Cabling and Fuse Question

[KRiSX]

prob asked a few times before, but searching fuses gave me heaps of results and i'm kinda desperate for an answer...


My setup when installed...

battery > 4g cable > 80amp glass fuse > 4g cable > Dist Block > 2 x 8g cable to amps (a 700w mono and a 400w 4 channel, one of which i know has 2 x 20amp fuses and the other is internal only so I'm not sure)

I just had some work done on my car and the idiots blew my 80amp fuse some how... anyway i just replaced it with a 100amp circuit breaker fuse (think its a flat fuse inside the box?) as I was having a hell of a time getting another 80amp glass fuse. Now i'm concerned that I'm pushing something too hard or I should really rethink the boot part of the install.

Everything is working, but I suspect that if something does go wrong, the 8g wires will fry. The dist block isn't fused at all so I guess that I'm pushing 100amp over the 8g which isn't a good idea from what I've read!?

Can someone confirm or guide me in the right direction on what I should do with my setup?

At the moment I'm thinking one of two things need to happen...

A. battery > 4g cable > 100amp fuse > 4g cable > Dist Block > 2 x 8g cable with fuses on each to amps
B. battery > 4g cable > 100amp fuse > 4g cable > New Dist Block > 2 x 4g cable to amps

would I be on the right track?

Thanks

[acarmody]

Gold AML Wafer Fuses 80 AMP - Jaycar Electronics

I would be using 4ga for the mono.

[HRVATSKI_VOJNIK]

basic rule to figuring which fuse is; wattage/voltage=amp

(700+400)/12=91A
14V whilst the car is running
(700+400)/14=78A

so at full power it'll be sucking 79A@14V. so a 80A fuse seems right.
(cranking the audio whilst the car is off is just flatting your battery IMO)

a circuit breaker(not fuse) should trip immediately under a short.

as for cabling, what you have is ok.
the power the cable can handle depends on the wire strand sizes.
turn you car on and crank the audio (just don't pi$$ off the neighbors) if you feel the 8G wire to the 700 getting warm, then I'd suggest upgrading to 4G cable. 8G on the 400 should be fine.

if you can't find the 80A fuses at Auto stores, you can go to stores which sell car audio E.g JB-HI

[StoneX]

In regards to the previous post, amplifiers aren't 100% efficient. So if they say 700W output, they'll be drawing more than that from the power supply. A standard multi-channel amp will usually be Class AB which can vary from 50%-70% in efficiency and mono amps are generally Class D which can be as high as 90% efficient.

You need to factor this into your current draw calculations.

[HRVATSKI_VOJNIK]

In regards to the previous post, amplifiers aren't 100% efficient. So if they say 700W output, they'll be drawing more than that from the power supply. A standard multi-channel amp will usually be Class AB which can vary from 50%-70% in efficiency and mono amps are generally Class D which can be as high as 90% efficient.

You need to factor this into your current draw calculations.

thanks for correcting me there, completely forgot about that

[KRiSX]

thanks for the replies guys... i did try JB (about 4 stores), Strathfield, Auto 1, Repco and a couple others... no one had the 80amp glass fuse...

i've got the 100amp one now, so you guys reckon it'll be ok?

i'll check out the wires while its turned up a bit, but should I be fusing the wires after the dist block? I just read somewhere that if there is a short the 8g wires could burn and i'll be in all sorts of trouble... don't want that!

if you calculation are about right and the 80amp should be sufficient is 100amp going to kill anything? I already forked out the money for this new one so i don't really want to have to buy another fuse if possible lol

[HRVATSKI_VOJNIK]

yeah the 100A will do for now. in short, a short circuit is when all of the batteries power is going from one terminal directly to the other. all this high current creates heat causing the wire insulation to melt if the current is higher then what the wire can handle and thus exposing more wire.

you only need one fuse, generally located within half a meter of the battery.
because if you put it near the amps, say the 4G wires get exposed on the firewall, the 4G power cable will short and keep shorting because there's no fuse breaking the line between the battery and short location.
but when its next to the battery and short happens the fuse blows. since its breaking the line right next to the power source, your amps and other electronics are safe.

all car batteries can deliver way more then 100A, so if there is a short in the 4G, the fuse will blow instantly

[acarmody]

Mate if the distribution block is near the boot, a couple of metres of 4ga will only set you back about $5. JB will sell it by the metre. If your worried about the 8ga getting hot then just spend the few extra dollars. The 8ga is probably sufficient but hell its only a few bucks and its good insurance.

[KRiSX]

yeah i just used 8g in the boot from the DB due to 1. having some spare and 2. the dist block that came with my wiring kit was 4g to 4x8g... so changing involves new DB and some 4g cable

so yeah its not my first install... just my first multi-amp install... so i wanna be sure its all good... i never worried about fuse sizes in the past lol