Calculating Consumption in Watts, Total System Draw

G

Gordon Brinton

Freshman
Jul 18, 2015
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Near Harrisburg, PA, USA
Is this basically the way it should be done? (I rarely ever see a clip light, so I am using 1/8 power rating for my amps.) I am in the US, so all figures are based on 120vac.

FOH/Rack:
(x2) DSR112: 1/8 power = 100w (x2) = 200w
(x2) DSR118W: 1/8 power = 100w (x2) = 200w
Ui16 Mixer: 25w
Laptop Wall Wart: 192w
(x2) EV RE2 Wireless Mic Reciever: 9w (x2) = 18w
MiPro MI-808T Wireless IEM Transmitter: 120w

Monitors/Stage Rack:
(x2) Crest Pro-Lite 3.0 DSP: 1/8 power = 200w (x2) = 400w
Behringer NU3000 DSP: 1/8 power = 125w
Behringer HA8000 Headphone Amp: 30w

Lights:
(x8) LED Lights: 60w (x8) = 480w
DMX Controller: 24w


Subtotal = 1814w

Add 10% for overhead and/or incidental extras such as phantom power, lamps, whatever = 1995 Total Consumption in Watts

Is this the correct way to figure it out? What am I missing?
 
Re: Calculating Consumption in Watts, Total System Draw

Ballpark, looks close. If you are trying to decide if you need one or two 20A circuits, since you're very close to 20% capacity, I'd plan on two to be safe.

 
Re: Calculating Consumption in Watts, Total System Draw

Where did you get the power consumption (1/8th watt) for the amps?

I did not look to find out-sorry.

If it is just the "calculated power", then that would be wrong. All electronics have idle current, that will add power consumption to the actual power output.

Also amps are not 100% efficient, so they pull more than they put out.

Also-just because the amps are not clipping does not mean they are not delivering more than you think

With some styles of music, it is quite possible to be close to full output power and still not clip the amp.

It depends on they dynamic range/crest factor of the music.

A sine wave draws and delivers quite a bit of power with a very small crest factor (3dB).
 
Re: Calculating Consumption in Watts, Total System Draw

Ivan Beaver said:
Where did you get the power consumption (1/8th watt) for the amps?

I did not look to find out-sorry.

If it is just the "calculated power", then that would be wrong. All electronics have idle current, that will add power consumption to the actual power output.

Also amps are not 100% efficient, so they pull more than they put out.

Also-just because the amps are not clipping does not mean they are not delivering more than you think

With some styles of music, it is quite possible to be close to full output power and still not clip the amp.

It depends on they dynamic range/crest factor of the music.

A sine wave draws and delivers quite a bit of power with a very small crest factor (3dB).
Click to expand...

I found each spec in the respective manuals. (See links below) The manuals for the amps actually said "1/8 power" which I understand to be at the point of clipping. Of course I understand that it is variable and subjective. I only run live bands and corporate stuff, not DJ music. I rarely push my system levels hard because I have sensitive hearing and assume that others do too. I consider 1/8 power to be a good reference point for judging where I stand as far as current draw. I just wanted to get a general idea of how many circuits I should seek out when I advance a venue or at setup time.

The DSR's are self powered. The remaining monitor amps are all operated at 8 ohms in stereo mode.

FOH, DSR112, Page 13 ---> http://download.yamaha.com/api/asset/file/?language=es&site=mx.yamaha.com&asset_id=48073
Monitors, Crest Pro-Lite 3.0 DSP, Page 35 ---> http://www.peaveycommercialaudio.com/cache/16684.pdf
Drum Monitor, Behringer NU3000 DSP, Page 19 ---> http://www.behringer.com/assets/NU6000DSP_NU3000DSP_NU1000DSP_M_EN.pdf

Thanks
 
Re: Calculating Consumption in Watts, Total System Draw

Ivan may be right...my FOH subs could very well draw more than 100 watts in the heat of battle. But on the other hand, I seriously doubt that my monitor wedges are keeping those Crest amps above 200 watts constant draw either. So, I'll consider that to be a wash.
 
Re: Calculating Consumption in Watts, Total System Draw

1/8 rated power is generally a good rough estimate of what your average power draw may look like. However, that doesn't take into account the peaks that can happen, which will draw significantly more. My new QSC amps have power meters built into them. Under most scenarios, they are drawing 2-3 amps. But it doesn't take much more and suddenly that jumps up to 12 amps. It's a pretty significant difference if you're looking at maximum possible current draw.

If you are looking at the current draw to determine how big of a circuit you should use, you are safer estimating 1/3 power instead. That gives you enough headroom in the event that things get a little louder than normal. It's also important if the cabling creates a voltage drop at the outlet. Switching supplies can keep going when voltage drops, but they draw more current to compensate. If your draw is right on the edge, that 50' of extra extension cord could be enough to push you over the edge. With the rig you have listed, I'd want 2 separate 20 amp circuits to run everything safely.

Of interesting note, the spec sheets for the DSR's say that current draw is 100w at 1/8 power, yet they list the power rating of the speaker at 1300W continuous. That math just doesn't work out. An amplifier can't produce more watts that it consumes. (it's actually joules of energy, and their calculations assume dynamic content so the amp capacitors can draw an average amount of power to build up their reserves to be used during peaks.) Anyway, if you put a continuous output at 1/8 power that drains the reserves, the amp would have to pull from the outlet to compensate for what it needs. This is extremely important to take into consideration when running from a generator. When plugged into the grid, there is more power available at the outlet for brief spikes than the breaker is rated at. The breaker will only trip when the average power exceeds the rated threshold for a period long enough to heat the breaker. Eg, if you have a kick drum hit that clips the amp, the amp could draw power for a brief moment and not trip the breaker. With a generator, that reserve does not exist. Total output power pretty much caps at the rated power, and thus those reserves are non existent. When sizing a generator, I recommend using the FULL rated power of your amplifiers so that you have plenty available. You may not need that much if you don't turn your amps to full, but on the same token, if you aren't turning your amps up to full, you could have gotten away with smaller amps too.
 
Re: Calculating Consumption in Watts, Total System Draw

Brian jojade said:
...This is extremely important to take into consideration when running from a generator. When plugged into the grid, there is more power available at the outlet for brief spikes than the breaker is rated at. The breaker will only trip when the average power exceeds the rated threshold for a period long enough to heat the breaker. Eg, if you have a kick drum hit that clips the amp, the amp could draw power for a brief moment and not trip the breaker. With a generator, that reserve does not exist. Total output power pretty much caps at the rated power, and thus those reserves are non existent. When sizing a generator, I recommend using the FULL rated power of your amplifiers so that you have plenty available. You may not need that much if you don't turn your amps to full, but on the same token, if you aren't turning your amps up to full, you could have gotten away with smaller amps too.
Click to expand...

This is good to know. I do have a portable generator, but I've never used it, (it's still in the unopened box). It is rated at...
Running Watts 3500 (They describe this as continuous draw)
Starting Watts 4375 (They describe this as short term for starting up electric motors)

It does have two 20 amp circuits and one 30 amp circuit. However, it is rated at 30 amps total output. Maybe I'll need a second one for lights and backline. If I ever need to use it, I'll be sure to downsize several things to lighten up on the overall draw. I think thatI will also invest in a good voltage stabilizer for peace of mind.

Thanks
 
Re: Calculating Consumption in Watts, Total System Draw

Gordon Brinton said:
This is good to know. I do have a portable generator, but I've never used it, (it's still in the unopened box). It is rated at...
Running Watts 3500 (They describe this as continuous draw)
Starting Watts 4375 (They describe this as short term for starting up electric motors)

It does have two 20 amp circuits and one 30 amp circuit. However, it is rated at 30 amps total output. Maybe I'll need a second one for lights and backline. If I ever need to use it, I'll be sure to downsize several things to lighten up on the overall draw. I think thatI will also invest in a good voltage stabilizer for peace of mind.

Thanks
Click to expand...

Gordon, what kind of generator is it? Unless it's a quiet inverter type such as the Honda EU series, you'll want to leave it in the box. Conventional generators are gig-ruiningly loud, and generally have poor voltage and frequency regulation. A voltage regulator won't fix all of that. Conversely, a Honda EU series generator doesn't need any outboard voltage regulation, are reliable, and sound like someone a block away is mowing their lawn.

On power draw - if the 1/8 power number comes from the manual, this will include the amp's idle current as well as the averaged peak current assuming you do not clip the amp. Some types of music may effectively be over the 1/8 power level even without clipping, but for most styles, the 1/8 power figure is a good number.

As to the number of circuits to use - if two are available, always use two. Less voltage drop means more performance from your amps. In a pinch you can probably fit on one as long as you're sure you get the whole circuit and aren't sharing it with the beer cooler.
 
Re: Calculating Consumption in Watts, Total System Draw

And to muddy the waters a bit, if you are running these calculations to determine what size power distribution you need (how many circuits of what size), it's best to use the current draw on the equipment, not the power consumption. This is because many pieces of equipment have non-unity power factor, and that can require more current available than the power consumption would indicate.
 
Re: Calculating Consumption in Watts, Total System Draw

Rob Timmerman said:
And to muddy the waters a bit, if you are running these calculations to determine what size power distribution you need (how many circuits of what size), it's best to use the current draw on the equipment, not the power consumption. This is because many pieces of equipment have non-unity power factor, and that can require more current available than the power consumption would indicate.
Click to expand...

yep, current draw rather than watts, is the issue in sizing....here's a pretty good article.... http://electronicdesign.com/energy/what-s-difference-between-watts-and-volt-amperes

I noticed in the link and page provided by OP (good help) for the crest 3.0 dsp amp at 1/8th power...that VA is 400 @8 ohms, vs 200 wattage.
 
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