I posted this in another thread, but I thought you would be more likely to see this if I was to copy it onto a new thread.
"After replacing the alternator, you only need to upgrade the wire form alternator to battery, battery to ground, and engine block to frame/chasis.(big 3)"
Glass,
If the stereo system is grounded by using a distribution block that is connected directly to battery negative as opposed to a chasis ground, do you see any reason to upgade the factory wire that runs from battery negative to the frame and the wire that runs from engine block to the frame after replacing a stock alternator with a HO alternator?? I can't think of one.
yes. the alternator grounds through the engine block's connection to the chassis, before it goes through the rectifier and voltage regulator, and the battery should have the negative to chassis connection upgraded because that's the primary path of current flow to ground for the battery, which acts as a voltage stabilizing and smoothing filter for the stereo system. there's no reason to ground the amplifiers to the battery post unless the batteries are in the trunk next to the amps.. even then you need a chassis connection to complete the circuit with the alternator for charging.
also remember the longer the route from source to ground for the current, the more heat you're going to build up and the larger the cable is going to have to be.. keeping runs shorter means you can use smaller gauge cable in some places and get the same results.
So, upgrading the battery to chassis and the motor to chassis cables is wise when upgrading the alternator because the alternator utilizes that ground circuit. That makes sence.
But, another thought regarding the grounding of amps..
Chassis ground utilizes factory spot welds which the manufacturer deemed suitable for the factory set-up. Needless to say, there was no high powered aftermarket stereo present. Do you upgrade those spot welds also??
Going strait to the battery with a guage equal to that of the power cable would be just as good or better than any chassis ground...correct.
With a chassis ground, the current travels through the amplifier ground wire that connects to a bolt somewhere (depending on installation), then through the body until it reaches the frame, then through the frame until it reaches the "battery to frame" cable then from there it goes to battery negative post. Along the way, the current goes through nuts, bolts and spot welds. How is that a shorter run than a cable to battery negative and why would that be better than grounding strait to the battery via a disrtibution block just like you would with power wire for the amps??
One time I measured the resistance from a random chassis ground to battery negative and got just under 5 ohms. Then I measured the resistance from a 4 guage wire to a distribution block that connected to battery negative via a 12 foot long 1/0 guage cable. I got just over 3 ohms. The ohm meter that I have is not digital (I don't like the digital ones) and thus I don't have EXACT measurements, but the difference was about 2 ohms.
Depends on the vehicle used too. If we grounded directly to the frame, like that of a truck or SUV (a REAL SUV, not some Honda CR-V or the like), the resistance of that would be lower than most wires you could run, simply due to the enormous area you're working with and the direct path for current flow. Some crap economy car with a unibody made of impure sheet metal and crappy tack welds won't fare so well, but they're still not god awful.
By the way, a 12 foot long 1/0 cable should show substantially less than 3 ohms resistance. Same goes for the chassis. Sounds like the meter or the leads are crap.
I took the measurement at the end of a 3 foot long cut of 4 guage wire that went through a distrubution block, then into a 12 foot long 1/0 guage and then to battery negative. So, this wasn't just a solid 1/0 guage wire that I was reading. There were some electrical connections. The ohm meter is an old, cheap Sears brand with even cheaper leads and yes they are crap. Before I took my readings, I measured the resistance of a 4 ohm voice coil and it my meter read 6 ohms. Then I measured the resistance accross a 2 ohm resistor and it read 4 ohms. So I know my meter is off by 2 ohms. But, I was mainly taking the readings to see which had more resistance...not to see exactly how much resistance each one had and thus accuracy was not critical. I did however conclude that the chassis ground did have more resistance than the cable to battery ground and again, that is what I wanted to know. Vehicle used - 1989 Mustang GT
all of your questions depend on a number of factors like how much current you're drawing, how the car was made, where things are mounted, etc. with some cars you're better off running cable to the battery negative if you're drawing very high amounts of current. by the way you never actually go through the "frame" but through the car's chassis/body. most cars don't actually even have frames anymore, and the ones that do are usually isolated for the most part from the body points used for grounding. one reason to use chassis point grounding instead of running more wire back to tha battery, is that the longer runs of ground wire can begin to act like an antenna, picking up EMI/RFI which can cause problems too. it really depends on how much work you want to put into an installation and how the install/system is set up. there's no one right answer that applies to every car.
Why would ground wire be more of an antenna than the chassis itself?? Well designed power/ground cable is (according to the manufacturers) 100% oxygen free. Being air tight, would it still be able to act as an antenna??
being OFC just means it's less likely to corrode inside the jacket. It has nothing to do with shielding. I don't really have time to delve into how an antenna works, but in short, the chassis acts as a ground plane. the wire, based on length, can act as an antenna depending on the wavelength of the interference. The wire also has more chance of running near a crossover or ignition wiring harness which will introduce noise easily and quickly into the system.
EMI is electromagnetic interference RFI is radio freq interference. try using google or wikipedia or howthingswork.com or something.. you could answer a lot of these questions with 2 minutes of reading
