where is the true ground?
Printed From: the12volt.com
Forum Name: Car Audio
Forum Discription: Car Stereos, Amplifiers, Crossovers, Processors, Speakers, Subwoofers, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=121347
Printed Date: May 15, 2025 at 2:48 AM
Topic: where is the true ground?
Posted By: rfhvhtoo
Subject: where is the true ground?
Date Posted: April 14, 2010 at 5:15 PM
I don't mean to stir up any emotions but i've stumbled on some compelling arguments of why it may be better to ground amps directly to the battery negative in the engine bay.
The argument is based on the simple concept of. "All Connections start and END with the Battery."
Now i've heard the "alternator case" is the "TRUE" ground but as the concept says, the alternator is also Connected positively to the battery and then grounded to the Firewall/Fram and from the firewall BACK to the Battery .
So now im seeing the Frame of the and other metal parts of a vehicle as just Representations of the negative terminal.
Its also said that Oxygen free Copper wire is Much less resistant than the frame of your vehicle. due to the rust, paint, rubber mounts, and dirt & things that cause resistance through out it getting back to the battery's negative terminal.
So my final questions are really does this make the Battery negative terminal via 0ga wire the best ground in a vehicle for amps considering this concept? if not where is the TRUE ground?
Thanks
PS. this is just a question, im not saying that im stating any facts.
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I can't hear you!
Replies:
Posted By: oldspark
Date Posted: April 14, 2010 at 7:20 PM
Ground is just a reference point - it's wherever you deem it to be. (Though it's usually "earth" - not a chassis/body etc.)
If you mean which is the lowest ground (potential), then it is the battery if the battery is supplying the load, or the alternator if it is supplying the load. (IE - the battery when not charging, and normally the alternator has the greatest voltage supply when charging.)
But normally audio systems are connected to the battery for noise reasons alone. Besides - ever mounted 4G etc to a alternator (and what's the point)?
Hence the audio-ground is the -ve terminal of the battery.
Any other ground will never be as "low" as either the battery -ve or the alternator (ie, its chassis hence engine etc).
Although OFC may have low resistance than bodywork, I doubt that cable resistance can compare to body/chassis resistance except where to different assemblies - ie, chassis to body; body to bonnet etc.
If internal rust is that much of problem, the audio will disintegrate the vehicle if not motion itself.
I have heard many say similar but have yet to see evidence (except for sectional bodies, fibreglass cars etc, and an old rusted out wood-framed vintage.....
Posted By: anonymous1
Date Posted: April 14, 2010 at 8:25 PM
rfhvhtoo wrote:
Its also said that Oxygen free Copper wire is Much less resistant than the frame of your vehicle. due to the rust, paint, rubber mounts, and dirt & things that cause resistance through out it getting back to the battery's negative terminal.
A lot of things are "also said" . . . a lot of them are just plain wrong. Some people think that voltage will ONLY travel on the outside of a conductor. :D Steel has a very low resistance as a solid condutive path and the paint, dirt etc doesnt play in to it. Where there are two pieces making a questionable physical connection, this can be a limiter as corrosion, oxidation etc is a poor conductive path. Having lots of clean metal together tightly will conduct huge amounts of current. You have to balance fanatic mysticisms with the laws of physics and a measure of common sense.
Posted By: oldspark
Date Posted: April 14, 2010 at 8:49 PM
So a capacitor will lower the ground and make up for corrosion? Cool!
(That's crap - I'm joking etc etc).
Not that I'm EVER one to question or quash spouse-tales (fanatic mysticisms etc), nor ever suggest that webland is full of errors, misquotes, misunderstanding, and DHs.
Try my alternate check - if you can't measure the voltage drops (because despite being fanatical enough to have the best or an expensive system with improved cabling, you don't have or can't use a $10 voltmeter), just feel the heat along the various cable sections. This may require long hands for body/chassis paths.
As to common sense (a la web logical but wrong), we all know that leads to a removal of cents from the common to the amassing few. (Don't we?)
Only Idiots and Anons to afraid to ID themselves along with senile codgers and a host of others hereon would attempt to disrupt that traditional and expending practice. (Blessed are the Meek for they shall take the Earth....)
Posted By: rfhvhtoo
Date Posted: April 14, 2010 at 11:22 PM
oldspark wrote:
If you mean which is the lowest ground (potential), then it is the battery if the battery is supplying the load, or the alternator if it is supplying the load. (IE - the battery when not charging, and normally the alternator has the greatest voltage supply when charging.)
(just making sure i understand)
So the Case of the alternator "When Charging" is the better ground than the Batteries Negative terminal. Unless the system is NOT being charged by the alternator (Engine Off) then the better ground is the battery negative...
So would running a 0ga wire back to the battery have less or more resistance than the cab of a truck? Because i dont know about anyone else does but I have a 8inch 0 gauge wire connecting my frame to my cab... unless you have a ford f150 as well.
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Posted By: the12volt
Date Posted: April 15, 2010 at 12:04 AM
When the vehicle is running, absolute ground is at the case of the alternator. When not running, it's at the negative terminal of the battery (or batteries). -------------  the12volt • Support the12volt.com
Posted By: rfhvhtoo
Date Posted: April 15, 2010 at 12:07 AM
So will running a wire to the Absolute ground be better or "just as good" as going through the frame?
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Posted By: anonymous1
Date Posted: April 15, 2010 at 12:49 AM
oldspark you crack me up! Those cables just get warm from the engine heat. If you want to really find the difference in the grounding, you have to lick your fingers and place them far apart from the frame to the positive on the battery.  Just to be clear, when I say things about believing fairy tales and buying swampland in Arizona, I'm not pointing at anyone in particular. In fact, really not anyone here, because let's face it, these threads are buried in raw genius :D I'm going to side with the12volt: When the vehicle is running, absolute ground is at the case of the alternator. When not running, it's at the negative terminal of the battery (or batteries). If voltage is the potential between two points in a conductive path, then the highest potential will be at the alternator output while the engine is running, making the alternator body the most absolute ground. In the instances where your ground cable goes from your battery to the engine block, which is closely related to the alternator, you're still not far the the battery post\terminal.
"So will running a wire to the Absolute ground be better or "just as good" as going through the frame?" It could be better, but if you have good clean connections with your grounding from the battery to the frame and a good clean connection to the frame elsewhere on the vehicle, you have good ground. How much resistance does the wire have? (rhetorical question)
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Posted By: oldspark
Date Posted: April 15, 2010 at 3:22 AM
anonymous1 wrote:
I'm going to side with the12volt: When the vehicle is running, absolute ground is at the case of the alternator. When not running, it's at the negative terminal of the battery (or batteries)
Whatcha mean siding with 12volt? That's what I said!
Though I added the case where the alternator is unable to keep up with the load - then it becomes the battery.
For BIG sound, for that reason - and because it's the only practicable solution - you use the battery.
When the alternator is above battery-full voltage (12.7V; shall we exclude surface charge?), it may seem sensical to use the alternator for 2 problems - how often do you see an alternator with 4G (etc) B+ connection, else how often do the alternators themselves use 4G (etc) internally from the rectifiers? And then there is the noise....
However, in that case, taking the ground from the alternator is feasible and does make sense... But of all the system voltage drops, the engine to chassis (and then battery -ve) should be the smallest.
The only time I recall alternator connections being regularly used was halogen lighting for rally cars etc. But that's where 0.1V and lower weight can make a big difference (allegedly).
As to the warm leads, I was being serious. Maybe I should have stated temperature differential? But point taken.
The test is valid though - eg, for starter cable/s after a cold start; battery cables before eBay heat up; boot/trunk wires.
Whilst one could use a temp meter like my $10 DMM for the temp differentials, I think that loses sight of what you are measuring - namely the voltage difference along that path - ie, just a DMM, not a temp meter!
I do admit however being somewhat jestive measuring chassis/body temp increases. Again, a DMM is easier!
Posted By: rfhvhtoo
Date Posted: April 16, 2010 at 4:14 AM
Yeah that makes sense, I Just want the most efficient ground because i think i may have a unibody issue. I'm into trying things myself so I'll save 10$ a week for 3 weeks to get a 15ft strand of 0ga cable for experimental purposes. Thanks a lot for the insight, this helped a lot with my understanding of the TOTAL PICTURE of "Ground." I don't think A lot of people (mostly noobs) into car audio would know these small things that then lead to explain the BIG picture and explain important concepts like "WHY" your ground has to be solid or the metal has to be "cleaned/shiny" and its better soldered.
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Posted By: oldspark
Date Posted: April 16, 2010 at 5:11 AM
It does get tricky....
Even the experienced have different views. Whilst other experienced are just plain wrong (...at times - it happens!).
But excluding ground loop issues (and cost & weight), there is little reason NOT to run ground cables as well. The total resistance will be less than that of the cable or metalwork (ie, parallel resistances).
I run a heavy figure-8 cable (ground & +12V) to my 2nd rear-mounted battery. But that battery is not body/tray/chassis connected. But no harm if I were to - assuming a good path, else never breaking the cable ground return!. FYI - it's merely a spare battery - used for occasional fridges, or if my main battery flattens.
I also run similar but smaller to my Alpine (which may only be 16W x 4, not the whopping 45W x 4 that I thought it was!), but that's more for noise (dedicated +12V from battery) and wiring simplicity. But it normally has its chassis grounded to my body/chassis too (just not for the last year or 3?).
But the biggest voltage difference (between gnd & +12V) is either across the alternator (B+ & its chassis) else - when the battery is supplying - across the battery terminals.
Anywhere downstream from those points has to be a lower voltage - even if the drop is negligible. (If it isn't get, a better or true-RMS voltmeter! Else find out why your wiring is auto-transforming itself to increase voltage.)
For large systems, the only way to minimise the impact of high-current surges is a second battery near(er) the amp etc.
I say second because main/primary batteries are usually flooded (wet) and designed for high cranking currents.
The 2nd "amp" battery must usually be sealed if mounted internally (boot/trunk etc).
And usually it's an AGM (aka Valve-Regulated = VRLA, often aka "Sealed(sic) Lead Acid" = SLA).
Gel cells are another alternative (are these NOT SLA batteries?).
Whether the 2nd battery is deep cycle or cranking depends on what you want it for (long running without the engine, or high-output surges) - batteries normally being either one or the other by construction. (Yes - I am familiar with the hype. And the field comments.) Interestingly, both battery types often have the same quoted ESR, but let's not go there...
But to minimise losses & dips, first upgrade your wiring (the big-3 etc); then the alternator if it needs it; maybe more wiring upgrades; and maybe a 2nd battery - AGM of course!
(FYI - other than ground loops, cost & weight - I see no harm in "continually" paralleling ground straps and cables. There are usually heaps of possible paths. And unlike hot +12V wiring, no hazards. (The only hazards being if ground straps are insufficient!) But there is a point where the gains become negligible - or the mpg increase outweighs the 0.0000632 uuOhms & 16+ tons of ground strap gains)
Although primary batteries can be upgraded, I consider that a waste or compromise compared to a 2nd battery. Even a primary AGM is compromised by cable losses.
Better to keep the same standard (cheap?) main/primary battery, and then add whatever sized AGM near the amplifier/subs - whether a small 1.2AH in place of a capacitor, or a larger 40AH, 100AH etc etc.
But I am assuming non-parallel batteries (which IMO should not be done - despite claims otherwise...) and something akin to my oft suggested charge-light actuated (or voltage sensing) relay that only interconnects the main & 2nd batteries whilst charging.
Hence no issue issues with different batteries, and you should have at least one reasonably charged battery for cranking...
Ooops, back to earth.... I ran away with the grounding issue - absolutely!
Posted By: anonymous1
Date Posted: April 17, 2010 at 1:29 PM
oldspark wrote:
(FYI - other than ground loops, cost & weight - I see no harm in "continually" paralleling ground straps and cables. There are usually heaps of possible paths. And unlike hot +12V wiring, no hazards. (The only hazards being if ground straps are insufficient!) But there is a point where the gains become negligible - or the mpg increase outweighs the 0.0000632 uuOhms & 16+ tons of ground strap gains)
There's a lot of good information in that post relavent to a number of threads. Regarding the quote. Vehicle manufacturers do not design electrical systems with consumer upgrades in mind, they do the absolute least and cost effective thing to get that vehicle on a sales parking lot. My Pathfinder isnt the first system I've seen where I'm almost astonished it keeps running after 5 years based on the chincy materials and workmanship in the electrical dept. On this vehicle, I used a dremmel and cleaned the existing contact surfaces, and added more clean bare surface area where ground distribution existed. I also added additional cables. My current application (no pun intended) is different, I just want to provide the best possible high current both front and back for my winch, which can suck 300+ amps depending on load. And do this, in a manner that doesnt jeapordies existing circuitry. *there are Nissan KB articles about where to ground to avoid fault codes* I totally agree that adding some additional grounding and cleaning up is worth every penny, about to and about $20 and an hours labor.
Posted By: oldspark
Date Posted: April 17, 2010 at 7:25 PM
anonymous1 wrote:
Vehicle manufacturers do not design electrical systems with consumer upgrades in mind
You are correct.
But elsewhere someone said something similar regarding alternators and their capacity, and I thought that was misleading.
They were suggesting that the alternator was NOT designed nor capable of handling extra loads - in this case low power entertainment stuff (meaning 100W-200W of carPuter etc, not BIG audio).
I thought how common it is - or was - to add driving lights without experiencing problems.
EG - add 2x100W lights and the system would handle it fine - the battery would not flatten over time etc.
Anon's context however is different and refers to the provision of cabling as well.
Yes - they keep it light & cheap.
They include cig sockets. Some recreational vehicles may include rear power plugs (cig sockets or other).
Hence they allow for some consumer upgrades - like GPS, mobiles(cells), chargers etc.
But when it comes to big consumer upgrades, it is taken for granted that consumer supplies the required heavy battery terminals, wiring, and distribution. And so many forget the grounds! (Was it in 12volt ~12 months ago that some Hummer or similar lost ~7-12 DVDs/screens and $thousands of dollars of equipment due to high voltage? I'm betting it was a ground break...)
All manufacturers have to provide is "sufficient" wiring and grounding so that their equipment functions. Hence a 1V ground drop may be acceptable.
But there is no harm lowing ground drops. Double the existing 1V drop cabling to halve it to 1/2V. Quadruple it for 1/4V. Etc.
And I recommend the12volt's "Big 3" method - do NOT replace standard ground straps - ADD to them - thereby negating "faulty modification" claims under warranty etc.
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