Using a vehicle's chassis\frame as a ground or ...

[- Rovin's car audio -]

wanted d thread title to be "Using a vehicle's chassis\frame as a ground or running a length of ground wire(-) from d alternator\engine" but all d words couldnt fit

lets discuss since im sure we see ppl on foreign forums doing this & wondered why they dont just use d vehicle's body as a (-) negative instead ? ....

[Brian Steele]

I'd like to see the reasoning behind running a -ve cable instead of just grounding to the car's chassis. I suspect that there might be a bit of "voodoo" behind it (like "breaking in subwoofers"), but I'll try to keep an open mind, for now

[- Rovin's car audio -]

i read about some "theories" but id like to hear what others have to say ...

[kurpal_v2]

I'd like to see the reasoning behind running a -ve cable instead of just grounding to the car's chassis. I suspect that there might be a bit of "voodoo" behind it (like "breaking in subwoofers"), but I'll try to keep an open mind, for now

It is quite, its a SPL myth that runs along the lines of sharing one starting and end point (front battery). Some guys think that when you run a + to your amp and - from your amp to battery terminal it acts like a closed curcit and you get a spike on the SPL reading...

[viking1705]

I'd like to see the reasoning behind running a -ve cable instead of just grounding to the car's chassis. I suspect that there might be a bit of "voodoo" behind it (like "breaking in subwoofers"), but I'll try to keep an open mind, for now

lol..if anyone can prove advantages of this method then my mind may change also.But once you ground properly up front then your vehicle's chassis is just as good.

[BrotherHood]

I always use the vehicles chasis and the system has functioned normally and performed well every time. No worries whatsoever with grounding to the chasis. Will continue to do so unless I see some facts about advantages of running a ground from the negative battery terminal.

[Sully]

I use the chassis as well, but always check that the resistance between the ground point and the negative battery pole is 0. There have been vehicles that I've worked on where the resistance isn't always 0ohms from the most accessible ground point.

[silent_riot]

Generally, in older cars, there is a risk with the integrity of the vehicle frame as a conductor. There was a voltage drop using the vehicle chassis in my older SPL car, than using a dedicated 0ga run. In my daily driver, I don't bother as it isn't needed.

In an SPL car, power is a big part of the equation, and assuming that a vehicle chassis has the same resistance and power loss as the 0ga +ve is a dubious thing to do. Keeping the resistance uniform, minimal and constant in the power supply (i.e. both +ve and -ve runs) will assure that you are not wasting much power in the power transmission.

[Brian Steele]

Generally, in older cars, there is a risk with the integrity of the vehicle frame as a conductor.

If the integrity of the vehicle is that so bad that the impedance of its frame is more than that of a 0ga run, then that vehicle should probably be consigned to the scrap heap, because that suggests that it's about to fall apart.

In an SPL car, power is a big part of the equation, and assuming that a vehicle chassis has the same resistance and power loss as the 0ga +ve is a dubious thing to do. Keeping the resistance uniform, minimal and constant in the power supply (i.e. both +ve and -ve runs) will assure that you are not wasting much power in the power transmission.

Do you have any actual measurements that suggest that a car's chassis offers more resistance than a run of 0ga cable?

FWIW, if I was to make an argument in favour of 0ga -ve run vs. using the chassis, I'd start with the fact that it eliminates one termination between the amplifier and the battery, and it's at these terminations you can see a jump in resistance. As to whether that minor impedance jump (which can be minimized by several means) actually makes a difference, well that's a whole other discussion .

[Kasey]

I'm with Brian on this one. If you did a big three ugrade, and did it well, ur vehicle chassis should be the best thing you can use as a grounding potential.

A vehicle chassis is (well suppose to be) pure IRON. Which, due to its sheer size/volume/surface area, should provide the least resistance to ground, even less resistance than two runs of Zero guage wire!! (believe it or not).

The key to grounding is doing it properly i.e. use proper sizes of lugs, crimping, soldering, sand the area on the Chassis properly, etc.

IMHO if a vehicle's chassis's electrical integrity is in question, one should question the structural integrity as well, because as Brian said, that vehicle is gonna fall apart soon!!

[BrotherHood]

I could only see the chasis as a ground to be a 'bad' or disfunctional ground if yuh chasis shake down or rotten down.

[silent_riot]

Well then you guys should be advising SPL world record holders that they should use their vehicle chassis as a ground for more power delivery.

A good place to start to look for proof is to look at DB Drag street class competitor builds or IASCA Stock class builds. i.e. proper SPL builds, not people who just want to see what they can do on a meter. Proper SPL build look at delivering the most amount of power efficiently within the rules of competition.

The proper builds are those who do NOT use the vehicle as a conductor. Additionally, why then do the competition organisations limit the number of power wire runs in these classes if there was nothing to gain from it?
If the vehicle chassis provides no limitations as a ground, then there would be no need for ground runs or the limitation on ground wire runs.

Anyone who does big numbers in these classes do NOT use the vehicle chassis in the power run, but rely on dedicated wires to their amplifiers. But hey, what do those guys know besides getting SPL world records.

Resistivity. The material that makes up a car alloy does not have the same resistivity as copper in good power wire. The total resistance of the vehicle chassis is not only dependent on the size/volume/surface area of the conductor, but the resistivity of the type of alloy used. Copper is only second to silver in resistivity, so unless your car chassis is made up of silver or a greater cross sectional area of copper, resistance is something to consider.

[LOUD AND CLEAR AUDIO]

agree silent riot i tried it made a difference anyways we used like 10 runs of 4guage like 3 yrs back

[Brian Steele]

Resistivity. The material that makes up a car alloy does not have the same resistivity as copper in good power wire. The total resistance of the vehicle chassis is not only dependent on the size/volume/surface area of the conductor, but the resistivity of the type of alloy used. Copper is only second to silver in resistivity, so unless your car chassis is made up of silver or a greater cross sectional area of copper, resistance is something to consider.

Read that to yourself again a couple of times, then ask yourself how much higher the resistivity of iron would have to be compared to copper, for something the size of a car's chassis to offer the same or more resistance than a run of 0 guage copper cable.

Sorry, I am a "show me the money" guy. I have seen no measurements that back up the suggestion that a 0 guage -ve cable run can offer less resistance than a car's chassis.

If you have any, I'd like to see them.

[Kasey]

Well then you guys should be advising SPL world record holders that they should use their vehicle chassis as a ground for more power delivery.

A good place to start to look for proof is to look at DB Drag street class competitor builds or IASCA Stock class builds. i.e. proper SPL builds, not people who just want to see what they can do on a meter. Proper SPL build look at delivering the most amount of power efficiently within the rules of competition.

The proper builds are those who do NOT use the vehicle as a conductor. Additionally, why then do the competition organisations limit the number of power wire runs in these classes if there was nothing to gain from it?
If the vehicle chassis provides no limitations as a ground, then there would be no need for ground runs or the limitation on ground wire runs.

Anyone who does big numbers in these classes do NOT use the vehicle chassis in the power run, but rely on dedicated wires to their amplifiers. But hey, what do those guys know besides getting SPL world records.

Resistivity. The material that makes up a car alloy does not have the same resistivity as copper in good power wire. The total resistance of the vehicle chassis is not only dependent on the size/volume/surface area of the conductor, but the resistivity of the type of alloy used. Copper is only second to silver in resistivity, so unless your car chassis is made up of silver or a greater cross sectional area of copper, resistance is something to consider.

Honestly I dont base my opinions on what a 'some other guy does' ('SPL' competetitor), I base it on my knowledge on the Electrical principles I was taught of in University. I am not saying that I know everything, but Electrical and Power engineering is my field, and based on my experience I still believe that a vehicle's chasssis is the best conductor.

Where did u get ur information on resistivity?

Anyway, to back up my claim, I did try this zero guage run yesterday evening, just to prove a point. IT MADE ABSOLUTELY NO DIFFERENCE. My voltages remained same (actually it was 0.1v less than when I grounded my amps to the chassis!). My car chassis is not copper too.

[silent_riot]

Resistivity is a physical property of a conductor. Any physics O' Level student will be able to explain what it is. You can google it and see the equations which relate resistivity to resistance. I can post them here if needed.

I think I understand what you guys are saying, and why you are not seeing my point.
1) You guys are stating that a vehicle chassis is a good ground. My problem with this is that, if it is, it needs qualification.
2) I say I don't agree that a vehicle chassis is a good ground (without qualification) because in large power applications, the vehicle chassis is not a good enough ground for the application, and multiple runs of 0ga are used to improve the power circuit.
3) In the smallest applications (eg. headunit only) or even my daily system of 4 amplifiers listening at low levels, there isn't the need for power circuit upgrades such as 0ga ground wiring. Not even the big 3 was done on my system, and there are no problems for 5 years going... Will I or have I used a vehicle ground for my spl system? NO.

If you guys are saying a vehicle chassis is a good ground, then say under what conditions it will suffice.

[Kasey]

It is obvious that you have extensive experience in car audio, and that you also know alot about electrical energy, but no one has ever shown me how a vehicles ground is 'better' than runs of thin copper wire (as compared to the big junk of metal that is the car's chassis).

What learnt about maximum current transfer, is that it doest only have to do with the resistivity of particular metals, but rather the 'resistance' of conductors. Resistance is what 'blocks' or 'limits' current flow.

I Think of it like if I increase my water hose diameter, a larger volume of water can pass through (pressure is not an issue). Now because the amps actually 'pull' what it needs for ur battery, then it 'sees' less restriction when it 'pulls', hence it performs more efficiently. This is largely due to the sheer volume and size of a vehicle's chassis as compared to two thin copper conductors.

Correct me if I am wrong anyone.


Resistivity and Conductivity (from the net):
The electrical resistance of a wire would be expected to be greater for a longer wire, less for a wire of larger cross sectional area, and would be expected to depend upon the material out of which the wire is made. Experimentally, the dependence upon these properties is a straightforward one for a wide range of conditions.

R=[P(rho) * L]/A where:
R=resistance
rho=resistivity
A=Crossectional area
L= Length

As we know, Current = V/R , so the less the resistance, the more current. And the greater the crossectional area, the less the resistance.

[ryan5030]

x2. Agreeing with Kasey.

[silent_riot]

What learnt about maximum current transfer, is that it doest only have to do with the resistivity of particular metals, but rather the 'resistance' of conductors. Resistance is what 'blocks' or 'limits' current flow.

Well, resistance depends on resistivity, so current transfer depends on the resistivity of the vehicle. Resistivity is not constant for a metal, and changes with environmental conditions, eg. heat.
In your water hose diameter analogy, think of copper as water, and peanut butter as a higher resistivity metal passing through the hose. My point: it does not have to do with size and cross-sectional area only.
I also think that while serving as a ground for other equipment, there would be potential differences along the vehicle chassis from other operating equipment. This would not make the vehicle chassis a uniform ground potential as opposed to a dedicated ground wire run to the battery ground (which should be at the lowest potential).

[Brian Steele]

In your water hose diameter analogy, think of copper as water, and peanut butter as a higher resistivity metal passing through the hose.

The difference in conductivity between copper and iron is nowhere near that amount. A more suitable analogy might be comparing the flow difference between water and rum

I think for the same length of cable, a cable made of iron may need about 5 times the cross-sectional area of a cable made of copper to achieve the same or lower resistance (someone can go check my numbers if they want). The car's chassis likely equates to a lot more than that.

I also think that while serving as a ground for other equipment, there would be potential differences along the vehicle chassis from other operating equipment. This would not make the vehicle chassis a uniform ground potential as opposed to a dedicated ground wire run to the battery ground (which should be at the lowest potential).

Because of the ultra-low resistance of the car's chassis, this is basically a non-issue. You're more likely to see a higher resistance across the junction points than between the car's chassis and the battery.

[silent_riot]

Brian, let's say I need to burp a 12,000 Watt amp off a single battery up front.
Will the car chassis suffice as a grounding circuit?

[Brian Steele]

Brian, let's say I need to burp a 12,000 Watt amp off a single battery up front.
Will the car chassis suffice as a grounding circuit?

At that power level, I'd be worrying a lot more about the ability of the battery to meet the power requirements, rather than the resistivity of the car's chasis.

[- Rovin's car audio -]

i agree with some points from both sides

for daily use "small power" even up to "medium sized" systems i cant see d need to run separate ground wire , d steel body (not iron i see some ppl loosely saying) shud suffice

however for those ultimate pure spl vehicles with shitload of power built strictly for spl use : i wud think d multiple copper wire runs wud be a better pathway for a better circuit , more than likely d body of this type of vehicle wud NOT be used for grounding so d multiple copper wire runs wud be made as d only path as a (-) for d circuit & we all know copper is a much better conductor than steel


99% of us posting on this forum wouldnt have real world experience with these types of SPL vehicles & most of us posting based on d experience we read from other pros who have done it since who has d time\$ to own such a vehicle\equipment to actually do it for ur self to test it unless 1 of those guys let u test it on their vehicle

there has to be a purpose gained by experience ppl doing it otherwise i doubt everybody just watching others on d internet & simply following like monkey see monkey do ...

[nigel1977]

First and foremost, resistivity and conductivity are the reciprocal of each other. Kasey was alluding to that. I think.

Lets look at a run of 0awg vs the vehicle's chassis. I think this was the spin off concern from the other build thread.

With a run of cable, you would expect uniform resistivity from end to end, because its a non stop run from end to end... connection point resistance can be ignored, because you still need to connect something to the battery in both cases.
With the chassis, unless its a truck like mine, and you bolt directly to the main beam that runs the length of the vehicle, you are going to have different pieces of metal, welded together to form the car's chassis.

Lets take an average japanese sedan. the front chassis section is welded onto the main cabin of the car. there is no main chassis running from front to back. this is what i think Silent was getting to. there are different types of metal involved, most of are spot welded to each other.

So for high power applications, we would be trying to force high current across a bunch of spot welds to get from the main ground point in the engine bay, to way back in the trunk area.

So, for the regular suv, sedan, I concede, that a single run of cable for ground will have lower resistivity and higher condcutivity for high current applications. a megger or "ring" test will reveal more scientific tests.

For vehicles with a "real" chassis, and the battery is grounded to it, and the equipment, grounded at the other end, I cant agree that a single run of cable, or many runs of cable, will be better.

[SR]

sigh
finally another good debate on this forum

unless you have had extensive experience in building spl vehicle applications you may not grasp the reasoning why the use of multi runs of copper


lemme ask somthing

what is the conductor that feeds the +ve to the amps
is it the same as the conductor that is the -ve

in other words it is keeping your current path on the same conductor rather than different conductors ensuring the best current flow possible to the amps which in turn may result in as little as .1db more as opposed to say using the chassis
but .1 makes a huge difference between 1st place and second

its similar to multi runs from a buss bar connected to the battery rack a proper build will have equal length positive and ground cables from the bus bar to the amps
agian ensuring delivery is equal to all amplifiers so that all subs fire at the EXACT same time as once that does not happen there will be cancellation resulting in a lower spl score


think about it

[Brian Steele]

i doubt everybody just watching others on d internet & simply following like monkey see monkey do ...

LOL - you've just described EXACTLY what happens on the Internet.

Witness the number of times people proclaim that a subwoofer has to be "broken in", when testing has confirmed that this is not the case.

Witness the number of times people advise "build a box tuned to nn Hz for the best results", with no relation given to the speaker used, the box size or even the car it's going to be in - the equivalent of recommending a tire without knowing the rim size or the brand/model of car the rim's connected to.

I can go on and on, LOL

Having encountered many of these "truths" over the years has just made me into a bigger skeptic. "Show Me The Money". In this case, determining which is the better conductor - 0guage cable or the car's chassis should be pretty easy to measure. So, if your measurements show that the 0guage cable shows a lower resistance than YOU car's chassis, hey, feel free to use it. But don't tell me that's it's true because "so-and-so uses it on his car", because there is a LOT of ignorance about this sort of stuff all around the Internet posing as fact.

[Brian Steele]

With a run of cable, you would expect uniform resistivity from end to end, because its a non stop run from end to end... connection point resistance can be ignored, because you still need to connect something to the battery in both cases.

Not true. In a direct cable run, only two connection points are involved - battery|cable and cable|amplifier. In a chassis-ground situation, there are at least four connection points - battery|cable, cable|chassis, chassis|cable, cable|amplifier.

With the chassis, unless its a truck like mine, and you bolt directly to the main beam that runs the length of the vehicle, you are going to have different pieces of metal, welded together to form the car's chassis.

Lets take an average japanese sedan. the front chassis section is welded onto the main cabin of the car. there is no main chassis running from front to back. this is what i think Silent was getting to. there are different types of metal involved, most of are spot welded to each other.

So for high power applications, we would be trying to force high current across a bunch of spot welds to get from the main ground point in the engine bay, to way back in the trunk area.

So, for the regular suv, sedan, I concede, that a single run of cable for ground will have lower resistivity and higher condcutivity for high current applications. a megger or "ring" test will reveal more scientific tests.

For vehicles with a "real" chassis, and the battery is grounded to it, and the equipment, grounded at the other end, I cant agree that a single run of cable, or many runs of cable, will be better.

It's a good hypothesis, but has it been backed up with actual measurements?

[Brian Steele]

think about it

I did, and couldn't make much sense of it, sorry.

BTW, like Kasey, I also have a background in Electrical Engineering, though I concentrated on Telecommunications and Controls.

If I wanted my subwoofers to fire "at exactly the same time" in an SPL vehicle (which I'd interpret as meaning "exactly in phase at the burp frequency"), I would be concentrating on ensuring that they have exactly the same large signal parameters (good luck with that, btw!), and they're being used in exactly the same alignments. Or perhaps I'd avoid all that trouble and just use one subwoofer that can achieve what I'm looking for.

[silent_riot]

Both nigel1977 and I have individual SPL builds under our belts. In my case, voltages were more stable during burps using 0ga than using the vehicle chassis, the electrical system is more reliable from my experience. I mentioned it before, but I'm not sure if you need a photo with my username and date or something.

My background is in both Physics (undergrad) and Electrical Engineering from UWI (postgrad). That being said empirical evidence is quite important to me as well.

[nigel1977]

someone who has time, and access to a megger, please contact silent riot and brian.