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Amp power cable and fuse


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Lew15 
Member - Posts: 4
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Joined: December 27, 2004
Location: United Kingdom
Posted: December 27, 2004 at 12:43 PM / IP Logged  

i have recently bought an amp, i have all the cables but i don't know what fuse to use for the + positve cable, can anybody tell me???????

Thanks, Lew

jazzcustom131 
Copper - Posts: 175
Copper spacespace
Joined: October 10, 2004
Location: United States
Posted: December 27, 2004 at 2:20 PM / IP Logged  
Look at the side of the amp. There should be fuse in the side of it. Probably right beside the Power intake on the amp. That's what you should fuse it for.
Greed is for amateurs.
Disorder,chaos,anarchy now THAT is fun!!
Lew15 
Member - Posts: 4
Member spacespace
Joined: December 27, 2004
Location: United Kingdom
Posted: December 27, 2004 at 2:54 PM / IP Logged  
thanks, so if i was running two amps just add it and fuse it fore wat it adds up to???
haemphyst 
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Joined: January 19, 2003
Location: Michigan, Bouvet Island
Posted: December 27, 2004 at 4:39 PM / IP Logged  
NO, NO, NO!!! You DO NOT fuse a power lead for the load on it, you fuse a power lead for the power lead itself. That fuse is there to protect the CAR, not the amplifiers connected to it. What size power cable is it?
It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."
jazzcustom131 
Copper - Posts: 175
Copper spacespace
Joined: October 10, 2004
Location: United States
Posted: December 27, 2004 at 6:56 PM / IP Logged  

What do you mean for the power lead itself?? You fuse an amp to control the amperageit can have.

Greed is for amateurs.
Disorder,chaos,anarchy now THAT is fun!!
haemphyst 
Platinum - Posts: 5,053
Platinum spaceThis member has been recognized as an authority in Electrical Theory. Click here for more info.spaceThis member has been recognized as an authority in Mobile Audio and Video. Click here for more info.spacespace
Joined: January 19, 2003
Location: Michigan, Bouvet Island
Posted: December 27, 2004 at 7:42 PM / IP Logged  
The amplifier SHOULD have it's own fuse protection. If not, you should be using a fused distribution block - that's what THOSE are for! The primary fuse in a wire is ONLY there to protect the car in case something happens to the insulation of the primary wire. If you get in an accident and a number 4 is your primary wire, and the insulation is compromised, but you do not have it fused at 150 amps, the battery can make FAR more current than that for long enough that it can cause that wire to get hot and possibly catch fire. The 150 amp fuse will prevent this from happening, also disconnecting the battery from dead-shorting against itself THROUGH THE POWER WIRE.
See this page proper fuse ratings for a given power cable. Use the chart in the lower right - the one called "Power & Ground Cable Specs". This is where you should ALWAYS fuse your power cable (or lower). That primary fuse's only job is to protect the car and primary wire, not the amplifier. Yes, if your total amplifier draw is more than, let's say 150 amps on a number 4, then you would use the next size wire, not just put a bigger fuse in, because you are already ending up with too much voltage drop to be acceptable.
Granted, IF you are running less than 150 amps through a #4, then yes you CAN use whatever size fuse makes you happy, but the fuse IS a resistance connection, and DOES contribute to voltage drop to the trunk, so why not just put the biggest safe fuse in there, and prevent as much of that drop as possible? It is OK to do that, but as I said, it's job is NOT to protect the amps... This would be simply a guideline to set the MINIMUM REQUIRED fuse value, but not the OPTIMUM DESIRED fuse value.
It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."
jazzcustom131 
Copper - Posts: 175
Copper spacespace
Joined: October 10, 2004
Location: United States
Posted: December 27, 2004 at 7:53 PM / IP Logged  
Why give an amp more power than what it can use?? I would think if something needs nothng more than 20 amps, then why give it 150? I'm confused. Are you saying put a 150 fuse at the battery and two twenties at the dist block? Where's the logisc in that. That chart has ratings of maximum amperes allowed for a piece of wire. I doubt he is pushing 150 amp through that line, so there is nothing wrong with running it that way.
Greed is for amateurs.
Disorder,chaos,anarchy now THAT is fun!!
jazzcustom131 
Copper - Posts: 175
Copper spacespace
Joined: October 10, 2004
Location: United States
Posted: December 27, 2004 at 7:58 PM / IP Logged  
I'm confused. Why give an amp 150 amps when it can only use 20? Fuse it at 40 at the battery, and two 20's at the dist block. That only makes logical sense. If a wire grounds out on metal, the fuse willblow man. I don't understand your logic. That guide is the maximum amperes that can be placed through that size wire. I've always been told to do it that way, and was told that by people that have been doing this for 30 some odd years.
Greed is for amateurs.
Disorder,chaos,anarchy now THAT is fun!!
jazzcustom131 
Copper - Posts: 175
Copper spacespace
Joined: October 10, 2004
Location: United States
Posted: December 27, 2004 at 7:59 PM / IP Logged  

my bad on the double post, hit private messenger button by accident and thought it had erased my first one.

Greed is for amateurs.
Disorder,chaos,anarchy now THAT is fun!!
haemphyst 
Platinum - Posts: 5,053
Platinum spaceThis member has been recognized as an authority in Electrical Theory. Click here for more info.spaceThis member has been recognized as an authority in Mobile Audio and Video. Click here for more info.spacespace
Joined: January 19, 2003
Location: Michigan, Bouvet Island
Posted: December 27, 2004 at 8:16 PM / IP Logged  
haemphyst wrote:
Granted, IF you are running less than 150 amps through a #4, then yes you CAN use whatever size fuse makes you happy, but the fuse IS a resistance connection, and DOES contribute to voltage drop to the trunk, so why not just put the biggest safe fuse in there, and prevent as much of that drop as possible? It is OK to do that, but as I said, it's job is NOT to protect the amps... This would be simply a guideline to set the MINIMUM REQUIRED fuse value, but not the OPTIMUM DESIRED fuse value.
#1) Read my last paragraph again...
#2) An amplifier will ONLY pull as much current as it needs, no matter HOW big the primary fuse is, and the amplifier has it's OWN fuse protection.
#3) There is NO SUCH THING as allowing a component more current than is necessary (see #2). Allowing it "more than is necessary" will simply prevent VOLTAGE SAG, and therefore allow MORE EFFICIENT OPERATION. (read: less heat)
#4) OK, well then I guess the people on this board with all of their possibly HUNDREDS of years, combined, (and my 16 years experience and USNavy high voltage distribution and USNavy low voltage electronics background) don't know ANYTHING AT ALL about what we are talking about.
Ya hear that DYohn, kfr01, et al? We've been doing it wrong all this time! Please read some of the posts from the more experienced people on this board before you start questioning the information provided.
It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."
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