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Stage power questions

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Stage power questions

Postby aekoi » Wed Apr 13, 2011 8:15 pm

Hi there,

Im trying to work out how much power a system I work with draws, and I also need to come up with a sensible 'plug it all in' type procedure. (I've read the Dec 05 SOS article PA Basics) Its mainly small venues we work in (fuction rooms and town hall type).

Im kinda baffled by this from the MACKIE SA1530z manual

"Line Input Power
Europe 230V, 50Hz
Recommended Amperage Service: 16 amps"

Is this saying that a 16amp circuit is recommended? And the spec sheet doesn't seem to list how much current the box will draw.

Can anyone shine a light on this? Thanks.

(ps -not homework)
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Re: Stage power questions

Postby PSR » Wed Apr 13, 2011 8:55 pm

If we take the advertised spec of the output from the amplifiers, and assume a normal sort or class B efficiency I make it 9.5 amps ish.
In practice, on normal program material, it will be less than this.
It will be happy with a normal 13A socket. Don't plug in too many on a 20A ring main though.
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Re: Stage power questions

Postby dmills » Wed Apr 13, 2011 8:56 pm

Assume maybe 3A per box (The transformer in the picture in the marketing glossies looks about 500Va or so to me), but you will want to fuse at 13A for the start up surge.

Sound power is seldom an issue in practise (Certainly not in an indoor situation using something like those Mackies), it is lighting load that kills you.

Do please use an RCD and do get a socket tester (a "Martindale"), it just might save your life.

For small stages I generally find that a 4 way each side at the back for the backline, one at the front for pedalboards and such with the backline and pedalboards fed from one RCD plugged into half a double socket and the pa plugged via a separate RCD into the other half of the double socket works well.
The advantage is that both sockets will be on the same phase (which shouldn't matter but may if there are some faults), and faulty backline will not take the PA down.

Feed the mixer and FOH racks with a cable taped to the side of the multi from the same supply as the stage side of the PA (Major hum reducer with cheap gear).

Regards, Dan.
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Re: Stage power questions

Postby aekoi » Thu Apr 14, 2011 1:33 am

Thanks. How do you calculate a 3amp draw based on the 500VA figure. I've been using this formula: VAxPF/230 where PF is 0.6. I grabbed that off google somewhere.

Thanks again
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Re: Stage power questions

Postby James Perrett » Thu Apr 14, 2011 9:42 am

aekoi wrote:
Recommended Amperage Service: 16 amps"

I wonder if they've just left the American value in there?

James.
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Re: Stage power questions

Postby aekoi » Thu Apr 14, 2011 1:01 pm

Thanks James, thats not the case tho, see below
(from the spec sheet)

Line Input Power
US 120V, 60Hz
Recommended Amperage Service: 20 amps
Europe 230V, 50Hz
Recommended Amperage Service: 16 amps
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Re: Stage power questions

Postby aekoi » Thu Apr 14, 2011 3:11 pm

Also, its often stated that FOH+mixer+racks, lights and backline should be powered from there own separate sockets (3 in total). Is it acceptable to power from both sides of a double socket and another adjacent socket, therefore all from the same ring main?
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Re: Stage power questions

Postby Mike Stranks » Thu Apr 14, 2011 5:36 pm

aekoi wrote:Also, its often stated that FOH+mixer+racks, lights and backline should be powered from there own separate sockets (3 in total). Is it acceptable to power from both sides of a double socket and another adjacent socket, therefore all from the same ring main?

Of course you've still got the limitation of the maximum current draw per socket BUT as Peter Russell (PSR) has stated above - the maximum you can draw from one ring is c. 20amps - something I only found out myself later than I should have done!

So you'll need to do the maths to ensure that the total draw and individual socket draws are each OK.

Lights can be (but aren't always) bad news for sound systems if on a shared ring because of dimming mechanisms. May be a good idea to invest in one or two isolation transformers (eg ART Cleanbox II) just in case. Sometimes gets me out of a buzzy-hummy hole! :D
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Re: Stage power questions

Postby Hugh Robjohns » Thu Apr 14, 2011 6:01 pm

The 16 amp thing looks like a generic suggestion to me. In the UK standard domestic outlets are nominally 13A anyway!

Esentially, what they are saying is that it needs to be plugged in to a sensible supply. As has been said, the typical average current will be a few amps at most, but there intial inrush current on switch on will be considerably higher, so don't try to turn everything on in one go!

If you need to know the real current and power consumption figures, invest in something like energy monitor. This one is marketed by Maplin inthe UK, but I'm sure you'll find similar devices from all the usual suppliers. You simply plug in the device you want to know about, and the display will give you the current and power being consumed, as well as the supply voltage and frequency. it's a really handy device and I use mine a lot when testing and checking equipment.

Regarding the use of wall sockets -- I'm with Dan. Assuming you are working with a PA and backline system that is consuming less than about 4kW in total (which would be most systems for a modest sized venue) then use a double socket to run all the audio equipment. That minimises any problems with ground loops.

Run all the backline from one side of the double outlet, and all the PA (FOH, racks, PA, monitors etc) from the other side. Supplying the two systems from their own RCDs is essential too, particularly from the point of view of preventing a backline fault from taking out the PA. If the musos want to use their own RCDs for their gear that's fine too!

Running the FOH on a long mains extension from the PA power supply socket (or distribution board) continues the theme of star grounding and will minimise the potential for ground loops in the PA system.

Run lighting from a different socket (or sockets) and try to keep the dimmer racks and cabling well away from the audio cables.

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Re: Stage power questions

Postby aekoi » Fri May 13, 2011 11:22 am

Thanks so far.

Where I'm at now is - having trouble getting all the specs to calculate current draw using pen and paper (every bit of kit quotes a different measurement unit, or no at all like the mackies). Energy monitor ha been requested.

In the meantime tho - I'm running a 6k system with 5 500w mons, all active. Does that sound like too much to plug into one domestic socket?

Thanks
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Re: Stage power questions

Postby Hugh Robjohns » Fri May 13, 2011 11:26 am

Yes...

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Re: Stage power questions

Postby aekoi » Fri May 13, 2011 12:31 pm

lol .. almost choked on my Hobnob then, such precision and economy ... many thanks ;)
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Re: Stage power questions

Postby TSH-Tim » Fri May 13, 2011 1:52 pm

Really i wouldn't get to mixed up with power ratings there are just sooo many different factors that can and will effect the results.

We ran this for 3 hours all off a one 13amp plug running down 80+ meters of cable (pink noise)

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Re: Stage power questions

Postby lightman » Wed May 18, 2011 2:12 pm

How much you can run will also depend on what type of circuit breakers that are used. (I should know which type these are but the grey matter isn't working great this morning....).

Some are more quick to trip on the louder 'peak' parts of the signal so you won't be able to get away with running as much from them.
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