David Ashton
Well-Known Member
Steve, could we have some examples of 2.4k dimmers which only take 1.9k as I've never come across any in Australia?.
Is it acceptable to put 4x S4s on a dimmer?
- Thread starterderekleffew
- Start date
I prefer Mike Wood's formulae, detailed here: http://www.controlbooth.com/forums/collaborative-articles/7664-mathematical-formulas-lighting.html.
Here's a follow up question:
Given four fixtures with HPL575/115 lamps; which of the following currents would flow through the dimmer?
a) 19.2A
b) 20.0A
c) 20.8A
d) 24.8A
For our International contingent, I'm speaking only of US practices and theories, where supply voltage is based on 120V.
STEVETERRY
Well-Known Member
Any Lutron dimmer, and there are probably others that use thermal/magnetic breakers. This would be especially true in 230V markets where ABB or Merlin-Gerin standard thermal magnetic breakers are normal in a lot of dimmers.
BTW, that's 1920W continuous, which means three hours or more. We assume loads in the theatre to be continuous in the US, simply because they can be.
Also, long tradition has dictated that professional theatrical dimmers be rated at 100% loading, using fully magnetic breakers.
ST
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Pip
Active Member
Crap... ^^ I checked my math... O noes! What did I do? *shakes head*
As I said in an earlier post Pip...reread the original question. There's a very important piece to this puzzle you're walking right over.
Here's a hint, your answer to Derek's question would be A).
And for the record it would be wrong.
Also for the record. 4 HPL 575w 115v lamps on a 20a 2400w dimmer is a bad idea.
(((psssst Pip! all the information you need is in the previous sentence)))
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I was always taught never to load a breaker at more than 80% of its rated capacity so I would say "no," but from the various posts here, I could be wrong.
When I worked at Colortran our resident electrical guru (this guy was one of the guys on the panel that wrote the theatre section of the NEC) explained that we used magnetic breakers because they have a built-in time delay (governed by how long the magnetic field in a coil takes to pull a slug through some sort of goo. When the slug reaches its limit of travel it pushes a button (or lever) and trips the breaker. A spring then pulls the slug back to its starting point). I don't know if we used breakers that were thermal as well, but vaguely recalling a discussion I had with said guru, I doubt it
Les
Well-Known Member
Said by STEVETERRY himself
STEVETERRY
Well-Known Member
Unless it's an ETC Sensor
Guys, what you are missing here is that a dimmer rated for 120V nominal does not deliver 120V at the outlet. You have the drop across the SCR, the choke, and the cable run to the outlet. That is precisely why a 575W HPL lamp is rated at 115V--so that you can get the expected lumen output and color temperature despite those voltage drops.
So, 4x575W 115V lamps on a 120V 20A dimmer rated for continuous full loading is just fine--as long as you don't exceed 115V at the outlet. And that would be hard to do without a line voltage higher than 120V.
ST
timeblazer
Member
McCready00
Active Member
I might be wrong here, but depending of the type of dimmer you are using, there is a heat dessipation consideration:
1. Portable Triac Based Dimmer : 2%
2. Thyristor Based Dimmer : 2.5%
3. IGBT or Sine Wave Based Dimmer : 3%
1. 2400W x .02 : 48W --- 2352W
2. 2400W x .025 : 60W --- 2340W
3. 2400W x .03 : 72W --- 2328W
575W x 4 : 2300
And as said before in this thread, the ETC Sensor Module will take 100% of the load:
CIRCUIT BREAKERS : Fully magnetic to eliminate nuisance tripping
20x inrush current rating
125%, 10-120 seconds, must- trip rating
Rated for 100% switching duty applications at
full load
I would not use it for an important event even though I still think it is safe. There is many factors inside the dimmer that can play with the numbers. So, I would use it for a small event but I would better play safe if I needed for something important.
Please kids, play safe !
1. Portable Triac Based Dimmer : 2%
2. Thyristor Based Dimmer : 2.5%
3. IGBT or Sine Wave Based Dimmer : 3%
1. 2400W x .02 : 48W --- 2352W
2. 2400W x .025 : 60W --- 2340W
3. 2400W x .03 : 72W --- 2328W
575W x 4 : 2300
And as said before in this thread, the ETC Sensor Module will take 100% of the load:
CIRCUIT BREAKERS : Fully magnetic to eliminate nuisance tripping
20x inrush current rating
125%, 10-120 seconds, must- trip rating
Rated for 100% switching duty applications at
full load
I would not use it for an important event even though I still think it is safe. There is many factors inside the dimmer that can play with the numbers. So, I would use it for a small event but I would better play safe if I needed for something important.
Please kids, play safe !
renegadeblack
Active Member
And after the first 5 times, it still doesn't work!Excuse me for butting in, but if I may, I'll drop some info that may answer the question.
A HPL575/115 lamp is "factory rated" to draw 575 WATTS at a line voltage of 115 VAC. Given that information, we can figure operating amperage of 5 AMPS and the resistance of the filament to be 23 OHMS when hot.
Now if your line voltage is 120 VAC, the current goes to 5.21 AMPS and the wattage increases to 625 watts.
If you are one of the lucky ones with a stiff power grid and run 125 Volts, then the current will run up to 5.43 amps, and the wattage will be a whopping 678 WATTS!
Now if you are running the lamps at less than 100% or you have your dimmers trimmed, or you don't pull them up to full immediately and you are running a preheat setting, you may get by running 4 fixtures.
Otherwise the full load at higher line voltages or the inrush current on cold filaments will most likely cause you trouble.
Had it happen on a stage where we had 4 575/115 watt lamps and kept tripping the breaker. If you ran the fader up slow it would hold, but if you ramped up fast, it would trip everytime. I have a factory note fron Leprechan about this very problem running 3 fixtures on a pack with a 15 amp cord on it. They were concerned about three lamps pulling over 16 Amps.
I'm pretty sure that Osram has 120 volt rated lamps for the S-4 fixtures and that may be an out if you have problems.
Break a leg!
A HPL575/115 lamp is "factory rated" to draw 575 WATTS at a line voltage of 115 VAC. Given that information, we can figure operating amperage of 5 AMPS and the resistance of the filament to be 23 OHMS when hot.
Now if your line voltage is 120 VAC, the current goes to 5.21 AMPS and the wattage increases to 625 watts.
If you are one of the lucky ones with a stiff power grid and run 125 Volts, then the current will run up to 5.43 amps, and the wattage will be a whopping 678 WATTS!
Now if you are running the lamps at less than 100% or you have your dimmers trimmed, or you don't pull them up to full immediately and you are running a preheat setting, you may get by running 4 fixtures.
Otherwise the full load at higher line voltages or the inrush current on cold filaments will most likely cause you trouble.
Had it happen on a stage where we had 4 575/115 watt lamps and kept tripping the breaker. If you ran the fader up slow it would hold, but if you ramped up fast, it would trip everytime. I have a factory note fron Leprechan about this very problem running 3 fixtures on a pack with a 15 amp cord on it. They were concerned about three lamps pulling over 16 Amps.
I'm pretty sure that Osram has 120 volt rated lamps for the S-4 fixtures and that may be an out if you have problems.
Break a leg!
Benchtech, that would be true if a lamp were ohmic. It's not. As you up the power being dissipated, the internal temperature increases - which is the colour temp change we see and as the temperature changes, the filament resistance changes, a higher resistance at a higher temperature. This then drops the current flow back, you have a negative feedback cycle. It will find an equilibrium at some point, but it most certainly will not be at the linear ohmic value you calculated...
