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Author Topic: Speccing a generator  (Read 1384 times)

Chris Grimshaw

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Speccing a generator
« on: June 09, 2017, 09:44:42 am »

Hi all,

Looking for some help on this. Client has asked me for advice on a generator, so I've looked at a few local suppliers, one of whom says I need something that sounds like overkill.

Edit - this is an outdoor gig. Rock and rap music. I suspect they'll want it pretty loud - I anticipate nudging the limiters on the subs.

Things I need to power:

(mostly Behringer)
- 1x NU4-6000, used for HF and monitors. It has an easy life at 8ohm/ch. 300w/ch, 4-channels
- 1x NU3000, used for 2x monitors per side, 600w/ch@4ohm
- 2x NU6000, used for mids and subs. These have a harder life, running 2KW/ch@4ohm.
- Assorted stuff like mixing desk, backline (2x guitar amps and a bass amp, maximum. All will be running through the PA and monitors, so they won't be cranked), processor, etc.

I believe the NU6ks are rated for around 700w continuous draw when they're clipping 1/8th power pink noise into their lowest rated impedance. The MF and LF amps will be in that situation, but the others won't be working so hard.

A supplier recommended a 25KVA generator after I told them the amplifiers came to about 10KW total. They didn't seem to get that the amplifiers have capacitors to smooth things out, that music has short-term peaks etc etc. Of course, it's in their interest to try and sell me the biggest generator they can.

I suspect I could just about run off a Honda EU3000, and certainly an EU6500i.
I don't want to spec something unreasonable, but I do want to make sure we've got a good solid mains supply for about 12 hours.

What do you all think?

TIA,
Chris
« Last Edit: June 09, 2017, 09:57:06 am by Chris Grimshaw »
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Robert Piascik

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Re: Speccing a generator
« Reply #1 on: June 09, 2017, 09:57:14 am »

I agree with you it's probably overkill but the price between renting a 6500 and a 25kW is about $100 in my area (if you can haul it and don't need spider box) so it's meh I say.
Consider whether anybody else needs to tap into the genny too: food vendors, the blow up toy guy, etc. it's always better to have excess capacity
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Mark Cadwallader

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Re: Speccing a generator
« Reply #2 on: June 09, 2017, 12:47:13 pm »

I don't think you can get a 12 hour run on a single tank of fuel with the EU7000i.  That may be as much a consideration as anything. You don't want to stop to refuel (or run out) once you are up and running....
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Brian Jojade

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Re: Speccing a generator
« Reply #3 on: June 09, 2017, 02:04:06 pm »

What you are missing is that power amps may have a low average power draw, but they do have short peak demand requirements.  Yes, there are capacitors that help smooth that out a bit, but the cheaper the amps, the smaller these reserve caps are.  If your power source can't deliver the power needed for the peaks, you will lose the peaks in your sound.  The iNuke is not an extremely robust amp when it comes to weak mains power.

If your generator is undersized, your sound will suffer. 

If you are planning to run for 12 hours, and need 12 hours of power, you need a generator that can fill those specs.  Your smaller  generators typically won't be able to do that on a single tank.
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Tim McCulloch

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Re: Speccing a generator
« Reply #4 on: June 09, 2017, 02:42:51 pm »

What you are missing is that power amps may have a low average power draw, but they do have short peak demand requirements.  Yes, there are capacitors that help smooth that out a bit, but the cheaper the amps, the smaller these reserve caps are.  If your power source can't deliver the power needed for the peaks, you will lose the peaks in your sound.  The iNuke is not an extremely robust amp when it comes to weak mains power.

If your generator is undersized, your sound will suffer. 

If you are planning to run for 12 hours, and need 12 hours of power, you need a generator that can fill those specs.  Your smaller  generators typically won't be able to do that on a single tank.

^^^^^ This.
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Philip Norman

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Re: Speccing a generator
« Reply #5 on: June 10, 2017, 04:17:11 am »

Hello,

We own several Honda EU65is and we own several inuke6000 for desert gigs. I would not recommend running any more than 2x nu6000 off one EU65is as the peaks push the genny quite hard occasionally lighting up the overload light.

A 15KVA SDMO genny on a trailer (or similar) should be better suited for what you have listed.
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Tim McCulloch

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Re: Speccing a generator
« Reply #6 on: June 10, 2017, 04:48:44 am »

Hi all,

Looking for some help on this. Client has asked me for advice on a generator, so I've looked at a few local suppliers, one of whom says I need something that sounds like overkill.

Edit - this is an outdoor gig. Rock and rap music. I suspect they'll want it pretty loud - I anticipate nudging the limiters on the subs.

Things I need to power:

(mostly Behringer)
- 1x NU4-6000, used for HF and monitors. It has an easy life at 8ohm/ch. 300w/ch, 4-channels
- 1x NU3000, used for 2x monitors per side, 600w/ch@4ohm
- 2x NU6000, used for mids and subs. These have a harder life, running 2KW/ch@4ohm.
- Assorted stuff like mixing desk, backline (2x guitar amps and a bass amp, maximum. All will be running through the PA and monitors, so they won't be cranked), processor, etc.

I believe the NU6ks are rated for around 700w continuous draw when they're clipping 1/8th power pink noise into their lowest rated impedance. The MF and LF amps will be in that situation, but the others won't be working so hard.

A supplier recommended a 25KVA generator after I told them the amplifiers came to about 10KW total. They didn't seem to get that the amplifiers have capacitors to smooth things out, that music has short-term peaks etc etc. Of course, it's in their interest to try and sell me the biggest generator they can.

I suspect I could just about run off a Honda EU3000, and certainly an EU6500i.
I don't want to spec something unreasonable, but I do want to make sure we've got a good solid mains supply for about 12 hours.

What do you all think?

TIA,
Chris

Rock and rap, outdoors?  You don't mention the speaker system you're using but I hope it pumps some air without much current.  Depending on your patience for or tolerance of clip lights you'll either have "just enough" or not enough rig.  I know you didn't ask but I had to go there...

As has been pointed out, the filter caps on these amps are not huge current reservoirs and cannot be relied upon to 'fill in the gaps' when the genset has no more current.  IIRC these amps are not power factor corrected so generators need to be up-speced for that reason, too.

The 25kW is the smallest genset we'll rent.  It tows behind a standard 1 ton van or pickup truck (or the shop will deliver & pick up for additional $) and if there's a problem a genny tech is a phone call away.

There is a place for small portable generators but bass-heavy music isn't one of them, IMHO.
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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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