forbidden

This is an old GM Technical Service Bulletin, but it should help anyone wanting to verify that their amp has a good ground:

METHOD OF VERIFYING ' GOOD ELECTRICAL SYSTEM GROUND ' #87-8-139 - (04/07/1987)
VEHICLES AFFECTED: ALL MODELS

When diagnosing electronic systems for incorrect operation, it is often necessary to verify that ground circuits are good. This article is intended to clarify what is meant by the term "good ground" and the preferred tools and methods for verifying it.

A "good ground" is a ground circuit that has a resistance of zero OHMS.

Ground circuit resistance can be measured in OHMS using a digital volt OHM meter (DVOM). When using a DVOM, it must be set on the 200 OHM scale to obtain an accurate measure of the circuit resistance. Many meters have both a 200 OHM scale and a 200 K scale. The 200 K scale will not measure zero OHMS accurately. If you are not sure how the meter is to be set for the 200 OHM scale, refer to the meter operating instructions for proper settings. If the meter is an autoranging or self-scaling meter, read the meter carefully to be sure which scale it is setting itself to.

Before measuring resistance in any circuit, the resistance of the meter should be measured by touching the leads together. A meter with a good battery and leads in good condition will read less than .2 OHMS usually zero. If the leads measure anything more, an accurate measure of the circuit resistance may not be possible.

Always remember - resistance cannot be measured accurately on a "live" circuit, All current flow through a circuit must be stopped by disconnecting its power source before measuring resistance.

Ground circuit resistance can also be checked by measuring the voltage drop across the circuit with a DVOM set on, the 2 volt scale. The voltage drop will be zero across a "good ground" circuit.

Remember, fully understand a meter's functions before using it!

To add to this, a good ground for car audio applications will have a return resistance reading of 1/2 ohm or less. I have yet to have a return reading of 0 ohms. If a ground return reading cannot be made to get below 1/2 ohm by means of the "BIG 3", then it is adviseable to ground direct to the battery. Electricity is an algebra equation, what you do to one side you must do to the other. Pay as much attention to the ground wire as you do the power wire.

The BIG 3 is a great place to start for a good ground, however it is the assumed proper method of grounding. What we are talking about here is the older and wiser 4th brother to the BIG 3 (the BIG 4).

So a proper ground wire will be as follows.

- clean of residue and paint.

- secure.

- have a resistance return of 1/2 ohm or less.

- be of adequate guage to carry the return as compared to the power wire.

To simplify the measuring of the return, use your meter as described. Disconnect the - battery terminal and disconnect the ground wire from you amp. If your dmm probes are not long enough, you will need to create a jumper extension out of some primary wire or whatever wire you have handy. Measure this wire for any resistance reading and subtract it from the total.

Many installers are not aware of this nor practice this method. It takes time and time = $ so don't get all pissy if you had a professional install done and this was not checked. A poor ground connection or high resistance reading may seem trivial under no load, but once you are pounding your nice new amp and it is drawing large amounts of current, this little reading has become a monster reading that has caused many an amp to fail for no apparent reason. It may be noticeable as a extremely hot running amplifier in a short time period, poor output levels or diminishing levels and of course a blown power supply or output section in the amplifier.

While the original article was written for the years gone by, it still is applicable to the newer generation of vehicles. A good ground is not about the amount or size of the metal in the return to the battery but about the resistance through it. Todays vehicles are a combination of metals, spot welds, glued together unibody panels and isolated chassis components. The return through these components is where the resistance reading comes into question and this is what we need people to understand, why the BIG 4 needs to be done if the BIG 3 does not solve the problem.

Rob @ Forbidden

DreamWarrior

I mentioned grounding to the battery to my installer this weekend when discussing potential issues with this car and the install. He mentioned that grounding to the battery is usually worse than finding a good chasis ground because it lends itself to adding noise. My guess would be in the form of "alternator whine" but that's just my assumption. Either way, this guy's been in the industry for a long time and has done many, many winning IASCA installs.

We'll see what he comes up with as a ground point for this car soon, however...I'll keep you posted. Regardless, I doubt he'll go back to the battery, and I'm sure he'll find a point of low resistance. He may have to pull a number of panels, pull away some upolstry, do some drilling, or whatever but I'm sure he'll find a good bolt somewhere.

MrWigggles

chasis ground should almost always beat using a return wire to the battery. A return wire to the battery will need to be very thick to work as well as a good chasis ground.

The article written in '87 probably didn't fully comprehend the power of today's audio systems. 1/2 ohms is WAY too much resistance for even a modest car audio system. With that amount of ohms a 30 amp system would experience a 15 volt drop which is more than your battery voltage!!!

You should be able to get a ground that is in the .01 or less range. Any more than that and you need to supply your own ground return.

Connection is the key, the seatbelt anchor for one of the rear seats is usually your best bet. Polish all of the paint off 'til you see shiny metal then use a ring terminal that is just as shiny. Mount the two together and you have a electrical connection that will be excellent.

-Mr. Wigggles

lurch519

im not sure how you can say that running a dedicated ground wire back to the battery would not be better than grounding to the vehicle chassis.

im sure that you are aware that everytime you make a connection in a wire, you are adding a bit of resistance to that wire. same thing applies to the chassis of a vehicle. you have components that are bolted together, welded together, and in some vehicles the frame is glued together.

so lets recap, you are saying that the ground connection through the chassis of a vehicle that is welded and bolted together is going to be better than approximately 20 feet of oxygen free copper connected directly to the battery?

i think not

DreamWarrior

Depends on the bolt you use and the chassis. A long run of a wire back to the battery could carry more resistance than the larger amount of metal in the chasis.

Also, lets assume you do get a similar resistance from a chasis ground. At this point, you're probably better off because you're less likely to introduce noise.

My bet, however, is that with enough searching around and pulling up carpets and such, a suitable low resistance chasis ground will be found.

forbidden

A good ground is not about the size or amount of metal in the return, it is about the ability of the return to pass as little resistance as possible. With todays unibody cars that for the most part do not have a chassis (in cars for example), the unibody is the return. The unibody is comprised of spot welded bolts, glued together panels and small ground wires for the most part. A good ground is one that has been measured and is under 1/2 ohm and correctly pointed out above, as low as possible. If you have a ground spot like this in the back of a vehicle, that is great, if you cannot find one, then it is off to the battery you go.

MrWigggles

As I stated earlier, the ground return needs to be WELL under .5 ohms. A small amp that draws 30A WILL create a voltage drop of 15 Volts if the return is .5 ohm and thus won't have ANY supply voltage to work with.

-Mr. Wigggles

snowrydr01

So the question to be asked is, where are your grounds?

truemagellen

that is why the AMP has a switched relay...so when it receives 12v signal from the HU's power 12v or the accesory signal (whatever u choose) it completes the circuit to draw power...the amp now is on

then when the 12v is shut off it cuts the relay and now no power is drawn

I have the same thing but in my 12v switched relay DC to DC powersupply for the modded xbox (although it was designed for a carpc...same thing)


edit: additional info:

almost all amps have the relay built in...only older amps and low power amps don't have them

the lower power ones probably assuming you won't need to have a direct connection to the battery since it draws so little power

but if u don't have one in the amp u can by and independent switched relay...it is very cheap u just must get one that can handle the load of the amp

but H if u are buying an amp without one...u are better off upgrading to one that has it

Astral

So, for the best ground, is it the consensus that the RX-8 requires a full run of the ground wire back to the battery?

Or have people been able to find spots in the trunk that yielded less than 0.5ohm resistance?

DarkBrew

Alternator whine can sneak into your system if you do not ground you head unit and amp to the same point.
The reason is that chasis is not zero ohms and and any two points will have a small voltage between them. With the gain of the amp, the ground noise may be amplified enough to be audible. (depends on design of the units)
Where ever you ground your amp, run the head unit ground on a separate wire to the same spot and the ground induced noise will vanish.

irfan

i lifted the rear seat cushions out and grounded to the bolt the seat backs were in.

forbidden

^^^^^ Read the grounding sticky to find out why that might not be the best idea.

Rx-Appreci-8

Getting a low ground DC resistance is important for all applications. Some applications (Audio, Video, Computer, etc.) also require low AC "resistance" (impedance) in the power circuit and for that we have the additional requirement of keeping "loop area" to a minimum.

To minimize loop area, run power and ground wires as close together as possible (twist them if necessary) and make the ground connection reasonably close to the 12V power connection. Don't go overboard, just minimize loop area as much as practical to avoid whine, hiss, pops, clicks, etc.

1 - Minimize loop area by choosing a grounding point near the fuse panel if 12V power is taken from the fuse panel.

2 - Minimize loop area by attaching the ground cable to the battery ground post (or a vehicle ground point near the battery) for high power circuits (e.g. subwoofer amps) where 12V is taken from the battery (don't forget an appropriate in-line fuse in the +12V line).

3 - Loop area in the power circuit can be minimized by connecting very low current appliances directly to the 12V, IGN, and GND wires going to the radio's rear connector. Make sure the additional current draw doesn't exceed wire guage and fuse safe limits (generally not a problem for PIE adapter, SAT tuner, etc.). To minimize warrantee issues associated with splicing into OEM cables, professional installers sometimes insert extension cables between the vehicle wiring harness connector and the radio connector and then tap (or, better, solder) power/ground onto the extension cable wires. I like this method for PIE and Sat radio installation because it allows connection to the same grounding point as the HU as suggested in DarkBrew's earlier email while also maintaining minimum loop area.

coolstorm92

iTrader: (1)

So running a return line back to the battery seems like extra work for me at this point. Does anybody have a good suggestion on a successful spot to ground to in the trunk. I know not all of you are running return lines to the battery.

lurch519

well, if you are looking for a usable ground, find a good body bolt to go to, such as the bolts holding the shocks in place on the left or right (the outside ones, not the ones directly attached to the shock). if you are looking for a good ground, go to the battery.

truemagellen

I'm running to the battery

Astral

One suggestion is the bolt where the tire mounting kit goes. On my so-so ohm meter, I got almost no increase in resistance at that point. Another member used it and said that he got a very low ohm resistance increase.

For now, I am using the point at which the upper rear seat portion bolts down (the bolt closer closer the center of the car). The bolt goes through the ring terminal that's between the metal and the U-shaped loop thing. I dremelled all the paint off around the bolt hole, and I also get a negligible ohm increase reading (within 0.1ohm). If I had a better DMM, I could give better numbers, but it seems to work pretty well. Honestly, that spot is a bit of a pain, as you have to unground your amps every time you take out the upper rear seatback (so I disconnect the neg. battery terminal every time I do that)... but it seems to work fine (I'm only pushing 600W RMS).

The system voltage reading on one of the amps seems to be identical to that obtained by the DMM directly across the battery (both while car is off and while running), and I hope that also suggests that the ground point I have doesn't suck completely.

G0t m4xx 21

I ran both my power and ground straight to the battery. I ran the cables through the boot that the main wiring bundle runs through on the left side (you just cut a slit in that boot and shove the cables though above the main bundle), then under the fuse panel, then through the trough under the door panel, and into the trunk behind the side trim panel. The cables are completely invisible from the hood to the back of the truck. I pulled my switched 12V for the remote on for the amps from the 12V jack in the center console.

truemagellen

except for the gasoline bubbling into the trunk

oh wait that is just tequila

yiksing

I hope your red cables are super heat resistant, the strut bar gets so hot even from normal driving/

BoosTED

iTrader: (2)

Install looks nice but is the capacitor sticking out of the plexi or is it an optical illusion?

Good to know on the ground testing. I was going to do it eventually but you saved me some work. Maybe I'll remount the battery to the trunk or add a second.

forbidden

No need for a second battery unless you are seeking extended play times. Even moving the stock battery is not needed, as you would still need to run lines back to the front to operate the vehicles electrical system. Just because you may have no issues now and the system is working, does not mean that over time the buildup of resistance on the ground return will not cause an amp to fail. It will, it has before and it will again. Good to see that someone took the time to measure the connections and verify what was found. 0 gauge line actually will fit under that white cover in the door sill as well, we ran the other 0 guage down the center of the 8 that we did here.

jstkilntim

I apologize to anyone that read my initial post (now deleted) about my saga of grounding in the trunk. While trying to figure out why my car had such horrible grounding characteristics I noticed that the draw of the trunk light was causing faulty readings. Once the battery was disconnetcted, all was well. I have edited this post to reflect my new findings.

While poking around the trunk this evening, using my trusty Fluke 87 III and a 10 foot jumper wire (#12 stranded wire w/ alligator clips on each end), I set out on a mission. To find a good ground.

I first hooked one end of the jumper wire to the bolt on the negative battery terminal & one end to the negative meter lead. Placing the positive meter lead on the same bolt, I "zeroed" my meter in the Relative & 4 1/2 Digit Mode. Heading back to the trunk and under the rear seat, I checked all bolts, brackets etc. that have been recommended above. Most read from .00 - .01 ohms. I re-zeroed and read them several times and came up with the same readings each time.

While taking these readings and focasing on low impedence, I realized that I have foolishly been overlooking one of the most crucial elements of any electrical circuit. If I have a #2 power wire (which I plan on using for about 1300W), what makes me think I can ground this system to the chassis anyway when the largest ground from the battery is a #4? (Without tracing the 3 ground wires through the loom, I am assuming the large one goes to the starter & the smaller 2 to various body or electrical components.) Anyone remember which way current flows? I see catastophic failure in the future! The ground wire ALWAYS has to be as large, or larger, than the power wire. Why do we forget the basic stuff?

I am going to add a #2 ground wire between the battery and a convenient spot under the hood. This should prevent any problems. If I have any noise etc., I will let you know.

By the way, the #2 fits fine in the white clips under the door sills.

Jedi54

iTrader: (7)

I'm still a little confused here as to the best method of doing this.

- Running a wire all the way back to the battery is the best way to go? If so: If I tell my installer that, will he know what the heck I'm talking about?