Street Rat

I'm in the process of putting a sound system in my 1981. I'm upgrading the positive wire from the alternator to the battery. I'm using 1/0 size wire. I want to add a fuse in the line near the battery.

I have read numerous posts over the last few hours. Some people say to size the fuse according to your alternator output. I have a 100 amp Power Master unit installed. Other people seem to be of the reasoning of sizing the fuse according to the size of the wire and it's capacity to flow current.

So my question is what size fuse do I need? I have an ANL fuse holder and will be using an ANL fuse.

Amorget

My non-professional advice. 1/0 can handle something along the lines of 150 amps. That being the case, I'd use a 100 amp fuse to put it in line with the output of the alternator.

Really the amperage you'd want is just slightly higher than what the curcuit should ever pull, but I'd think you'd be safe running a 100 amp fuse. I have a 1996 Chevy 2500 that I added a stock GM fuse holder to that goes between the battery and the main fuse box/rest of the truck. It's on a 4 gauge wire and is 100 amps as I recall and came from a Suburban of the same generation. I would guess that a modern(ish) Suburban is pulling a whole lot more amps than your 81.

7T1vette

Fuses that size, and their holders, can become costly. You might consider installing a fusible link for 100 amp service in that line. If GM were to have installed a fusible link in that line, it would have consisted of a 3-4" length of #4 awg wire WITH NON-FLAMMABLE INSULATION and with epoxy covered connections to your 1/0 line. That would make the fusible link non-flammable IF it needed to melt from a very high current overload.

But, either a 100 amp fuse or a circuit breaker would do the job, also.

Amorget

A 100 amp fuse for his style holder is 5 bucks. He could also get them from the junk yard for basically free.

7T1vette

Not sure how I feel about having a 100 amp fuse blow inside a plastic cover....

If it works for you, go for it.

Gazehound

You always size a fuse to protect the wire. You don't want to burn stuff down by having a fuse to big for the wire size.

augiedoggy

And in the case being discussed here, if you use the smaller 100a fuse thats also rated for the max amount of amps being fed/drawn through that wire how does this NOT protect the wire?
My point is your right but in cases where someone is going overkill on wire size its still smart to size the fuse to the max amount of safe amps being fed through it...

I ran a separate fused main wire which split off to my amps in all of my installs. (FYI if your looking for reference. I had a 75 amp alternator and optoma yellow top in my jeep and it was (barely) able to keep up with driving 800watts rms to each of my four sub voicecoils and power my 400w amp for the mids and highs.... It was one of those crazy over the top systems that could pop the windows out of the hard top (very stupid but fun at the time)..I did use a cap and the engine would race from the load on the alternator at a stoplight or parked.
My 84 vette had a system in it too but it was only 1000 watts.... also did fine with stock battery and alternator. (and air conditioning)

7T1vette

These massive sound systems are about like buying a $20K bass boat, a $5K trailer, and a $60K SUV to haul them (with $10K matching paint job, of course).....so that you can catch a fish.

40 years ago I played bass in a rock band and had a 100 watt amp head for my speakers. I had it tested and found that for an average-sized room, the volume setting I used [3-4 on a 10 dial] was only putting out around 10 watts (RMS) of actual sound power!

Hmmmmm.... Got any idea what more than 100 watts of sound power will do to your ears?...IN A CAR!!!

{Sorry about digressing....had to share....}

Amorget

The things guys do to catch "fish"...

Shark Racer

Houses are a lot quieter than cars.

That said, you don't need a lot to have very good volume in a 2-seat car. Considering most audio is 2 channel, if I went for a "max effort" sound system in my 78, I'd want 6.5" component speakers (woofers+tweeters) and a 10" subwoofer in the back. If I really liked bass, I'd go with a 12" subwoofer.

mrvette

Much less than CAR audio is rated as BS......I dunno if McIntosh still does car audio or not, but their stuff worked.....

I sat here for a few seconds looking at wife with my fingers on the keyboard, she lifts her hands up with fingers curled, and shouts...'BORING' after I explained I was thinking of the various tech ASSpects of car audio......

she is correct....as usual.....

lionelhutz

That wire is the same size as the battery to starter wire but I bet you haven't fuse it?

For industrial applications which are much more stringent than automotive applications a 1/0 wire would use a 150A fuse. You could use 200A or more in a car for that wire.

I'm still trying to figure out why you're bothering with a 1/0 charging wire on a 100A alternator.

You're also probably using a 1-wire alternator and losing the remote voltage sensing ability of every good alternator.

But then you are also probably running this wire the alternator all the way to the battery instead of using the heavy wire that already exists between the battery and the starter as part of the circuit.

Street Rat

In the audio world it's called a "Big Three" upgrade. 1. Alternator to battery size upgrade. 2.Battery ground to frame size upgrade. 3. Ground from frame to engine size upgrade. Yes I was planning to fuse the battery to starter wire as well. I could have just as easily chose to use 4 or 2 gauge wire. But I chose to use 1/0 because like carburetors bigger is always better...right?

augiedoggy

And do you have any idea how hard it is to hear the 100w stereo in a lifted jeep with the top down at 75mph or 100 feet away while its acting as the sound system for a beach party
in all honesty it was a hobby... Funny to see all the opinionated hypocritical comments here) Depending on how you look at it, its just as practical as dumping thousands into a 40 year old 200hp car to turn it into a 500hp car that restricted by a 65mph speed limit on the street (especially when compared to a modern automobile...) Oh I got one for you... lets spend <10k for a paint job on a car thats barely worth 12.... thats ok right?

augiedoggy

yes a lot of the cheap stuff is grossly exaggerated... The stuff I had (and still use tree cars and 12 years later) was higher end orion HCCA and audioart mostly the amps were 1/2ohm stable and 1 ohm stable bridged and thats the way I ran them. I actually had two subs melt and burst into flames on me once....
looking back it was kind of a foolish way to spend my money but There were far more foolish ways I could have spent it.
In any case its far from boring... That statement sound an awful lot like what many wifes would say about there husbands talking shop about cars...
There is actually quite a bit involved in doing things right.

Street Rat

For those few of you interested in learning something here is some good information. http://knowledge.sonicelectronix.com...tview-157.html

lionelhutz

If you say so...

If you were using 20' of wire and required 100A then pick #4 wire so the voltage drop would be 0.5V. To compensate, you connect the voltage sensing wire from the alternator to the battery end and then the alternator output voltage would increase by 0.5V to compensate. Nothing is gained by using a larger wire.

7' of #4 between the alternator and the solenoid would have 0.17V drop and 7' of 1/0 from the alternator to the solenoid would have 0.07V drop. So, all that extra money for the 1/0 gains you a possible 0.1V advantage.

7T1vette

In today's car audio systems, 200 watts of power means TOTAL power...as in, when the system is running and at full volume, the device is drawing 200 (instantaneous-peak) watts from the car's power system (battery/alternator). And, with that INPUT power, the actual RMS output (sound) power to EACH of the four speakers is about 16 watts (rms).

So, yes, today's audio systems electrical ratings are "funny money" in order to sell you that a pee-wee system is "really powerful".

But, 16 watts (rms) of sound power (per channel) is about what the early C3 radios had in them.....still plenty of sound to hear, but at high volume levels it was pretty distorted.

Needing an actual 100 watts (rms) of power to hear a radio in an off-road Jeep? Nope! But, it might be enough for ALL of the Jeeps in the area to hear [without the sub-woofer running].

P.S. Most of that audio power is absorbed creating the low bass frequencies in the audio spectrum. So, that level of 'peak power' is only used [intermittantly] when significant amounts of bass level (less than 250 Hz) are needed. Playing ZZ-Top?? Yep, you eat a lot of 'juice'.

Street Rat

Thanks for all of the responses. I got some input over on the Audio Forum also. I've decided to use a 200 amp fuse for the heavy gauge battery cables.