Power Problems

Discussion in 'Location Recording' started by Codemonkey, Aug 11, 2009.

  1. Codemonkey

    Codemonkey Well-Known Member

    Split from stealthy's thread.

    dvdhawk has informed me that our rig draws almost 8A at theoretical maximum load (cheers).
    This reminded me that, last Sunday, during the sermon, both PCs and the mixer died simultaneously. I figured it was a power problem.

    I'm convinced the surge protector that it's all plugged into is fused at 13A so even 80% of that would be enough. Also the system was nowhere near full load. The heating was off at the time and I'm sure it didn't kick in then.

    Any glaring culprits or anything I should watch for? (other than speaker failure)

    Hopefully we can prevent any more speakers going pop, or as a member of the congregation thought, "a bomb went off".
     
  2. dvdhawk

    dvdhawk Well-Known Member

    Mr. Monkey we meet again.... Sorry to hear you're experiencing difficulties at the church. Good time to buy that multi-meter and learn how to use it! nudge, nudge

    I will share a few things I've learned along the way, studying for my "Don't Die at the Gig" Class. Hopefully Davedog and others with the EE degree (Electrical Engineering) can clarify or correct if I mis-state anything.

    A) Your 500w/ch amp can potentially consume more than 1000watts. Electrical inefficiency / heat and all that. But for the sake of discussion let's say it uses 1000w.

    B) Your 500w/ch amp would only sustain that 1000+ watts of consumption if you were recreating a sound comparable to the wailing and gnashing of teeth of hell at unmerciful volumes for prolonged periods of time.

    C) While playing music the electrical draw of your amps will fluctuate, dip, and spike right along with the musical content. Often spiking over the circuit's rating, but for such a short time the breaker doesn't overheat and trip / fuses however are often less forgiving in that way unless they're specifically designated as "slo-blow."

    D) Unless it's got a malfunction most sound equipment will not draw it's theoretical limit under normal use. A 1000w amp may idle at 80watts and average between 1/8th and 1/3rd of it's max power rating for the bulk of the performance- with only the loudest peaks reaching the 1000w.

    E) Lighting equipment however is an absolute. An undimmed 1000w PAR lamp draws 1000w continuosly from the second it is switched on.

    F) All the devices upstream (electrically speaking) should be overrated to provide a margin of error/safety. That would include the plug, receptacle, wire, breaker, panel, meter base, service entrance, transformer and so on. Nothing should be pushed to the point of failure.

    I'm not saying you didn't take an electrical surge, but it's highly unlikely a 13A surge protector would crash with less than 13A of current being used.


    ** I've decided to issue a stern warning with every post involving electricity:

    LISTEN UP!! Electricity is LETHAL !!! And even with all the training and knowledge they receive as they master their trade - there are a lot of good electricians out there with fewer than 10 fingers. When working with high voltage, it only takes a momentary lapse of concentration, or one assumption to vaporize a digit or two. If you're lucky you'll get knocked across the room and live, and adapt to picking your guitar and your nose with the remaining fingers. So if you're determined to start dancing with Mr. Edison without doing your homework and/or professional supervision, all I can say is - you've been warned and....

    tat3.jpg
     
  3. Codemonkey

    Codemonkey Well-Known Member

    Cool image - thanks for the post.

    I knew that the usage was way lower, and I'd picked up that amps will draw power according to the peak volume. I didn't know that about lights, and such. No way are we ever near merciless volumes. I'd figure we peak under 100dB when going full-force (the drummer uses nylon sticks) but I'd be as well pulling a number out of a hat than trying to judge.

    (I had originally written that we are under 100 when going at it fully and that the drummer has nylons).

    An SPL meter and multimeter, and a horde of other things, too bad the local equivalent of radio shack is a rip off. In lieu of a multimeter I've gotten used to patching cables (1/4" leads that always seem to die) from insert jacks to inputs on other working channels.

    Would something as simple as this or that do or would it need to have other things like a voltage generator (for testing cables)?

    I skipped physics and did Biology/Chemistry in school when I was 14/15, then changed back and did a crash course when I was 16, and got an A. And I still dunno how to use a multimeter effectively...

    Oh, and while I'm at it... budget SPL meter and here's a combo SPL/multimeter which is a little more expensive. None of the Maplin gear comes calibrated, although I can try places online.
     
  4. Davedog

    Davedog Distinguished Member

    The manufacturers rating of watts consumed is only rated at full power for one minute. Thats all they have to report in order to get a UL label...or a CSA...or whatever they're tested with.

    That doesnt sound like much, but have you ever seen the heat that can be produced in under a second by a serious direct short?
     
  5. Thomas W. Bethel

    Thomas W. Bethel Well-Known Member

    There are a lot of unknowns.

    What is the rated impedance of the speakers? The lower the impedance the more wattage the speakers will draw from the amplifier. If you go below 2 ohms (which is very easy to do) the amplifier may go into thermal overload and trip the fuse or the sensor on the heat sink. What gauge wire do you have coming to the amplifiers/mixer. You are probably using 220 volts and not 110 like the US. A minimum wire gauge would be 14 gauge for a 15 amp supply here in the US and most circuits are 12 gauge for 20 amp circuits. If you wire size is too low you could be suffering from insufficient voltage draw and it would be a good idea to get a VOM and measure the voltage at the outlet as the system is called on to produce loud sounds. As the voltage goes down the current needed goes up and you can trip a fuse or circuit breaker very easily by being "underpowered".

    Honestly this is NOT a job for you. The church should hire a qualified electrician and have him trouble shoot the problems. The last thing you need is to have electrical problems and try and solve them yourself. It have seen to many "fixes" that are just problems waiting to happen including things like putting pennies under screw in fuses, or lengths of copper pipe being used for cartridge fuses or my favorite is to use some electrical wire to tie off circuit breakers so they won't trip (after all isn't that why the switches have holes in the handles???) The are liability and safety issues that are too important not to have this done by a pro.

    Best of luck and do get yourself a VOM or something like this http://www.amazon.com/dp/B00009MDBU/?tag=recording.org-20 This one is for 110 volts AC but I am sure they make something similar for 220 volts.

    Best of luck!
     
  6. Link555

    Link555 Well-Known Member

    That actually depends on what UL or CSA rating is being applied for. There are many many different standards a design can be tested for.
     
  7. Codemonkey

    Codemonkey Well-Known Member

    8ohm each side, it's pretty thick gauge wire. Noone told me any numbers.
     

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