Determining fuse size?

[grandam888 10+ year member]

if there aren't any fuses on the amp, put a smaller fuse about 4-6 inches in front of the amp, and another a short distance from the battery, to protect the car if there was a short, or if you try to run too much amperage through the wire.

 

[aRE? 10+ year member]

Unfortunately I do not have a manual, although I have been looking all over the web for one. (It's a late 90's Nakamichi PA-1002, if anybody has one please let me know?)

Why two fuses? And does it matter where on the wire or how close to the amp it is? I figured I'd just do what anybody else does, and install it on or close to the battery? Am I safe with 60 amps? I don't care as much about the car as I do the amplifier (it's probably worth more even)..

 

[aRE? 10+ year member]

I got a 70A automated fuse. Any bets on how that's gonna work out?

 

[keep_hope_alive Premium Member]

here's a lesson on fuses and their role in the car audio environment.

fuses provide three forms of protection

1. short circuit protection for power source

2. over current protection for wire

3. over current protection for device

1. short circuit protection prevents the battery or power source from exploding in the event of a short circuit - i.e. power wire touches metal. short circuit protection will happen regardless of the fuse size and is why you always fuse at the battery to minimize the length of unprotected wire.

2. over current protection for the wire prevents the wire from melting or catching on fire if you sustain current greater than it's rating. yes, i've seen cars with power wire that literally melted and caught fire. when the wire insulation melts it exposes copper which can then short. we always size fuses for the wire ampacity (current rating). we use charts and tables to determine wire size vs current draw vs length since wire is sized to minimize voltage drop as well as handle expected current draw. you size wire then you size the fuse for the wire.

3. over current protection for the device is important when the device (amp/head unit/processor/etc.) doesn't have an onboard fuse. in this case the mfr will recommend a fuse size so that the device is protected. in this case, the fuse will likely be smaller than a fuse sized for the power wire.

with your amp, you want the single fuse at the battery to perform all three functions stated above. for that you want to know what size fuse the mfr recommends. since you don't know, you can just start small and work your way up.

start with a 20A fuse at the battery. it may be plenty for the amp. if the fuse pops only when you turn up the music, try 25A, then 30A. i doubt the amp will ever need more than 30A. this is the only time i ever recommend someone increase fuse size when the fuse blows - because you are experimentally determining what the current draw of this inefficient Class AB amplifier is. when you know the recommended fuse size, NEVER up-size a blown fuse as a blown fuse is an indication of a problem.

 

[keep_hope_alive Premium Member]

others recommended two fuses. this can be beneficial if you want to add other amps later. you can use a fuse sized for the wire at the battery then install a fuse distribution block at the amp so you can fuse for the amp load, and add another amp later.

5 awg power wire is good for about 100A.

when the device has an onboard fuse, we can eliminate #3 above from our fusing criteria. #1 and #2 are always present in the role for the fuse at the battery.