dimmer pack question...power limits...(total newbie!!)

[allank44]

hi all...total newbie here again...

Here's the deal...we've got a dimmer pack (have a DMX 512 controller to run it...so all good)

The dimmer pack is rated at 5A per channel (it's a 4 channel) and 15A total...

SO...we'd like to run 2 source 4 750s on that pack.

If I'm doing my math right one 750 would draw 6.25 amps...therefore 2 750s would draw 13A.

SO...we're alright for the total rating on the pack but a bit over on the per channel rating.

I'm thinking 1.25 amps over and I'm hoping that's doable...

OR...to be safe we relamp down to 575 watts...4.75 amps and all is well.

Are we on the right track??

TIA...(this site is great!!)

 

[derekleffew]

... The dimmer pack is rated at 5A per channel (it's a 4 channel) and 15A total... SO...we'd like to run 2 Source Four 750s on that pack. ... I'm thinking 1.25 amps over and I'm hoping that's doable. ...

No.

...OR...to be safe we relamp down to 575 watts...4.75 amps and all is well. ...

Yes.

...(this site is great!!)

Many of us here like to think so.

 

[techieman33]

I would call the manufacturer, you may be able to run the 750's. We rented some dimmers for a small gig and they were similarly rated and I didn't have any lamps with a low enough wattage to fit the specs. So I called the guy we rented from and he called the manufacturer and they gave the ok to run the higher wattage lamps as long as we didn't go over the total rating of the packs. They might shoot that idea down but it could be worth the call.

 

[Les]

Yeah, most of those packs don't take very well to be loaded to their limit (or even slightly under in some cases), so exceeding the limit will likely get you. Two fixtures at 575w is about all I'd trust -- any more is kind of a roulette-type of thing.

 

[mstaylor]

I agree with Les, it might work but do you want to find out it doesn't in the middle of a show? I would lamp at 575 and be safe. This is a good site to help with your questions.

 

[derekleffew]

... and he called the manufacturer and they gave the ok to run the higher wattage lamps as long as we didn't go over the total rating of the packs. ...

I don't suppose anyone was willing to put that in writing? It seems to be a particularly egregious statement, especially coming from a manufacturer. Each dimmer channel's OCPD is sized for an intended maximum load. Purposefully exceeding that load is playing with fire, literally. It also voids the UL Listing--not that many dimmer, shoebox are listed, by NRTL in the first place.

-----

I found a peculiar statement on my shoebox dimmer pack. A well-known brand, but perhaps the least expensive pack on the market. It came with a 14/3 SJTW 5-15P to IEC (C13 / 60320) power cord. It uses one "F10A 125V 5x20mm" fuse per channel (4).

CAUTION!
Rick of Electric Shock.
DO NOT OPEN.
This product must not be continuously
used for a long time under 15A
total output load.

Bad translation, anyone?
Would I risk a show running two 750W lamps on this pack? No way. Even though the pack tells me I could.

 

[JDurnford2011]

"... The dimmer pack is rated at 5A per channel (it's a 4 channel) and 15A total... SO...we'd like to run 2 Source Four 750s on that pack. ... I'm thinking 1.25 amps over and I'm hoping that's doable. ...
No.

Quote Originally Posted by allank44 View Post
...OR...to be safe we relamp down to 575 watts...4.75 amps and all is well. ...
Yes.

Quote Originally Posted by allank44 View Post
...(this site is great!!)
Many of us here like to think so. "

I can second that. Its not safe to go over in amps as you will fry something if the breaker doesn't go off though it probably will unless the dimmers broken.

You would be better off lamping down to 575w.

-
Justin Durnford

 

[RickR]

I found a peculiar statement on my shoebox dimmer pack. A well-known brand, but perhaps the least expensive pack on the market. It came with a 14/3 SJTW 5-15P to IEC (C13 / 60320) power cord. It uses one "F10A 125V 5x20mm" fuse per channel (4).

Bad translation, anyone?
Would I risk a show running two 750W lamps on this pack? No way. Even though the pack tells me I could.

Could this be related to the definition of "Continuous use"? Some items (like standard circuit breakers) are only good for 3 hours at the nominal rating. It only takes one weak link in the chain...

 

[allank44]

thanks all for the advice...we're not ones to push the limits..not when it comes to electrics and lighting!!

So..we go down to the 575W lamps.

BUT...is my math correct?...would a 750W S4 draw 6.25 amps?...all things being equal.

AND..therefore we'd need a dimmer pack rated at say, 10amps and 2400W total..which seems to be what's available as the next step up??

(and again..a great site!!)

Mark aka allank44

 

[JD]

thanks all for the advice...we're not ones to push the limits..not when it comes to electrics and lighting!!

So..we go down to the 575W lamps.

BUT...is my math correct?...would a 750W S4 draw 6.25 amps?...all things being equal.

AND..therefore we'd need a dimmer pack rated at say, 10amps and 2400W total..which seems to be what's available as the next step up??

(and again..a great site!!)

Mark aka allank44

6.25 amps would be the run current for a 750 lamp running at 120 volts. Inrush is much higher, but most dimmers are designed to deal with the expected inrush for their rating.

Common dimmer sizes are (were) 1.2kw (10 amp), 2.4kw (20 amp), 3.6kw (30 amp), 4.8kw (40 amp), and so on. These days, 2.4kw is the most common. Most likely due to the DPC (Dimmer Per Circuit) mentality that started back in the 80's. This size has some inherent advantages:
1) 20 amps is what 12AWG wire handles, and minimum extension gauge in theater is 12/3 S cable. In other words, you would still have to use that size even if the dimmer was smaller.
2) 20 amps gives you some wiggle room in the DPC layout as you have room to load a few more fixtures on a dimmer if needed.
3) Dimmers larger than 20 amps would require the complete run to all fixtures to be upgraded to a heavier cable, or would required secondary breakers to limit the dimmer-fixture runs to 20 amps.

There are still some loads out there that require a bigger dimmer, but with fixtures becoming more efficient, the trend still pushed toward 2.4kw. For example, most of the old fixtures I dealt with in the 80's were 750 watts or 1k. These days, a 575 watt S4 puts out more light then the old 750-1000w clunkers.

 

[allank44]

thanks...great answer..but a follow up question..

A 4 channel pack is rated at, as an example, 10 amp per channel but 20 amp overall.

How so?...shouldn't it be rated for 40 amps -- 10 x 4??

I admit ignorance upfront...so is it a question of safety or a question of electrical logic, so to speak.

Mark

 

[Les]

You'd think so, huh. I believe the overall limiting is based on the capacity of the power cord and power supply inside the pack. If you ever opened one up, you'd see why it could be a bad idea to run 40 amps through it ;-).

 

[derekleffew]

... A 4 channel pack is rated at, as an example, 10 amp per channel but 20 amp overall.
How so?...shouldn't it be rated for 40 amps -- 10 x 4?? ...

Les is correct. Total of the pack is limited by the power cord and load connector used. Most, if not all 4 x 10A dimmer, shoebox (like mine) have a male 5-15P, and thus are limited to 15A total. It's best to pretend that all packs of the type are 4x600W, and even then, don't load up all four channels with 500 or more watts if you know you're going to need all four dimmers on at the same time.

At the other end of the spectrum is the ETC Sensor SP6 dimmer pack (either 12x20A, 6x50A, or 3x100A) that has 3x 400A hot male connectors (E1016 Cam-lok). But there's no appropriate multi-pole connector in the 3x100A range. (No one likes the pin and sleeve connectors, they tolerate them for some applications, but no one "likes" them.)
.

 

[DavidNorth]

thanks...great answer..but a follow up question..

A 4 channel pack is rated at, as an example, 10 amp per channel but 20 amp overall.

How so?...shouldn't it be rated for 40 amps -- 10 x 4??

The one really nice thing about having a per circuit rating of 10A, is that if for some reason you need to put a heavy load on a pack that is near 10A, you can do that, and then lightly load the rest of the pack. With dimmers that are 600W max each, you are limited by how you can distribute that power.

Have fun with your lighting!

David

 

[len]

We use shoebox dimmers all the time. Several factors (and there will be more) come to play.
1. Obviously, the rating of the dimmer pack and its cord limit capacity. If it's 600 watts, per channel, that's it. The cord is probably only rated for 15 amps, so don't cheap out, use a max of 2 x 575 watt lamps, and that's it. Need more? Getter a better pack or more packs.

2. Most shoebox dimmers have an edison plug on them. So if the wall outlet is 15 amps, that's the most you're going to get anyway. There are Leprecon and other brands which can be plugged into two, separate, 15-amp circuits, Leprecon ULD-360 & ULD-340 Dimmers but since the original poster didn't specify those I'm assuming he's using a product that has less capacity than that.

3. Even if you find a 20-amp circuit, so what? Is that full 20-amps available and exclusively for that pack? Probably not. If one part of the system is rated for 15-amps (back to the pack power cord again) that's what's available. And even so, if there are other draws on that circuit, you don't get the full capacity of that circuit anyway.