__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