grounding question

[ill_ace 10+ year member]

I am ready to start my install but I was confused about picking the right grounding point. The manual for my ppi amps says that if the system has over 300 watts then you should ground to the battery. This doesnt seem right to me because i dont think it is that common for people to ground to the battery. Does anyone have any suggestions for finding a good spot. I know I have to make sure there is no paint and stuff like that.

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[Acidburn 5,000+ posts]

seat/seat belt bolts are usually pretty good

 

[JimJ 5,000+ posts]

Wherever you get very close to 0 ohms on a DMM, measuring the resistance from the battery's negative terminal...

 

[lotas 10+ year member]

I agree with Frost, you should use a DMM if you have one. If you dont have one, you should go buy one, $10 or something at radio shack. You will want one if you are into car audio. Anyways, you dont NEED to use one to find a good grounding spot. Make sure your ground is well sanded, it should be clean of dirt, grease, paint, basically you want a strong metal-->metal contact. Use a bolt to secure your ground if you have to drill your own hole, and use a ring terminal or something similar to contact the bolt.

If you dont want to get/use a DMM, dont worry about it, just sand, keep the wire pretty short, and make a strong connection. If you have alt whine/ or induced noise after you get everything set up, then you might want to find a better grounding spot.

By the way, ive never understood the whole "grounding to the battery" deal. I mean running a ground all the way back to the - terminal and then your battery itself gets grounded to the car chassis...

Im no expert though...so maybe i'm missing something.

 

[forbidden 10+ year member]

You are, it's called resistance on the ground return and it equates to you eating a foot long sub and having your butt cheeks sewn 90% shut..... A good ground is under 1/2 ohm of resistance. A seatbelt bolt is generally not a good ground point as typically they are spot welded on which adds resistance, so not a good idea overall. Precision is correct, follow their advice.

 

[supa_c 5,000+ posts]

Uhmm...

Just about every piece in a honda car is spot welded.

So what am i going to do now ? //content.invisioncic.com/y282845/emoticons/rolleyes.gif.c1fef805e9d1464d377451cd5bc18bfb.gif

 

[AVSTANG02]

how do u read the ground spot with a DMM ?

I dont have noise but im curious how good I did....

 

[forbidden 10+ year member]

Take one probe and attach it to the neg terminal on the battery, take the other and touch it to the spot where you intend to ground. Set meter to read ohms resistance and off you go. Test it in multiple spots, you'll see how crappy a ground return most cars really have.

 

[supa_c 5,000+ posts]

you will need a piece of wire to run back to the battery that hooks on the DMM's probe

I used jumper cables //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif

 

[tracyrick 10+ year member]

Old thread but I want to try this - Do you have to disconnect the terminal that goes to the negative post on the battery? And then you hook up your DMM lead to the - battery post, or the the terminal?

Also, how do you check the resistance of your extension wire? Supposed to subtract that resistance from the total number.

 

[helotaxi 5,000+ posts]

A good ground is under 1/2 ohm of resistance.

Yeah, WAY under a half ohm. At a half ohm you would get a half volt drop across your ground for every amp flowing through the ground path. If you can measure the resistance of the ground that you choose directly with a basic DMM, it's not a good ground.

A seatbelt bolt is generally not a good ground point as typically they are spot welded on which adds resistance, so not a good idea overall.

The nut that the the seatbelt bolt threads into is usually held in place by some pretty good welds and is on the most substantial piece of metal in the car (not that that is saying much in many cases)

Precision is correct, follow their advice.

I ground back to my battery but I also wired a small system with 1/0. Total overkill in my case. 300W should be completely fine with a normal chassis ground.

By the way, ive never understood the whole "grounding to the battery" deal. I mean running a ground all the way back to the - terminal and then your battery itself gets grounded to the car chassis...

Actually that is totally backwards, the chassis is grounded to the battery. The ground plane in a car is the negative battery terminal, not the chassis.

 

[Louisiana_CRX 5,000+ posts]

one quick question...While measuring for resistance I was playing with my battery and ground...I got different readings depending on if I used the pos or neg probe....I tried this with another meter the same thing...So question...Which probe do you use on the battery side? //content.invisioncic.com/y282845/emoticons/confused.gif.e820e0216602db4765798ac39d28caa9.gif