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my power supply idea

Discussion in 'Amps and Cabs [BG]' started by Phat Ham, Apr 24, 2003.


  1. Phat Ham

    Phat Ham

    Feb 13, 2000
    DC
    Ok my band is a cover band that plays mainly frat parties. My friend has his own PA and runs sound for us. This summer he is going to be getting subs and running a boatload of power to them, which means combined with everything else we power in the band your standard 15A or 20A circuit isn't going to provide enough current. We were thinking of hooking up some sort of rig that takes the 30A 220V outlet that the dryer is plugged into and steps it down to 120V and running everything off of that. I've seen some bands tap directly into the breaker box with big alligator clips to accomplish the same thing, but that's a little too dangerous for my taste. My question is, would it be that hard to make something like this? Would I need more than a transformer and some outlets wired in parallel to the secondary of the xformer? And how much should I expect a transformer that can handle that amount of current to cost?
     
  2. I've seen what you are talking about done many times. They use some sort of splitter that creates 2 120volt outlets. Get with a GOOD electrician that knows house and industrial wiring to set this up for you. This sh!t can kill you.
     
  3. Disclaimer: Don't try this at home - get a competent electrician to make you a cable and outlet box.

    Having said that, I've done this a few times.

    All you need is to split off one hot and one neutral from the dryer socket. 220v service is a three-wire service - two 110v hot conductors and one neutral.

    It takes all three conductors to make 220v - if you only use one pair you get 110 - but one wire has to be hot and one neutral.
     
  4. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    There are companies that make power distros like you describe. Motion Labs is one that comes to mind. You can also have an electrician build a custom one for you, but it'll probably be pricey.
     
  5. search ebay for a "step down transformer"

    or like others have said have an electrican split the hot leads.

    BTW I have run 10,000 watt systems on a 20 amp plug. You must be really cranking to need more then 30
     
  6. Phat Ham

    Phat Ham

    Feb 13, 2000
    DC
    Well we played a couple gigs where we borrowed subs that were powered by a QSC RMX 1850HD bridged into 4 ohms. Together with the rest of the PA we were running about 4000W, and regularly tripped breakers if we tried to run everything off of one circuit. Sometimes it can be a pain to find more than one free circuit in a frat house (every kid has a mini fridge in his room), so I figured the easiest way would be to use the dryer's circuit that every house is guaranteed to have.

    One thing I'm not sure of with the 240V dryer connection. I realize there are 3 prongs, two 120V hot leads that are 180 degrees out of phase (I think) and a neutral. If I took one of the hot leads and the ground I'd get 120V, but would it be able to handle a 30A load?
     
  7. Depends on the building wiring and the value of the breaker on the circuit.

    Another option would be to split the dryer socket into two 110v sides - a four-outlet box would be pretty handy for this.
     
  8. The dryer plugs don't have 4 prongs? That means they're pretty old. It also means that ground and neutral are strapped together which doesn't leave you any failsafe if there's a ground or neutral fault. I'd avoid using audio equipment on those types of circuits, or find a way to get a dedicated ground path. This generally involves running a piece of wire outside, driving a piece of rebar into the ground and connecting the wire to it.... Sounds paranoid, but if there's a fault in the neutral/ground your gear will be damaged or you might become a ground path if you happen to be touching a mic.....
    Anyhoo, with the single phase 30A circuits, both hots are in phase (that's why they add to 240V as opposed to 208V in a 3-phase system) and each will handle 30A. So you don't need a transformer or any fancy equipment, just run some outlets off each hot leg ground and neutral.
    My advice would be to get a ready made (approved) distro or to get one made by an electrician and approved by an inspector. You can't be too careful with electricity...