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Author Topic: Counting Power Draw from PA system  (Read 15857 times)

Chris Hutagalung

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Counting Power Draw from PA system
« on: July 29, 2014, 11:02:18 pm »

Hi folks,

I am a newbie here and I need some guidance on power wattage since I want to start a new sound rental company and i need to have some good knowledge about power. I hope people here can help me and I really appreciate that.

So in my country we need to have our own power generator since most of venues here they dont let use their mains.

My starting setup would be JBL PRX series consisting 2 JBL PRX712 and 2 PRX718XLF Sub. All of them rated on 1500W per unit. How do I count the power draw to determine which generator should i buy.

Thank you so much guys,
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TJ (Tom) Cornish

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Re: Counting Power Draw from PA system
« Reply #1 on: July 29, 2014, 11:08:05 pm »

Hi folks,

I am a newbie here and I need some guidance on power wattage since I want to start a new sound rental company and i need to have some good knowledge about power. I hope people here can help me and I really appreciate that.

So in my country we need to have our own power generator since most of venues here they dont let use their mains.

My starting setup would be JBL PRX series consisting 2 JBL PRX712 and 2 PRX718XLF Sub. All of them rated on 1500W per unit. How do I count the power draw to determine which generator should i buy.

Thank you so much guys,
The output power rating doesn't necessarily relate to the current consumption of the device. Most speakers and amplifiers have an input power rating in the specs that is a better number to use. The 1/8th power value is usually a good place to start If that is specified.

What country do you live in and what types of generators are available?
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Chris Hutagalung

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Re: Counting Power Draw from PA system
« Reply #2 on: July 29, 2014, 11:16:43 pm »

The output power rating doesn't necessarily relate to the current consumption of the device. Most speakers and amplifiers have an input power rating in the specs that is a better number to use. The 1/8th power value is usually a good place to start If that is specified.

What country do you live in and what types of generators are available?

I live in indonesia where voltage is 220 and I see a lot of honda generators with the most common are 5,5 kVa
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Brian Jojade

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Re: Counting Power Draw from PA system
« Reply #3 on: July 30, 2014, 01:27:00 pm »

The problem with using speakers/amps on a generator is that they are not a consistent draw device.  With most common generators, when you put more load on them, they will ramp up to accommodate that load.  With things like lights, that works great.  With audio, the problem is, by the time the generator ramps up, the amplifier no longer needs that load.   Making sure you have good voltage regulation is key on a generator.

When working with speakers, the average power draw is going to be pretty low, but the peak draw can be much higher.  When plugged into a traditional outlet, there is extra reserve power available from the grid that can far exceed even the rated power of the breaker for short periods.  i.e., if your average draw is 10 amps, but you need 25 amps for a brief second, a 20 amp circuit will not trip.  On a generator, that unlimited reserve is not there unless you significantly size the generator appropriately.

So, as a general rule of thumb, I like to match my generator to whatever the rated power of the amps will be.  So, with your 4 1500 watt speakers, I'd want a 6000 watt generator.  Sure, you could probably plug all 4 speakers into a 20 amp circuit (at 120V, which is 2400 watts) and it would work fine.  Generators you want more headroom.
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Brian Jojade

Joe Brugnoni

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Re: Counting Power Draw from PA system
« Reply #4 on: August 06, 2014, 04:21:52 pm »

Hi folks,

I am a newbie here and I need some guidance on power wattage since I want to start a new sound rental company and i need to have some good knowledge about power. I hope people here can help me and I really appreciate that.

So in my country we need to have our own power generator since most of venues here they dont let use their mains.

My starting setup would be JBL PRX series consisting 2 JBL PRX712 and 2 PRX718XLF Sub. All of them rated on 1500W per unit. How do I count the power draw to determine which generator should i buy.

Thank you so much guys,
For what its worth,, I have a bunch of K 12 stuff,,, 6 tops and 2 subs.. I routinely run the entire system off one 15 or 20 amp 110 circuit with no issues.. I try to find two and will use two but Just did a gig this weekend with a loud band and kicked it hard on one circuit
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Brian Jojade

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Re: Counting Power Draw from PA system
« Reply #5 on: August 07, 2014, 01:54:47 pm »

For what its worth,, I have a bunch of K 12 stuff,,, 6 tops and 2 subs.. I routinely run the entire system off one 15 or 20 amp 110 circuit with no issues.. I try to find two and will use two but Just did a gig this weekend with a loud band and kicked it hard on one circuit

But what needs to be considered is the peak power draw.  When plugged into an electrical service, there is a mighty reserve hanging out in the grid.  The breaker will trip when the average power exceeds the breaker rating for a period of time.  There could be short draws of power that far exceed the breaker rating.

With a generator, there is no such reserve there.  If you need a peak draw of 25 amps to create that bass note, the wall outlet will have it available, but the generator won't. The result is less power available for the amp, and possibly a significant voltage drop causing all sorts of other issues.
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Brian Jojade

Robert Piascik

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Re: Counting Power Draw from PA system
« Reply #6 on: August 07, 2014, 10:34:43 pm »

I routinely run the entire system off one 15 or 20 amp 110 circuit with no issues.

This doesn't tell us anything because we have no way of knowing how hard you are driving it. I can theoretically run ANY system off of one circuit if I barely turn it on.
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Tim McCulloch

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Re: Counting Power Draw from PA system
« Reply #7 on: August 07, 2014, 11:23:58 pm »

This doesn't tell us anything because we have no way of knowing how hard you are driving it. I can theoretically run ANY system off of one circuit if I barely turn it on.

I had 48 Crown I-Tech amps on a 30 amp, 120/240v split phase service (24 I-Techs on each leg).  For updating firmware and setting IP and HiQNet addresses....

That said, the average draw with 28 I-Tech 8000 powering VerTec 4889 tops (9/side) and 4880 subs (6/side) on a recent Pat Benatar concert was about 30 amperes per leg, 3 phase 120/208v service.  I didn't have peak hold capability at that show but estimate them at around 50 amperes.  Venue was half-set arena, about 4000 seats.  The American Idol tour was in the same venue last week and the Clair i3 rig with Old Iron Macrotech power was drawing about 40 amperes per leg and it wasn't as loud as Pat.  I think the extra 10 amperes went to the big-ass EQ bump from 4k to 6k3... very spitty and sibilant.

Chris, when I plan for electrical needs I use the figures published by the amp manufacturer for 1/8 continuous power (occasional clipping) multiplied by 1.20 as my basis for the tops, and 1/3 continuous power for subwoofer amps.  Crown and QSC have this data readily available on their web sites, and I'd expect others to offer such specifications too.

Your comment about the venue not allowing their client to use the mains power strikes me as very, very odd compared to how things are done in the USA - access to sufficient electrical service is a Really Big Deal, and venues are expected to have it available.  What is the reason for this in your locale?
« Last Edit: August 07, 2014, 11:27:15 pm by Tim McCulloch »
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Steve M Smith

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Re: Counting Power Draw from PA system
« Reply #8 on: August 08, 2014, 03:11:24 am »

Your comment about the venue not allowing their client to use the mains power strikes me as very, very odd compared to how things are done in the USA - access to sufficient electrical service is a Really Big Deal, and venues are expected to have it available.  What is the reason for this in your locale?

I have seen references in a few threads here about hotels and similar sized venues in the US charging for electricity use.  Is that normal practice?

Here we just turn up, plug in and do the show!


Steve.
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Tim McCulloch

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Re: Counting Power Draw from PA system
« Reply #9 on: August 08, 2014, 04:13:39 am »

I have seen references in a few threads here about hotels and similar sized venues in the US charging for electricity use.  Is that normal practice?

Here we just turn up, plug in and do the show!


Steve.

Yes.  Multi-function exhibit spaces sell power; you can't even plug in as the outlets are under lock and key or use a security fastener/cover plate.  Hotels sell everything they can, it's about maximizing "revenue per guest" rather that the old metric "revenue per guest night".  Hotels will even send a houseman into ball rooms, salons and meeting rooms and count how many outlets are in use and the charges just appear on the bill.  Higher amperage services or break-outs (distro) will certainly be billed for.

I'm not sure how our downtown arena bills for utilities but I wouldn't be surprised if the show power transformers were metered separately from offices & HVAC and usage charged to the client.  Our convention center/PAC charges flat rates based on ampacity/voltage of service in exhibit areas and building exterior; auditorium technical power (recently upgraded) is included in the rent.
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"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
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