Ground to batt?

[NJack2AF 10+ year member]

I've always wondered about this and please don't flame me if it's already been discussed. Is there a reason that people don't just run their ground wire from the amp directly to their batt??? It seems like it would work much better than grounding to the chassis to me... I know I'm a n00b //content.invisioncic.com/y282845/emoticons/rolleyes.gif.c1fef805e9d1464d377451cd5bc18bfb.gif

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[squeak9798 5,000+ posts]

Most chassis have less resistance than most gauges of wire, which means that the chassis would be a better ground than running a wire to the negative battery post. "What gauge" of wire is commonly disputed...so it's really hard to say conclusively. I've seen some valid tests that show that most vehicle chassis' have a resistance equivalent to ~14' run of 4ga wire (which would mean if you are using larger than 4ga wire, it would be better to ground directly to the battery), but I've also seen valid tests that show most chassis' to have a resistance equivalent to that of 0/2ga wire (which would mean it'd only be better to ground directly to the battery if you are using a wire larger than 0/2ga).

 

[iceteebone 5,000+ posts]

the battery is grounded to the chasis anyways, so if you improve your battery ground under the hood (big 3) that'll make the chasis ground better.

 

[squeak9798 5,000+ posts]

the battery is grounded to the chasis anyways, so if you improve your battery ground under the hood (big 3) that'll make the chasis ground better.

It'll improve the grounding (less resistance) between the battery and the chassis. But the chassis is still going to have XX amount of resistance over XX length. You can't change that.

 

[iceteebone 5,000+ posts]

It'll improve the grounding (less resistance) between the battery and the chassis. But the chassis is still going to have XX amount of resistance over XX length. You can't change that.

i was looking at it that the battery is grounded to the chasis so it would have the same ground as grounding an amp to the chasis so there would be no need really in grounding back to the battery

 

[squeak9798 5,000+ posts]

i was looking at it that the battery is grounded to the chasis so it would have the same ground as grounding an amp to the chasis so there would be no need really in grounding back to the battery

Which is where the conversation regarding the resistance of the chassis compared to the resistance of X length of X gauge of wire comes into play //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif The chassis isn't resistance free. There is going to be a certain amount of resistance between the two grounding points of the battery and the amplifier. If the wire you are using has less resistance than the chassis over that length, then you would be better off running the ground wire directly back to to the negative battery terminal.

 

[iceteebone 5,000+ posts]

Which is where the conversation regarding the resistance of the chassis compared to the resistance of X length of X gauge of wire comes into play //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif The chassis isn't resistance free. There is going to be a certain amount of resistance between the two grounding points of the battery and the amplifier. If the wire you are using has less resistance than the chassis over than length, then you would be better off running the ground wire directly back to to the negative battery terminal.

that's why you test the ground first. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif i myself don't put this much effort in a ground. if i'm getting a consistent volatge and zero noise it's good enough for me

 

[NJack2AF 10+ year member]

Thanks a lot. //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif So I guess just like anything else, it depends. Just seems like a lot of newbies will pick a shitty ground spot and have probs with it (the guys a CC that installed my first sub), when running a wire back to the batt would probably be better. It also seems it would eliminate the need for having to do the big 3.

I'm more than happy with the way my system is now, I was just curious that's all //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[iceteebone 5,000+ posts]

Thanks a lot. //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif So I guess just like anything else, it depends. Just seems like a lot of newbies will pick a shitty ground spot and have probs with it (the guys a CC that installed my first sub), when running a wire back to the batt would probably be better. It also seems it would eliminate the need for having to do the big 3.
I'm more than happy with the way my system is now, I was just curious that's all //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

why would that eliminate the purpose of the big 3? there was a good tutorial somewhere to test grounds using a dmm and a piece of wire

 

[helotaxi 5,000+ posts]

Grounding back to the battery doen't eliminate the need for the Big 3. You still need to beef up the bat->alt (+) connection and the block->bat (-) connection and you may as well upgrade the bat->chassis (-) connection while you are there though it doesn't need to be as big.

The utility of a direct ground to the battery is entirely dependant on the car and the amount of current being drawn by the system. Unibody cars are far from good conductors. You only have a handful of tack welds to actually conduct current and steel is an OK conductor at best anyway. Factor in the way that current flows nonuniformly through sheet steel and the potential for ground loops and induced noise from accessories increases. By grounding back to the battery you know that all of your components have an equal ground potential and the nothing else is sharing the ground path. The only real drawback is the initial cost of the extra wire and the trouble of running it through the firewall.

iceteebone--just to clarify, the battery isn't technically grounded to the chassis, the chassis is grounded to the battery. True ground is defined as zero potential and the only place you will find that is the negative post of the battery with the car off and the chassis of the alt with the car on. If you do the Big 3 these two should be really close to the same. If you compare the potential there to somewhere else on the chassis you will see a difference.

 

[Rattlebrain 10+ year member]

ground is defined as zero potential and the only place you will find that is the negative post of the battery with the car off and the chassis of the alt with the car on. If you do the Big 3 these two should be really close to the same. If you compare the potential there to somewhere else on the chassis you will see a difference.

So, in doing the "big 3" would there be an advantage if you were to add a "4th" and add a ground wire form the alt. chassis to the car frame/body?

 

[helotaxi 5,000+ posts]

So, in doing the "big 3" would there be an advantage if you were to add a "4th" and add a ground wire form the alt. chassis to the car frame/body?

In 99% of cars the chassis of the alt is electrically connected to the engine block by the alt bracket. It's a pretty substantial piece of metal and relatively short in length. It is connected to the engine block (the most substantial hunk of metal in the car) which is connected to the battery neg terminal. By beefing up the connection between the block and the battery you have beefed up the connection between the battery and the alt. If you've upgraded the battery to chassis cable you have also upgraded the alt to chassis connection as well.

 

[forbidden 10+ year member]

Here is a link to my grounding sticky.

http://www.the12volt.com/installbay/forum_posts.asp?TID=49445&PN=1

 

[Rattlebrain 10+ year member]

In 99% of cars the chassis of the alt is electrically connected to the engine block by the alt bracket. It's a pretty substantial piece of metal and relatively short in length. It is connected to the engine block (the most substantial hunk of metal in the car) which is connected to the battery neg terminal. By beefing up the connection between the block and the battery you have beefed up the connection between the battery and the alt. If you've upgraded the battery to chassis cable you have also upgraded the alt to chassis connection as well.

Thanks Helotaxi. I know the alt was grounded to the engine, I just wanted to see if there would be an additional advantage by grounding it also to the frame or body of the car. Thanks for the reply. //content.invisioncic.com/y282845/emoticons/thumbsupwink.gif.129404938effda6ad9cca39e7f4b58a3.gif

Forbidden: I printed out your link and shall read it here in a short.

Again Thanks!

 

[NJack2AF 10+ year member]

Cool thanks, I learn so much on this site every day... I wasn't sure about that icetee, and now I know I was obviously wrong heh.