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Question about ground loop.

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  • Question about ground loop.

    Hey forum. i am prety sure there are posts like this out there, but i dont think its bad to keep the forum active... so :

    1) if a system, lets say , 2 bats, 1 carpc, 1 amp, and one LCD, have noise problems, cause by a ground loop , then , is the ground loop located, somewhere, INSIDE that system, or can it be somewhere else in the car (say , the ignition system) , and affect the carpc system>?

    2), lets say, that you want to COMPLETLY change, everything that has to do with the system (cables, connections, etc...) in regards to the noise, then what parts would have to be changed??

  • #2
    actually, my system looks like that:

    Click image for larger version

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    the alt is prety old. even with a new voltage regulator, it still has voltage drop (not less than 13v) when it has big load on it..
    isolator is a diode type. gonna change it with relay anyway
    bat1: is connected to chasis, via 2 fat wires (that bot to the chasis)
    carpc: use the M4atx dc-dc
    the lcd is powered from the m4-atx, and has VGA signal. (15.6" )

    the signal from the carpc, to the amplifier, has to pass through an RCA ground loop isolator, or else it get much noise in the speakers (i still get noise, during pc startup, even with the isolator)
    the LCD, has noise on the image.
    both noises increase in freq, with the engine RPM...

    [Edit]: Least but not last. the LCD is a 15.6" home monitor, that i have hooked u.
    at the begining, i had a smaller monitor, with the M4-atx. no noise then
    then, i tried to install the big LCD, wich was powered by an inverter (Since ir required 220hz). that is when the noise firstly came.
    then i used this: i had an inverter, that powered both my pc (DC->AC->DC from home PSU) and the Monitor no noise that way.
    after that, i changed the LCD's power supply, with a DC converter, so now it took 12v, and 5v from the carpc PSU. still had noise with the M4-atx, but now i also have nosie with the dc-ac-dc build...
    also, in all those cases, the longer the VGA cable, the stronger the noise( no change in freq ofc).. so, i HAVE to consider, that maybe the LCD intself is the culprit...
    Last edited by settra; 11-05-2013, 09:16 AM.


    • #3
      A ground loop is a loop. The loop generates the noise and anything attached to that loop can pick up that noise.

      But are you sure there are no other sources - eg, the plethora of switching circuits you have? (inverter, M4 especially; PC and its internal & external grounding, etc)

      And all the above will be worse with longer leads, poor shielding etc.

      But we have already gone thru all that....


      • #4
        we have gone through that millions of times... i know and i am sick about it. but i cant accept that the god damn noise is stronger than me >_>. i have also started thinking of poor grounds. that the chassis, is not a good ground at all... how would i make a perfect ground?? Bolt a wire , directly to the ALT, and pull it all the way back to the trunck??

        also, is there any change, that the alternators Rectifier, is broken, and allows AC to leak through??


        • #5
          Well technically, AC (ripple) does leak thru, but that's not a problem.
          However a broken rectifier creates noise.

          Broken alternator rectifiers should always be repaired.


          • #6
            Originally posted by OldSpark View Post
            Well technically, AC (ripple) does leak thru, but that's not a problem.
            However a broken rectifier creates noise.

            Broken alternator rectifiers should always be repaired.
            Alternators make A/C and the Rectifier makes it into DC. If any part of the rectifier goes bad and it drops out the part of the AC current it is responsible for and your straight DC will have a cyclic drop out of voltage due to the missing current. This is heard as noise in your system. Replacing it will of course bring back the straight DC power and get rid of the dropouts. Some vehicles add capacitors to try and smooth out the remaining ripples that may be in the power after the alternator but in most cars your battery is the capacitor that smooths out the remaining ripple. However the ripple due to one of the diodes being bad can not be masked with the car battery where your audio system is concerned. Not to mention you just lost anywhere from 1/4 to 1/2 the power output capacity of your alternator with a blown diode and the alternator will have to work harder to make up the difference which can make the problem more pronounced. In other words... Get it replaced...

            Ground loops in essence are due to your equipment seeing different voltage levels in different locations. This can happen due to undersized wiring or bad grounding locations. If you test your voltage at different locations in your system you are likely to see different voltages. Realize that the majority of cars use the chassis as its ground wire to save having to install nearly twice the number of wires currently required. The OEM has chosen the locations of grounds carefully in most cases due to the requirements of the power and how solid of a path back to the battery. When you look at how our cars are put together and how the panels are attached you can see where you have issues. Since most panels are tack welded and then have their seams bonded with some sort of sealing material they do not make very good ground paths. You need to find things such as the sub frame or other substantial components to connect to. One of the suggested areas to connect a ground to is the seat belt mounting point. Just be careful that any connection you use does not affect the original intent of the mount point. Otherwise if you run a cable back to the front you want to run it directly to the battery if you can. With power cables you want good quality cable that is rated for more than you will ever use. Too small of a wire can cause voltage loss issues that turn up sounding like "ground loop" issues. These grounding potential differences can be very annoying to find. You are best off talking to other people that have your vehicle that have already done the work in the past and can tell you the best ground points for your vehicle. Car audio shops are sometimes a good source as are forums for your vehicle assuming such exist.

            Also realize if you are running your ground to the chassis you are also running the power through the frame to the engine block ground strap and from the engine block to the battery through the battery to block ground cable. My experience with the ground path of all cars is limited but every vehicle I have owned has the battery grounded to the block and the block grounded to the frame. There are small ground wires going to the body from the battery but I believe those to be to help the antennae have a better ground. Check out the ground path for your vehicle and make sure that all of the cables from your battery to the body have been upgraded to handle the power required by your system as well as the rest of the car.

            Good luck.

            Oh and as a last note, in the classes we had they mentioned you could use a volt meter to try and identify good ground locations but they are only rough estimates and that nothing beats hooking your wire to the location and seeing if it works. In my vehicles I try to save the hassle and run good quality wire right to the battery.


            • #7
              Mainly a note re the last - a voltmeter or DMM etc cannot find a good ground location, but it can be used to confirm a good ground or location when the load is running at full load.

              Also it's only 1/6th power loss due to one diode being open (1/3 if shorted, but that is unlikely for very long). It's the increased harmonic content that makes "noise" worse, and the dc-offset can cause other issues.

              And to clarify, I consider DC mathematically - DC is the "smooth" or zero-frequency voltage and any ripple/noise is superimposed AC (that's easier for circuit understanding etc). Many consider DC to be "always on the same side of GND", hence a car system is DC irrespective of the noise or transient(AC).


              • #8
                Originally posted by OldSpark View Post
                I agree with what you said.. The diodes I was not 100% sure on because the bridge rectifiers we looked at were 4 Diodes. There are different designs and I won't claim to know all design configurations. All I know is that an alternator creates AC and the bridge rectifier takes the AC and combines it to make it into a pseudo DC. if we look at the unfiltered output it is more of a wave than a straight DC output. Current vehicles depend on the system battery to smooth out this ripply DC into much smoother DC.

                The two indications you have that you may have a Diode bad is the lesser power and the extra noise. Sometimes you can see your headlights flickering to the RPM of the car as well.



                • #9
                  Ah - you looked at a "bridge" diode package - a 4 terminal device with 4 diodes used to "full wave rectify" a non-center-tapped transformer output.
                  The equivalent full-wave rectification for a center-tapped transformer (output) requires only 2 diodes.

                  Alternators have three center-tapped windings - hence "3-phase" - and thus require 3 x 2 = 6 diodes.

                  The ripple factor is Vac (RMS) / Vdc and that's 0.042 (4.2%) for an unfiltered alternator (3 phase aka 6 pulse etc; and that ripple frequency is six times the base AC frequency - ie, alternator speed).

                  IMO a 4% ripple or about 6% peak to peak (DC +/- 3%) is pretty good on its own especially in comparison to the other noise (spikes and transients) that get induced or injected onto vehicle's DC voltage.
                  But as said, batteries filter that even further.


                  • #10
                    i would think that bolting a wire, directly to the alternator would make for a better ground. why you prefer the battery??

                    p,s. i will remove my alternatort to check the diodes, but it will take some time, because the car is so god damn old, that the bolts are rotten...


                    • #11
                      As long as you know you have to dismantle the alternator to get to each diode to test them. Otherwise it's done with a waveform tester (CRO etc).

                      Re the GND point, the main issue is a single ground point. Usually that's neither the alternator nor the battery, but some common point - eg chassis or fusebox of DB.

                      Common grounding at the alternator body is rare and usually done by non-practical people else for very specific requirements. To a lesser extent, grounding at the engine or gearbox etc is likewise rare.
                      Common grounding at the battery -ve terminal is usually impractical or unreliable.

                      Interestingly the last argument I saw for "absolute GND" {sic} was by someone with a small sound system. (They grounded at the alternator.)
                      Last edited by OldSpark; 11-06-2013, 04:59 PM.


                      • #12
                        Realize where your power is coming from and it makes sense to go to the battery directly. Anywhere else and you have to upgrade the wires going from the battery. Look at the size of the wire from your alternator to the battery. It is generally quite small in every car I have ever owned. Somewhere in the 10gauge area. It does not provide large bursts of power on a moments notice. That is the batteries job. The alternator is more of a constant battery charger than anything else. You do NOT want to run ANYTHING directly off the alternator without a battery present. There is a reason car manuals specifically state to never run the vehicle without the battery installed...

                        I know that people tell you to ground your battery to the Alternator bracket when you jump a dead battery but this is to keep the sparks away from your battery. A charging battery off gases hydrogen and if you mix hydrogen, oxygen and an ignition source things go boom... Like your battery. I have had a battery explode next to me and luckily I was wearing boots otherwise when the pieces hit my ankle it would not have been fun. I was a new employee and the equipment I was testing had not been run in a long time and the battery was bad. My partner was not aware they had abandoned the equipment so we were not supposed to run it.

                        So wherever you ground your system you want to make sure it has a good solid path back to the battery. Again this means upgrading all of the wiring from the battery to the place you are using your power.

                        In my area it is very common for people with large systems to ground their systems directly to their battery. But it can be expensive otherwise. I remember buying 1/0 high quality wire that was like $10 a foot or more. In my car I needed to run 15 feet of the wire so I ran both positive and ground to the battery. No worry about voltage drop there. The big difference between high quality wire and cheap stuff like welding wire is the size of the wire and the flexibility. The high quality stuff I had was about the size of OEM 4 gauge and was as flexible as a thick rope. Very easy to work with but the copper actually burned when I tried to solder it to a connector. (Had to use a propane torch because of the size of it.) Soldering 1/0 gauge wire is probably not the best solution. In that vehicle the 1/0 wire ran to a series of distribution blocks that fed the 3,000 watts of real power in that system. It was only rated at 500 watts but we used "cheater" amps. I used 2 Optima batteries and originally used a Diode Isolator but ended up with a Constant use Solenoid to charge these batteries. It was after losing 10 different chromed battery connectors to 4 different Optima batteries that I found out that Optima batteries are crap and not intended for use in daily driven vehicles and definitely not for car audio. One of my batteries was a factory replacement and the other was powering the system. One ground wire went to the negative grounding block and it was also grounded against the frame to ensure that the ground potential of the system battery was the same as that of the vehicle battery.

                        Sorry if I went a little off topic there.


                        • #13
                          My god Red, you mean we agree - Optima is crap?
                          I'm curious how you "lost" the battery connectors tho - Optima like AGMs should not leak acid. Or was it electrolysis, or the brittleness of chromed items?
                          Funny you say Optimas are "definitely not for car audio". Audio & car forums I have seen would strongly disagree. But I wonder what else Optimas are good for... AGMs are not as suited to cranking (as wets) except for long standing vehicles (eg, vintage cars only used once or twice a year) provided they are disconnected else have no parasitic loading. Not that I'd use an Optima when far cheaper and better AGMs are available.

                          Optimas like all(?) AGMs are easier for a common terminal connection (eg, GND) because they have boltable hard metal terminals unlike most wets that have lead terminals. Not that that prevents internal damage from all the weight/inertia and cables bolted to their terminal(s).
                          As you say, it's the battery that provides the power when the alternator is lacking - eg, high loads at idle; audio etc loads that exceed alternator capability; initial inrush currents and step changes. Hence the battery -ve terminal is "the" ground (or absolute ground as some refer to it).
                          But normally it is the alternator that supplies the power, hence the alternator is "the" ground.
                          The common compromise is an intermediate ground - normally the chassis or some other distribution point. Then infinite wires and bulk can be added and commonly grounded without stressing battery terminals or alternator bolts or having real estate issues, and you avoid the elevated temperatures and vibration of the alternator or engine block terminations.
                          Of course certain applications may warrant actual battery or alternator grounding (welders, winches, etc) but IMO that generally implies insufficient ground wire conductance which IMO should be rectified (as in fixed).
                          Ye olde rallyers used to terminate driving-light +12V at the alternator output for maximum voltage (a bonus being that no alternator B/B+ output to battery+ cable upgrade was required - hence a fully add-on system), but that is totally redundant with modern HIDs & LEDs.

                          FYI - the main reason car manuals specifically state to never run the vehicle without the battery installed is because there is then nothing to absorb high voltage transients that may damage car electronics.
                          If driving without a battery, any step change like flashers, brake lights, wipers etc is likely to collapse the alternators output, hence dead electrics as well as a dead engine (except perhaps for diesels and steam cars).
                          In old vehicles, no battery usually meant a higher alternator output voltage that could damage or destroy vehicle electrics. The same is still true but modern alternators are usually limited to a max of 16V in such circumstances (typically ~15.5V).


                          • #14
                            My battery terminals were eaten by the battery acid that leached out of the optima batteries. While it is commonly stated that they are leak proof this is simply not true.

                            My understanding is that Optima batteries were built for off road racing where they needed quick starts, high load capacities for winches and other related items. Someone decided to try using them in car audio and it took off from there. They are not designed for the type of use someone would get in a daily driver. In my vehicle I used the top mount posts and they swapped out my batteries in warranty twice. It was obvious it was battery acid eating up the connectors because of how it was happening. The guy from the battery shop actually ran his fingers on the battery posts and tasted it and said "yup battery acid". (Won't even get into how bad of an idea THAT was... NEVER taste battery acid... )

                            The AGM batteries you mention I believe are the same type of batteries I was told to use many years ago.

                            If you read the design specs on the Optima batteries the Sulfuric acid is locked up in some sort of material and wrapped into spirals thus the 6 cylinder style compartments. My understanding is this is similar to racers using foam in the gas tanks to prevent fuel splash. It keeps the liquid in place during high performance maneuvers and was NEVER intended as a leak preventative. I think they used to advertise they were leak proof and this was how I was able to keep swapping out batteries but I don't believe the last ad boasted that anymore.

                            And yes I didn't spell it out but those are the same reasons I was referring to for making sure the battery was in place. The electronics in cars now adays are much more sensative to power surges and spikes than they used to. Cars back in the 70's had very few actual digital processors compared to todays vehicles and disconnecting the battery while the car was running didn't do much damage if any. But today's charging systems require the battery to be in place to operate for the reasons stated.


                            • #15
                              Yup - AGM = Absorbent Glass Mat; the mat is soaked in acid. No free acid per se - you can break open an AGM and it should not spill any acid and will probably still hold charge for a day or so.
                              However charging is another issue and acid can "boil" off.
                              AKA VRLA - Valve Recombination Lead Acid - the discharge hydrogen is held near the plates so it can recombine when charged. (Wiki reckons VRLA include gel cells but I only knew AGMs to be VRLA. But both are "sealed" or "maintenance free".)

                              One of their misconceptions is that they don't vent hydrogen or acid. You have experienced the LOL re the latter.

                              Another misconception is that people confuse the ability for an AGM to be able supply more current (because they typically have half the internal resistance of an equivalent wet cell) with their suitability for high discharge.
                              AGMs do not like high discharge currents, nor high recharge currents, and certainly not over-voltage recharging nor excessive discharge without immediate recharge (AGMs do not recover after an excessive discharge whereas wets usually do albeit with compromised capacity or life).

                              They are popular for winches because they typically require hundreds of Amps (500-900A) and are then usually subject to immediate recharge.
                              Audio systems do not fare so well except in competitions (ie, high discharge followed by the trip home at rechargeable levels) though I noted the higher use of wet cells at the last comp I attended (ha ha - higher SPL boys - no caps??).
                              AGMs are usually ok for campers & RVs and PCs because of the low discharge rates; it's usually excess discharge or delay between recharges that kills them.

                              In a previous millennium, Exide/Chloride released their "Torquestarter" battery which was "the ideal" cranking battery for cars. It was withdrawn approx 1 year after release due to the overwhelming warranty returns. IMO it was simply ahead of its time - alternators still often had external electo-mech regulators but others often also charged way above 14.4V. And no vehicle had under-voltage trips; some Euro vehicles had headlights linked to the IGN key; not even headlight/parker warning buzzers were common.
                              A great idea in academic theory, but killed by enough overcharges or the one forgotten headlight-on experience. But I often wonder how the Torquestarter would fare today?
                              Of course as I often say, an AGM is not the ideal "everyday cranking battery" - wets are far better - but the Torquestarter should have fared better.

                              Modern electronics should not be sensitive to voltage spikes etc. Early electronics were because (IMO) they were designed by idiots or people inexperienced with vehicle electrics (theory & practice) - viz jumper leads with spike suppressors (MOVs etc) - how farken ridiculous.
                              However modern vehicle electronics should be robust. The idiots learned the usual 8-16V rule etc AND that they needed to handle spikes up to 400V as well as heat extremes & vibration.

                              Not that the above helps the OP's groundloops - I too am hijacking. But since it's been a while since I've addressed "absolute grounds" and basic AGM considerations etc and I realise some readers are unaware of my past writings (viz diode isolators)...
                              But now I'll bug out. Most relevant groundloop and noise issues have been covered in Settra's other threads. As for an ad hoc system involving inverters, domestic monitors, noisy M4 or Mx PSUs etc, since the preventive measures have not been applied it now rests with problem solving - aka search and destroy - and most know I'm into prevention and not interested in fixing resultant preventable problems. There are plenty of people that earn good money (or whatever) doing that.