Wire Guage

**Stang70Fastback** · 01-01-2008, 09:46 PM

Two relatively quick questions:

1. What wire gauge would be recommended to power a system running an M3-ATX? And what rating fuse should I put in line from the battery?

2. Is there reason to worry about the alternator keeping up with all the stuff in my car if I run a Carputer, 150 Watt amp, and say the headlights and fog lights and air conditioning and maybe both front seat heaters and the wiper heaters and heated mirrors and rear window defroster and wipers and the stereo that came with the car (which has it's own 200 watt amp under the driver's seat?) Lol. It's a 98 Subaru Legacy Outback (200,000 miles and still the same alternator).

**h3rk** · 01-01-2008, 10:35 PM

1. 12 AWG minumum Wire

2.

M3 ATX_____________________15A
Amplifier_________________150W
extra total_______________156W
extra amps_________________10Amps

headlights high beam_______65W
headlights low beam________45W
fog lights_________________35W
wiper motor max____________40W
HVAC blower max___________400W
seat heater x2____________110W
heated mirrors_____________25W
rear window defroster_____200W
factory stereo amp________200W
other loads(ign, ltg, etc)100W
stock max total__________1220w
current(worst case max)___101Amps
Total amps MAX____________115Amps
Alt capacity_______________90Amps
Battery Drain______________25Amps
continued operation like this will drain the battery. Keep in mind these are estimated maximum values. Even my estimated stock loads exceed the alternator.

probably my error.

Your stock alternator is around 90 amps
these are just estimate values, you could look up your own and do similar calcs and see for yourself
Also you could run all of these things and get a clamp-on DC ammeter and read the alt current and batt current (see if your battery is charging or discharging to add or subtact battery current to/from alt current).
You could also read each load's fuse, divide that value by ~125% and add those up.
hope this helps.

**Stang70Fastback** · 01-02-2008, 12:29 AM

Alright. I gather then that if I use 10 gauge wire, I'll be fine then. I guess I'll be wanting a 20A in-line fuse after the battery then, right? Is that the best place to put a fuse?

Regarding the amperage, I'll trust that you surely know more than I do :P I guess the logic then is to try not to run EVERYTHING at once, lol. I gather, though, that I should be fine running the carputer in most situations. Thanks for the help!!!

**h3rk** · 01-02-2008, 01:08 AM

Originally Posted by Stang70Fastback

Alright. I gather then that if I use 10 gauge wire, I'll be fine then. I guess I'll be wanting a 20A in-line fuse after the battery then, right? Is that the best place to put a fuse?

Yes and yes.

**crooper** · 01-02-2008, 04:08 AM

Usually better to go a bit bigger than just the bare minimum, especially if there's the possibility of adding more stuff down the road. It's a b**** to rewire the whole thing again (I've done this when I went from 8 to 4 awg when I added a bigger amp, it sucks).

**tacobandit** · 01-02-2008, 04:39 AM

i have a 4 ga running to my distributor block, then 8ga to each amp and im going to do 8 ga to my m2 atx

**Stang70Fastback** · 01-02-2008, 10:07 AM

Alright, thanks guys. I'll use 8 awg. I'm trying not to get TOO big only because I just plan on tucking the wires under the molding in the center console - and if you get too many wires running under it the flap bulges out a bit...

One LAAAAST question: I've got two 12V rocker switches set up for the carputer and the amp in the center console, through which I'll run the positive wires. If I use 4 AWG wire, would that be big enough to use one wire as the 12 volt source for BOTH the amp and the carputer from the battery, and split it to two 8 awg wires just before the rocker switches, to keep it neat? I'll use this where it splits:

http://www.radioshack.com/product/in...entPage=family

**Stang70Fastback** · 01-04-2008, 02:57 PM

If anyone has the answers I've got a few more questions regarding my M3-ATX.

1. I've been told that I should use a 20 Amp fuse in line to the PSU, but on the little sheet that came with the PSU it states "Input Current Limit (fuse protected): 15A" so should I be using a 15 Amp fuse instead then?

2. I've decided to not use the third ignition cable for the PSU but instead installed a rocker switch on the positive power cable to the PSU. I haven't installed it yet, but will it be possible to have the PSU start up whenever it just gets a current? (AKA the rocker switch?) Should I just splice the 12 V positive cable and connect it to both the positive and ignition inputs on the PSU?

3. Whats the best way to connect wires to the connectors on the PSU that would make it easily removable... or isn't there a way?

Thanks once again for all your help!

**h3rk** · 01-04-2008, 03:07 PM

1. use a 15 amp (I'm assuming you are talking about the fuse on the battery side of the wire you have going to the power supply), unless you are powering something else off of that wire. In essense that will provide double-protection for the power supply in addition to protecting the wire. If you wanted to power something else off of that unncessarily large (but conservative so it won't hurt anything) supply wire then you would put a larger fuse to allow for it.

2. Yes it's possible, there is usually a setting in bios to allow a computer to restart after a power outage. That what I think people use who do it that way.
I think you just need it on the positive.

3.you can buy molex connectors pretty cheap. There are tons of connectors (male and female) online. Just check out mouser or digikey. <-not the only choices but common ones.

**Stang70Fastback** · 01-04-2008, 08:51 PM

Thanks for the help. I am very happy I stumbled across this site

Would it be at all possible for you to link me to the sort of molex connectors I'd be looking for? I have no idea what I want exactly, and the site format (lists and stuff) is awfully confusing for me, lol.