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Fuse Keeps Blowing Out

Discussion in 'Audio' started by ZfromNJ, Mar 26, 2001.

  1. ZfromNJ

    ZfromNJ Registered Member

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    I recently put in my 74 a head unit (sony) a box with two 10's and a 300 watt amp. BUt the system keeps blowing out my fuse in the fuse box. What did I hook up wrong?
     
  2. Hathaway

    Hathaway 1/2 ton status

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    Could be a lot of things. Fuse could be too small. Part of your power wire could be grounding to the chassis and blowing fuses. First thing I'd guess though is your fuse is too small.

    Dan, '86 K5, 5.0L v8, NP208, TH700R4, open 10bolts front and rear, 3.43gearing, K&N filter, 31x10.50R15 Trailhandlers
     
  3. ZfromNJ

    ZfromNJ Registered Member

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    That is what I thought but I tried changing the fuse and even when I went up to a larger fuse it would last a small while and then blow again. DO you think that it is the ground? Chevy recommends running a 10 A but I have put everything in there from a 10 A to a 30 A, and like I said maybe it might last 5 minutes then blow.
     
  4. Blazer79

    Blazer79 1/2 ton status

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    Seems like you're feeding power to the amp from the factory fuse. If that is the case, it will blow it immediately because that fuse and wiring was designed to feed a tiny am/fm radio, not a monster 300w amp. You should run a wire to the amp directly from the battery with an inline fuse rated the same amps as the fuse in the amp. The fuse in the fuse box should be OK for the head unit only.

    Hope this helps.

    <font color=blue>//////
    <A target="_blank" HREF=http://blazer79.coloradok5.com>http://blazer79.coloradok5.com</A>
    </font color=blue>[​IMG]
     
  5. Hathaway

    Hathaway 1/2 ton status

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    Blazer 79 has it right on. Run a 10awg (I'd go with 8awg personally) power wire from the battery directly to the amp. Make sure you fuse the power line within 18" of the battery.

    Dan, '86 K5, 5.0L v8, NP208, TH700R4, open 10bolts front and rear, 3.43gearing, K&N filter, 31x10.50R15 Trailhandlers
     
  6. ZfromNJ

    ZfromNJ Registered Member

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    Thanks Fella's I am going to try it then let you know. WHat if I already ahve it hooked up that way? Then what? Could it be the Radio itself.
     
  7. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    The other option could be that the speakers are wired in such a way that they are creating too small of a load on the amp. (Ohms, that is)

    If your amp is not able to drive low impedence loads it will get very hot, or burn up, shut itself down internally, or simply blow the fuse.

    To double check this as a possible issue, connect only 1 speaker to the amp and see if it runs cooler (and doesn't blow the fuse)....

    Also, speakers have a nominal ohm rating (like 4 ohms) but that doesn't mean that they are 4 ohms across their entire operating frequency. At certain frequencies, the impedence could be as low as 1 ohm. If you have a couple of these speakers wired in paralled to each other, you would be presenting a 1/2ohm load to the amp at that frequency....not good. This is more obscure possibility, but if this is what's happening you can build a simple "Zobel Network" for each driver to ensure that it's load on the amp is nice and consistent, no matter what frequency it's playing.

    Also, PLEASE put the correct size fuse back into the amp....Using a bigger fuse is NOT the answer. Find the source of the problem and fix it the right way. I have seen vehicles burned to the ground because someone didn't bother to use a fuse, or "cheated" the fuse up to a higher rating. It's just not worth the risk.

    Good Luck!

    -Greg72
     
  8. Hathaway

    Hathaway 1/2 ton status

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    I highly doubt that running the amp at an impedance lower than its rated is going to blow fuses. Fuses blow when too much current runs through them. If the impedance is too low the amp will just go into protect mode.

    I'm willing to bet that the guys problem stems from the fuse being too small (a 10a fuse in the factory fuse box).

    And also, you wanna explain the "Zobel Network" I'm curious to see how you think you can get impedance to stay exactly the same through out a range of frequencies.....

    Dan, '86 K5, 5.0L v8, NP208, TH700R4, open 10bolts front and rear, 3.43gearing, K&N filter, 31x10.50R15 Trailhandlers
     
  9. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    BigBrownK5,

    Yeah I hear ya...I have a feeling the guy wired his amp to the fuse block instead of the battery. He began asking for more 'obscure' reasons for a failure so I suggested the low-impedence thing.

    Here is a quick link I found on Zobel networks: <A target="_blank" HREF=http://www.customcarsound.com/calc_cr.html>http://www.customcarsound.com/calc_cr.html</A>

    It will give you the idea of what I was referring to....

    Talk to you later,

    -Greg72
     

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