ProSoundWeb Community

Please login or register.

Login with username, password and session length
Advanced search  

Pages: [1]   Go Down

Author Topic: Power requirement guesstimating?  (Read 439 times)

Tim Hite

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 808
    • Bad Quail
Power requirement guesstimating?
« on: June 26, 2020, 10:39:11 pm »

What's rule of thumb for estimating power needs for powered speakers in order to size a generator?

Thinking 1/8 RMS wattage?

Suggestions?
Logged
Bad Quail
Sound + Light
Joshua Tree, California
Authorized Dealers for all this stuff

Tim McCulloch

  • SR Forums
  • Hero Member
  • *
  • Offline Offline
  • Posts: 21503
  • Wichita, Kansas USA
Re: Power requirement guesstimating?
« Reply #1 on: June 27, 2020, 02:23:06 am »

I like headroom in my genset.  I use 1/3.
Logged
"Practicing an art, no matter how well or badly, is a way to make your soul grow, for heaven's sake. Sing in the shower. Dance to the radio. Tell stories. Write a poem to a friend, even a lousy poem. Do it as well as you possible can. You will get an enormous reward. You will have created something."  - Kurt Vonnegut

Geert Friedhof

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 643
Re: Power requirement guesstimating?
« Reply #2 on: June 27, 2020, 08:11:31 am »

Diesel gensets don't like to run at light loads for a longer time. A fenomenon called 'Wet Stacking' can occur, which can lead to a lot of problems.

Sound is a very dynamic load, so you should use a ballast load, like some tungsten lights or HIT moving lights, to keep a minimum constant load above 25-30%. I use 1/4 to 1/3 RMS for the soundsystem. So about 1/3 Pmax(genset) for both loads. You also have to consider the powerfactor, which will be 1 with resistive loads, but can be as low as 0.5 with other loads. I like to use a powerfactor of 0.75 for soundsystems.
Gensets are rated in kVA. kVA=Watts*powerfactor.

When you do the math the genset should be the RMS power of the soundsystem devided by the powerfactor, which leads to kVA(genset)=RMS(soundsystem)*1.33.

So a 20kW(rms) soundsystem would need a 27kVA genset, with a 8kW ballast. This leaves you at least 1/3 headroom. Don't forget to add other loads.
Logged

Paul G. OBrien

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1065
Re: Power requirement guesstimating?
« Reply #3 on: June 27, 2020, 10:01:18 am »

Use the combined power output ratings of the speakers and add the continuous load of an small signal electronics and lighting.
Here is why. Modern powered speakers use class D amplifiers with switch mode power supplies that typically have relatively little energy storage capacity so current draw from the AC supply source will tend to be peaky. The typical 1/8 and 1/3 power consumption ratings completely ignore the peak draw partially because this doesn't matter when connected to the grid as it has massive peak supply capacity, but you have to cover that peak draw when on a generator or it will simply shut down. So you will need a bigger generator than a 1/8 rating would suggest but you don't need a tow behind diesel and load bank for a couple SOS either.
« Last Edit: June 27, 2020, 10:03:31 am by Paul G. OBrien »
Logged

Tim Hite

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 808
    • Bad Quail
Re: Power requirement guesstimating?
« Reply #4 on: June 27, 2020, 03:23:31 pm »

I like headroom in my genset.  I use 1/3.

Just dial in the headroom you need with the voltage regulator. . .
Logged
Bad Quail
Sound + Light
Joshua Tree, California
Authorized Dealers for all this stuff

Caleb Dueck

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1285
Re: Power requirement guesstimating?
« Reply #5 on: June 27, 2020, 04:52:46 pm »

Modern powered speakers use class D amplifiers with switch mode power supplies that typically have relatively little energy storage capacity so current draw from the AC supply source will tend to be peaky.

Small side comment - this is true for older/cheaper amps, but most of the current higher end amplifiers have PFC to keep the power draw from being as peaky.  It's also less of an issue for large systems when the loads are balanced across the phases.  For small SOS type systems - yes it is something that needs to be kept in mind, especially for subwoofers.
Logged
Experience is something you get right after you need it.

Tim McCulloch

  • SR Forums
  • Hero Member
  • *
  • Offline Offline
  • Posts: 21503
  • Wichita, Kansas USA
Re: Power requirement guesstimating?
« Reply #6 on: June 27, 2020, 10:44:25 pm »

Just dial in the headroom you need with the voltage regulator. . .

Conflating current with voltage?
Logged
"Practicing an art, no matter how well or badly, is a way to make your soul grow, for heaven's sake. Sing in the shower. Dance to the radio. Tell stories. Write a poem to a friend, even a lousy poem. Do it as well as you possible can. You will get an enormous reward. You will have created something."  - Kurt Vonnegut

ProSoundWeb Community

Re: Power requirement guesstimating?
« Reply #6 on: June 27, 2020, 10:44:25 pm »


Pages: [1]   Go Up
 



Page created in 0.04 seconds with 22 queries.