grounding questions...

[jdrockafella 10+ year member]

Yes, and so did you. The difference is that my ground is with a piece of 1/0 copper wire and yours is probably a foot of copper wire and 10+ feet of unibody steel. I'll wager mine has lower resistance.

are you saying your 1/0 has less resistance than a huge piece of steel?

I'll take that bet any time of day, any day of the week, any week of the year.

 

[soundstreamer 10+ year member]

are you saying your 1/0 has less resistance than a huge piece of steel?
I'll take that bet any time of day, any day of the week, any week of the year.

i think you are looking at it wrong...

amp big *** wire battery

vs.

amp wire huge piece of steel wire battery

 

[kingpin_jeffie 10+ year member]

Huh. My wiring must really **** then. I have a 15+ foot ground for all of my amps. If your amps are in your trunk, yours probably are, too.

I was referring to the fact that it makes no sense to run a ground all the way from the cabin back to the trunk just so it can go all the way back to the battery through the frame.

Also I would like to hear your reasoning behind how a single piece of 0/1 has less resistance than an entire automobile frame? Granted the copper wire is oxygen free and conducts like a charm but the overall size of the frame would lead me to believe it has less resistance. (Just based on the water hose metaphor) ie - garden hose compared to a fire hydrant kind of thing.

 

[tommyk90 5,000+ posts]

I was referring to the fact that it makes no sense to run a ground all the way from the cabin back to the trunk just so it can go all the way back to the battery through the frame.
Also I would like to hear your reasoning behind how a single piece of 0/1 has less resistance than an entire automobile frame? Granted the copper wire is oxygen free and conducts like a charm but the overall size of the frame would lead me to believe it has less resistance. (Just based on the water hose metaphor) ie - garden hose compared to a fire hydrant kind of thing.

Surface area in a 1/0 wire > surface area of a framerail?

All i know is that i grounded my amp back up to the battery (actually, 2 runs of + and 2 runs of -, us SPL people are crazy //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif)

I know that there has been tests done in the past where a cars frame was actually comparable to a piece of 4 gauge, and i know there is a way to test this on your own car, but i don't know off the top of my head.

All i know is that if i have the opportunity to ground straight to the battery I do, but in most cases grounding to the frame works just fine. But for all out SPL competitions, grounding straight to the battery has been proven to be much more effective (i.e., less resistance)

 

[forbidden 10+ year member]

Did you happen to notice the part of his quote that said unibody steel which of course is full of high resistance spot welds and super high resistance glued together unibody panels......

 

[helotaxi 5,000+ posts]

I was referring to the fact that it makes no sense to run a ground all the way from the cabin back to the trunk just so it can go all the way back to the battery through the frame.

You're right that makes absolutely no sense. If I was going to use a chassis ground in that instance, I would ground everything close to the amps in the cabin.

Also I would like to hear your reasoning behind how a single piece of 0/1 has less resistance than an entire automobile frame? Granted the copper wire is oxygen free and conducts like a charm but the overall size of the frame would lead me to believe it has less resistance. (Just based on the water hose metaphor) ie - garden hose compared to a fire hydrant kind of thing.

Several flaws in your line of thinking. First, electrical current doesn't flow thru the entire cross section of the sheetmetal. It flows in heavy concentrations along lower resistance paths through the metal. If you could see the current flowing, it would resemble a river delta. Along these pathways are chokepoints where all the different pathways must come together. These are typically spot welds joining two or more panels together. Welds are marginal conductors when new. As they age they only get worse. Steel has 10 times the resistance of copper for a given cross section and once you factor in how thin the sheetmetal on a typical car is and that the entire structural cross section isn't conducting, it's pretty easy to see why a straight ground to the battery is the best route.

If you want to see how good your ground point is, get a wire of known resistance and a DMM. Using the wire as a jumper because the DMM leads probably won't reach far enough, measure the resistance from your ground point to the neg terminal of the battery. Subtract the resistance of the wire and you have your ground path resistance. Realistically, if you can measure the difference with a basic DMM, you have a really bad ground. Where you really run into problems is when you consider that most chassis are roughly equivalent to a 4 Ga wire, and that the max current rating of 4 ga is in the neighborhood of 130A. At 125 amp you are losing over a volt to wire resistance with 4 ga. This is on each side of the amp. 1 volt on the + side, 1 volt on the -. With 1/0 you are losing less than .5V on either side. Your total loss with 1/0 is less than your + side loss with 4ga. Still not worth running the extra bit of wire?

 

[gatorgrizz27 10+ year member]

If my alt puts out 14.4v and the voltage to my amp is 14.2v, I am only losing 0.1v on the + and 0.1v on the -, correct?

 

[n2audio 5,000+ posts]

I know that there has been tests done in the past where a cars frame was actually comparable to a piece of 4 gauge

That is JL's stance. As I understood it those were tests Manville did himself.

Some of the other engineers/tech's at carsound have said their results were somewhere around 1/0, possibly 2/0.

Esoteric Audio did extensive tests and concluded about 1/0 - they sell a great deal of wire and would benefit from proving a chassis isn't very conductive.

I'm not trying to tell people how to wire their stuff, but those are the few tests I'm aware of.

I run 1100-1200w through the chassis with less than .1v drop. Only stock wiring upgrade is about a foot of 8 ga from the alt to B+.

 

[n2audio 5,000+ posts]

If my alt puts out 14.4v and the voltage to my amp is 14.2v, I am only losing 0.1v on the + and 0.1v on the -, correct?

No - there's no way to know where it's dropping w/o probing it at various points.