How do you calculate power usage?

[musicology]

I meant to ask this a while ago but have just been asked again by a marquee company how much supply I need. So how do I work it out? I assume lighting wattage is different from sound output watts. As for total amps..haven't a clue!

[Imagine]

I'm sure someone will have the correct calculation somewhere - but all of the items should have their consumption ratings on them.

I always personally tell them that I need the equivalent of 2 x 13 amp sockets, not shared with anyone else which has always worked for me.

[Excalibur]

I always personally tell them that I need the equivalent of 2 x 13 amp sockets, not shared with anyone else which has always worked for me.

The default setting. Always wise to ask for this. Sadly, sometimes, marquee companies take that to mean two sockets with only your plugs in. You then get what's left over after the marquee lights, heaters, catering ovens et al have had their fill upstream of you.

To calculate power usage, very roughly, add up all the power consumptions of your kit ( eg, a 250watt halogen light may take 300-350 watts overall, whereas a 1000watt amp may claim to need 750 watts. Don't ask why, the explanation's complicated. ) and when all the figures on the back of your kit are added together, you should have a figure of say, 2500watts. Divide this by 250volts ( which isn't really accurate, nowadays, folk seem to be working on 230, but the maths is easier with 250 ) and you'd have 2500/250= 10 amps. Not accurate to the last milliamp. but close enough for Rock and Roll.

I have extension leads which are used exclusively for the disco, and on many occasions, I have run a full rig from one of them. One day, I used such a cable to power a large table saw, and blew the fuse instantly. Turns out, I'd been running a large disco satisfactorily on a five amp fuse for ages, so don't panic that you'll need thirty two amps from the distribution board in the marquee. As suggested earlier, ask for two thirteen amp sockets for your sole use, and you'll be fine, unless you are running Five kilowatts of light, and ten kilowatts of sound. :eek::eek:

However, life isn't always that simple. Anyone prepared to stand me a pint of Trusselthwaites Old Sock Rotter at BPM could be regaled with tales of when the electrickery supply wasn't up to the job. Many tales. With quite a few involving numpties. Numpties who think that if you start with one thirteen amp socket, and plug a further twelve into it, you'll have thirteen amps available on every one.

[Chris1984]

As has been said - total watts divided by voltage = amps.

However it is bad form to use 250v as it will give you a lower figure and as such you can easily be using more power than you think.
The standard for power in UK is 230v and this will give you a better idea what you are using.

Most uk power is provided at 230 +/- a few volts where as most generator companies still seem to use 240v.

either way working out at 230v will give you the correct answer and it does make a massive difference.


eg

3000w @ 230v = 13.043A

3000w @ 250v = 12A

so you could easily be overloading a 13a socket and be unaware...

[musicology]

I'm sure someone will have the correct calculation somewhere - but all of the items should have their consumption ratings on them.

I always personally tell them that I need the equivalent of 2 x 13 amp sockets, not shared with anyone else which has always worked for me.

Exactly what I say but a marquee company will tend to press me further so I try to explain what I've got.

I will simply have to go through all my kit and look at the consumption numbers then do the calculation. I only have to do it once then I'll know. Must to remember to make a note somewhere or I'll just forget! Thanks for the input everyone.

[stormproductions]

Like Chris, I tend to be dealing with larger numbers regarding power, but the majority of 'small' discos nowadays will happily and safely run off a single 13A outlet. That doesn't mean you shouldn't be finding out what your total loading is, but basically if you've only got a sound system suitable for let's say 100 people (and I realise that could be anything, but I'm thinking a "typical" DJ set up of playout system and a couple of Mackie SRM350s or vaguely similar) and some LED lighting then you're likely to be absolutely fine.

However, if you've got a bunch of traditional PAR56s with a smoke machine, some discharge moving lights, or a significantly bigger PA etc then power consumption can quickly add up.

But you really should check - if needs be stick a list of kit up here and folks will help out.

And think of it from the point of view of the power provider and the end customer who's paying for it - they need to know the likely consumption of possibly several other contractors such as caterers, loos, band, photo booth, chocolate fountain etc in order to provide a suitable supply, but the end customer doesn't want to be paying for vastly more than is required so complete guesses aren't overly helpful to them.

[DJColsie]

I have a little £10 gizmo from Maplins. If I run off 1 socket I plug it in to keep a eye on the power I am drawing.

Even with 2 tops, 2 subs, upto 8 LED lights, plug in mixer, laptop, radio mics etc still never been over 2500 watts.

[musicology]

...

But you really should check - if needs be stick a list of kit up here and folks will help out...

..

2 x Yamaha DXR12
Numark bluetooth CD/Mixer combo
Laptop
2 x Abstract Extreme XP3 (250w)
2 x Abstract Extreme XP5 (250w)
2 x 300mw Lasers
2 x 4 way spot banks (8 x 100w Par38s total)
1 x 700w smoke machine
1 x 1500w Strobe

[stormproductions]

Well I wonder how much power your speakers actually consume as the Yamaha specs for them claim they only consume 110w each. Now I don't claim to know a huge amount about audio (and nor do I want to really), but that sounds like a fib to me. Let's work on their rated output power of 1100w each so total 2200w. Now a lot of the time they won't be using anywhere near that.

Elsewhere, the Numark, laptop and lasers will be insignificant.

The 4 Abstracts total 1000w (or 1kW).

Allowing for all 8 spots to be on at the same time, that's another 800w.

Add the smoke and strobe (working at the power figures you've given - I know both of those are items that could actually use different amounts than quoted) you've got a potential load of 6200w, or nearly 27 amps at 230v.

Which is a little more than you could safely (or sensibly) draw from 2 separate 13A outlets.

But you've got diversity which essentially is where you're not using everything to it's max at the same time so you don't actually need a supply big enough to do so. I don't know how much of the kit you use at the same time (for one I'm guessing that not all 8 spots are all on at the same time?) so there's no way of us really guessing that - suffice to say that in my opinion you should easily be able to run that lot from 2 separate 13A supplies and the chances are that in fact it would all run from one without any issues, but I personally wouldn't want to risk that by any means. Use 2 would be my advice.

[musicology]

Thanks for that. Yes you're completely right to say it's never all on and at full power at any one time.
I had to try running it all from one socket once and the fuse blew about 2/3rds through the night. So I reckon if I say
20 amps total I'd be close enough for a guide to a marquee company?

[mattydj50]

Your Yamaha speakers will only draw 110 watts of incoming electrical power from the 240v mains. This then gets converted into 1100 watts of sound output power which will be at a much lower voltage.

So for your power consumption calculations, 110watts IS the correct figure to use.

[stormproductions]

That was probably when you banged the strobe on?!

Yep, tell them you'll be running around 20A but peaking at a touch more and that you definitely require 2 separate 13A feeds. With the emphasise on the separate feeds so they realise that you don't just want a 4 way 13A socket supplied from a single 16A feed.

Marquee companies can vary a huge amount with their power supplies, from properly serious outfits through to ones that supply downright scary electrics and really wouldn't see the danger in replacing a fuse with a nail! But speaking to them in advance will help avoid unexpected issues once you're on site.

[DJ Jules]

Your Yamaha speakers will only draw 110 watts of incoming electrical power from the 240v mains. This then gets converted into 1100 watts of sound output power which will be at a much lower voltage.

Um, that's not quite how it works:

Power = Current x Voltage

The Voltage to the speakers does drop, but the current will increase so the power stays the same. There'll be other reasons for the 110w rating on the supply - most probably due to the way the rating has to be calculated based on the average load over a normal duty cycle (I don't know exactly what might be going on here).

It could possibly be just because they dropped a 0 off the label :D

Julian