Need Help with Fuse Block Question

[Bluesky 07]

I'm getting ready to install an amp. I've done stereo installs on many vehicles with no problem, but this is a new situation I'm not sure about. Google searched and looked around on here too with no luck.

The amp has a replaceable 15a fuse on it so obviously the power wire can be attached directly to the positive battery terminal. But I also want to mount a Blue Sea 4-circuit block on my positive terminal. Is it okay to connect the amp power to the block since the power line would then be fused at each end? Seems it would as long as the fuse at the terminal block isn't larger than the one on the amp. Is that right?

Thanks for any insight.

 

[SeriousZebra]

I would definitely have a fuse at both ends. You want a fuse as close to the power source as possible, if anything shorts the power line between the battery and the amp it will be bad.

 

[4RunAmok]

I would definitely have a fuse at both ends. You want a fuse as close to the power source as possible, if anything shorts the power line between the battery and the amp it will be bad.

What Zebra said.

You ALWAYS fuse as close to the power source as possible.

Typically the fuse on an amplifier protects the circuit board from various issues and has not much to do with power protection, which requires a much larger fuse more in line with the current the amplifier draws.

When I put a blue sea fuse block into a vehicle, I look at the current capacity of the fuse block (100A in most cases) and I will put a fuse or breaker as close to the battery as possible that is rated at the capacity of the fuse block, and I will use cable that is capable of carrying more amps than that rating (I usually use 6 gauge if under the hood - which is WAY overkill, but still not too expensive). Always side on a little overkill, and your vehicle won't burn down.

 

[4RunAmok]

Is it okay to connect the amp power to the block since the power line would then be fused at each end? Seems it would as long as the fuse at the terminal block isn't larger than the one on the amp. Is that right?

Thanks for any insight.

I would say no, it's not ok of the top of my head, but that all depends on your specific amplifier.

Check the manual, it will usually tell you that you need to use a certain size fuse for the power feed to the amplifier. Small amps can get away with a 30A fuse, larger amplifiers can go much higher, but typical amplifiers use 75A.

You should also note that most Blue Sea fuse blocks have a maximum current draw of 30A per circuit and a 100A bus maximum. From Blue Sea's website:


If the amplifier requires larger than 30A, then no, you can't go directly to this block.

You could instead use one of these:


And buy the fuse rated at what the amplifier needs.

 

[riceandpho]

what amp is it? i would run a minimum of 4 gauge ofc to the inside of car from the battery post, atleast fused the wire with 30amp to 80amp fuse, and run a fused distro block inside, then you can branch off the same wire, be aware that if inside block is using 2 50 amp fuse thats branched out, a 100amp fuse is require at the main line.
why im telling to run a thick cable now vs later, is when you plan on upgrading, the power wire is there and you dont have to do the job twice. some amps are small enough to fit under the driver and pass seat.

 

[Bluesky 07]

Should have specified the amp, it’s the Kenwood KAC-M1804, so a modest one power-wise, 45w each through 4 channels.* I don’t see anything in the directions even calling for a fuse other than the one integrated one on the amp. Am I missing something?

* I have a powered Bazooka sub.

EDIT: Got my question answered by Crutchfield. They said what I thought would be the case, that a fuse at the battery end is fine as long as it doesn't exceed the 15A rating of the one on the amp. Thanks to those who responded, always glad to have multiple perspectives.

 

[riceandpho]

always put a fuse directly after battery, 15 amp is fine, 20 is fine too, a nice 12gauge to inside the car, the fuse at the battery is to prevent any major things from happening, let say you have a cut in the wire, the fuse must blow to prevent a fire.

Should have specified the amp, it’s the Kenwood KAC-M1804, so a modest one power-wise, 45w each through 4 channels.* I don’t see anything in the directions even calling for a fuse other than the one integrated one on the amp. Am I missing something?

* I have a powered Bazooka sub.

EDIT: Got my question answered by Crutchfield. They said what I thought would be the case, that a fuse at the battery end is fine as long as it doesn't exceed the 15A rating of the one on the amp. Thanks to those who responded, always glad to have multiple perspectives.

 

[Bumbo]

EDIT: Got my question answered by Crutchfield. They said what I thought would be the case, that a fuse at the battery end is fine as long as it doesn't exceed the 15A rating of the one on the amp. Thanks to those who responded, always glad to have multiple perspectives.

That's not entirely correct...

First off, you are using a fuse to protect the electrical line, not the amp. Everything in your car is designed like that. Each circuit is calculated based on the size (gauge) of the wire, the length of the run, and the max load. More advanced calculations take into consideration temperate, like inside an engine room, and acceptable voltage drop as a %.

If you are running 12 or 10 AWG from the fuse block to the amp, you can safely run a 30 amp fuse.

The fuse on the amp is to protect the amp internally... it's not going to do anything to protect from an external short.

You can use a smaller fuse on the line, but the smaller fuse has a higher resistance also therefor increases the voltage drop at the amplifier under load.

For best performance, use the largest fuse that is allowable for the given wire size. Pretty simple.

You can also use your fuse block for distribution... totally acceptable practice assuming everything stays within the specification ranges.

You can even feed a fuse block with a fuse block... also totally acceptable. Its like having a sub-panel in the garage that is tired into the main breaker panel of a house, it's no different.

I even have a sub-panel inside my 4Runner, being fed off the main fuse block. 30A max on the sub-panel, but its all I need for smaller accessories inside. That 30 amps is then carved out and distributed inside.

If the total load inside exceeds 30A, I pop 1 single fuse in the main panel only...

 

[Bumbo]

What Zebra said.

You ALWAYS fuse as close to the power source as possible.

When I put a blue sea fuse block into a vehicle, I look at the current capacity of the fuse block (100A in most cases) and I will put a fuse or breaker as close to the battery as possible

My comments here have nothing to do with this thread, but I felt like it’s worth mentioning with all the dual battery threads around... I do see people use breakers as fuses sometimes.

Breakers and Fuses… both are protection devices, but they are not necessarily interchangeable. A breaker is NOT a replacement for a fuse.

Where a breaker could fail, a fuse would not.

I’ve have seen breakers used in applications where there was a hard short and the breaker essentially welded itself on.

Breakers are thermal devices, and they trip when they get hot enough. The reaction is not instant. Such a massive inrush of current could causes one to fail.

 

[4RunAmok]

My comments here have nothing to do with this thread, but I felt like it’s worth mentioning with all the dual battery threads around... I do see people use breakers as fuses sometimes.

Breakers and Fuses… both are protection devices, but they are not necessarily interchangeable. A breaker is NOT a replacement for a fuse.

Where a breaker could fail, a fuse would not.

I’ve have seen breakers used in applications where there was a hard short and the breaker essentially welded itself on.

Breakers are thermal devices, and they trip when they get hot enough. The reaction is not instant. Such a massive inrush of current could causes one to fail.

Which is why it's suggested for a fuse block, and not the amp itself. Battery to breaker rated for the load of the fuse block, breaker to fuse block, fuse block with fuses to devices. In fuse block and dual battery installations, I use MRBF fuses which reside right at the battery posts, but lots of folks don't like them because it's a fuse they have to carry a spare for.

 

[Bluesky 07]

[MENTION=144483]Bumbo[/MENTION], everyone posting here clearly knows far more about electrical than I do so I'm not questioning, just hoping you can help me understand something you stated that seems counterintuitive:

For best performance, use the largest fuse that is allowable for the given wire size. Pretty simple.

By "largest," do you mean highest amp rating? If I understand correctly, since the fuse will blow when the load exceeds the fuse's rating, it seems the level of protection would be inversely proportional, meaning a lower rated fuse would offer more protection than a higher one because it would blow at a lower load on the wire.

So in my example, wouldn't 30a through the wire be more of a hazard than 15a? Or no because the wire can take the 30a?

I can explain airline pricing but this stuff gives me a headache. :noidea:

 

[Bumbo]

Which is why it's suggested for a fuse block, and not the amp itself. Battery to breaker rated for the load of the fuse block, breaker to fuse block, fuse block with fuses to devices. In fuse block and dual battery installations, I use MRBF fuses which reside right at the battery posts, but lots of folks don't like them because it's a fuse they have to carry a spare for.

I wasn't picking at your post or making a comment in reference to what you said... It just put me on the though process to talk about fuses and breakers so I took that as an opportunity to do it. Plenty of people on this forum aside from you that might benefit from the discussion.

From a design standpoint, mains wiring and branch wiring are really two different things. The fuse block is still considered an accessory as far as I am concerned.

In a perfect world, off the battery, you would have a mains fuse, breaker, then a fuse panel.

MRBF fuses are fantastic... I also like ANL or MEGA fuse. Anything that is bolt/stud mounted to accommodate lug connectors I like. Really dislike a lot of the typical car audio stuff which uses a set screw.

Not wanting to carry a spare is a silly argument for not following best practices. I carry spares, but due to proper design and during normal operation, its very unlikely that I would ever need to replace... but if I use a breaker in conjunction (which I don't), ill have it rated accordingly to pop before the fuse. The fuse is only there to protect from a catastrophic event.

 

[Bumbo]

[MENTION=144483]Bumbo[/MENTION], everyone posting here clearly knows far more about electrical than I do so I'm not questioning, just hoping you can help me understand something you stated that seems counterintuitive:

For best performance, use the largest fuse that is allowable for the given wire size. Pretty simple.

By "largest," do you mean highest amp rating? If I understand correctly, since the fuse will blow when the load exceeds the fuse's rating, it seems the level of protection would be inversely proportional, meaning a lower rated fuse would offer more protection than a higher one because it would blow at a lower load on the wire.

So in my example, wouldn't 30a through the wire be more of a hazard than 15a? Or no because the wire can take the 30a?

I can explain airline pricing but this stuff gives me a headache. :noidea:

For argument sake, lets make some assumptions...
We are using 12 AWG wire
The length of the wire is no more than 4 feet

"30 amp wire" doesn't mean anything... it could be 14 awg for a short run, or 10awg for a long run. both are 30 amp wires...

Sure, a lower rated fuse will offer more protection, but it will also increase resistance.

I am taking into account voltage drop when I make my argument.
Resistance = heat
Resistance = loss of pressure
Resistance increases voltage drop.

From a performance standpoint the larger fuse and larger wire will have less resistance and therefore less voltage drop.

Just because your electrical system is putting out 14 volts, doesn't mean that's what your amplifier sees when its working.

12 AWG wire is damn well capable of handling 30 amps in a 4 foot run. You are selecting a fuse to protect the wire used for that circuit.

The choice as a designer is really yours... opt for more protection and fuse at 15, or maximize on performance and minimize voltage drop.

Voltage drop is a big deal... may not sound like much, but as the voltage reduces, the current goes up when trying to draw the same power (watts), and so does heat. Appliances like amps work less efficiently, and you can get less than your advertised power levels. Maintaining good voltage across the system is a positive thing, it's actually healthy.

Here are some charts to help you... the first being a bit more conservative. Online calculators are also available to help your calculate voltage drop.

 

[mscot]

[MENTION=144483]Bumbo[/MENTION]
My audio guy is telling me not to run the amp off a fuse block that is shared with non-audio accessories - such as lights, compressors. He said you want it to be a clean draw straight from the battery and not sharing with other accessories (my poor translation of what he said, anyway).
What is your take on this?

 

[Bumbo]

[MENTION=144483]Bumbo[/MENTION]
My audio guy is telling me not to run the amp off a fuse block that is shared with non-audio accessories - such as lights, compressors. He said you want it to be a clean draw straight from the battery and not sharing with other accessories (my poor translation of what he said, anyway).
What is your take on this?

I would venture to guess your audio guy is concerned about either feedback or noise being introduced into the audio from the power circuits, or voltage drop because its pulled from a “shared source”. The ham radio people would essentially tell you the same thing… direct to battery. I honestly feel like this has come about because most people have no idea what they are doing, and its easier for a manufacture to troubleshoot, or get less support calls because of poor wiring jobs. Direct to battery eliminates variables they have no control over.

If it’s a noise issue, I’ve found the biggest cause is running your power cables in parallel with your source/signal/rca cables.

If its voltage drop, then it’s really about how strong or well designed the distribution architecture is. You gotta keep it mind, “all road lead to Rome”, or all wires lead to the battery. All this stuff is connected in parallel anyways, it’s not like it’s an isolated circuit…

Personally I have no problems wiring accessories off a distribution point like that. Sometimes you get lucky, sometimes you don’t. If you found noise in the audio, then you could re-work troubleshoot it and try to resolve, but going off my fuse block would be my first choice and I would test and correct if needed. All my radio communications equipment is fed off a primary or secondary fuse block, no problems. That said, I have had my ARB fridge, only when running, cause some type of interference on the radio, but my antenna lines are running next to or in parallel with the fridge power.

If you are talking about a power amp that has large mains cable because it uses that much current, then the BEST thing you can do is literally install a 2nd battery closer to the amp, or use very large cable to reduce voltage drop, and obviously none of this would go through a small fuse block, but nothing stops you from using a large buss bar either. What if you have 5 stereo amps? Really only so much junk can go direct to battery. You have to use a buss bar…

Think about it... everything in a factory / OEM designed car comes off a fuse block... radio, navigation, gps, critical saftey system, ecu... if everything had to go direct to battery it would be a real shit-show under the hood. It's about doing it right...

 

[mscot]

So it sounds like at a minimum I should run a single cable to a distribution block and then have the winch, amp, and an accessory fuse block come off of that.

 

[Bumbo]

So it sounds like at a minimum I should run a single cable to a distribution block and then have the winch, amp, and an accessory fuse block come off of that.

Sure, that would be perfectly acceptable, if not the recommended way of dealing with a bunch of connections for large cables.

 

[mscot]

[MENTION=144483]Bumbo[/MENTION]
And there's no problem with a winch that can pull up to 500a running off a distribution block? Granted, I wouldn't have the audio on if I were running the winch.

Looking at this:
https://www.bluesea.com/products/2104/PowerBar_600A_BusBar_-_Four_3_8in-16_Studs

Do I need two that size or can I get a smaller one for the common?

 

[Bumbo]

[MENTION=144483]Bumbo[/MENTION]
And there's no problem with a winch that can pull up to 500a running off a distribution block? Granted, I wouldn't have the audio on if I were running the winch.

Looking at this:
https://www.bluesea.com/products/2104/PowerBar_600A_BusBar_-_Four_3_8in-16_Studs

Do I need two that size or can I get a smaller one for the common?

I think it would be pretty self explanatory just looking at the published specification... 600A DC continuous rating.

Anything you move though the positive post of a battery, you are going to need to move though the negative post.

To complete the circuit, the ground/common connection needs to be able to pass the current otherwise you are going to end up with an issue regardless of what you decide to use for the negative branch.

Its like trying to bring a 4 lane highway down to 1 lane and back to 4 lanes... its only as good as the smallest component. A bottle neck anywhere is the circuit is going to be an area of high resistance during high loads.

 

[mscot]

Thanks. I wasn't sure how that worked as I haven't grounded anything directly to the battery before - I've always used the frame for amps.