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Thread: Your prefered set up - 1 gound...vs...many

  1. #1
    Constant Bitrate
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    Your prefered set up - 1 gound...vs...many

    OK So i bought soe more toys and will be installing a bunch of power realted things FINALLY. What i was wondering today...Do you prefer a ground distibution box or just run straight wires to each item?

  2. #2
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    I run a ground distribution for everything.

  3. #3
    Raw Wave
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    I usually run ground wires for everything including my HU and 2nd battery.

    Whether to use a single ground is another issue. It's often beneficial or required for audio interconnects, and often required for certain sensors (eg, high impedance types used for ECUs etc).

    For power wiring it's usually not required, but it is essential to have good engine-body/chassis-battery- ground bonding (the "BIG 3" refer). The engine to battery- is essential for the starter motor (heavy current, typically 100-300A). The alternator also requires good bonding to the battery- for correct voltage sensing (alternator voltages are designed for battery charging & life), and also the body/chassis to ensure voltage drift does not occur - ie, in many systems, a bad alternator (engine) to body/chassis ground can cause voltages in excess of 16V which will damage most electronic equipment.


    I have never used a ground distribution box, though I have fitted multiple spade-connector "breakouts" for convenient addition or removal of grounds, though most of my added grounds are multiple eyelet crimps sharing a suitable chassis/body screw or bolt. However my HU and 2nd battery grounds go to the battery- terminal.

  4. #4
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    When your devices are sharing a common electrical path you really need to have them all using the same ground point. Doesn't really matter HOW you do it. A distribution block for ground is just to make things pretty. Distribution blocks for +12 makes sense if it allows you to fuse each wire separately.

    Factory wiring have a very limited number of ground points for the same reason.

    Since ground is using the body of the car there is a possibility of different ground potentials which can end up showing up as differing voltages. In an audio system these differing ground potentials show up as static or hum.

    Anything not dealing with the audio path and "going on its own" isn't as sensitive to a single ground point. Although with sensors etc you still have to be weary of noisy OEM equipment. If you have noisy OEM equipment it can make a security sensor appear to be bad or inaccurate.

    When dealing with audio if you have a fiber optic cable that connects from your radio to a processor and then from the processor to your amplifiers then it would NOT be beneficial for the items at either end of the fiber to be connected to the same ground point. Probably won't hurt but the point of using fiber is to transport the clearest audio to your processor and you also isolate your amplifiers etc from your audio source.
    You also have to be careful of where you ground because some OEM devices are very noisy and can interfere again with your audio.

  5. #5
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    I think I will get a ground distrib. box. Clean up the install. heres a stupid question. I bought a 12 v distrib. box and wanted a ground box that looked the same but apparently they don't make a ground box that looks the same. I don't really think there is a difference right? I could probably use the same box as a ground distrib right?

  6. #6
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    And now I am thinking about getting another stretch of wire and hooking my ground right to the battery...what ya'll think?

  7. #7
    Raw Wave
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    Yeah - a dist box is a dist box. The only difference is that the +12V dist box needs to be chassis insulated, and it's probably red. But they should be the same electrically - just don't connect the two together!!.

    Arguably it makes good sense to mimic the same "electrical" dist box for GND as for +12V as that should ensure at least a matching GND capability.
    Some make the unfortunate and often expensive error of beefing up +12V cables but leaving undersized GND cables. It is not uncommon to have heavier grounds (and they are usually cheaper being shorter lengths) or even redundant (extra) grounds because the one circuit you DO NOT want to break is GND - that can often lead to electronic destruction and other burn outs.
    The only drawback is that you will get a similar voltage drop along the GND wires as you get in the +12V distribution, hence doubling your voltage drops. But if you also GND the loads locally...


    IMO there is nothing wrong with using chassis/body GNDs however some reckon modern cars have light metal work and poor panel bonding.
    However with the exception of aforementioned audio and signal, IMO there is nothing wrong with adding full-load capable GND wires back to a good GND point (battery- or engine, or a compromise point). That can only improve the GND path - ie, lower its resistance and hence any voltage rise it might experience (and hence effect audio, sensor signals, etc).

    As I said, I trust my vehicle's metal body & chassis grounds. (A 1960's ute with rubber mounted tub/tray).
    However, my HU is grounded and powered direct from the main battery -ve & +12V (to ensure a cleaner supply), and I chose to connect my tub-resident 2nd battery via a dedicated fig-8 cable to the main battery (with (UIBI!) isolator and TWO fuses/circuit-breakers of course!) though in part that's because I had good telco twin-core DC distribution cable and also wanted chassis/tub GND independence to be able to move the battery elsewhere.
    Last edited by OldSpark; 01-19-2013 at 12:16 AM.

  8. #8
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    Also realize that with the larger power wires you will want to carry them larger than you need. There is a resistance in every wire which increases over a distance. If you consider the power feed wires as if they were pipes there is friction inside of them against a flow. To reduce this friction you go with bigger wire. This is a good reason for a distribution block. If you run your wires to the battery you will likely want to go with 1-2 sizes bigger than you would other wise do. There is no such thing as too large of a wire with the power feeds. Another consideration is that when wires do run parallel that they tend to cancel out any noise because it comes on both of the wires. One of the best low level audio cables I have used was simply taking two 16 gauge wires and using a drill to twist them together and adding my own connectors on the ends.

    If you look at the IASCA numbers they come up with what seem like crazy sizes but they work. I ran 1/0 gauge wire in one of my vehicles but it was designed to use a dual feed Alternator that put out a warm and cold rated 130 amps. Was also using cheater amps that allowed me to get rated at 500 watts but would actually be about 3000 watts. And especially when using unregulated amplifiers the power source is one of the most important things.

    I used nice looking distribution blocks that were plated. Realize that unless your connectors are gold plated any plating will be a resistance against the power cable. If you are doing it for looks it is almost better to have a copper block machined to how you want it and hide that behind the scenes and display a fake plated block with wires connected to no where. But up to you. The voltage drop from a good quality plated connector is likely hard to measure as long as you are not using a bunch of them in the line.

    The Battery is a large Capacitor as well so it works to filter out some of the noise in the system. Other then the potential voltage drop OldSpark already mentioned, as long as you are using good quality, over sized cables you are probably providing the best power source for your system to go directly to the battery. I also agree with the ground wires being at least 1 size larger than your positive lead. A second battery is always a good thing if you have the room for it. And due to the off gassing I would strongly suggest mounting it under the dash. You SHOULD separate the batteries electrically if you do have two batteries. And they should be the same or very similar model of battery. When I was at Metra's installer school they showed us how trying to start a car with two almost dead batteries in parallel was impossible. However each of the batteries on its own was able to start the car.

    You can use a passive (diode) isolator such as one available at an RV shop. These are cheap and hard to break. But they will lower your voltage by about a volt and some installers tell you that you may want to raise the voltage on your alternator to make the charging system work properly. I have used these and have had no issues with it other than the voltage drop.

    You can also use a constant on solenoid, these are also cheap and are available at RV shops. These are a standard starter type solenoid that is intended to be on all the time unlike a standard short duty starter solenoid. With these they really only isolate the batteries when the power is off so you can play your auxiliary battery and not drain your main battery. Since the solenoid doesn't engage until you have the car running this is not a bad solution.

    With either of the first two if you turned your car off and left your lights on you can jump yourself by jumpering the power. The first one you have to jumper between the outputs with a heavy gauge wire, the second all you need to do is engage the solenoid.

    The third style I am aware of is more expensive than the first two but is totally digital and most of these are more flexible than either of the previous two but can be significantly more expensive depending on the quality of components.

    Also for the wire you should use high grade, multi strand wire. The more strands the better and you want high purity copper wire if possible. It will last longer, generally be easier to work with because it will be more flexible, and will be smaller.

  9. #9
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    Actually straight parallel wires will usually have more noise induced as compared to a single wire. But twisting is different, and counter-twisting cancels noise from EMI sources and each other (viz Cat-6 cable, AC distribution, etc).

    Introducing a distribution block adds more resistance and unreliability than using a straight cable. But DBs are often more practical, and for grounds can mean emphasis on a good grounding point rather than a collection of suspect body screws etc.

    Both the above can be argued, but it often depends on the situation.
    Bearing in mind those pedantic issues, redheadedrod and I agree, except for diode isolators. IMO they are expensive, large, and wasteful, and can be problematic in dual-battery systems - ie, which battery do you sense the voltage from? (And non-remote sensing alternators are totally unsuited to diode type isolators!)
    Diode systems are a legacy from the pre-alternator days (mid-1960s) and for systems that needed to ensure battery independence when the engine was running but undercharging (eg, idling older vehicles, or modern vehicles with higher than normal loads). But these days even emergency vehicles like ambulances with patient-critical equipment tend to use relays/solenoids with extra battery monitoring (eg, current sensing else maybe voltage sensing).

    But you can't parallel the batteries with a diode isolator unless you fit a relay (solenoid), so why then bother with the diode isolator? Just energise the relay using the charge light signal (ie, the "UIBI") or even a spark sensing circuit if desired for parallel cranking (which should increase battery life if at a similar %age of capacity). [I recently obtained an Audi fuel-pump relay which is the typical VAG spark-sensing type. It is merely a 555 circuit triggering a relay.]

    I think the 3rd type redheadedrod mentioned is the voltage-sensing aka "smart" isolator. They are not digital per se, but may use digital processors (uPCs, PICs etc) for circuit simplicity or cheaper production. IMO they are flawed or inferior for various reasons which I have often discussed elsewhere, but they are the common system used for fixed rotor aka "stator" alternators (ie, no regulator with charge-light circuit, as found on marine systems, and some RVs, motorcycles, etc).

    And when using an automatic battery isolator, the age and model of the batteries is irrelevant. They need only be matched when connecting in series, or if permanently connected in parallel. The only proviso is that neither of the batteries should be in poor condition ie, collapsed cells etc, and of course they both need to be 12V lead-acid types (wet, gel, AGM).
    [ Keep in mind that the batteries are only interconnected whilst charging. Hence no discharging of one into the other etc. ]

    The cheapest isolator should be the mere charge-light controlled relay. Decide what capacity you need. $3 for 30A, $10 for ~100-150A, and say $20 to $50 for 200-400A etc. Larger relays may require a smaller (eg 30A or less) buffer relay or other circuit so as not not overload the alternator's charge light circuit.
    Voltage sensing or smart isolators are ni principle the same relay plus the added circuitry which typically adds usually ~$50 but can be up to $300.
    Of course any voltage-sensing isolator can merely drive the relay of your choosing if it does not have the required capacity, or if you want to isolate multiple batteries.
    Diode isolators or their newer MOSFET counterparts are usually over $100 for a dual-100A capacity. But they suffer voltage drops usually around 1V and higher for higher loads, and they hence get hot. (2x100A @ 1V = 200 Watts of heat.) And surges, voltage spikes and bad batteries can blow them. (Relays are far more robust, cheaper, have negligible voltage drop, and only "waste" 3W to maybe 25W of power.)


    BTW - venting batteries should not be used in a cabin - it's usually illegal to have a vented battery internal to the vehicle (ie, cabin, van, or boot/trunk). Hence AGM batteries are used, else vented (wet lead acid) batteries enclosed in a sealed externally vented enclosure. (Not that AGMs can't vent hydrogen, but I'm merely talking legalities and accepted practices.)

  10. #10
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    Batteries should be mounted under the hood.. Not under the dash... Sorry about the typo..

    Diode Isolators can work but from my experience are only desirable if you want something dependable that isn't going to burn up. Otherwise I agree with what oldspark says here. I have NO experience with the third type of isolator.

    In general, most professional RV shops can help you choose a good isolator for your vehicle if you are unsure.

    As to the batteries, I disagree with OldSpark about the batteries not needing to be the same. At least when using a solenoid style system where the batteries are directly connected. In a Semi truck or similar multi battery systems you will never see them have one battery in a pack a little different. They will always be the exact same battery. The only time you will see anything different is when you have a cheap operator that doesn't want to do it right. We also have multi battery systems with a bunch of our larger generators at work and for the same reasons they never use different batteries. If one goes bad they replace the whole lot.

    The reasoning is this. When you are sharing a charging system and you have different batteries in the system. Each battery will have a slightly different charging rate, a little different capacity, a little different internal resistance. What this generally means is that one battery will be prone to be more charged than the others and it can reduce the lifespan of some of the batteries. You may also overcharge some of the batteries in order to get the weaker ones charged. This is a bigger problem the more different the batteries are. So if you use the factory battery that works great and is 3 years old and you pair it up with an optima yellow top battery that you commonly run down you may find that you go through the factory battery quickly. Or if you have a 1200 cold cranking amp battery and a 650 you may run into problems. The 650 will charge faster than the 1200 and the 1200 may never reach full operating voltage. Unless of course the 1200 has lower internal resistance then it may try to charge faster and the 650 may never fully charge. Either way, you don't want to mix batteries any more than you have to if you are using a solenoid style charging system. With a diode isolator or one of the other style "intelligent" isolators they generally don't have issues with different batteries like this.

    I have never heard of it being illegal to have a battery inside a car. Some cars actually have the battery installed under the back seat or in the trunk from the factory. It is a bad idea to have the battery in the vehicle because as it charges it can vent hydrogen gas. Hydrogen gas in a car with a spark and the proper mixture makes the car go boom. If you DO have an automotive battery of ANY type inside your vehicle it is a good idea to use a battery box that is designed to vent any gases to the exterior of the vehicle and then make sure to vent to the outside of the vehicle.

    Before you tell me I am crazy...
    Models of BMW, Mercedes, VW bug, Olds Aurora, Buick LeSabre and many other cars have the battery mounted under the backseat or in the trunk. But in all cases these are well ventilated and it is imperative that the venting system is fully operational.

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