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  • amp fuse calulator

    hi im new too this site so i want to make it simple i was planing on getting two KENWOOD KAC-9104D MONO amps, thinking of useig them on 2 12 w7 or diamond audio subs. I would like to use a 0 gauge main wire and a dual amp fuse holder but im lost when it comes to calulte what size fuse to get, is there a site that can help me cause i know later on i may choose difernt kinds of amps but like to know how to choose the rite fuse...


    my 2nd question would be if anyone can give me some advice on choosen some good bass hitting subs an amps i like a good clean bass plus i knwo some use caps should i use them how bout useing oGuage wire rite know my project car is a ford expoler but i have a lil civic hatbac soo smaller space then a ford.. anyways if u can help please give me your option thanks


    alex.....

  • #2
    for fuse size, just add up the fuses on the amps.

    for caps-- you could also burn your money, or better yet, give it to me

    basically, caps end up drawing more than they can add to the overall power level of the system-- so a extra battery would have a better effect.

    for subs-- everyone has their own preferance-- go to a local shop and listen to a couple your self.
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    • #3
      just food for thought, but what happens to your alternator when both of these badboys start suckin down battery juice? however u end up wiring your speakers, if you drop below 4 ohms resistance, seems like the inductor coils in your alternator are going to scream for mercy.

      again, just a thought to keep in mind when picking your drivers...

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      • #4
        yea thats why i wanted to know should i use caps or another battery ive seen people upgrade there wires from the battery to the alternator useing bigger wire bigger ground wires... thanks for ur insight sound mann but id like too hear other people exp with differnt subs and amps

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        • #5
          Originally posted by kid617 View Post
          yea thats why i wanted to know should i use caps or another battery ive seen people upgrade there wires from the battery to the alternator useing bigger wire bigger ground wires... thanks for ur insight sound mann but id like too hear other people exp with differnt subs and amps
          Just remember there is no free power. You only have what the alternator outputs to work with. Extra batteries will help stabilize the system and give you more short bursts of power but if the alternator output is "x" and your system draws "x" + 20amps, you arn't going to win. Research doing "the big 3" upgrade and that will be a good start.
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          • #6
            Don't worry about poor old alternator strain - it is self limiting.
            Load wise, adding a battery or cap doesn't significant difference when averaged over time, except that a battery does add an extra load (about 1% of its c20 rate) but that is insignificant - typically 1-2Amps.

            If the alternator isn't big enough, a battery or capacitor will merely extend the battery reserve time - they will still need recharging, and neither will keep the voltage above 12.7V (compared to typically 13.8-14.4V for an alternator)

            And no matter what the situation, an AGM battery will leave a cap for dead - even small 1AH AGMs, though 7AH are more common (cheap for size) unless using a full-sized 2nd battery. (But even then, if the big AGM is too far from the amps, a 1AH where the cap was/is to be mounted will still be better.)

            As to fusing, as soundman said, you can add all your fuses.
            But if that exceeds your cable rating, the fuse for the cable instead.
            And equipment fuses indicate a maximum current they can draw which may be far greater than average (motors and capacitive loads are renowned for that) which may lead to overpriced fuses. (And avoid glass type fuses.)

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            • #7
              Originally posted by OldSpark View Post
              Don't worry about poor old alternator strain - it is self limiting.
              Load wise, adding a battery or cap doesn't significant difference when averaged over time, except that a battery does add an extra load (about 1% of its c20 rate) but that is insignificant - typically 1-2Amps.
              "Self Limiting"? Yeah, limited to the point where you fry the brushes and voltage regulator by pulling too much current through it. And adding another battery without an isolator will put much more load on an alt. than just 1-2 amps.

              Originally posted by OldSpark View Post
              If the alternator isn't big enough, a battery or capacitor will merely extend the battery reserve time - they will still need recharging, and neither will keep the voltage above 12.7V (compared to typically 13.8-14.4V for an alternator)
              A cap will not add to a battery's reserve time. A cap is pretty much instantaneous charge/discharge, regardless if it's 1 or 30 Farads in size.

              Originally posted by OldSpark View Post
              And no matter what the situation, an AGM battery will leave a cap for dead - even small 1AH AGMs, though 7AH are more common (cheap for size) unless using a full-sized 2nd battery. (But even then, if the big AGM is too far from the amps, a 1AH where the cap was/is to be mounted will still be better.)
              How exactly will a sealed battery "leave a cap for dead"?

              Originally posted by OldSpark View Post
              As to fusing, as soundman said, you can add all your fuses.
              But if that exceeds your cable rating, the fuse for the cable instead.
              And equipment fuses indicate a maximum current they can draw which may be far greater than average (motors and capacitive loads are renowned for that) which may lead to overpriced fuses. (And avoid glass type fuses.)
              In a perfect world, on a perfect day with the gain turned up all the way, and the volume up all the way, a decent amp that contains say a 80A fuse will pull 70A. The rating of each individual amp is slightly above what the amp could possibly do. Why? for safety, to lessen the possibility of burning your car down. Yes, add the value of all fuses to arrive at the value to use at the battery. But what's with the comment about glass fuses? an 80A glass fuse is actually superior to (the only other type of fuse that isn't glass) a 80A circuit breaker. A circuit breaker's armature can stick, causing it not to detach the load when it exceeds it's rating. I'd rather have a glass fuse that pops and needs replacing, than a CB that starts a fire.

              Honestly Oldspark, I'm not trying to attack you, but making comments like that are kinda misleading. OP, buy yourself a high-output alternator, upgrade your under-hood wiring to a thicker gauge (especially the battery to frame connection), and keep your battery in good shape. Optionally, buy a small (1 Farad) capacitor to help with transient current draw. (It eases the hit the alternator takes when a big system pulls a lot of current for a big bass hit) The only thing extra batteries will do for you is increase your listening time when the motor is off. I think the OP should be more concerned with the gauge of wire and the length of it. Here's a good chart to help you out: http://www.the12volt.com/info/recwirsz.asp
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              • #8
                i agree with snooch 100% and will add in addition to grounding straps the alternator positive lead is usually <8 gauge wire and will over heat, melt, ground out, causing damage in multiple forms.

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                • #9
                  Originally posted by Snootch View Post
                  "Self Limiting"? Yeah, limited to the point where you fry the brushes and voltage regulator by pulling too much current through it. And adding another battery without an isolator will put much more load on an alt. than just 1-2 amps.
                  Ha ha - as if full amperage goes through the rotor and voltage regulator.
                  The alternator stator itself is self limiting (back emf matches forward etc) - unless it's a really crap or "to the limit" stator winding.
                  Main diodes that can't handle it are undersized (I know many Bosch don't).
                  Ditto for regulators that can't handle the rotor current (which should be limited to not burn the rotor).


                  Originally posted by Snootch
                  A cap will not add to a battery's reserve time. A cap is pretty much instantaneous charge/discharge, regardless if it's 1 or 30 Farads in size.
                  I rest my case - pretty much instantaneous discharge - ie, no extra reserve time to hold up a load.
                  Alas I know what you mean - but do the calcs - essentially you are correct and that is my point.


                  Originally posted by Snootch
                  How exactly will a sealed battery "leave a cap for dead"?
                  Ok - feed me the caps and the load, the ESR etc..... Nah... it's been done before.
                  If the ESRs match (even though they become negligible compared to all but the biggest amps), then isn't it simply the AGM's surface charge vs capacitance down to 12.7V? Below that, the battery wins hands down.


                  Originally posted by Snootch
                  In a perfect world, on a perfect day with the gain turned up all the way, and the volume up all the way, a decent amp that contains say a 80A fuse will pull 70A. The rating of each individual amp is slightly above what the amp could possibly do. Why? for safety, to lessen the possibility of burning your car down. Yes, add the value of all fuses to arrive at the value to use at the battery. But what's with the comment about glass fuses? an 80A glass fuse is actually superior to (the only other type of fuse that isn't glass) a 80A circuit breaker. A circuit breaker's armature can stick, causing it not to detach the load when it exceeds it's rating. I'd rather have a glass fuse that pops and needs replacing, than a CB that starts a fire.
                  When I say glass fuse - I mean the AG series (3AG 0Ag etc) - ie, glass tube with end caps - the blades (bolt in etc) are more reliable (no problematic cap bonding).
                  The amp fusing is not to protect the car - it's to protect the amp. Cable fusing is to protect the car. Not that I'm sure what point you are trying to make here...
                  I reckon my comments are valid - you can fuse to match the end load draw provided that does NOT exceed each cable's rating....
                  And when I say glass - I mean the AG series (3AG 0Ag etc) - ie, glass tube with end caps.
                  BTW - an 80A fuse will probably take over 1 hour to blow at 85A (very depended on the fuse type).


                  Originally posted by Snootch
                  Honestly Oldspark, I'm not trying to attack you, but making comments like that are kinda misleading. ]
                  Sorry if I'm misleading - I may be overestimating my audience and writing too generally.
                  But some of the statements before my reply are more they misleading - they are incorrect. I was hoping to correct that....


                  But caps are rarely worth it. And if they could be connected flat to the alternator, you would probably notice its load on the alternator (a discharged capacitor is initially a short circuit when connected to a voltage).
                  Long term, a cap is negligible load - it is effectively 100% efficient, whereas a battery always has a small charge current (say 1-2A). And whilst they both provide/absorb energy (charge), the battery does it with inefficiency (maybe 20% or more charging; I'm unsure about discharge).


                  But since you mention the12volt.com, feel free to argue the validity of caps there. (Not that it's much different to responses I've seen on here!)

                  Depending on your installation, I could probably point you to a $35 AGM that will beat your cap and probably jump start your car as a bonus. Or I could size the AGM to suit the new price of the cap.

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