Jump to content

What size fuse for alternator power wire


Recommended Posts

If you fuse over 150A the fuse is pointless ON THE ALTERNATOR END for your application. If the alternator can only put out 145A how in the hell do you guys expect the fuse to do ANYTHING if it's 300A? IT CAN"T!!!! the alternator will just keep pumping out the magic fire pixies at maybe 160A (because of dead short) and shit is gonna fry until the driver realizes shit is frying and shuts the engine off or the rectifier cooks. The 300A fuse belongs at the BATTERY end but even then that is overkill because the wire is only being asked to carry 145A MAX so why fuse to the limit of the wire? All that is going to do is let more magic fire pixies out before the fuse pops.

So why get 1/0 ofc? Everyone loves overkill right? Why not get 4 guage ofc wich is rated at 150 (for that short of a run it should be good) 150 amp fuse and 145 amp alt. Now all 3 match.
Link to comment
Share on other sites

  • Replies 74
  • Created
  • Last Reply

If you fuse over 150A the fuse is pointless ON THE ALTERNATOR END for your application. If the alternator can only put out 145A how in the hell do you guys expect the fuse to do ANYTHING if it's 300A? IT CAN"T!!!! the alternator will just keep pumping out the magic fire pixies at maybe 160A (because of dead short) and shit is gonna fry until the driver realizes shit is frying and shuts the engine off or the rectifier cooks. The 300A fuse belongs at the BATTERY end but even then that is overkill because the wire is only being asked to carry 145A MAX so why fuse to the limit of the wire? All that is going to do is let more magic fire pixies out before the fuse pops.

So why get 1/0 ofc? Everyone loves overkill right? Why not get 4 guage ofc wich is rated at 150 (for that short of a run it should be good) 150 amp fuse and 145 amp alt. Now all 3 match.

Big difference between harmless overkill and burning your rig to the ground. Also he never stated what vehicle he has. For my big 3 I have to run a 20' alternator lead to my trunk.

Link to comment
Share on other sites

If you fuse over 150A the fuse is pointless ON THE ALTERNATOR END for your application. If the alternator can only put out 145A how in the hell do you guys expect the fuse to do ANYTHING if it's 300A? IT CAN"T!!!! the alternator will just keep pumping out the magic fire pixies at maybe 160A (because of dead short) and shit is gonna fry until the driver realizes shit is frying and shuts the engine off or the rectifier cooks. The 300A fuse belongs at the BATTERY end but even then that is overkill because the wire is only being asked to carry 145A MAX so why fuse to the limit of the wire? All that is going to do is let more magic fire pixies out before the fuse pops.

So why get 1/0 ofc? Everyone loves overkill right? Why not get 4 guage ofc wich is rated at 150 (for that short of a run it should be good) 150 amp fuse and 145 amp alt. Now all 3 match.

Big difference between harmless overkill and burning your rig to the ground.

How is a 300 amp fuse on a wire rated for 300 amps overkill. And the alt is not going to put out more than 145 amps just because you have a 300 amp fuse on your wire.

Link to comment
Share on other sites

So.... Lets start from the top

You want the big 3 to minimize the voltage drop in your charging system. So it stands to reason you'd use a large, readily available wire size, like 0ga. That's all fine and dandy.

Now lets imagine a wire rubs though, or the rectifier in the alternator shots out, effectively creating a ground path for the current. It can come from potentially 2 places. Either from the battery or from the alternator. Once the alternator stops rotating(you shut your engine off) it can no longer produce power. It's an easy disconnect in that sense. The issue lies with the battery, it will continue to discharge all the way down to 0v. If you have multiple batteries they too will be feeding this short circuit. Remember, they're in parallel.

Without a fuse, there is nothing to interrupt the current from the battery. You see where I'm going with this.... Your fuse(placed near to the battery) will break the circuit.

If you put the fuse near to the alternator and a short occurs closer to the battery, you're hosed. Hence why it's good practice to fuse nearest to the battery as it practical.


As to what size fuse to run: You could theoretically run a 150a fuse in the system. But not all fuses are created equal and depending on manufacturing tolerances, some may have enough resistance to act as a heat source, melting your plastic fuse holder. Not enough to blow the fuse, but enough to reach the melting point of plastic. Not the first time I've seen it happen either. That being said, your fuse options are 200, 250, and 300a. All are acceptable as they will not add a significant source of resistance to this circuit, and all will break circuit in the event of a short, which is why you fuse in the first place

Link to comment
Share on other sites

If you fuse over 150A the fuse is pointless ON THE ALTERNATOR END for your application. If the alternator can only put out 145A how in the hell do you guys expect the fuse to do ANYTHING if it's 300A? IT CAN"T!!!! the alternator will just keep pumping out the magic fire pixies at maybe 160A (because of dead short) and shit is gonna fry until the driver realizes shit is frying and shuts the engine off or the rectifier cooks. The 300A fuse belongs at the BATTERY end but even then that is overkill because the wire is only being asked to carry 145A MAX so why fuse to the limit of the wire? All that is going to do is let more magic fire pixies out before the fuse pops.

So why get 1/0 ofc? Everyone loves overkill right? Why not get 4 guage ofc wich is rated at 150 (for that short of a run it should be good) 150 amp fuse and 145 amp alt. Now all 3 match.

Big difference between harmless overkill and burning your rig to the ground.

How is a 300 amp fuse on a wire rated for 300 amps overkill. And the alt is not going to put out more than 145 amps just because you have a 300 amp fuse on your wire.

I never said the alternator was going to put out 300A, I did say it might have a spike when the dead short occurs. I am of the belief that (in my case with a 20' charge lead) that a fuse near the alternator and the battery is good practice. picture an alternator on the left and a battery on the right with 20' of 0ga ofc between them. The battery can get a 300A fuse and the alternator (a 145A model) gets a 150A fuse. Now a dead short happens dead center of the wire what happens? The battery fuse pops because the battery instantly surges way more than 300A correct? and now the fuse at the alternator end pops because the dead short calls on the alternator to run max output. Now the same scenario except there is a 300A fuse on both ends. The battery fuse pops like before but now your alternator is pumping out full power to the short and the 300A fuse could care less so now its up to the driver to kill the engine. I would rather have a split second fuse pop rather than wait for a clowd of smoke tell me something is wrong.

I'm not saying I am correct here just that this is how I have come to understand it while looking for the same answer and building my own conclusion out of pretty much the same answers found in this thread. I do know I have a lot to learn in this hobby so If I am dead ass wrong let me know.

Link to comment
Share on other sites

these types of fuses blow at 20% over value so even using a 100 you should never blow the fuse but using a 150 puts you at more than the alt can output... yes you can shut off the engine to cut off the alt but in the case of a short and the engine is not cut off its best to fuse at both ends of a wire if power is on both sides of said wire.... alot of people do not fuse this wire because its common practice that if you add 1 fuse you have to add 2 just like when you add a second bank of batterys .... that said I always choose to not fuse a stock alt with a big 3

Link to comment
Share on other sites

these types of fuses blow at 20% over value so even using a 100 you should never blow the fuse but using a 150 puts you at more than the alt can output... yes you can shut off the engine to cut off the alt but in the case of a short and the engine is not cut off its best to fuse at both ends of a wire if power is on both sides of said wire.... alot of people do not fuse this wire because its common practice that if you add 1 fuse you have to add 2 just like when you add a second bank of batterys .... that said I always choose to not fuse a stock alt with a big 3

That's not how it works

Link to comment
Share on other sites

these types of fuses blow at 20% over value so even using a 100 you should never blow the fuse but using a 150 puts you at more than the alt can output... yes you can shut off the engine to cut off the alt but in the case of a short and the engine is not cut off its best to fuse at both ends of a wire if power is on both sides of said wire.... alot of people do not fuse this wire because its common practice that if you add 1 fuse you have to add 2 just like when you add a second bank of batterys .... that said I always choose to not fuse a stock alt with a big 3

That's not how it works

ok so i read your post and i guess ill go with 250amp fuse because its kind of in the middle, but enough to keep my system safe.

One other question, i'm also thinking of buyin the Crescendo s1500.1, how do i know what fuse size to use for that?

is it the same deal as with the alternator or is it different?

Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.

  • Recently Browsing   0 members

    • No registered users viewing this page.
  • Who's Online   1 Member, 0 Anonymous, 353 Guests (See full list)




×
×
  • Create New...