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#1509059 - 11/10/08 12:26 PM under fuse?
10hz maniac
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SD Ralph Wiggum


Registered: 30/08/07
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Loc: PA

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I've read somewhere that someone smoked their amp simply by under fusing it. the wiring and all the connections were correct size and done well, he simply put a smaller fuse in line that he probably should have. fuses don't blow until a current well over the rating is put through it for a length of time, and that had something to do with it from what i understand.

is this right, if someone has a system that draws about 40-50 amps, would it be better to put a 100 amp fuse inline or would a 60a fuse suffice? can this really harm your gear?
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#1509073 - 11/10/08 02:59 PM Re: under fuse? [Re: 10hz maniac]
BC1
SD Ralph Wiggum


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 Originally Posted By: 10hz maniac
I've read somewhere that someone smoked their amp simply by under fusing it. the wiring and all the connections were correct size and done well, he simply put a smaller fuse in line that he probably should have. fuses don't blow until a current well over the rating is put through it for a length of time, and that had something to do with it from what i understand.

is this right, if someone has a system that draws about 40-50 amps, would it be better to put a 100 amp fuse inline or would a 60a fuse suffice? can this really harm your gear?


No sir. Using a smaller fuse than recommended cannot harm the equipment. Please stop and think about your logic for a second. If it takes a while for a smaller fuse to blow, how much longer would it take a larger fuse to blow if ever?! The fuse was NOT what killed that gentleman's stereo if he used a fuse smaller than recommended.
Fuses are there for 1 reason. It's not to protect your equipment despite what people may say. They are there to keep your vehicle from burning to the ground in the event of a short. The fuse is really there to protect the power wire from acting as a lightbulb during high current draw. The fuse blows before this happens and nothing catches on fire. Too small of a fuse will prematurely blow causing normal use to break the circuit. Nobody wants that either.
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#1509078 - 11/10/08 03:39 PM Re: under fuse? [Re: BC1]
Thumper26
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^ what he said. I try to underfuse as much as possible. If something happens to go wrong with my stereo, I want the electrical circuit broken as soon as possible. My main battery fuse is underfused, as is the fuses on the distro block for my amps.
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#1509117 - 11/10/08 07:14 PM Re: under fuse? [Re: 10hz maniac]
TtownCLS Moderator
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 Originally Posted By: 10hz maniac
I've read somewhere that someone smoked their amp simply by under fusing it. the wiring and all the connections were correct size and done well, he simply put a smaller fuse in line that he probably should have. fuses don't blow until a current well over the rating is put through it for a length of time, and that had something to do with it from what i understand.

is this right, if someone has a system that draws about 40-50 amps, would it be better to put a 100 amp fuse inline or would a 60a fuse suffice? can this really harm your gear?


I don't know who you heard this from. I'm an Electrical Engineer, so I would love to hear the theory behind this. A smaller fuse than required blows up equipment????? If your system draws 50 amps of current, and you fuse it at 30 amps, you will blow fuses regularly. That's all. If your system draws 50 amps of current and your wire will only handle 60 amps, then you fuse it at 100 amps. You run the risk of burning your car to the ground because the wire will melt before the fuse blows.
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#1509168 - 11/10/08 10:49 PM Re: under fuse? [Re: TtownCLS]
10hz maniac
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SD Ralph Wiggum


Registered: 30/08/07
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Loc: PA

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my thinking behind it was i know that i had much trouble years ago with an undersized power wire with a overpowered system. i was trying to power 2 amps that are about 800 watts combined power with an 8 guage wire. my lights were dimming real bad when i turned the volume up and when i used a DMM at the amps terminals, the voltage was dropping to about 10v. i know if you run an amp at a low voltage, that can harm the amp.

so using a smaller than required fuse (inline with a sufficient wire size) wouldn't lower the overall voltage that the power lead carries? i'm not much of an electrical theorist.
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#1509254 - 12/10/08 10:32 AM Re: under fuse? [Re: 10hz maniac]
BC1
SD Ralph Wiggum


Registered: 01/02/08
Posts: 50

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 Originally Posted By: 10hz maniac
my thinking behind it was i know that i had much trouble years ago with an undersized power wire with a overpowered system. i was trying to power 2 amps that are about 800 watts combined power with an 8 guage wire. my lights were dimming real bad when i turned the volume up and when i used a DMM at the amps terminals, the voltage was dropping to about 10v. i know if you run an amp at a low voltage, that can harm the amp.

so using a smaller than required fuse (inline with a sufficient wire size) wouldn't lower the overall voltage that the power lead carries? i'm not much of an electrical theorist.


Well in electronics and electricity, we usually pretend that wires have 0 resistance as long as their gauge and length are capable of carrying the current draw. We know that they actually do have some resistance and this becomes apparent under high current draw like you saw with your 8 gauge wire. To give you an example of this, 1 20 ft strip of 4 gauge wire will have the same resistance as 2 40 foot strips of 4 gauge in parallel. This shows you that not only the gauge but length plays an important role. Now, we put the fuse there to be the weakest link, because if anything fails we surely want it to be the fuse but it's just not LONG enough to make a big difference on the overall resistance. Does it have higher resistance than the wire? Sure it does. That's what makes it work. Does it hinder the performance of your system? I think if you were able to measure the difference it would be so small that it wouldn't matter. It definitely would NOT be a large enough benefit to warrant running without one.
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#1509377 - 12/10/08 06:20 PM Re: under fuse? [Re: BC1]
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yeppers, well done BC1.
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