# Running ground from battery, vs close grounding point (bolt, dedicated) spot, etc.



## Cooluser23 (Dec 23, 2009)

Somebody at work asked me this question and I didn't have a good answer, so I figured I'll post it on the forum.

Why when you install a HAM radio, CB, etc. do you run both positive and ground straight from battery into the car?

but 

When you do a stereo install you only have about 12" of negative (ground) cable to a dedicated bolt, bare metal, etc. while only positive is run straight from battery?

What is the origin/reason behind this?

What would happen if the scenarios were reversed?
i.e: running Ham radio, CB, other radio amplifier from a grounding post close to the amp, or even the same distribution block as the stereo?

or, the stereo amplifier with a negative ground cable all the way from battery?
(if so, is there a maximum length for the ground cable run?)


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## trumpet (Nov 14, 2010)

I install two-way business band radios and running power and ground to the battery is a last resort. For CB radios, if these are getting installed in a passenger car it's possible there aren't any accessory feeds open that supply adequate current, which is why power would be run right off the battery. The ground really should go to the chassis, and from there the circuit is completed by a ground close to the battery, just as in a car.

The reason for doing this is most times the vehicle body is an adequate ground plane. It's getting to be less of a "go-to" ground method as new cars have less steel in the body, more joints, and so on that add resistance.

If you choose to ground the audio system to the battery it's important to ground to the chassis, then ADD a ground to the battery ground up front. If you ground your amplifiers directly to the battery you can create a ground loop. Use the same size cable for the ground wire as for the power wire.


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## supermotofan (Nov 29, 2010)

Cooluser23, thanks for asking the question as I had thought that the best route was to run positive and negative straight to the battery.

Trumpet, thanks for setting me straight.


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## jcollin76 (Oct 26, 2010)

trumpet said:


> I install two-way business band radios and running power and ground to the battery is a last resort. For CB radios, if these are getting installed in a passenger car it's possible there aren't any accessory feeds open that supply adequate current, which is why power would be run right off the battery. The ground really should go to the chassis, and from there the circuit is completed by a ground close to the battery, just as in a car.
> 
> The reason for doing this is most times the vehicle body is an adequate ground plane. It's getting to be less of a "go-to" ground method as new cars have less steel in the body, more joints, and so on that add resistance.
> 
> If you choose to ground the audio system to the battery it's important to ground to the chassis, then ADD a ground to the battery ground up front. If you ground your amplifiers directly to the battery you can create a ground loop. Use the same size cable for the ground wire as for the power wire.


Just for clarification, your saying if a dedicated ground run is to be used, ground to the chassis as well?

I ask because all my amps and hu will be grounded right under my dash to a cap/dist block, and I planned on a dedicated run to the bat (dedicated system bat). All in an effort to eliminate noise from the power supply...


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## chad (Jun 30, 2005)

trumpet said:


> The reason for doing this is most times the vehicle body is an adequate ground plane. It's getting to be less of a "go-to" ground method as new cars have less steel in the body, more joints, and so on that add resistance.


Actually when using a flat car surface AS a ground plane to lower the angle of radiation, as it should, you want to run the ground to the battery because any RF induced on said ground plane can creep back up the power supply side of the radio, old skool radios can tolerate this but the new radios that are heavily microprocessor driven can have that stray RF creep back in side and cause all kinds of ****s. Yeah, coax is grounded to the RF deck and is attached to said plane via inductive coupling or a solid mount, but these days the 12V feed is only cap coupled to the chassis.

Now getting High power RF and audio in one cage is a rootin tootin good time, I managed to get ti to work with absolutely NO NOISE issues. 

What was even more shocking was firing up the yaesu RF deck parked on top of 2500W of carver int eh shack/shop, and not having a hint of noise. But I need to shut up before I jynx myself.


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## chad (Jun 30, 2005)

also if you ground electronics to the battery you must fuse the ground in case of a main ground failure.


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## jcollin76 (Oct 26, 2010)

chad said:


> also if you ground electronics to the battery you must fuse the ground in case of a main ground failure.


Thanks, I hadn't thought of that.


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## ahardb0dy (Feb 19, 2012)

I've always run my grounds as close to what ever I was grounding, never back to the battery, My Kenwood Ham radio I used to have said to run the ground back to the battery and I didn't and never had a problem with it, no noise or anything.


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## trumpet (Nov 14, 2010)

chad said:


> Actually when using a flat car surface AS a ground plane to lower the angle of radiation, as it should, you want to run the ground to the battery because any RF induced on said ground plane can creep back up the power supply side of the radio


I'm trying to understand this. I've heard the term "ground plane" a hundred times but I haven't taken it upon myself to truly understand what it means. If you're grounding multiple electronic devices to the car's chassis, using the body as the ground plane, the RF emissions can travel into the radio?


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## Danometal (Nov 16, 2009)

I run a dedicated ground from my ground block on my amp rack all the way back up front under the hood to where all the factory stuff is grounded to the chassis right by the battery. And, then another foot of 0 gauge from that termination point to the negative battery terminal. And, then from the battery negative to the alternator case.

Alt case >> batt neg >> chassis ground under hood >>>>>>>> amp rack

Works great. Reduced a lot of dimming on heavy bass lines.


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## chad (Jun 30, 2005)

trumpet said:


> I'm trying to understand this. I've heard the term "ground plane" a hundred times but I haven't taken it upon myself to truly understand what it means. If you're grounding multiple electronic devices to the car's chassis, using the body as the ground plane, the RF emissions can travel into the radio?


Let's use the term properly, let's use "Ground plane" in an RF sense and what you are referring as a DC ground as a "buss bar."

When a radiator is placed on a a surface that RF has a hard time penetrating it bounces off of it, Just as an omnidirectional speaker would bounce off of a hard surface. What's soooo cool about RF is that you can use many of the same principles you use in audio, especially when understanding reflection, waveguides (beams,) and antenna arrays. So let's say in your band, and using the 150ish MHz (not knowing which biz band you are in) you place a short antenna in the middle of the trunk or on the roof on a standard NMO mount. That antenna will TRY to be an omnidirectional radiator but since the trunk or roof is a RF reflective surface and also tied to the coax shield via the NMO mount the lid rejects penetration, bounces the wave off of it and the pattern becomes a semi-circle, Because of this you just increased your ERP by AROUND 3dB, free power.

So far so good, but as we both know we do not live in a vacuum at absolute zero and there will be some losses somewhere. What happens is that you can saturate the ground plane and at some point it will absorb some RF, harmonics of the original signal, etc. Because the body of the vehicle has an RF component on it now, using it as a "buss bar" for DC grounding can cause that stray RF to sneak back into the PS section of the radio via an easy path. Think of it as a Faraday cage, it can become saturated, you are safe inside it, don't touch it if you are not at it's potential.

So next you think well if the battery is tied to the body isn't the same amount of RF on the negative battery terminal as on the car body? Well at Absolute Zero, yes. But RF, she works in mysterious ways. The car body, being thin and wide makes an excellent conductor of RF due to skin effect, yes, for the first time in the history of an audio forum we can use that terminology. Because the car body is tied to the negative battery terminal via a maze of wire of different path-lengths, wire that has a terrible velocity factor at 150 meg, the grounding system that's fantastic for DC is terrible for transferring RF energy and the amount of stray RF at the battery terminal is nil. The beauty of unintentional engineering.

Now, as you mentioned, as an installer it really blows to run that extra wire. Quench the RF yourself. You probably have a hella long chunk of black wire. Wrap it 5-10 turns around say a chunk of 3/8 PVC, you made a choke (inductor) RF hates these because it's a low pass filter. It's not getting into the ass end of the radio. This trick works for other things, let's forget about the RF the radio produces for a second and look into the "Ford Phenomena" Ford's fuel pumps are ungodly noisy in the RF arena, as are Hondas. You can buy a couple harness plugs, put an inductor (can be home made) between the fuel pump DC supply and the fuel pump and it will quench the RF coming out of the fuel pump. I actually have a Pi filter on my Honda fuel pump because the RF coming off that thing would de-sense my Icom so bad that at some frequencies it was completely worthless. Ironically it also lowered the noise floor of the system too! This can also work for class D amplifiers for those of us that still listen to AM radio


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## Lars Ulriched (Oct 31, 2009)

Subscribed


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## trumpet (Nov 14, 2010)

chad said:


> .......
> 
> You can buy a couple harness plugs, put an inductor (can be home made) between the fuel pump DC supply and the fuel pump and it will quench the RF coming out of the fuel pump. I actually have a Pi filter on my Honda fuel pump because the RF coming off that thing would de-sense my Icom so bad that at some frequencies it was completely worthless. Ironically it also lowered the noise floor of the system too! This can also work for class D amplifiers for those of us that still listen to AM radio



That was a great post. It's fascinating to learn how the worlds of RF communication and car audio can collide. We happen to be an Icom shop. My dad has been doing the business band radio stuff for my whole life, but I haven't gotten involved with it until the last couple of years.


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## chad (Jun 30, 2005)

trumpet said:


> We happen to be an Icom shop.


I got freaky enough to actually INSTALL mine when I did the system install.


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## Aaron'z 2.5RS/WRX (Oct 24, 2007)

Thoughts on a relocated battery set-up?

My amps power and ground is about 3', but I'm 8' from the HU.. and the HU is normally chassis/harness grounded.

In terms of inducing noise, I no longer have the battery to act as a "filter" right off of the alt., it's now 10' from the alt., with the "car" inbetween.. 

What sort of gremlins could be possible here?? (asking for myself AND for anyone with a relocated set-up)

I actually installed a 1F cap under my hood last fall to act as my filter (140A alt, Sears DHP, 1/0awg throughout), just before the car came offthe road, didn't have a lot of time to test anything... 

Just kicking that out there.. mine(and others) ground/filter structure could be all screwy because of this.. 

Thoughts..?


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## Cooluser23 (Dec 23, 2009)

trumpet said:


> I'm trying to understand this. I've heard the term "ground plane" a hundred times but I haven't taken it upon myself to truly understand what it means. If you're grounding multiple electronic devices to the car's chassis, using the body as the ground plane, the RF emissions can travel into the radio?


I'm likely the wrong person to answer this as I'm still learning myself. I've studied this for a possible cell phone amplifer purchase. (they do work btw. I tested a weak version, now I'm ready to move on to more amplification.) If I goof somewhere, somebody please correct me.

Ground plane is like a second antenna. The vertical whip is the receiving antenna, the ground plane (basically any piece of horizontal metal) acts as the second antenna for sending information. The metal ground plane needs to be a certain size. (for cell phones the minimum seems to be 3.5" diameter, larger obviously won't hurt. (for plastic/fiberglass cars/RV's you glue on a piece of metal that acts as the ground plane.) )

Antenna's should be perfectly vertical, as most senders (except TV) are vertically polarized. If you angle the antenna it may look better, but you're actually doing yourself a disservice. 

Glass lets radio waves through, but attenuates them a bit, hence the antenna on the outside. Cell phone antennas, which are wireless inside the vehicle have 2 antennas and both antennas need to be separated by either 10', or by a solid piece of metal. (possibly the ground plane.)

RF ground is different from electrical ground, as RF ground travels of the surface of the conductor. (Hence grounding straps in cars being this really wide mesh = maximum surface area) Electrical ground travels inside the conductor. 

Then there is things such as SWR's (Standing wave radio), and that is where I'm lost and it's over my head.


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## Cooluser23 (Dec 23, 2009)

trumpet said:


> That was a great post. It's fascinating to learn how the worlds of RF communication and car audio can collide.


I never thought about it that way, but speaker sound is a radio wave, just like FM, or any other "radio" wave. the only difference is we can hear what's coming out of the speaker. Dogs and Bats can hear higher frequencies better, then you get into HF (High frequency), VHF (Very High Frequency), then UHF (Ultra High Frequency), etc. - My radio friend once said that's because when they came up with the names they had no idea how high the frequencies could go. They had to invent new terms.


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## chad (Jun 30, 2005)

Cooluser23 said:


> Ground plane is like a second antenna. The vertical whip is the receiving antenna, the ground plane (basically any piece of horizontal metal) acts as the second antenna for sending information. The metal ground plane needs to be a certain size. (for cell phones the minimum seems to be 3.5" diameter, larger obviously won't hurt. (for plastic/fiberglass cars/RV's you glue on a piece of metal that acts as the ground plane.) )Antenna's should be perfectly vertical, as most senders (except TV) are vertically polarized. If you angle the antenna it may look better, but you're actually doing yourself a disservice.


A lot of FM broadcast has circular polarization. And it's also best to think of the ground plane as PART of the antenna as opposed to a second antenna, there's no co-phasing going on there. It would be like assuming the grounded elements in a beam antenna are second antennas, they are not, they merely alter the pattern of the radiating element.





Cooluser23 said:


> Glass lets radio waves through, but attenuates them a bit, hence the antenna on the outside. Cell phone antennas, which are wireless inside the vehicle have 2 antennas and both antennas need to be separated by either 10', or by a solid piece of metal. (possibly the ground plane.)


Gotta watch this, in doing your research did they mention passivated glass? Ain't **** that gets through that. Should have been mentioned in the through glass antenna section of of your studies. A large percentage of vehicles use passivated glass.




Cooluser23 said:


> Then there is things such as SWR's (Standing wave radio), and that is where I'm lost and it's over my head.


The Standing wave ratio is the ratio of reflected versus output power. Because of this I hate the term SWR, and just prefer to use reflected power. When an antenna system is non resonant, as in the impedance of the antenna system does not match the output impedance of the output of the transmitter it will reflect power, much like a tube amp does with an impedance mismatch. Many "SWR meters" are dual needle, with one needle being power output and the other needle being reflected power, they are on opposite sides of the meter face and where they intersect is your "SWR" I find these much easier to use as you can see transmitter power fold back at big mismatches, you don't constantly have to calibrate them like a SWR meter.



Cooluser23 said:


> RF ground is different from electrical ground, as RF ground travels of the surface of the conductor. (Hence grounding straps in cars being this really wide mesh = maximum surface area) Electrical ground travels inside the conductor.


I flip-flopped your post a bit because I'm going to use terminology described above.

The most important reason to understand the differences in typed of ground is not due to skin effect. Screen is also used often in RF grounds, works great, we use copper plated screen in all of our studio Faraday cages. BUT 1/2" thick plate steel would do the exact same thing. The strap/screen is used because it's more practical and cost effective, and does the exact same thing.

What IS important to remember is that a ground can and will be resonant, just line an antenna. For example you can take a chunk of wire, attach one end to the transmitter output and the other end to the ground point at which the transmitter ground is attached. At one point in frequency (and multiples of that point providing the transmitter output is clean) you will have ZERO reflected power (a 1:1 SWR) this is because you found the resonant frequency of that wire. Many AM skirt antennas use this configuration. it makes a beautiful doughnut shaped patters (I like to call it the "death-star explosion" pattern.) You know the myth of putting your key FOB under your chin to increase range? It's true. with your feet on the ground and that under your chin you set up the same style of antenna with your body. look at the freq of most FOBs and the height of the average human from chin to ground  One good example is the Solarcon IMAX2000 10 meter/CB antenna. If you shove your DMM across the shield and feed it's a DEAD short. But at it's tuning frequency it's 50 Ohms on the dot. Like speakers, inductance and capacitance dictate impedance whereas coil length and composition sets up your resistance. When looking at RF grounds it's best to NEVER look at resistance, you MUST look at impedance, a cheapo antenna analyzer will help greatly with this.


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## chad (Jun 30, 2005)

Cooluser23 said:


> I never thought about it that way, but speaker sound is a radio wave, just like FM, or any other "radio" wave.


Wrong, sound is not an electromagnetic wave. Sound travels at the speed of sound, electromagnetic waves travel at just shy of the speed of light. If this were true you would not be able to sit in a radio studio and hear the same material on your confidence monitor as you hear as the source... And satellite TV would be UBER behind. Imagine the Doppler effect on your car radio while driving if electromagnetic waves traveled at the speed of sound.


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## CrossFired (Jan 24, 2008)

I run my ground to the chassis, but I also make sure I've got a good ground from the battery to the chassis/frame.


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## Cooluser23 (Dec 23, 2009)

Mp3car.com: Providing the latest news on in-car entertainment, and a community to connect people. Interesting. This video suggests that running ground straight from battery removes noise.


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## 07azhhr (Dec 28, 2011)

My battery came stock in the hatch/trunk area so I grounded my amp to the same bolt that the battery is grounded at. I should actually say that BOTH of my cars have the batteries in the hatch/trunk and both are grounded this way. One car is using a mid 90's SS ref amp and the other is using a new PPI Phantom amp. Neither system has any noise issues.


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## Bnixon (Mar 7, 2011)

I have a 3 amp setup in my mastercraft boat and I have 1/0 ground and power running directly from the battery to two distribution blocks. There is zero noise in the system. Obviously you can not ground to a fiberglass boat like you can in a car. 

How is it any different changing your ground point from the battery post vs 8" away where the negative cable grounds to the chassis from the battery? There should be no difference in theory, does the terminal at the battery not see exactly what is at the termination point of the negative cable less any impedance drop from the actual wire?

I am ignorant in the science of this just applying what little common sense i have to the situation.

B


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