150 amp fuse for a 80 amp alternator. big 3.

[The Camry]

Running Knu Colossus 1/0 wire. fusing between pos alt and pos bat. is that an ok fuse to use?

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[adulbrich 5,000+ posts]

Its ok, but I would use a 200 or 250 amp fuse with that wire.

 

[72Impala 10+ year member]

You fuse for the wire. 300 for 1/0 ofc

 

[adulbrich 5,000+ posts]

Didn't know it was ofc. Yes, 300 amp would be best. Fuse to wire, like stated

 

[keep_hope_alive Premium Member]

You fuse for the wire. 300 for 1/0 ofc

you guys are doing it backwards. you size the fuse for the source and load and then size wire to be greater than the fuse.

In totality, you fuse for the wire AND the load AND the source... and the minimum size is used. fuses provide short circuit protection of the source, over-current protection of the wire, and over-current protection of the source and load. example, if the amp doesn't have onboard fuses, you size the fuse for the amp recommendation. you can have an 80A fuse on 1/0 wire.

the problem with 300A fuses is the amount of current they let through in a short.

i size fuses for the source and load and use wire sized greater than the fuse rating and then up-size wire for voltage drop. the result is 100A-150A fuses on 1/0 wire. perfectly fine and safe.

the only concern with using too small of a fuse is nuisance blowing of the fuse when the load demand is greater than the fuse size.

for the big three, the batt to alt wire needs short circuit protection for the battery, over-current protection for the wire, and overload protection of the alternator.

a 100A fuse is fine for the alt to batt wire, especially when in parallel with the factory wire (which means each wire sees only half).

 

[keep_hope_alive Premium Member]

I see "fuse for the wire" all of the time. and as a result fuses are oversized and sources/loads are not protected. it's a regurgitation of a statement without understanding.

the above method is how you account for all three aspects of fuse sizing. if the source or load can be damaged if current is greater than what they are rated to handle, fuse sizes are smaller than wire ratings.

 

[72Impala 10+ year member]

I'm not gonna get into a pissing match. I agree with fusing for the source to a point. If your 4 channel amp has internal fuses honestly you don't have to fuse for that source. It's like putting two fuses inline right next to each other. For amps that require external fusing, you fuse as close as to possible to the amp, the fuse at the other end (origin of power), should be fused for the wire.

If you have a H/O alt charging your front battery, you would not want a 100a fuse because you will cause unwanted resistance at the point of the fuse, resulting in power loss and added heat at the fuse AND alternator. I would then fuse for the wire and output of the alt, which would be 250-300 most likely.

 

[adulbrich 5,000+ posts]

I see "fuse for the wire" all of the time. and as a result fuses are oversized and sources/loads are not protected. it's a regurgitation of a statement without understanding.
the above method is how you account for all three aspects of fuse sizing. if the source or load can be damaged if current is greater than what they are rated to handle, fuse sizes are smaller than wire ratings.

All my amps have fuses built in, so I just fuse to the wire. My alt is rated more than my max fuse size, but I know fuses can take more than rated before blowing.

If amps are internally fused, do you still have to fuse for the load?