As a side note, why is that most of the amps still have in the instruction manual that comes with it (not that any of you read it //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif ) that the ground wire should be kept as short as possible, usually it says less than 12". Perhaps these engineers need some enlightening.
You think that engineers write the manual? Seriously?
I don't do SPL. I don't compete in SQ mostly cause I just don't have the time, but my focus is SQ. The long and the short...
The alt cannot provide current for large transients. It simply cannot react fast enough especially with newer cars where the voltage regulator is part of the ECU. My current car takes seconds to ramp up alt output in response to a demand which is sad because the factory alt is a 165A model. The battery provides the excess current until the alt can catch up. This is just as true with high current alts as with factory ones.
I've never seen an alt wire go to the fuse box. Every car I've worked on went to the battery and from there to the distro panel.
The battery is only a load when it is discharged. As long as the alt can keep up with the average load of the car and system, adding an extra battery can and will help more with headlight dimming and transient voltage drops than a high output alt will. When the demand exceeds the output of the alt, the battery picks up the slack and then when the demand drops or the regulator ups the alt's output, the alt recharges the battery. Only when the average total current draw exceeds the capacity of the alt does the alt need to be upgraded.
Grounding to the battery is a sound practice both for the SPL and SQ competitor. For the SPL guy it gives you the possibility of the lowest resistance path for power. For the SQ guy it give you a known good ground and coupled with making a proper ground for source units and processors makes it much less likely that you'll pick up noise.
The whole shortest possible ground thing makes sense for a small amp where you're using small diameter power and ground wire. The chassis will be a lower resistance than that small wire back to the battery. I use 4ga for 50w amps though. I am a firm believer in good enough isn't good enough. When you think about it though, the ground is going back to the battery anyway, whether through the chassis or through a dedicated wire. I personally would much rather know exactly what my ground path is and what is sharing part or all of that path with my amps and processors. The battery neg post is the ground reference with the car on or off. The engine block (connected to the case of the alt which is its negative terminal) should be properly connected to the battery neg post and the alt pos to the battery pos. The result is a parallel connection that should result in the difference in potential between the battery and the alt being effectively zero. That means that for all intents and purposes, the battery neg post is reference ground.
The chassis is not a uniform conductor. Not by far. The forming and welding processes change the uniformity of the steel and the result is a myriad of different decent conductive pathways where the majority of the current flows interspersed with a ton of poor conductive areas. What this means to you is that the whole body of the car may be much larger than your wire, but the vast majorty of the car is not conducting your current. Compound that with the fact that copper is more than 10x more conductive than steel and it should become pretty obvious what is the more certain route.
