's how and why:

Each current dimmer channel ends up becoming two channels. One outputs the + section of the waveform, the other outputs the - section. The divider that goes next to the fixtures is simply a diode box. To run a conventional, you must group those two channels back together via a soft patch at the board.
There is a failsafe by design:

The doubler dividers go at the fixture end of the run and divide up the + and - waveform sections. If you were to accidentally plug a doubler into un-switched power, each fixture connected would still only get half the waveform, and the 77 volt lamps would light at full brightness. No damage done.

Conversely, If you were to plug a conventional fixture (120 volt) into one of the dimmers set to doubling, and not bring up both sub channels, the lamp would simply only get to half brightness. Again, no damage done.

The output of the divider is a twist-lock connector and your fixtures with 77 volt lamps should also be equipped with twist-lock so that they do not get plugged into a 120 volt source. The trick with a mixed environment is to make sure the 77 volt lamps don't end up in fixtures that can be plugged into 120 volts! Your concept of converting only one type of fixture for use should help simplify that.

[derekleffew]

If you switch the whole rack to Dimmer Doubling, you can still run conventional 120 volt fixtures, here's how and why: ...
Conversely, If you were to plug a conventional fixture (120 volt) into one of the dimmers set to doubling, and not bring up both sub channels, the lamp would simply only get to half brightness. Again, no damage done. ...

So, JD, your solution is to set the entire rack to DD, and then for the 120V circuits without a DimmerDoubler™ installed, at the console, softpatch both sides (A&B or n & n+256) into the same control channel so both sides always run together?

Neat trick! ETC folks, will this work?

[DavidNorth]

Yes, JD and Derek are correct. Place the MPE in DD mode, which DDs every dimmer, and then either double patch or split patch depending on whether you use 120V or 77V lamps.

I highly suggest that the 77V lamp caps have the correct L5-15 placed on them so as not to accidentally send 120V into them when moving fixtures around.

This is a very good solution to get more control out of existing circuits.

David

[mstaylor]

Is there constant, nondim power on the electric anywhere. If so couldn't you use shoebox dimmers to augment your dimmers. I think the doubling/undoubling is a viable and interesting solution. The only problem is it doesn't give you any more control, just control over more instruments, if I understand DD correctly.
Edited to add:
I didn't understand the control side, if you understand how to do it, ignore my suggestion. My suggestion is good if you can't find any DDs used.

[rochem]

The only problem is it doesn't give you any more control, just control over more instruments, if I understand DD correctly.

Dimmer doubling is great when you have a bunch of lights that you want single circuited - you can get twice as many instruments onto the same number of dimmers and have individual control over every one. However, if you routinely have 3 or more units that you want to put on the same dimmer, DD can be annoying because you can't twofer into a dimmer-doubled circuit, so you end up using more dimmers than you otherwise would need to.

[mstaylor]

Dimmer doubling is great when you have a bunch of lights that you want single circuited - you can get twice as many instruments onto the same number of dimmers and have individual control over every one. However, if you routinely have 3 or more units that you want to put on the same dimmer, DD can be annoying because you can't twofer into a dimmer-doubled circuit, so you end up using more dimmers than you otherwise would need to.

Yeah, I went and read about it. I understood what they were doing on the light end, I just didn't understand how it worked, control wise, on the dimmer end. I have some other questions but I will start a new thread so I don't steal this thread.

[xander]

However, if you routinely have 3 or more units that you want to put on the same dimmer, DD can be annoying because you can't twofer into a dimmer-doubled circuit, so you end up using more dimmers than you otherwise would need to.

That's not true. You can two-fer into a DD. You have to be careful because it does not magically give you more than 2.4kw on the whole dimmer, but you can two-fer.

-Tim

[rochem]

That's not true. You can two-fer into a DD. You have to be careful because it does not magically give you more than 2.4kw on the whole dimmer, but you can two-fer.

-Tim

Really? I was always told that you couldn't due to something to do with different RMS values, even though the math technically says you should be able to, and I've never really needed to explore it any further. Can you two-fer into both sides of a DD at once, for a total of 4 lamps on one dimmer, or can you only double on one at a time, for a total of 3 lamps on one dimmer? Thanks!!

[sk8rsdad]

Theoretically, it is possible to twofer both upstream and downstream of the DD. On the upstream side it would get expensive since you need multiple DDs.

The total load must be no more than half rated power of the D20 on either leg; that is, 1200 W per leg. So, 2 instruments lamped with 550W/77V lamps per leg, for a total of 4 lamps per dimmer is the operating maximum. If there were a 375W/77V lamp option then you could get 6 lamps on a D20, but there isn't so you can't.

Imbalance between the A/B legs is not an issue. There is no requirement to use both A and B sides of the DD. A DD is little more than a pair of diodes with a massive heat sink.

[derekleffew]

That's not true. You can two-fer into a DD. ...

I believe this was changed somewhere along the way. ETC now recommends only one (77V HPL575 or 750W) lamp per side of a Dimmer Doubler™.

...From DimmerDoubler_vF.pdf:

How many 77V lamps can I use with a Dimmer
Doubler?
You can place a total of two 550W, 77V lamps on a Dimmer Doubler,
one on each side.

(Documentation has not been revised to take into consideration the 77V HPL750 lamp.)

-----

Is there constant, nondim power on the electric anywhere. If so couldn't you use shoebox dimmers to augment your dimmers. ...

The problem with this "scheme" is that when mixing Sensor and shoebox dimmers, they won't have the same dimmer curve or response time, which can prove infuriating. Most inexpensive dimmers have horrid curves, see Dimmer voltage experiment .

[JD]

Inside the "power cube" are two SCRs operating back to back.* The cube is rated for a 20 amp, 2.4kw load with each SCR handling 1200 watts or 10 amps prorated as they only get 1/2 of the waveform. (I am sure the SCR has a higher rating, but the package rating takes into effect what heat must be dissipated.) If you were to put two 750 watt loads on one side of a DD output, then the SCR handling that side of the waveform would have a full-wave equivalent of 3000 watts, which is higher then the device rating. Even though the dimmer is rated at 2.4kw, and 1500 watts will not trip the breaker, you are stressing the part harder then it was designed to be stressed. I am sure ETC builds headroom into their product, but it's a pretty safe bet that you will shorten the life of the cube. On the other hand, it is a sure bet you are operating outside of the warranty of the dimmer!

(*= Yes, I know, some cubes actually use a triac. Same rule applies.)

[mstaylor]

I believe this was changed somewhere along the way. ETC now recommends only one (77V HPL575 or 750W) lamp per side of a Dimmer Doubler™.



(Documentation has not been revised to take into consideration the 77V HPL750 lamp.)

-----
The problem with this "scheme" is that when mixing Sensor and shoebox dimmers, they won't have the same dimmer curve or response time, which can prove infuriating. Most inexpensive dimmers have horrid curves, see Dimmer voltage experiment .

Valid point about the dimming curve, it was a fallback suggestion, in case he couldn't lay his hands on the DDs.

[rochem]

I believe this was changed somewhere along the way. ETC now recommends only one (77V HPL575 or 750W) lamp per side of a Dimmer Doubler™.

Wait, so now I'm confused. So according to the Dimmer Doubler manual and spec sheet that I just downloaded, you cannot twofer into a dimmer doubler, which is what I've always thought, but it sounds like you guys have all done this in the past. However, neither the spec sheet nor the manual refers to anything other than the HPL550/77(X), so I'm not sure how accurate this document really is. So why the change? Did something change about more recent DD devices that makes twofering inadvisable? Is it still something that you can do safely, but ETC just recommends that you not to make things simpler? Was it always a bad idea, but people just did (and continue to maybe?) do it anyway?

And finally, is there any sort of updated document that talks about the 750/77 lamp? Until I saw one spec'd on a plot very recently, I never knew that there were 77v lamps other than the 550, and even now, I've never seen any kind of documentation that talks about their existence or use.

[sk8rsdad]

And finally, is there any sort of updated document that talks about the 750/77 lamp? Until I saw one spec'd on a plot very recently, I never knew that there were 77v lamps other than the 550, and even now, I've never seen any kind of documentation that talks about their existence or use.

The Source Four Revolution uses a 750W/77V lamp.

[JD]

This might be more about the wisdom of using a twofer when the power is -not- standard 120 volts. (The output of the DD module is pulsed DC.) Great for controlling two fixtures that are near each other independently, but once you start making up extensions and twofers, how long will it be before someone starts using stage pin adapters so they can take advantage of their existing inventory of extensions? You can guess what would happen next.

I think this is more about keeping it simple. I don't think there is any harm in using two 550 watt lamps on one leg as the total is 1100 watts. Still, I defer to ETC's recommendations as they underwrite the warranty.

[Malabaristo]

Wait, so now I'm confused. So according to the Dimmer Doubler manual and spec sheet that I just downloaded, you cannot twofer into a dimmer doubler, which is what I've always thought, but it sounds like you guys have all done this in the past.

The problem is that you can't just add the total wattage of the lamps in order to calculate the total load on the circuit. With (4) 550W lamps you end up with a total of about 20.2A. This puts you in a fuzzy range where the breaker may or may not trip depending on its tolerances. In some cases you can get away with it, but it's not always a safe* bet.


(*safe in the sense of working reliably. The worst that would happen is that the breaker might trip.)