How big of a fuse for these (2) amplifiers?

[deadken]

I had a Alpine 300W amp in my car (75x4 @ 2 Ohms). IIRC, it has 2 x 30A fuses. I've since bought a Alpine 500W amp for the sub-woofer (1x500 @ 2 Ohms). It has 2 x 30A fuses. I'm running a (true) 4 gauge power cable which will feed a fuse block that has (1) 4 gauge input and (2) 8 gauge outputs. Each leg of the 8 gauge will feed one amp. I should also mention that there is a fuse inline with the 4 gauge cable right near the battery.

Now, my question is how big of a fuse should I put in each location? I'm guessing that if each amp has 2 x 30amp fuses, each should draw a maximum of 60 amps. I'm guessing that each leg of the fuse block will need a 60 fuse. If that is correct, then the inline 4 gauge fuse should be 120 amps.

If I had to guess: I could *probably* run a 50A fuse in each leg with a 100A fuse for the main. But I'm just guessing that the amps should never draw nearly their maximum rating on each leg.

Please let me know if I am wrong. Please feel free to educate me if you care to.

-Thanks, Ken

 

[phucheneh]

You fuse the wire...for the wire. Not for the amps.

You should have a 125a fuse at the battery (that would be the common size; if you can get 120's, that's fine). It should be as close to the battery as possible; don't be one of those dudes with four feet of wire looped around his engine bay before the fuse. Anything between fuse and batt is unprotected.

Your distro block should have two fuses to protect your 8ga runs. 60a on each side is okay if you've got quality wire.

In reality, you could probably use an 80 and two 40's and never have a problem. But it's good to have some overhead in your wiring (which you do).

 

[Raduque]

I've got a 125 on my main power wire, about a foot from my battery, and my distro block has two 80s. I'm using an identical distro block for my grounds, so they are fused with two 80s also.

Combining grounds like that is not the way it's normally done, but hey, it looks cleaner and you only need one ground point.

The wires are feeding a "300w" Kenwood amp that's maybe 80w RMS (40w*2, 2x30a) and a 300x1 Soundstream (2x40a) amp.

 

[phucheneh]

...fused grounds, eh?

 

[Raduque]

...fused grounds, eh?

I had a spare distro block lying around and didn't feel like running two ground wires. Like I said, not the way it's typically done, but it works and I haven't had any issues.

 

[deadken]

I have installed and mounted everything. I'll need to go back later and clean up a few things and make some adjustments, but the large part is done.

For what it is worth I have a 60 amp fuse right near the battery and a 40amp fuse for the amp with the 2x25amp fuses (they are 25a, not thirty) and a 50amp fuse for the sub amp with the 2x30amp fuses. I've run it last night and today and have yet to blow a fuse. I'll still need to go back and adjust my settings on the amp but I'm thinking if these fuses hold up for a month or so, I'll drop down to a 30amp and 40amp fuse and see how they hold up.

FWIW: My buddy has a junk yard. The fuses used for the distribution block are the large spade type. He told me to feel free to raid his stash. So, I grabbed 2x30, 2x40, 2x50, and 2x60. I'm fine with running a smaller than expected fuse since the block is easy enough to access. I'll just install a larger fuse if I blow one.

Thanks for the responses and suggestions. If I might clarify a few things: You fuse the circuit, for all of the components in the circuit, not just the wire. I'm fine with using a single ground point for both of my amplifiers. I just have two wires going to it, not one. I didn't have a spare fuse block around, and if I did, I probably wouldn't have used it the way you did. But, I think it's great that your install is tidy and as long as you are happy with it, that is great.

 

[rommelrommel]

Well, you should never fuse past the wire as that defeats the purpose of a fuse essentially. You're fusing against ground shorts, so overfusing the circuit within the limits of the wire is fine.

Single ground is good, really doesn't matter how many wires go to it.

 

[Pulsar]

If I might clarify a few things: You fuse the circuit, for all of the components in the circuit, not just the wire. I'm fine with using a single ground point for both of my amplifiers. I just have two wires going to it, not one. I didn't have a spare fuse block around, and if I did, I probably wouldn't have used it the way you did. But, I think it's great that your install is tidy and as long as you are happy with it, that is great.

No, you absolutely do not.

Fuses between the battery and the amp are for the WIRE. This is a standard in every electrical manual and text you will find. You fuse the WIRE to prevent it from starting the insulation on fire. You can quickly look up what size fuse you should have for what gage wire.

Next - each of your amps has fuses already, as you noted. THAT is to protect the individual components.

You fuse for the wire. Period.

You might argue that you are actually constraining the wire to carry less current that it might by fusing to the components, but it is still a practice that is not adhered to because it is too easy to fall into the trap of forgetting to check the wire gage chart to fuse to the wire.