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Kva - Gennys - Ohms Law - Genral Advice


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#1 jeffwall

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Posted 26 July 2008 - 04:21 PM

Ok, thought I would just write a post, giving some general info on electrics including KVA ratings and generator advice. Following on from another thread....

OHM'S LAW

Ohms law is a formula which can be applied to a electrical circuit to calculate the volts, current, resistance or wattage/demand

So in this simple example, we will use OHM's law to find out what power supply we need for a gig.
This is the only example that really relates to DJ work in my opinion. The most common question for us DJ's is... How much power does my rig take?

Look at the electrical tags on the back of the gear, stickers which give the wattage of the unit...

Ok, listing my gear as a example......

1 Amp 1 ( 1,200 watts - power demand running at max)
2 Amp 2 (1,200 watts - power demand running at max)
3 CD players (65 watts)
4 MP3 players (65 watts)
5 datamoon (250 watts)
6 datamoon (250 watts)
7 datamoon (250watts)
8 datamoon (250 watts)
9 smoke machine (800 watts)
Lap top (15 watts)

Total watts I am using is - 4345 watts

Using Ohms law, this can give us the Amps required (4345 watts divide by voltage (230v)
remember not to use 240v as volt drop in buildings makes the actual power available @ 230V

4345/230v = 18.9 amps

A single socket outlet will only give you 13 amps......

So 2 supplies is required for this example, and you need to split it up so one supply does not exceed 13 amps, or your fuse in the plug will blow!

Lights on one
laptop/amps//cds/mp3s on the other!

Considerations to remember

Amps will take a power surge to start up, because they have internal power transformers which are high resistance, and inductive... basically making the "start up" amperage twice or even more for a split second.

They have anti surge fuses built into the amp, which allows for this sudden start up current.
But your fuse in the plug does not!!! XXX START YOUR AMPS FIRST ONE BY ONE XXXX to limit the surge per item. Never start all your amps at once or AFTER loading up the supply with lights etc.

KVA (for generators)

Generators are "sized" in KVA which is short for Kilo/Volt/Amperes

The formula used to work out the KVA needed for a Generated supply is as follows.....

Amps times voltage divide by 1000 divide by 0.8 power factor

So in the example above....

18.9 amps x 230 volts divide by 1000 then divide by a power factor of 0.8 = 5.433 KVA genny required!

However always add 30 percent onto your total, giving you (rounded up) 7KVA required!

Hope this helps

#2 patrickman123

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Posted 12 January 2010 - 11:52 PM


wacko.gif This is very confusing all i know is sockets are 13 amps and you should never overload them
i need some more inside information on this!!

cheers

Edited by superstardeejay, 14 January 2010 - 06:30 PM.


#3 vokf

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Posted 13 January 2010 - 08:04 AM

QUOTE(patrickman123 @ Jan 12 2010, 11:52 PM) View Post

wacko.gif This is very confusing all i know is sockets are 13 amps and you should never overload them
i need some more inside information on this!!

cheers


Hi Patrick,
Basic advice on a "normal rig", ask for 2 power sockets.
Keep lighting/CD/Laptop/mixer/etc on 1 socket, and the amp(s)/active speakers on the other.

13A Socket should be able to provide nearly 3000W (230V x 13A = ~3000W). This is not 3000W of power to your speakers, but for simplicity most of us do not have a 3KW RMS Sound Rig.
(mine is probably 1.6KW RMS)
For an average gig, we're probably 1KW or less, and so you can see this should not be a problem on a single 13A Socket.

Lighting *should* also be fine;
My typical lighting is;
-2 x Dynatwins
-1 x Dynaroll
-2 x Par64 uplighters
-Led Starcloth
-Diffraction Laser

The Dynatwins/rolls are all halogen, and so will take about 1 or 2 amps each, so 6A total (worse case)
Uplighters are about 20W (I can't remember!), so very low (<0.01A)
Not sure about the starcloth! Should also be low as also LED.
Laser - also not sure (without checking, but will probably be 1A).
This is also fine, running off a single socket.

If you have a powerful sound system, and *lots* of big lighting (moving heads/old fashioned par cans), then you may need more than 2 sockets.
Large rigs may take advantage of a 32A supply, and large venues may well have sockets for these.

If you do have a large sound rig, and lots of "heavy" (power wise) lights, then post a list of the kit used in a large set-up and we'll try to clear things up.

Jeff's post is very good - he is a qualified electrician.
For most mobile guys, getting 2 proper power sockets will be fine. In fact, this is mentioned in my terms and conditions.
Realistically, if only 1 socket was provided, I would simply only run one Active Bass bin, or possibly just my Mackies.


Hope this helps,
Jason

#4 gadget

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Posted 13 January 2010 - 10:08 AM

QUOTE(vokf @ Jan 13 2010, 08:04 AM) View Post

Hi Patrick,
Basic advice on a "normal rig", ask for 2 power sockets.
Keep lighting/CD/Laptop/mixer/etc on 1 socket, and the amp(s)/active speakers on the other.

13A Socket should be able to provide nearly 3000W (230V x 13A = ~3000W). This is not 3000W of power to your speakers, but for simplicity most of us do not have a 3KW RMS Sound Rig.
(mine is probably 1.6KW RMS)
For an average gig, we're probably 1KW or less, and so you can see this should not be a problem on a single 13A Socket.

Lighting *should* also be fine;
My typical lighting is;
-2 x Dynatwins
-1 x Dynaroll
-2 x Par64 uplighters
-Led Starcloth
-Diffraction Laser

The Dynatwins/rolls are all halogen, and so will take about 1 or 2 amps each, so 6A total (worse case)
Uplighters are about 20W (I can't remember!), so very low (<0.01A)
Not sure about the starcloth! Should also be low as also LED.
Laser - also not sure (without checking, but will probably be 1A).
This is also fine, running off a single socket.

If you have a powerful sound system, and *lots* of big lighting (moving heads/old fashioned par cans), then you may need more than 2 sockets.
Large rigs may take advantage of a 32A supply, and large venues may well have sockets for these.

If you do have a large sound rig, and lots of "heavy" (power wise) lights, then post a list of the kit used in a large set-up and we'll try to clear things up.

Jeff's post is very good - he is a qualified electrician.
For most mobile guys, getting 2 proper power sockets will be fine. In fact, this is mentioned in my terms and conditions.
Realistically, if only 1 socket was provided, I would simply only run one Active Bass bin, or possibly just my Mackies.
Hope this helps,
Jason


I also mention a minimum of 2 sockets in my terms/contract, although I use more if available. Ideally - sound stuff on one through surge lead(s). Each t-bar on its own mains socket, and if fog machine in use then that really ought to be on its own surge protected socket/lead too...

Also useful if you only have a single socket, and there's another one a bit further around the room, then use a long lead and use that. At least one hall I know only had three single sockets - each of them slap bang in the centre of their walls..! One community centre ner here also only had one double socket at each corner.. again another candidate for having a long extension lead in the back!

Cheers,

David
DJ David Graham
Tel: 01204 537716 / 01942 418415
Email: hello@djgraham.co.uk
FB: http://facebook.com/djdavidgraham
Web: [under construction - it really is coming soon :)]

#5 Dukesy

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Posted 14 January 2010 - 11:42 AM

QUOTE(patrickman123 @ Jan 12 2010, 11:52 PM) View Post

wacko.gif This is very confusing all i know is sockets are 13 amps and you should never overload them
i need some more inside information on this!!

cheers


OK, the thread maybe general info on electrics, KVA ratings and generator advice, but if you are unsure if you are overloading a plug socket with your disco gear, then it might be an idea to speak to someone qualified about the kit you regularly use to work out the load (and to avoid a potential claim situation!)

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#6 gadget

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Posted 14 January 2010 - 04:28 PM

QUOTE(Dukesy @ Jan 14 2010, 11:42 AM) View Post

OK, the thread maybe general info on electrics, KVA ratings and generator advice, but if you are unsure if you are overloading a plug socket with your disco gear, then it might be an idea to speak to someone qualified about the kit you regularly use to work out the load (and to avoid a potential claim situation!)


You could always get one of those plug-in measurement meter devices - I picked one up for a fiver from the bargain bin at B&Q. Tells you Volts / Watts / Amps / kWh used, and you can even set the price per kWh and it will tell you how much it would have cost... Quite useful if you're not 100% sure what you're putting through the socket!

Cheers,

David
DJ David Graham
Tel: 01204 537716 / 01942 418415
Email: hello@djgraham.co.uk
FB: http://facebook.com/djdavidgraham
Web: [under construction - it really is coming soon :)]




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