Power wire dilemma
 

I'm in the process of upgrading my stereo system, and it time to wire the power lines. Now I know how to wire a car stereo in a standard car with the battery in the front, but with the battery in the rear I am wondering if the 4 AWG wire run to the battery from up front will be ok over all that distance with the extra 120A stereo system running. Will I need to replace that with a larger wire and/or upgrade the alternator? I wouldnt think so at these low levels, but just hoping to get some advice from those who have done this before. Thank you.

If you think about that a sec yyou'll answer your own question......
Ask yourself, where are you mounting the amps? In the rear? which is right near where the battery is? If your woried about the head unit, you don't need that kind of wire for it.The HHR is short compared to other vehicles which take miles of wire to refit.
The only reason to wire to the front would be for the extra alternator which you'd be hard pressed to find a place for, and your not running a 2nd battery up there either.

so what does the main power line from the battery go to? I thought it went to the starter / alternator.
If it does, and if the amplifiers are drawing more than the cable from there can supply, eventually the battery will run down. im not sure my line of reasoning is correct though, so im open to advice.

Ok, after re-reading your post I see your actual question,,,, your worried about the load on the alt wires back to the battt...fair enuf...
Since I don't know the actual size of the feed wire I really can't answer this...But I'll say unless your running some monster high amp system, the starter is probably pulling more then your avg stereo system will....

OK i did some more research and it seems this is one of the items covered in the 'Big Three" upgrade, which consists of upgrading 1) alternator positive to battery positive, 2) battery negative to chassis, and 3) engine ground to chassis. Some people replace the factory wiring; others add additional cables to the factory wiring.

Since its a further distance (being rear mount battery) than most cars, I was thinking that the current load would be more than the current 4AWG cable could handle.

Maybe i should upgrade the big 3?

Yea i already know all about that, and that doesnt really answer my question because i dont know how much current passes through that wire (not feeding my amps, feeding the battery) if I had the right tools, i guess it would be possible to measure, but only after the system is hooked up and already possibly causing fires...:scared:

is that main line at least fused somewhere? anyone know where if so?

Its my understanding that the amps are powered more by the battery than the alternator. People upgrade to multiple batteries before upgrading the alternator.

even if only running the system while the car is running?

P.S. Thanks for everyone's input on this. I just am trying to make sure my car doesnt catch on fire when i first power everything up. :confused:

Fire No way!!!
 

Doesn’t anybody know Ohms Law?

With the info given:
A 4AWG wire of unknown length
120 Amp draw from OP
I’ll add my guess of a 10-foot length of wire.

A 4AWG wire, according to a wire distributor I have dealt with, has a DC Resistance of 0.25 Ohm at 20 deg C. for each 1,000 feet. Resistance will go up with temperature.

10 feet is 1/100 of a 1000 feet - 0.25 Ohm divided by 100 is 0.0025 Ohms for the 10 feet of wire.

Take the 0.0025 times the 120 Amps equals a 0.3 Volt drop in the power wire. Assuming, at worst case, a similar drop in the ground return you can figure on a 0.6 Volt difference between the source voltage(battery or alternator) and the Amplifier. OK IMHO.

I feel your real concern should be: can the alternator or battery handle the 120 amp draw of the Amplifier. That I cannot answer.

On the plus side the 120 Amp specification is most likely the max the amplifier would ever draw at the highest volume.

Fire - NO. At worse degraded audio at full volume.