This is how my set up was Alternator > Starter > Battery...really was mad when I found that out because my alternator + description on the alternator itself said battery. So ended up using (2) gauge from the starter to the alternator and 0 gauge from the starter to alternator. Was a pain. =(
My approach is somewhat different than most installs I've seen, but it's worked well for me.
Apologies for the long post.
For the audio portion of my car's wiring, I float the ground. The + cable runs from the battery to an appropriate fuse as close as possible to the battery and then to a single point via a distribution block. The - cable runs to an appropriate fuse as close as possible to the battery, and then also to a single point via a distribution block. Although not strictly necessary for electrical safety under normal conditions, I fuse both sides, reasons at the last few paragraphs.
With most aftermarket gear, using a floating ground is not much problem to implement ... just make sure no electrical ground exists elsewhere, in particular from the amp chassis to vehicle ground. I use a wood panel to mount amps, distribution blocks, etc and secure that to the chassis, providing the isolation.
Where there will be problems will be with your factory installed portions, or factory mount locations.
The deck (factory or aftermarket) for example, since the factory locations provide a ground point at the mounting location (deck chassis to vehicle gnd via the mounting of the deck itself). I used various bits of rubber to isolate the chassis at metal points in the car's deck mount location, along with nylon screws or screws/bolts as appropriate.
This may necessitate modification of the deck mount area and will make going back to the stock deck problematic to a certain extent if the car is sold and conventional mounting is attempted at a later date (there will be no chassis gnd which the deck expects). As long as a subsequent owner understands the issue a gnd can provided from deck chassis to vehicle gnd via a wire connecting the deck's mount bolts to a chassis gnd.
Other Issues:
The final issue that can arise is an antenna for FM or AM/FM radio as provided in most cars from the factory. This in all likelihood will have a gnd incorporated somewhere. You will need to isolate that ground point, which is often at the fender mount.
In cases where you have the GM wire-in-windshield antenna, disconnect the connection at the base/middle of the windshield, or if that bothers you just avoid using the stock connector at the deck. Again, in my case one windshield with this type was replaced often enough due to rock chips and cracks which are prohibited by law in the driver's field of vision (this vehicle was a truck that saw gravel roads often). I just have them use the non-radio version of the windshield (and have zero-deductible glass coverage).
You can then add a different antenna mount with consideration given to isolating the antenna mount, cable, etc or some other appropriate solution.
Ground loops are to be avoided; the whole point of isolated ground and star grounding via the distribution block is to kill noise (and it most definitely works).
ALL power, both + and gnd, comes from the two power distribution blocks. This includes the deck (I usually end up using around 12 GA to the deck but read on for more on that). ALL audio devices and anything connected to them must be isolated from chassis gnd.
Power Wire Gauge:
Audio system power wiring wire gauge is up to the installer. The solutions that say "use X gauge" are correct except insofar as suggesting a specific gauge of wire for every install. The load the wire is expected to carry is one aspect but it's critical that the length of any power wiring be taken into account. The longer the wire, the larger gauge of wire is needed for a given current draw objective.
There is math to figure that out, but just as an illustration, if the audio system battery and the distribution block are close to each other (don't forget to fuse things, folks, as close to the battery as possible) a 4-gauge wire may support the same currents as a system with a 2-gauge wire that needs to travel longer or even a 0 gauge wire that travels a large distance (battery in the trunk of your classic Caddy, anyone?).
You should also consider heat sources, and overall cooling of the power cable. The warmer the wire, the less current it can carry. It also needs to dissipate some heat itself. Most guys in car audio know that power cable becomes less efficient with length, but sometimes they fail to pick up on where that lost power goes ... it's lost as heat.
It might help to keep in mind that your home electric stove coil could be described electrically as a very crappy cable in a flat circular coil ... it's so bad as a cable that it releases almost all the power applied to it as heat, which we use to cook our breakfast in the morning.
Copper is both expensive and heavy, so there is no real need to go higher than necessary just to follow a rule of thumb when the math is just sitting there waiting to provide an answer that will most definitely work fine. Ford says with a compact car 100 extra lbs = 1 mpg lost.
Depending on your particular car's power wiring layout, it might not hurt to address other power wiring issues in the vehicle. With this system you really need only address alternator to chassis gnd (as this is critical for good alternator function) but it won't hurt to look at wiring to the starter as well ... most cars use the bare minimum for the task, so a single gauge step up can make starting easier, or a two gauge step if you need cold weather starting performance since this is usually not really taken into consideration when sizing the stock wiring by the manufacturer. Also (again depending on the system used) the battery charging circuit may be made more efficient by upping + wiring improvements as well.
Safety:
Definitely consider your planned wiring layout carefully and use grommets any time either cable goes through the vehicle chassis. (I also apply heatshrink to the cable where it passes through the grommet). I strive to ensure power wiring is physically separated (+ and - cable) by at least 12" and more where possible.
It won't hurt to apply robust sheathing at any point where sharp metal may contact the cable in an accident, and secure the wire appropriately with cable ties (the nylon ones with a mounting tab are ideal) or other wiring aids (nylon cable clamps, etc). There is a real danger of fire whenever you run power wiring and are involved in an accident. Prevent that possibility before it happens.
I've used this system effectively in a few personal vehicles and it's worked very well for me. I would be appreciative, however, if Perry Babin would chime in with his valuable opinion on it.
Apologies for the long post.
For the audio portion of my car's wiring, I float the ground. The + cable runs from the battery to an appropriate fuse as close as possible to the battery and then to a single point via a distribution block. The - cable runs to an appropriate fuse as close as possible to the battery, and then also to a single point via a distribution block. Although not strictly necessary for electrical safety under normal conditions, I fuse both sides, reasons at the last few paragraphs.
With most aftermarket gear, using a floating ground is not much problem to implement ... just make sure no electrical ground exists elsewhere, in particular from the amp chassis to vehicle ground. I use a wood panel to mount amps, distribution blocks, etc and secure that to the chassis, providing the isolation.
Where there will be problems will be with your factory installed portions, or factory mount locations.
The deck (factory or aftermarket) for example, since the factory locations provide a ground point at the mounting location (deck chassis to vehicle gnd via the mounting of the deck itself). I used various bits of rubber to isolate the chassis at metal points in the car's deck mount location, along with nylon screws or screws/bolts as appropriate.
This may necessitate modification of the deck mount area and will make going back to the stock deck problematic to a certain extent if the car is sold and conventional mounting is attempted at a later date (there will be no chassis gnd which the deck expects). As long as a subsequent owner understands the issue a gnd can provided from deck chassis to vehicle gnd via a wire connecting the deck's mount bolts to a chassis gnd.
Other Issues:
The final issue that can arise is an antenna for FM or AM/FM radio as provided in most cars from the factory. This in all likelihood will have a gnd incorporated somewhere. You will need to isolate that ground point, which is often at the fender mount.
In cases where you have the GM wire-in-windshield antenna, disconnect the connection at the base/middle of the windshield, or if that bothers you just avoid using the stock connector at the deck. Again, in my case one windshield with this type was replaced often enough due to rock chips and cracks which are prohibited by law in the driver's field of vision (this vehicle was a truck that saw gravel roads often). I just have them use the non-radio version of the windshield (and have zero-deductible glass coverage).
You can then add a different antenna mount with consideration given to isolating the antenna mount, cable, etc or some other appropriate solution.
Ground loops are to be avoided; the whole point of isolated ground and star grounding via the distribution block is to kill noise (and it most definitely works).
ALL power, both + and gnd, comes from the two power distribution blocks. This includes the deck (I usually end up using around 12 GA to the deck but read on for more on that). ALL audio devices and anything connected to them must be isolated from chassis gnd.
Power Wire Gauge:
Audio system power wiring wire gauge is up to the installer. The solutions that say "use X gauge" are correct except insofar as suggesting a specific gauge of wire for every install. The load the wire is expected to carry is one aspect but it's critical that the length of any power wiring be taken into account. The longer the wire, the larger gauge of wire is needed for a given current draw objective.
There is math to figure that out, but just as an illustration, if the audio system battery and the distribution block are close to each other (don't forget to fuse things, folks, as close to the battery as possible) a 4-gauge wire may support the same currents as a system with a 2-gauge wire that needs to travel longer or even a 0 gauge wire that travels a large distance (battery in the trunk of your classic Caddy, anyone?).
You should also consider heat sources, and overall cooling of the power cable. The warmer the wire, the less current it can carry. It also needs to dissipate some heat itself. Most guys in car audio know that power cable becomes less efficient with length, but sometimes they fail to pick up on where that lost power goes ... it's lost as heat.
It might help to keep in mind that your home electric stove coil could be described electrically as a very crappy cable in a flat circular coil ... it's so bad as a cable that it releases almost all the power applied to it as heat, which we use to cook our breakfast in the morning.
Copper is both expensive and heavy, so there is no real need to go higher than necessary just to follow a rule of thumb when the math is just sitting there waiting to provide an answer that will most definitely work fine. Ford says with a compact car 100 extra lbs = 1 mpg lost.
Depending on your particular car's power wiring layout, it might not hurt to address other power wiring issues in the vehicle. With this system you really need only address alternator to chassis gnd (as this is critical for good alternator function) but it won't hurt to look at wiring to the starter as well ... most cars use the bare minimum for the task, so a single gauge step up can make starting easier, or a two gauge step if you need cold weather starting performance since this is usually not really taken into consideration when sizing the stock wiring by the manufacturer. Also (again depending on the system used) the battery charging circuit may be made more efficient by upping + wiring improvements as well.
Safety:
Definitely consider your planned wiring layout carefully and use grommets any time either cable goes through the vehicle chassis. (I also apply heatshrink to the cable where it passes through the grommet). I strive to ensure power wiring is physically separated (+ and - cable) by at least 12" and more where possible.
It won't hurt to apply robust sheathing at any point where sharp metal may contact the cable in an accident, and secure the wire appropriately with cable ties (the nylon ones with a mounting tab are ideal) or other wiring aids (nylon cable clamps, etc). There is a real danger of fire whenever you run power wiring and are involved in an accident. Prevent that possibility before it happens.
I've used this system effectively in a few personal vehicles and it's worked very well for me. I would be appreciative, however, if Perry Babin would chime in with his valuable opinion on it.
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Connections With Large Gauge Wire:
To make large gauge wiring work I use welding cable, grommets where appropriate, and soldered connections throughout.
To solder welding wire, I pre-heat the copper at the wire end with a heat gun. You will find solder flows fairly well throughout all strands this way when you apply the iron and solder to the cable for tinning the cable end. Very lightly tin the connector end (remember to add your heat shrink tubing to the cable, before soldering the connector on), mate and if you haven't over-done the connector tinning you can at this point crimp. Then preheat and solder, it will flow very nicely.
If you use a copper crimp connector for large gauge wire you can trim down the bolt connection side to fit your distribution block if necessary. A little work with a file on both sides or sometimes with one side on a hole-type connector to make it a "C" style that will fit works well. Do this before you solder so you can tin the modified areas with solder.
I like to then move the heatshrink to the connector/wire junction, add a waterproofing agent in a thin even layer over the connection (automotive "Goop" brand sealant is fine; there are others you can use provided they are safe for copper/electrical) and shrink with the heat gun.
If you use welding cable check it carefully for nicks in the rubber or silicon insulation ... it's very good insulation electrically but is susceptible to mechanical damage ... heat shrink it at any damage areas, and also at any points where mechanical damage is a risk. You can double up on the heat shrink if you like (second layer an inch longer at each end than the first).
Heat shrink stiffens the welding cable considerably which makes handling, routing, etc somewhat more difficult but the remainder is very flexible so this is rarely a big issue.
Whenever you do wiring don't forget to leave appropriate slack (e.g. with a "U" section on both sides of a through-wall area, at the battery end, etc). It needs to be able to accept tension or movement without any strain on the cable.
Multistrand wire works well in movement/vibration applications like cars and trucks, and soldered connections are not an issue as far as a lack of flexibility is concerned as long as you provide that flexibility with an appropriate section or loop, securing the cable immediately after that point. Not too tight with your mounting points ... it should be able to slide with a bit of friction but with no cable sheathing damage through your mount points.
To make large gauge wiring work I use welding cable, grommets where appropriate, and soldered connections throughout.
To solder welding wire, I pre-heat the copper at the wire end with a heat gun. You will find solder flows fairly well throughout all strands this way when you apply the iron and solder to the cable for tinning the cable end. Very lightly tin the connector end (remember to add your heat shrink tubing to the cable, before soldering the connector on), mate and if you haven't over-done the connector tinning you can at this point crimp. Then preheat and solder, it will flow very nicely.
If you use a copper crimp connector for large gauge wire you can trim down the bolt connection side to fit your distribution block if necessary. A little work with a file on both sides or sometimes with one side on a hole-type connector to make it a "C" style that will fit works well. Do this before you solder so you can tin the modified areas with solder.
I like to then move the heatshrink to the connector/wire junction, add a waterproofing agent in a thin even layer over the connection (automotive "Goop" brand sealant is fine; there are others you can use provided they are safe for copper/electrical) and shrink with the heat gun.
If you use welding cable check it carefully for nicks in the rubber or silicon insulation ... it's very good insulation electrically but is susceptible to mechanical damage ... heat shrink it at any damage areas, and also at any points where mechanical damage is a risk. You can double up on the heat shrink if you like (second layer an inch longer at each end than the first).
Heat shrink stiffens the welding cable considerably which makes handling, routing, etc somewhat more difficult but the remainder is very flexible so this is rarely a big issue.
Whenever you do wiring don't forget to leave appropriate slack (e.g. with a "U" section on both sides of a through-wall area, at the battery end, etc). It needs to be able to accept tension or movement without any strain on the cable.
Multistrand wire works well in movement/vibration applications like cars and trucks, and soldered connections are not an issue as far as a lack of flexibility is concerned as long as you provide that flexibility with an appropriate section or loop, securing the cable immediately after that point. Not too tight with your mounting points ... it should be able to slide with a bit of friction but with no cable sheathing damage through your mount points.
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Ground loops through audio signal cabling:
Sometimes there are paths to ground through signal cabling, especially from factory decks or processors to the amps. This will defeat the work you've put into single point floating ground power to eliminate hum and noise.
In that case you can maintain the isolation of the ground via an appropriate transformer. By "appropriate" I mean one that blocks DC but has good linearity in the audio band.
Although this approach bothers some due to their experiences, there is such a thing as a high quality audio grade transformer and it works very well. The less power it's expected to carry, the lower the cost, so line level or small-power speaker level is where it should be inserted.
You have an opportunity to modify gain here as well, so if you use one, consider what the best gain would be, either 1:1 or perhaps higher gain. You could also lower gain, although consider if that will affect S/N detrimentally.
You might have to source it outside the car stereo section of your local store, though ... some of those sold are not recommended (in my opinion) for best sound quality.
Sometimes there are paths to ground through signal cabling, especially from factory decks or processors to the amps. This will defeat the work you've put into single point floating ground power to eliminate hum and noise.
In that case you can maintain the isolation of the ground via an appropriate transformer. By "appropriate" I mean one that blocks DC but has good linearity in the audio band.
Although this approach bothers some due to their experiences, there is such a thing as a high quality audio grade transformer and it works very well. The less power it's expected to carry, the lower the cost, so line level or small-power speaker level is where it should be inserted.
You have an opportunity to modify gain here as well, so if you use one, consider what the best gain would be, either 1:1 or perhaps higher gain. You could also lower gain, although consider if that will affect S/N detrimentally.
You might have to source it outside the car stereo section of your local store, though ... some of those sold are not recommended (in my opinion) for best sound quality.
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Unless an amp is VERY poorly designed or defective, mounting it directly to the vehicle body will have absolutely no effect on noise.
Fusing the ground is a bad idea. In a fault of the ground fuse the system will seek other points of ground not suited for the current capability required to operate the equipment. The only thing necessary is to upgrade the body grounds to match the positive feed. This is often overlooked. Most noise is caused by improper cable routing or as Perry pointed out, poor amp quality or a defective amp.
I didn't read every post so it may have been stated before but the OP wanted 14.4 volts. Well that is only possible with the engine running. Car batteries are 12.6 volts and the 14.4 volts facilitates the charging process. If you want rock solid performance then use amps with regulated power supplies. This will ensure that the output will be the same with a voltage variation of 10 volts to 16 volts.
Extra batteries are an extra load and only facilitate longer engine off play time. They do not supply fast voltage recovery from heavy current drain. You may find that even if you have a high current alternator that it may not be able to keep the batteries fully charged with added load of dual batteries. Battery isolators tend to add to this problem as most use diodes and create a voltage drop reducing chargin efficiency. Use a relay if you go the dual battery route so it will separate the batteries while the engine is off or they will seek each others charge level.
Capacitors are the best for intermittent voltage drop as they discharge and recover quickly. Music is dynamic and will not create a constant current drain unless you enjoy listening to test tones. Capacitors will balance out the dips in voltage and make the system more stable. They don't even require fusing as they do not store long term output. They discharge quickly and do not have the capability to melt anything down.
All in all a little voltage bounce is normal. That is physics. The voltage will vary slightly during heavy drain and that is just the way it is.
I didn't read every post so it may have been stated before but the OP wanted 14.4 volts. Well that is only possible with the engine running. Car batteries are 12.6 volts and the 14.4 volts facilitates the charging process. If you want rock solid performance then use amps with regulated power supplies. This will ensure that the output will be the same with a voltage variation of 10 volts to 16 volts.
Extra batteries are an extra load and only facilitate longer engine off play time. They do not supply fast voltage recovery from heavy current drain. You may find that even if you have a high current alternator that it may not be able to keep the batteries fully charged with added load of dual batteries. Battery isolators tend to add to this problem as most use diodes and create a voltage drop reducing chargin efficiency. Use a relay if you go the dual battery route so it will separate the batteries while the engine is off or they will seek each others charge level.
Capacitors are the best for intermittent voltage drop as they discharge and recover quickly. Music is dynamic and will not create a constant current drain unless you enjoy listening to test tones. Capacitors will balance out the dips in voltage and make the system more stable. They don't even require fusing as they do not store long term output. They discharge quickly and do not have the capability to melt anything down.
All in all a little voltage bounce is normal. That is physics. The voltage will vary slightly during heavy drain and that is just the way it is.
Should I read that to mean no amplifier uses chassis as ground, or that you think floating the ground is unnecessary and a waste of effort?
There should be no other points of ground available; it's easy to test that this is the case during installation or anytime afterward.
I do it because of safety reasons; in particular if there is an accident involving the vehicle, which I had thought would bring up the possibility of shorting (damage to + and - leads connected to the battery) in the passenger compartment through the wiring installed for the system, or the possibility of the - lead acting as a more ideal path to ground than via the chassis ground should it come into contact with accident-damaged electrical devices.
It may be unnecessary though; I will think about it, and your comments, and may revise my practice.
Your point about addressing the body grounds is well taken; certainly in the case of all the chassis grounded electrical equipment in a car (including under the hood) it would act just as you described; seek a new ground with inevitably higher resistance and likely inadequate current carrying ability.
Many car audio installations suffer from inadequate grounding or fail to upgrade paths to ground when they upgrade power wiring.
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No amplifier (properly) designed specifically for use in a car has the audio ground directly connected to the amplifier's chassis/primary/battery ground circuit. They either use a balanced/active input circuit or a floating secondary ground for the audio power supply.
There were a few kicker amps with a design flaw that caused the heatsink to be directly connected to the secondary ground but it was not intentional (or if it was, it was a bad choice on the part of the engineer who designed them). These amps would have noise problems if the heatsink was screwed to the chassis of the vehicle. The fix for this is simple (use a nylon screw to mount the board to the heatsink).
Many amps have the heatsink connected directly to the amp's chassis ground internally.
There were a few kicker amps with a design flaw that caused the heatsink to be directly connected to the secondary ground but it was not intentional (or if it was, it was a bad choice on the part of the engineer who designed them). These amps would have noise problems if the heatsink was screwed to the chassis of the vehicle. The fix for this is simple (use a nylon screw to mount the board to the heatsink).
Many amps have the heatsink connected directly to the amp's chassis ground internally.
If you're referring to the Amplifier ground to the Battery ground...which I'm sure you're not...but if someone gets confused on this...kinda of what a blonde myself would..Having your ground wire from your amplifier ground to your battery ground IS THE WORST thing to do...keep your ground wire as short as possible.
Didnt have the budget for the batcap, but man they are nice. Also I found that one of the stereo battery manufactures make a battery with three posts: Ground, 12v+, and a 16v+ third post. This is cool because you can just hook your cars electrical system up conventionaly to the 12v side and dedicate the 16v post to the stereo. But again budget says "No". So I got a yellow top optima.
I now have all 1/0 pure copper welders cable everywhere under the hood, but I still have one last run from the 140a breaker under the hood to the amp rack in the trunk(15-16ft). I currently have some crappy 4ga offbrand in there now. I want to use something heavy enough that I have the option to add another battery in the trunk at a latter date.
For a 15-17ft run is the 1/0 AWG welder cable good enough?_
Or should I use 2/0 AWG welders cable (AKA... garden hose) for future upgrades?_
I now have all 1/0 pure copper welders cable everywhere under the hood, but I still have one last run from the 140a breaker under the hood to the amp rack in the trunk(15-16ft). I currently have some crappy 4ga offbrand in there now. I want to use something heavy enough that I have the option to add another battery in the trunk at a latter date.
For a 15-17ft run is the 1/0 AWG welder cable good enough?_
Or should I use 2/0 AWG welders cable (AKA... garden hose) for future upgrades?_
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