Ugh, Brainfart (Ground Question)

[yacob.naif 10+ year member]

I used to know this stuff forwards and backwards, but i've been out of the loop, and trying to figure it out again.

In a car's electrical system, is the ultimate point of voltage return the engine block (alternator) or the negative terminal of the battery?

I'm working on a new project (resurrecting my 01 jetta.) I'm doing the big 3, dropping in a 260A alternator, and relocating the battery to the trunk/replacing it with a kinetik 2400.

I need to know if it'd be most beneficial to simply ground the engine block to frame, and the battery to the frame, or run a cable all the way up front, and ground the battery directly to the engine.

I think i'm confusing myself. It's just been so long...... I've got plenty (70+ feet) of 1/0 here, so i want to do this the best way possible. (I've still got a opti4000d that's never been used, that's begging to be utilized in a project)

Just want to get the rudimentary electrical stuff out of the way at the same time i do my turbo/intake/exhaust/intercooler work, so this summer i can just drop in my amps, and be done.

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[jco1385 5,000+ posts]

if you have the wire, run it. i would use the chassis/frame of the car but there's resistance issues sometimes. and if you plan to run anything with some power you should probably run the wire

 

[yacob.naif 10+ year member]

Only reason i'm confused is that normall when people run a ground up front, they're grounding an amplifier, and the ground goes to the negative terminal of the battery.

The ground i'm running is the battery itself.....

The ground for the amps is going to be going directly to the negative terminal of the battery.

You see why i'm confused? Hahaha. I could just be overthinking this.

Is there a benefit to running a ground directly from the engine block to the battery?

 

[qkassidyw 10+ year member]

I would use your meter and test the resistance from where you want to ground it to the frame in the trunk and where you are going to ground it to the frame in the engine bay. If it is really low (Under 2 Ohms)

Then you can avoid running it all the way to the front. OR you could do both //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[loopkiller 10+ year member]

OP, I would run the wire since you have it. The alternator case is the end point for all grounds. When the alternator is making the power, the electrons have to make it back to the alternators NEG- side (the case) in order to complete the circuit. The shortest, least resistive path to that point is the best. Usually 1/0 wire will have much less resistance than 10 pieces of steel welded together. I would still run ground from every NEG- battery terminal to the chassis as well. This is for any device that uses the chassis for ground and is powered by the battery when th engine is off. Otherwise, those grounds would have to travel through the alt case to get to the battery. That would be bad.

I would use your meter and test the resistance from where you want to ground it to the frame in the trunk and where you are going to ground it to the frame in the engine bay. If it is really low (Under 2 Ohms)
Then you can avoid running it all the way to the front. OR you could do both //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

The issue with testing the resistance from the trunk to the engine bay would be you would need really long test leads on your DMM. I have never seen DMM leads that long, likely because they would add resistance themselves if they were that long. //content.invisioncic.com/y282845/emoticons/rolleyes.gif.c1fef805e9d1464d377451cd5bc18bfb.gif

 

[yacob.naif 10+ year member]

i'll measure resistance.

I'd do both, but i don't want my battery terminals to get overcrowded.

The ring terminals i'm using are hard to stack, and i'm already planning on grounding my amps directly to the battery.

And in either case, i'm still going to run a ground strap between the engine and the chassis, independant of the ground for the battery, so that should handle all the current from my in-car accessories.

The alternator case is the end point for all grounds. When the alternator is making the power, the electrons have to make it back to the alternators NEG- side (the case) in order to complete the circuit.

That's what i was really looking for. I was stuck in a brainloop, and couldn't decide if my original plan made any sense or not.

I couldn't remember if the circuit terminated at the battery, or back at the alternator.

Should've trusted my gut. Thanks a lot.

 

[loopkiller 10+ year member]

i'll measure resistance.
I'd do both, but i don't want my battery terminals to get overcrowded.

The ring terminals i'm using are hard to stack, and i'm already planning on grounding my amps directly to the battery.

And in either case, i'm still going to run a ground strap between the engine and the chassis, independant of the ground for the battery, so that should handle all the current from my in-car accessories.

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