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Author Topic: Calculating Current and Generator Needs  (Read 3116 times)

Steve Cook

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Calculating Current and Generator Needs
« on: September 01, 2015, 07:56:26 AM »

I've searched the forums but can't find a definite answer, and the stuff that I've found on google just confused me.

How do I calculate what my rig is going to draw via current and amperage so I can determine what size generator is perfect?  I've just used a WAG type, and then usually got a little bigger if the cost was nominal on a rental generator. 

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Mark Cadwallader

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Re: Calculating Current and Generator Needs
« Reply #1 on: September 01, 2015, 09:43:27 AM »

A common rule of thumb is to figure 1/8 of the nameplate amperage for your PA system for a rough approximation. Double that, and then add the draw of other items (board, wireless, etc) at the rated amperage. Round up if close to the genny's continuous rating. EDM requires more power; if you are using an inverter generator it usually can be a bit smaller. A "big boy" generator (Whisperwatt or similar) usually needs less of a margin for big hits.

 Don't forget lighting loads. Incandecent lights figure at 100%; LEDs at 200% (due to power factor).

The approximation above is better than a WAG, but it is not a measurement.

The AC power and grounding sub-forum should have several threads on topic.
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Steve M Smith

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Re: Calculating Current and Generator Needs
« Reply #2 on: September 01, 2015, 11:25:00 AM »

A common rule of thumb is to figure 1/8 of the nameplate amperage for your PA system for a rough approximation. Double that...
Then why not just 1/4 ?!!


Steve.
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Steve Garris

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Re: Calculating Current and Generator Needs
« Reply #3 on: September 01, 2015, 04:18:18 PM »

This is a topic of confusion for me as well. I was recently asked how much power was needed for my PA so they could rent an appropriate generator. I really did not know what to tell them. They then asked if a 5000 W generator would work. I discovered at the gig that it did indeed work perfectly for me, so now I at least have some sort of reference point (in Watts).

So do I need to look at and add up all the amp ratings on my gear? Sorry to be electrically challenged here...

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Doug Fowler

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Re: Calculating Current and Generator Needs
« Reply #4 on: September 01, 2015, 05:17:04 PM »

I've searched the forums but can't find a definite answer, and the stuff that I've found on google just confused me.

How do I calculate what my rig is going to draw via current and amperage so I can determine what size generator is perfect?  I've just used a WAG type, and then usually got a little bigger if the cost was nominal on a rental generator.

What you need is a proper kVA figure. If you know what your PA needs (2 legs at 30 amps each, for example), you can use that to get the kilovolt-amps figure.

Most production genset rental operators can take your (for example) 30 amp figure and use that. But, they also probably don't have anything that small, unless it's a Honda. 

"I need a single phase production generator, expecting to pull less than 50 amps per leg".   If you don't have a distro you can get a spider box at the same time. 

http://www.rapidtables.com/calc/electric/Amp_to_kVA_Calculator.htm
« Last Edit: September 01, 2015, 05:22:50 PM by Doug Fowler »
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Mark Cadwallader

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Re: Calculating Current and Generator Needs
« Reply #5 on: September 01, 2015, 08:00:45 PM »

Then why not just 1/4 ?!!


Steve.

Because 1/8 is used as the (a) rule of thumb, for figuring the estimated amperage for AC mains. The doubling is to (hopefully) have sufficient reserve in generator capacity.

But yes, 1/8 x 2 = 1/4.
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Steve M Smith

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Re: Calculating Current and Generator Needs
« Reply #6 on: September 02, 2015, 02:46:11 AM »

Makes more sense when there is a good reason to show.  Thanks.


Steve.
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Mark Cadwallader

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Re: Calculating Current and Generator Needs
« Reply #7 on: September 02, 2015, 08:51:33 AM »

Makes more sense when there is a good reason to show.  Thanks.


Steve.

You're welcome. As is often the case, the quick answer provides incomplete information, and as a result, leads to confusion. (As Ivan so often points out.)  In retrospect, I should have been more thorough in my original response.
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ProSoundWeb Community

Re: Calculating Current and Generator Needs
« Reply #7 on: September 02, 2015, 08:51:33 AM »


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