What size fuse to use?

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kencat21

Member - Posts: 12

Joined: July 06, 2006

Location: United States

Posted: November 16, 2006 at 11:59 PM / IP Logged

I need help deciding what size fuse to use for my system.

i have a 72x4rms @4ohms amp, powering 4 speakers and i have 2 svc 12" 4 ohm subs wired in parallel @ 2 ohms to get around 400 watts rms from a 1 channel amp. Plus i'll have a 1.5 farad capacitor.

any help will be greatly appreciated.

I plan on wiring it like this pic plus i'll have the second sub.

kymadan

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Joined: March 25, 2006

Location: United States

Posted: November 17, 2006 at 3:30 AM / IP Logged

Use Ohms Law.........Watts divided by Volts = Amperes

Take the total amount of system wattage....... Divide it by 12....... And that will equal the Amperage of the fuse needed. The fuse needs to handle the power that will flow through the cable under maximum operating conditions (full power) and no more (ideally).

Like if you get 58 amps you would go with a 60 amp fuse. If your blowing fuses and it has been sized correctly, there is a short circuit that needs to be addressed. If you came between fuse sizes, you could go to the higher amp rating fuse (Which is what I would do.) for less of a chance of accidentally blowing the fuse, or you could go with the lower size that will have better short circuit protection.

haemphyst

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Posted: November 17, 2006 at 6:04 AM / IP Logged

If you are asking what size fuse to put in your fuse holder, at the battery, in the red line on your diagram, then we need to know what size the power cable is.

If using a #4, fuse it at 150A, a #2 at 225A, and a #0 at 350A. That fuse is there to protect the car and the power cable in the event of a catastrophe, not for the amplifiers.

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."

xtremej

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Posted: November 17, 2006 at 7:54 AM / IP Logged

Make sure to fuse the power cable at the distro block either a fused distro block or fuse holders right after it. Just a a reminder, I didn't see it in your diagram.

1lowgalant

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Joined: September 15, 2005

Location: United States

Posted: November 17, 2006 at 2:25 PM / IP Logged

nice diagram. What size fuse to use? -- posted image.

knowing wire size would indeed help. as haemphyst said, power wire fuse is to protect the vehicle and the wire, not the amps, but as mentioned, a fused distrobution block would be a good idea.

Whatever you do, DO NOT let the white smoke leak out of the wires.....

aznboi3644

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Posted: November 17, 2006 at 5:46 PM / IP Logged

kymadan wrote:

Use Ohms Law.........Watts divided by Volts = Amperes

Ohm's law??? fuse is to protect the wire

kencat21

Member - Posts: 12

Joined: July 06, 2006

Location: United States

Posted: November 17, 2006 at 7:34 PM / IP Logged

thanks for the responses, i will be using 8 gauge wire until it reaches the power block and then 4 guage after that until the battery. Haemphyst are you sure it would be 150? I was thinking more like 100 can you show me the math you used?

Im still not sure on how to mathematically do it because i read somewhere that you get the total rms power of both amps, multiply by 2, then divide by 13.8. But do i use the 4 0hm rating or however many are used. I dont know if this is right, but let me know if it is or not.

72x4=288

288+400=688

688x2=1376

1376/13.8=99.7

so wouldnt i use a 100amp fuse?

and at the power block use a 60amp fuse for the 4channel amp and a 40amp fuse for the mono amp?

thanks for the help.

haemphyst

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Joined: January 19, 2003

Location: Michigan, Bouvet Island

Posted: November 17, 2006 at 10:01 PM / IP Logged

Here...

No math required, all you need to know is the safe current capacity of the wire you are using, and fuse for THAT capacity. You are making it FAR harder on yourself than you need to... What size fuse to use? -- posted image.

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."

kencat21

Member - Posts: 12

Joined: July 06, 2006

Location: United States

Posted: November 18, 2006 at 3:13 AM / IP Logged

so ur saying i should use a 150a fuse at the battery and two 100amp fuses at the power block?

xtremej

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Location: United States

Posted: November 18, 2006 at 9:45 AM / IP Logged

Yes although imo you generaly can fuse it to a low rating ie if something does happen it will pop a little sooner. As it is to protect the wire and not the amps is something that is understood, but I know several installers that use the theory of going 10 to 20 amps higher than the combined total of the amps fuses for fuse sizing of the power cable.. I hope that made sense What size fuse to use? -- posted image.

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