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Max Power?

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Max Power?

Postby Zan Man » Fri Nov 26, 2010 11:17 am

G'day all........
While certainly not the biggest providers of sound re-inforcement in the world (far, far from it), we are starting to acquire more stuff, as you invariably do as the years go by. Most of the venue that we do are medium sized halls, ranging from 250 - 500 people capacity. These places, so far, just have the standard ring main supply for mains power supply. With the stuff that we have, what is the amount of amperage in reserve from the supply without the mains decideing enough is enough and tripping out. Is there a formula for this? (never paid too much attention in physics and now it comes back to haunt!)Stuff we have running at any one possible moment are two active stacks (powered tops and subs per side), desk, outboard racks (comprising of 3 x 2 channel graphics 4 x 2 channel compressor / gates, fx units, radio mic base units), 4 x 2 channel stage monitor amps and 2 active monitors. Plus, depending of the amount of stuff the band have, possibly 3 guitar amps, 2 keyboards for example, how much juice is this going to draw if it all running at a reasonable sound level? We haven't experienced any trouble so far, but it is something I would like to know. I do not have a 16 amp distribution board, but if I'm "close to the edge" I will most certainly get one, probably a good idea anyway for gigs in marquees etc but the places so far as I said only have had the usual ring main juice supply. As a rough guide, am I anywhere near a 13 amp max?
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Re: Max Power?

Postby Mike Stranks » Fri Nov 26, 2010 11:59 am

The best way to determine current/power used is with one of these:

Mains Meter

It'll show you either amps or watts - for your purposes. You'd normally plug this direct to the mains and then run everything else from that. The current drawn will depend particulary on how hard the amps are working so it's a good idea to get someone to look at this at several key points throughout a concert.

Don't forget you can use two adjacent (correctly wired) sockets to give you 2 x 13 amps. The only caveat here is that if the stage and the FoH are on different mains rings then you make get an earth/ground loop when you interconnect them with your stage and FoH gear.

I'm not going to offer any advice on what the likely maximum current draw is as I don't know your gear. I'd tend to quite happy as long as the peak amps is never above about 11.5 - assuming all your cables are correctly rated.

Always switch on and off gear in a sequence rather than all at once - with amps last on and first off, again in sequence.

In terms of calculations:

Watts (electrical) is volts x amps

Amps is volts divided by resistance

Volts is amps times resistance

Resistance is volts divided by amps.

So a 13 amp socket delivers 13 x 240 = 3120 watts (electrical not Audio "RMS"!)

HTH
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Re: Max Power?

Postby Zan Man » Fri Nov 26, 2010 9:15 pm

Thanks Mike....... Just checked the price of one of those meters, and they aint much more than a tenner, so I will get me one of those..... When I do I will get around to letting you know what we are drawing. Again, many thanks, oh knowledgeable one.
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Re: Max Power?

Postby dmills » Fri Nov 26, 2010 10:57 pm

Mike Stranks wrote:
Don't forget you can use two adjacent (correctly wired) sockets to give you 2 x 13 amps.

Be very careful here, while it might be true for two separate sockets provided there is not too much else on the ring (Watch out for caterers), a standard double 13A socket is only actually rated for 20A total load in most cases (The MK Metalclads are a notable exception).

Now the thing is that fuses (and up to a point circuit breakers) respond to RMS current, so a short term transient will be unlikely to case a problem, thus you can run far more then 3KW of amplifier off a 13A socket without any real problem AS LONG AS THE RING IS NOT ALREADY ON THE EDGE.....
By the time you hit 500 capacity rooms you should be safely clear of lighting rigs running from the ring main and the worst of the sort of 'caterer' that plugs 3 tea urns and a toaster into a 4 way, but being aware of things like large smoke machines which can pull a lot of current is a good idea.

TBH at that level there should be a dedicated 16, 32 or 63A supply available, I would look at a small distro board as being a worthwhile investment.
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Re: Max Power?

Postby PSR » Sat Nov 27, 2010 6:08 pm

(Some good advice from dmills.)

Forget the outboard quipment - that's only peanuts in terms of power used.
Add up the power output of your PA amplifiers - multiply by two.
Add up the power output of your guitar amplifiers - multiply by three
Add these togther to get an approximate value for total watts needed.

In thoery you can take up to 3000 watts from a 13A socket, and rings are often rated 20 or 30 amps so you can have perhaps 6 or 9,000 watts total over a number of sockets - need to examine the fuse box if possible. I really wouldn't recomend taking more than 2000 watts off any one socket since dirty ones tend to over heat and eventually the 13A fuse can blow.

BUT 1. If you have an old fashioned lighting rig (not an LED one) then you need to take this into account (- which is why I used to wire in tails when the venue provided a box - we had about 3K PA and 20K of lights)
2. Many venues have crap wiring (I call it "landlords wiring" because he did it himself rather then calling the electrician - see most pubs in Britian). So best not to pull everything off one socket.

Hope this helps.
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Re: Max Power?

Postby Mike Stranks » Sun Nov 28, 2010 8:58 am

dmills wrote:
Mike Stranks wrote:
Don't forget you can use two adjacent (correctly wired) sockets to give you 2 x 13 amps.

Be very careful here, while it might be true for two separate sockets provided there is not too much else on the ring (Watch out for caterers), a standard double 13A socket is only actually rated for 20A total load in most cases (The MK Metalclads are a notable exception).

Now the thing is that fuses (and up to a point circuit breakers) respond to RMS current, so a short term transient will be unlikely to case a problem, thus you can run far more then 3KW of amplifier off a 13A socket without any real problem AS LONG AS THE RING IS NOT ALREADY ON THE EDGE.....
By the time you hit 500 capacity rooms you should be safely clear of lighting rigs running from the ring main and the worst of the sort of 'caterer' that plugs 3 tea urns and a toaster into a 4 way, but being aware of things like large smoke machines which can pull a lot of current is a good idea.

TBH at that level there should be a dedicated 16, 32 or 63A supply available, I would look at a small distro board as being a worthwhile investment.

Thanks for that Dan. All good stuff!

Prior to this helpful info from you I'd just accepted the standard nostrum that each 13amp socket can deliver... well... 13 amps! Your caveats and explanations are helpful and informative - I have read learnt and inwardly digested! :D

Cheers.

Mike - still learning after 40 years doing this stuff!
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Re: Max Power?

Postby Scatamonkey » Wed Feb 29, 2012 6:23 pm

I read so many things on this forum and think - how has my rig lasted so long without catching fire !!! :headbang:

I have 2 1900 watt power amps that are always running pretty close to redlining of one power board out of one 13amp plug socket...which also has a 150 watt monitor amp, my EQ and a laptop plugged into it...and sometimes a desktop fan to keep the amps cool!!!

I know 1900 watts doesn't mean exactly "1900" watts at all times, but I bet its over the 3KW maximum that Ive just learned is all you should put through a standard 13amp socket!
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Re: Max Power?

Postby ef37a » Wed Feb 29, 2012 6:59 pm

As well also to have a UPS keeping comms systems, READING LAMPS(!) alive in the event of a blackout whether caused by you or not!

Back in the day we had a CTH 30W PA with floating car battery so that we could announce a "Don't panic Mr Mannerin" message.

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Re: Max Power?

Postby Mike Stranks » Wed Feb 29, 2012 10:00 pm

Scatamonkey wrote:I read so many things on this forum and think - how has my rig lasted so long without catching fire !!! :headbang:

I have 2 1900 watt power amps that are always running pretty close to redlining of one power board out of one 13amp plug socket...which also has a 150 watt monitor amp, my EQ and a laptop plugged into it...and sometimes a desktop fan to keep the amps cool!!!

I know 1900 watts doesn't mean exactly "1900" watts at all times, but I bet its over the 3KW maximum that Ive just learned is all you should put through a standard 13amp socket!
I think you're confusing "output power watts" with the power consumption of the amp.

Assuming we're talking about your Numarks then, according to the manual, the max power consumption is 10amps. That's 2.4KW per amp - maximum. The reality is that even when working hard, most amps draw well below their rated value. As long as you switch amps on one at a time you should be fine, BUT don't just hope or, heaven forfend, go on my sayso!. Get one of those meters I mention earlier in the thread and check out what the load per socket is like when your system is working at normal levels.

... and of course, regularly check all mains plugs and sockets for integrity - all fuses at rated values, all earths securely fastened, all screw terminals nice and tight and no 'whiskery' bits of wire evident in plug or trailing socket housings.
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Re: Max Power?

Postby dmills » Wed Feb 29, 2012 11:43 pm

Amplifiers do not run anything like full power all the time (nothing like it), and 1/8th of full output for an average over a few tens of seconds is generally considered typical, so those 1900W amps are probably putting out ~220W or so on average, and assuming a typical sort of efficiency will be drawing maybe 500W average from the supply over a few second integration time. I doubt they are power factor corrected so that might euate to 750VA or so, but still that is only about 3A.

The peaks might be very much higher, but fuses and (to an extent) circuit breakers respond to RMS current not peak, so as long as the voltage drop stays reasonable on peaks you can power a hell of a lot of PA off a 13A socket.

I used to routinely run 6kW of Camco off a single socket, and sometimes 12k off a double with never a problem.

Power, especially time varying power, is not simple.

Regards, Dan.
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Re: Max Power?

Postby Scatamonkey » Thu Mar 01, 2012 12:28 am

Thanks Mike and Dan for the peace of mind - I did have a wee mini panic when I read all that, but I was pretty sure about the "amps not putting out maximum" all the time bit!

Still, always better to check with the experts...thats you guys by the way! :bouncy:
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