Running powerhungry (2.8kw+) poweramps?

Discussion in 'Amps and Cabs [BG]' started by Dan Loader, Oct 16, 2003.

  1. I'm sound tech'ing for a gig Sunday after next at a local school, my largest yet - around 300 people.
    I was talking to the lighing tech for the night who said he was still in the dark as to how much he could run off of their system. With a 16 amp large plug it's 3.8kw, with a 13 amp standard plug socket (@220volts) it's 2.88kw. It only occured to me then that a few people on TB have rigs over 2.8kw. How do they run their rigs? Crest and Peavey I know both do poweramps over 3kw in a 2U space with a single plug, how does this work?

    The 2.88kw is derived from 13amps * 220volts, so therefore in the USA, were power is 110(?), surely the largest rig you can run off of a wall socket is only 1.44kw?

    Can anyone elighten me on this subject?
  2. Stu L.

    Stu L. Supporting Member

    Nov 27, 2001
    Corsicana, Texas
    I've run the Peavey CS3000 and a few of the GPS3500's on one circuit before, with no problem. It all comes down to the breaker and the amps, IME. If all the amps go on at once, chances are the breaker will trip. Power 'em up one at a time and all should be ok. just IMO, IME of course :)
  3. In the US, the normal outlet is 120V at 20A, so that gives maximum of 2.4KVA. It all boils down to the fact that the amps rarely draw their rated power, so amps adding up to higher than 2400 Watts can be run, but if they try and pull more than 20A then the breaker will trip.

    In commercial situations, the soundguy usually just taps right into the 240V mains at the circuit breaker panel and then he can pull 60A or more at 240V which = 14.4KVA max.

    Even though we use 120V in the US, the main power entrance comes in as 240V with a center tap, so our big stuff like airconditioners, ovens, clothes dryers, etc. all run on 240V. We just don't run 220V to everything in the house like you crazy Brits! :D

  4. Cheers for the info chaps.
    I realise that a 3500watt amp isn't going to be pulling 3500 all the time, even if it's turned all the way up, but the lighting techie reckons he'll be using 2x2kw (2 different dimmer racks) trhoughout the gig, so it's probably best I plug my poweramp into somewhere else...


    Oct 13, 2003
    Most amps are class AB and only 20% of the power taken from the mains goes to the loudspeaker.

    Of that, only 5% of the electrical energy supplied to the speaker gets converted to accustic energy.

    If you want to get the maximum out of a mains socket, you should use switch mode amps that are main transformerless (Class D), or (Class T), they are about 85% efficancy to the speaker.

    Also keep wiring very short because if you use 2 ohm speakes, wiring resistances can be as much as 0.5 Ohms, so more energy is lost.

    Most class AB amplifiers have a simple bridge rectifier & capacitor power supply that generates +80V and -80V. This causes the voltage and current to flow from the mains with distortion, this causes the fuse to blow when the load power is less.

    For example 240V 13A into a resistive load =3.120KW.

    But a power supply that make +80V and -80V will only be able to drive a load of about 2KW before the fuse blows.
  6. Petebass


    Dec 22, 2002
    QLD Australia
    Hey I resent that. Please go back and edit yout post to include us Australians in that insult. Actually we run 240v so we're a little bit crazier again :)
  7. notanaggie

    notanaggie Guest

    Sep 30, 2003
    For sure try to get away from the lighting.

    Even if the power were OK, the dimmers (even new CE ones) seem to put out a lot of crap that can make unwanted noises.

    But also, the lights are a constant load, and will pop breakers way before amps of nominally equal power.

    In the states, we can run quite a bit more power than it seems, because most of the circuit breakers will stand short overloads. So if you have a 20A circuit, you can usually pull 40 or even 60 every so often for an instant and have no problem. Keep it up and you have to reset it, though.

    Generally audio will draw no more than a quarter or so of the power rating or it sounds terrible from clipping. if its clean, it may be even less.

    For a bass amp though, it s higher, maybe a third. If you use a limiter or compressor like some amps have, you pull more because you can play into the compressor and the average level is higher.

    Power draw depends on style too. One player playing really loud jazz might not bother anything, but someone playing industrial punk might be popping breakers all the time.

    You can run whole shows off a couple of 20A outlets for folk type bands, but generally no way for rock, etc.
    The one time we got stuck with that kind of deal, we had someone stand by the breakers and reset them. They got kinda hot, but we got through it cuz the sound was always back on fast and the audience was cool. It was in a picnic shelter type place, and the power was not as advertised..... (is it ever?)