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How Big a Generator?

Discussion in 'General Advice' started by photoatdv, Feb 13, 2009.

  1. photoatdv

    photoatdv Active Member

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    Okay so we are trying to figure out how big (power wise) of a generator we need for an outdoor charity event. The event is about 2 months away, but we need to spec the genny now. Unfortunately, the genny will be powering all of the staging as well as regular power needs for concessions, radios, tvs, ect. We also don't have the final specs for the staging and won't for at least a month. From the specs I have we will have 5-10kW of MLs, a sound system for a large outdoor event, and some video from a projector. The 'other' not technical stuff will probably need 10kW to be safe.

    How big of a generator do we need? Do we need some kind of seperate (intermediate) breaker between the genny and the 'other' stuff so if they put something bad or overload it we don't lose the power to staging?

    Note: We will have someone there qualified to do the hookup, so that's not an issue.
     
  2. derekleffew

    derekleffew Resident Curmudgeon Senior Team Premium Member

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  3. hsaunier

    hsaunier Active Member

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    Most often 2 seperate genies are used. One for light and the other for audio. Put all the conscession stuff on the light genie. Short of that make sure a very, very, good earth ground has been placed (deep). Many times the audio gear does not like lights operating on the same source, dimmers will make an obvious buzzing.
     
  4. photoatdv

    photoatdv Active Member

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    While I agree that asking the generator supplier would be a good idea, they aren't quite so helpful when we're trying to get them to either donate the use of the equiptment or give us a huge discount. We pretty much have to go in saying this is what we need. I'm trying to figure out how much extra we need (I read in FOH magazine that you want 2x what you think you will need). As I sain in the Sound forums-- we DON'T know what the sound setup will be yet.
     
  5. Chris15

    Chris15 CBMod CB Mods Premium Member

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    Getting a genny that's too big can bite you as it will be idling and probably won't maintain it's frequency as well as it would under load. Expect also that your voltages will be a lil hot.

    So issue no 1 is that you spec generator sizes in kVA not kW. They are not the same. kW = kVA * Power factor. You could assume a 0.8 power factor, most people use that sort of a number for rough guesses. Actual PF will vary dependent on your load characteristics. The closer to 1 the more efficient...

    Are any of your concessions (right so showing my flag now - I take concessions to be stalls, food vans etc?) using urns, toasters, microwaves, hot water units or any such power hogs? How far away will they be from the genny? Do you have means to distribute the power that will work and meet relevant codes?

    The trcik if you do use a single genny for lights and sound if you can is to distribute your loads such that audio is one one phase and the lights are mostly on the other two.

    Now to slighlty conytradict the last statement, balancing loads on generators is far more important than load balancing for a mains install because the demand by other devices on three phase tends to even out and a few amps is neither here nor there in the couple of hundred (or double that in the US?) amps at the nearest stepdown transformer... Get it wrong on a generator and the thing will not be a happy camper.

    Re intermediate breaker question, you'll need a power distribution system rated to your needs and code compliant and all that fun stuff...
     
  6. len

    len Well-Known Member

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    If you know the rough demands of everything and where approximately it will be within the venue (area), I'd pass this along to a couple of rental companies and ask for their input. They may see some things that you maybe didn't think of. IN my experience, rental vendors like to help, because they're trying to get you as a long term customer and they also don't want their equipment abused. Allowing them some input as opposed to saying (I need a genny with this output on this date. How much?) will build you some good will for the future as well.
     
  7. lieperjp

    lieperjp Well-Known Member

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    Chris brings up an excellent point. What are you using for Concessions? Don't forget food warmers like Nescos, refrigerators, nacho cheese warmers or popcorn machines. If you are getting a common concessions truck/trailer (i.e. small), most have a limit of 15 amps for food service and another 5-10 amps for lights. Of course, that doesn't stop you from bringing in your own electricity.

    Also, to save money on this, definitely check with your local Pepsi or Coke distributor, (or adult beverage center) as they usually do free rentals on trailers if you buy their product and sell it exclusively. These even come with soda fountains, however all other equipment must be furnished by you.
     
  8. David Ashton

    David Ashton Active Member

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    The concessions are your friend, they will keep a base load on the genny, your sound load can go from virtually nothing to full draw over seconds and badly load the generator, moving lights are good on generators as they are a constant load, dimmers can be a nightmare, with changing loads and wave chopping and high neutral currents, they need serious attention.As a general rule if you have dimmers on a genny, load it up with everything you can find to ameliorate the problems.
     

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