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  • Issue with Alternator Noise through Car PC

    Hello! I'm having an issue with my Truck PC system and am looking for some pointers.

    My system is as follows:
    - 2nd Battery connected to main battery/alternator via one cable & negative mounted to screw in chassis/bed
    - Pure Sine inverter connected to 2nd battery
    - Car PC connected to inverter
    - USB 7.1 Sound Card, connected to two amps. (One for speakers, one for sub)
    - Computer Connected to Double Din VGA touch screen
    - Running Windows 7 & Centrafuse 3

    When the vehicle is operating I get a VERY annoying whine which corresponds to RPM. I've tried a number of things to remedy the issue:
    - Plug in PC to normal wall outlet (Solved Problem)
    - Try new inverter (Did not solve problem)
    - Try DC-DC PSU (Did not solve problem, made problem dramatically worse.)
    - Try 3 different computers & power supplies (Did not solve problem)
    - Tried using a laptop (Solved Problem)
    - Disconnected power to 2nd battery (Solved Problem)
    - Tried new sound card (Did not solve problem)

    The problem is obviously with the computer/inverter, not the amps or sound system itself. The laptops power supply must be able to filter this out. But I am at a loss on an acceptable solution, short of replacing my system with a laptop. Conventional wisdom says its a grounding problem.... but since the inverter is connected to that 2nd battery, wouldn't that help filter it? Would using too small wire to the inverter itself cause this? Any suggestions?

    Thanks!

  • #2
    chasing gremlins is fun!

    what is the size of the wires(both power and ground), and how is everything grounded?

    it definatly sounds like a ground loop, which is usually related to a poor power connection somewhere, so check that everything is not only securly grounded, but that everything has good ground connections(paint sanded off, good metal-to-metal connection)
    My OLD 2001 Mitsubishi Eclipse GT:
    "The Project That Never Ended, until it did"


    next project? subaru brz
    carpc undecided

    Comment


    • #3
      I realize that the *right* way to solve this problem is figure out the grounding issue but have you tried a ground loop isolator between the audio outputs of the PC and the inputs of the amp?

      You've already tried a bunch of time consuming and costly options. This one will cost you about $20.
      Originally posted by ghettocruzer
      I was gung ho on building a PC [until] just recently. However, between my new phone having internet and GPS and all...and this kit...Im starting to have trouble justfiying it haha.
      Want to:
      -Find out about the new iBug iPad install?
      -Find out about carPC's in just 5 minutes? View the Car PC 101 video

      Comment


      • #4
        That I have not tried. I will try it once I can get my hands on a ground loop isolator.

        The wire to the 2nd battery (Which is long) could it be a culprit? The cord runs from the battery under the hood to the bed of the truck. The ground is connected to the body of the bed. It's not a huge wire ... but since power is being drawn from the 2nd battery I figured that wouldn't be a big issue.

        Everything is grounded to the body of the vehicle in one manner or another. The amps are, the inverter is. However, because it works fine if the PC either has a filtered supply (Laptop) or is powered by something not otherwise connected to the PC, I am thinking it's not specifically a grounding issue with the amps.

        But... now I'm thinking... the amps are inside the truck. Grounded to the body. The 2nd battery is grounded to the bed of the truck, and the inverter is grounded to that. If the power flows through the truck to get to the main negative, perhaps the amps (Being in the middle) are being affected by the inverter?

        Maybe I should try running a negative directly to the 2nd battery instead of grounded to the bed.

        Comment


        • #5
          1. The ground from the truck bed is probably not as good as the ground in the cab. That could easily be a cause for a ground loop.

          2. Are you using a battery isolator for the 2nd battery? It should not simply be connected in parallel as the two batteries will have slightly different resistance and one battery will supply power to the other, particularly when you start the truck. If you don't have a heavy enough gauge wire on the second battery, you could melt the wire if your first battery ever gives out.

          When the batteries charge, one will charge less than the other and have a lower voltage. When the truck is off, one battery will recharge the other until the voltages are similar.

          A battery isolator will eliminate this problem.
          Originally posted by ghettocruzer
          I was gung ho on building a PC [until] just recently. However, between my new phone having internet and GPS and all...and this kit...Im starting to have trouble justfiying it haha.
          Want to:
          -Find out about the new iBug iPad install?
          -Find out about carPC's in just 5 minutes? View the Car PC 101 video

          Comment


          • #6
            Yeah, I do not have a battery isolator. It's high on my list of parts to get, but recently things have been tight. (Most of the options I tried before were either done when I had more cash, or from parts I had laying around) I have an engine issue that comes first at this point, then battery isolator... thinking mid this month.

            That melting of wire is an issue I thought of, so have installed a conservative fuse. Which was a good idea, because that happened and the fuse blew.

            I will try running a ground directly to the battery and see what that does.

            It might be worth mentioning that there is a slight whine with just the amp, when the PC is not on. It's not really loud enough to be annoying or even audible when at any speed, compared to the horrid scream the PC causes.

            What do you guys think of those DC to DC power supplies that will turn the PC on and off? Why would the noise be worse (so bad the screen flickered, and eventually the computer blue screened) with that than an inverter? Does the conversion to AC partially filter this out?

            Comment


            • #7
              typically, the dc-dc's cause less noise, because they switch at a higher frequency than dc-ac-dc conversions, so i am kind of thinking that it is a issue with the second battery being poorly grounded in the bed, whereas the amps, and main battery might be better grounded inside the truck.

              another super cheap mod that you can try is to ground the negative conductor of the rca, to try to 'bleed out' the noise in case the rca's are transmitting it.

              also, what are your gains on your amps set to? i had a gl issue in my car that was solved by getting a preamp and turning the gains down-- i had them maxed to compensate for the low output level of the carpc, and the amps actually picked up the noise.
              My OLD 2001 Mitsubishi Eclipse GT:
              "The Project That Never Ended, until it did"


              next project? subaru brz
              carpc undecided

              Comment


              • #8
                I hope that is the cause, if providing better grounding to the 2nd battery is all that is needed, it shouldn't be too hard to do.

                Two other interesting symptoms:
                - There is more noise/added buzzing sound if my screen is displaying something bright. (White page) (Screen poorly grounded? I think I used the power that was already there, I cannot remember though).
                - My truck has a light "dimmer." The lights go out over 1-3 seconds instead of just off, and when this is occurring it makes a buzzing noise related to the intensity of the lights.


                A separate problem that I'm having is occasionally the screen will blur/streak to the right. There doesn't appear to be any relation, and I am using a very long VGA Cable. Was thinking it's either the cable getting some interference or my PCs graphics chip overheats or something. Any thoughts? (I'm using a double din touch screen by liliput) I suppose a quick way to test it would be to skip the long cable and connect to something close, see what happens. But I'm sitting at work right now and can't go do that this second. I'm sure you understand! lol

                Comment


                • #9
                  Originally posted by soundman98 View Post
                  also, what are your gains on your amps set to? i had a gl issue in my car that was solved by getting a preamp and turning the gains down-- i had them maxed to compensate for the low output level of the carpc, and the amps actually picked up the noise.
                  I don't think this is my issue, if I remember right my sound card (USB Sound card) has a pretty solid output and no increasing was needed. But also, if I use any other source other than the computer tied to the second battery, the problem is gone. For example, a laptop, zune, hte usual PC plugged into a actual outlet via extension cord.

                  When I get off work I'm going to try another inverter directly connected to the main battery, plug the computer into that, and see what happens.

                  Comment


                  • #10
                    Well, I tried connecting another inverter (With alligator clips) to my main battery, and it mostly solved the problem. (Except it's a modified sine inverter so I get a nice buzzing, but NO ALTERNATOR WHINE! SWEET!) anyway then I connected the same inverter to my 2nd battery, same results.

                    The sine inverter I am currently using is not connected with alligator clips, it is under a nut on a screw terminals, along with other connections including the charge cable. Perhaps the power is being used "First" by the inverter, which is basically trying to pull power thru a long wire and a probably lacking ground in the bed, causing the whine. VS the alligator clips which is pulling from separate terminals on the battery.

                    I am going to try rigging the sine inverter with thicker wire, and connecting it to the 2nd terminals with terminal clamps and see what that does.

                    Also, might try regrounding my amp, installing a battery isolator, and running a direct ground to the 2nd battery for charging, to wrap up any remaining (although comparatively small) whine.

                    Comment


                    • #11
                      When you get to your battery isolator, try a relay energised from the D+ (or L) charge lamp circuit from the alternator.

                      I have posted details elsewhere....


                      PS:-
                      Originally posted by highamperage
                      ... but since power is being drawn from the 2nd battery I figured that wouldn't be a big issue.
                      Be aware that that cable carries all the load current plus 2nd battery recharge & float current.

                      It also acts like an antenna for noise etc (though the battery might remove a lot of that since it's a big capacitor).

                      True-sinewave converters generate more noise internally since they use PWM techniques to produce the sinewave. If insufficiently filtered & shielded, they'll probably be worse than early DC-DC converters for noise. (Sinewave users generally care about the load. Some manufacturers are yet to realise that some also want input DC filtering!)

                      Comment


                      • #12
                        Battery Isolator

                        I have a Schottytec (however u spell it) battery isolator in my car.. 2 optimas and a hp slimline pc 14" screen upfront, and a 24" in back connected to a ps2 in my aspire.. I have a similar problem but it turns out my inverter was (it died) a modified sine wave. it is definatly a ground. Do the big 3 upgrade, and get a good isolator will solve that whine. My radio used to do that before the upgrade. Now all is fine except when using that crappy inverter.. I have 3 amps.. mono for bass, front/rear and had noise like crazy when i fist installed it... do the big 3 and get a isolator and you'll be good with that pure sine wave.. Thats next on my list


                        Update: 4 amps.. did away with radio and have 7.1 from the pc.. Hella sweet.. used a 5v relay to turn the amps on and off.. new thread on this
                        Last edited by Simbalage22; 08-20-2011, 10:31 AM.

                        Comment


                        • #13
                          Talk about awakening of the dead.

                          I presume your isolator is a diode type (Schottky)? I don't think they are too popular here except for small installations.

                          And yes, a sinewave shoiuld always be quieter than a mod-sinewave; both on the output (should be zero noise) and often the input as they tend to be of higher quality (ie, design) and may spread the input over a wider pulse (though that isn't certain).


                          EMI occurs with any modulating or switching electrics. It occurs in digital displays & gauges, alternator regulators, alternators, big audio amplifiers, dc-dc converters and inverters, etc. The primary solution is design (circuit, frequencies) and shielding. Then comes external suppression.

                          Comment


                          • #14
                            yup correct on the isolator.. 260amp from ems at bone yard...

                            Comment


                            • #15
                              260A diodes? Wow! What a pity the batteries can't be paralleled....

                              But that whine is usually independent of battery isolators, it's just that yours blocks the noise from the inverter into the other battery & load. It won't block any alternator noise.
                              And for many, diode isolators are not suitable or economical.

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