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RMS power and fuse ratings

  1. Sep 12, 2014 #1
    I just bought a few car audio amplifiers, they are advertised as 6000 watts and 800 watts respectively but the fuse ratings are 60ampsx2 and 20ampsx2 so am I missing something here? I purposely bought higher wattage amps because I believe their only advertising peak power (assuming they use slo-blo fuses).

    am I correct in buying high wattage advertised amps assuming I can get 1440 and 480 true rms watts out of them?

    I plan on getting a low distortion high spl 18" sub in a first order bandpass box and 4 6-1/2" coax speakers and building a active crossover hooked up to a deck with a usb interface for an ipod.
     
  2. jcsd
  3. Sep 12, 2014 #2

    psparky

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    What you are saying is reasonable I beleive.

    Maybe the bigger amp can produce 6000 peak watts.....but it is likely to make that at 99% distortion.

    Perhaps it makes its 1440 watts at .1% distortion....don't know, have to read specs if available.

    But this brings up another concern. Is your alternator powerful enough to produce a steady 160 amps and still run your car accessories? If not, will likely need bigger alternator.
     
  4. Sep 12, 2014 #3
    I won't be running it at full blast, and it won't be on all the time so it should be ok.

    btw they say .1% distortion but not at what levels.
     
  5. Sep 12, 2014 #4

    jim hardy

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    Physics says energy is conserved.
    You can't get more out than you put in.

    Power is rate of doing work or using energy.
    http://hyperphysics.phy-astr.gsu.edu/hbase/work.html
    For a brief instant you can take energy out of something faster than you're putting it in
    but then you have to reduce output and let it restore the balance.

    Less than highly principled marketeers use the term "peak instantaneous power" to roughly quadruple the claimed power output of their products. Power numbers sell .

    You're right to question claimed power versus fuse on input.
     
  6. Sep 12, 2014 #5
    thanks jim, I knew the power claims were funny, I just wanted to be sure.
     
  7. Sep 12, 2014 #6

    psparky

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    If you are actually running 120 amps to an amp, make sure you use at least a #2 wire.....or else your wire will be the fuse itself....also known as an electrical car fire.

    Just keep the rated output of your alternator in the back of your head....it may work, it may not. I'm pretty sure your average car alternator these days puts out 100 to 120 amps in general....it will use all it's power to run if many car accesseries are on. If your alternator is not big enough, no biggy, buy a 300 amp high out alternator and you will be all set.

    You know you will have a problem if the headlights dim or the windshield wipers slow down when the stereo is cranked. But as the smart guy I assume you are, you will work this out ahead of time. You were crunching numbers at the fuses of your amplifiers....crunch the numbers all the way to the source. The source will actually be your limiting factor.
     
    Last edited: Sep 12, 2014
  8. Sep 12, 2014 #7

    jim hardy

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    and upsize the wires between alternator and battery.

    I could tell an anecdote about a Corvette that ate alternators.... suffice it to say I put the seventh one on it and found the trouble. That made the owner very happy.

    old jim
     
  9. Sep 12, 2014 #8

    psparky

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    True that.

    One more thing....if you run that stereo without the engine on, it will drain your battery in a big hurry....leaving you with no music and NO power to start your engine. Stranded with no tunes....not good. And that's with all the perfect wiring and 300 amp alternator.

    Incidentally, at least a 350 MCM or 185mm^2 is the wire you will need from 300 amp alternator to battery.
    That's a BIG wire!!!! Lots to think about in building high power systems that weren't orgininally designed to be there!
    It can be done, just needs to be well thought out.

    Which brings up one more thought....is your battery capable of being charged with a max of 300 amps? Prob should consider increasing the ground size from the battery to the chassis as well!
     
    Last edited: Sep 12, 2014
  10. Sep 12, 2014 #9

    psparky

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    This statement is like saying you are building a 350 small block engine to make 600 HP at 8,000 RPM.

    But to save money you are going to use cast iron pistons and rods with a cast iron crank instead of using all forged parts. To justify this, you say that you will only rev the engine to 5500 RPM and only produce 400 HP.

    In other words, why would you build a high powered system unless you are going to use all its power with confidence?

    Do the job 100% correct to start. No regrets.
     
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