Fusing on alternator

[BanginGMC 23]

DC Power,

I have a 320 amp alternator, I haven't clamped it yet but I will very soon.

Would you agree that if I fused the positive run connecting the alternator and battery with a 300 amp fuse that it would blow once the alternator is reaching high rpms?

If it wouldn't blow then would you agree that the alternator is actually overrated?

[jcarter1885 995]

Fuse ratings dont always work the way your thinking, the fuse is their to protect the wire and not the alternator. If your theory was true then people with stock alternators would blow fuses all the time since the fuse is not as high as the alt amperage usually.

[altoncustomtech 773]

Actually, no on both counts. A fuse will not blow at its rating no matter the size even if it's built to do so like a "quick blow" fuse is. The current flowing will have to be over the rating to blow it and over that rating for a given period of time. Obviously the higher it is over the rating the less time it will take to blow, but that's how they work. Just because your alt isn't blowing a 300amp fuse I would not discount it's ability to output 320amps at all. First of all, how do you you've even put a load on it heavy enough to pull a full 320amps of current? Second, was it already hot? As the alt heats up it's output capability will be somewhat reduced. Third, IMHO 20amps over isn't going to blow a 300amp fuse on any day.

[ssh 924]

If there is no load drawing / requiring 300a then your alt wont ever produce 300a, regardless of rpm.

[BanginGMC 23]

Thanks for the input guys, cleared some things up for me

Alton, I'm pretty sure i'm capable of pulling 320 amps with the system i'm running. I didn't know once the alternator heats up its output is reduced. Once I get some time i'm going to do a lot of testing with this alternator.

[ssh 924]

Dc lists their output ratings when hot iirc

[altoncustomtech 773]

Thanks for the input guys, cleared some things up for me

Alton, I'm pretty sure i'm capable of pulling 320 amps with the system i'm running. I didn't know once the alternator heats up its output is reduced. Once I get some time i'm going to do a lot of testing with this alternator.

True, the 3500's should easily pull more than 320, I wasn't thinking of that testing situation really. No matter the testing situation you'll have to be sure to adjust the engine RPM's to get the right alternator armature rpm's to be sure you can get full output from it, anything less than that and it won't produce the full 320A. I don't think you'll have any problems getting the rated output from it as you test though. Good luck with it, I'm looking forward to your findings.

Dc lists their output ratings when hot iirc

I always forget they do that.