Car stereo USB question

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  • stretch0069
    Screwed Up Super Moderator
    • Oct 2003
    • 2658
    • oooo ess aaaaaaaaa

    #1

    Car stereo USB question

    I just bought a JVC KD-AVX77. Nice little stereo for the pickup.

    I was reading through the manual and it has a warning:
    "Do not start the car engine if a USB device is connected."

    I thought maybe having a USB device connected would initiate firmware update or some crap.


    So I emailed JVC Customer Support and this is the answer I got:

    "I understand that you are inquiring about the USB port of your JVC Mobile stereo. The main reason why the manual is suggesting to disconnect all USB devices while starting your vehicle's engine is to protect the unit (as well as your USB device) from any possible electronic feedback that may occur during the engine cranking process. This feedback will cause any electronic devices to glitch or malfunction over time."

    I don't pretend to know everything....but I can't imagine how a simple thumbdrive would be affected. MAYBE a powered USB device like an iPod, but even then.......


    Anyone have any ideas??? I have a cheap 1GB thumbdrive that I wouldn't care if it got toasted, but I am a bit concerned about the head unit.
    "Its all about the boom....."

    Guns kill people like spoons made Rosie O'Donnell fat.

    We now return you to your regularly scheduled drinking.

    "Fear accompanies the possibility of death.....calm shepherds its certainty"

    Originally posted by Topcat
    AWD is just training wheels for RWD.
  • shovenose
    Send Doge Memes
    • Aug 2010
    • 6575
    • USA

    #2
    Re: Car stereo USB question

    liability...if you lose your data or your ipod dies you cant sue them

    Comment

    • yyonline
      Badcaps Veteran
      • Jul 2009
      • 692
      • USA

      #3
      Re: Car stereo USB question

      I'm not an expert on car audio stuff. That said, here goes...

      When you start your car, your alternator starts spinning. This causes a brief surge as your power goes from battery power of ~12.5V to alternator power of ~13.5-14V. The head unit is designed to deal with this, since it's for automotive use.

      Any USB device you have plugged into your USB port may not be designed to handle such a surge. USB power is 5V, but there still may be a brief surge as the circuitry in the head unit compensates for the change in power.

      So, the warning is there for the sake of the connected USB device, not the head unit itself. Is it very likely you'll fry your USB device? I would guess no, but the waning is in the manual just to cover their butt should it happen.

      Edit: Now that I think of it, there's going to be a voltage drop as your starter is energized, and then a voltage surge as the alternator kicks in.
      Last edited by yyonline; 11-26-2010, 05:50 PM.

      Comment

      • stretch0069
        Screwed Up Super Moderator
        • Oct 2003
        • 2658
        • oooo ess aaaaaaaaa

        #4
        Re: Car stereo USB question

        yeah...see...if the thumbdrive dies, its no biggie. Taking what I know about cars and stereos and 'puters......i just can't see the thumbdrive, or any USB device, getting messed up.

        ....hmmm...maybe i'll borrow the digital o'scope and watch the 5v line.....
        Last edited by stretch0069; 11-26-2010, 05:52 PM. Reason: typo
        "Its all about the boom....."

        Guns kill people like spoons made Rosie O'Donnell fat.

        We now return you to your regularly scheduled drinking.

        "Fear accompanies the possibility of death.....calm shepherds its certainty"

        Originally posted by Topcat
        AWD is just training wheels for RWD.

        Comment

        • seanc
          Badcaps Legend
          • Nov 2008
          • 1319

          #5
          Re: Car stereo USB question

          When I had my Seat Ibiza, starting it up would cause my iPhone to reboot when it was connected to the car charger.
          Usually only did it after I'd filled the tank up with fuel :/

          Comment

          • stretch0069
            Screwed Up Super Moderator
            • Oct 2003
            • 2658
            • oooo ess aaaaaaaaa

            #6
            Re: Car stereo USB question

            Originally posted by seanc
            When I had my Seat Ibiza, starting it up would cause my iPhone to reboot when it was connected to the car charger.
            Usually only did it after I'd filled the tank up with fuel :/
            don't ya just love those "undocumented features"???? sometimes i think there is a bit of "seat-of-your-pants" engineering with electronics.
            "Its all about the boom....."

            Guns kill people like spoons made Rosie O'Donnell fat.

            We now return you to your regularly scheduled drinking.

            "Fear accompanies the possibility of death.....calm shepherds its certainty"

            Originally posted by Topcat
            AWD is just training wheels for RWD.

            Comment

            • dood
              Deputy dood
              • Mar 2004
              • 2462
              • USA

              #7
              Re: Car stereo USB question

              I have a Pioneer receiver with a USB port. I've used it with USB thumb drives, as well as a 1.8" laptop drive hooked up to a USB converter. With the thumb drive, it's been plugged in for about 6 months with no problems. The hard drive doesn't seem to be effected by starting, either.

              The point about the increase in voltage when the alternator starts spinning should make no difference. The USB port is a 5v regulated output. If the HU is sending any power to it at all, it should be 5v or nothing.

              One interesting thing about my HU is that it is a USB spec, and claims to be able to charge iPods and the like from the port while playing. However, if I hook up a 2.5" drive to my IDE->USB converter, it will not spin it up, even though that's the only way the converter works with 2.5" drives. The only way I got a HD to spin up on the converter is to have a 1.8" drive that's in a 2.5" shell with a standard 2.5" ATA connector. I guess it's not capable of as high of a power output as standard desktop USB ports are.
              Ludicrous gibs!

              Comment

              • alexanna
                Member
                • Mar 2010
                • 1346

                #8
                Re: Car stereo USB question

                Automobiles interrupt the voltage supply to everything except anything that’s needed for the car to start.
                Hell I’m so old I wouldn’t know what a USB dose with a stereo ,But if that’s where it’s getting power from it couldn’t be good.
                Al.


                I should have said interrupted power to accessories
                Last edited by alexanna; 11-26-2010, 08:01 PM.
                Whatever I do, I consider it a success, if in the end I am breathing, seeing, feeling and hearing!

                Comment

                • kc8adu
                  Super Moderator
                  • Nov 2003
                  • 8832
                  • U.S.A!

                  #9
                  Re: Car stereo USB question

                  may get corrupted if it does not get dismounted properly.like pulling one from the pc while it is still being accessed.

                  Comment

                  • stretch0069
                    Screwed Up Super Moderator
                    • Oct 2003
                    • 2658
                    • oooo ess aaaaaaaaa

                    #10
                    Re: Car stereo USB question

                    I'm in the same mindset as dood. I haven't put the o'scope on it to confirm, but I'll try Wednesday. I'm guessing there won't be any issue.

                    I does say not to remove when its reading the thumbdrive......but to me, the worst that would happen is the data on the thumbdrive would get horked. No biggie for that.
                    "Its all about the boom....."

                    Guns kill people like spoons made Rosie O'Donnell fat.

                    We now return you to your regularly scheduled drinking.

                    "Fear accompanies the possibility of death.....calm shepherds its certainty"

                    Originally posted by Topcat
                    AWD is just training wheels for RWD.

                    Comment

                    • Agent24
                      I see dead caps
                      • Oct 2007
                      • 4951
                      • New Zealand

                      #11
                      Re: Car stereo USB question

                      If the headunit can't keep a reliable 5v supply to the USB port when engine is starting doesn't that mean it's a piece of junk?
                      "Tantalum for the brave, Solid Aluminium for the wise, Wet Electrolytic for the adventurous"
                      -David VanHorn

                      Comment

                      • kc8adu
                        Super Moderator
                        • Nov 2003
                        • 8832
                        • U.S.A!

                        #12
                        Re: Car stereo USB question

                        most unnecesary loads are shut off during starting.this includes radio's.cranking while the radio is reading is like pulling it out of your pc while it is reading/writing.
                        might corrupt it but thats all.

                        Comment

                        • Agent24
                          I see dead caps
                          • Oct 2007
                          • 4951
                          • New Zealand

                          #13
                          Re: Car stereo USB question

                          Yeah, that makes sense. But this doesn't:

                          disconnect all USB devices while starting your vehicle's engine is to protect the unit (as well as your USB device) from any possible electronic feedback that may occur during the engine cranking process. This feedback will cause any electronic devices to glitch or malfunction over time.
                          Whatever this "Feedback" is - surely the headunit will be designed to prevent against it? I mean, the thing is designed for use in a car where this "Feedback" will potentially occur. If it can't handle the environment it's designed for, then it's not a very good design, in my opinion.

                          They suggest to disconnect your USB drive, well what about the headunit itself? Do you need to disconnect that as well in case of "Feedback"? or does the simple act of removing the USB drive prevent any problems happening to the headunit, as the quote suggests? Sounds pretty weird to me...
                          "Tantalum for the brave, Solid Aluminium for the wise, Wet Electrolytic for the adventurous"
                          -David VanHorn

                          Comment

                          • alexanna
                            Member
                            • Mar 2010
                            • 1346

                            #14
                            Re: Car stereo USB question

                            Wonder if the head unit is smart enough to protect itself [shut itself on power interruption]
                            Where the USB is not?
                            Al.
                            Whatever I do, I consider it a success, if in the end I am breathing, seeing, feeling and hearing!

                            Comment

                            • Agent24
                              I see dead caps
                              • Oct 2007
                              • 4951
                              • New Zealand

                              #15
                              Re: Car stereo USB question

                              The headunit is supplied with around 12volts from the car - USB devices run on only 5volts.

                              So there will be a regulator or whatever in the headunit to supply the 5 volts to the USB drive, all that will be powered from the headunit, if the headunit's power is cut off, then the USB supply would be off as well.
                              "Tantalum for the brave, Solid Aluminium for the wise, Wet Electrolytic for the adventurous"
                              -David VanHorn

                              Comment

                              • beggarmaster2000
                                New Member
                                • Sep 2010
                                • 1

                                #16
                                Re: Car stereo USB question

                                hey, guys here is a neat trick for usb audio users!
                                use a usb card reader and memory card instead of a thumbdrive. and noise from your alternator/ac/engine will be eliminated!
                                enjoy music without the hiss

                                Comment

                                • kc8adu
                                  Super Moderator
                                  • Nov 2003
                                  • 8832
                                  • U.S.A!

                                  #17
                                  Re: Car stereo USB question

                                  nonsense!only difference is the reader and flash are seperate.
                                  Originally posted by beggarmaster2000
                                  hey, guys here is a neat trick for usb audio users!
                                  use a usb card reader and memory card instead of a thumbdrive. and noise from your alternator/ac/engine will be eliminated!
                                  enjoy music without the hiss

                                  Comment

                                  • 370forlife
                                    Large Marge
                                    • Aug 2008
                                    • 3112
                                    • United States

                                    #18
                                    Re: Car stereo USB question

                                    Even so I don't get any noise with my radio with a flash drive plugged in.

                                    Comment

                                    • Agent24
                                      I see dead caps
                                      • Oct 2007
                                      • 4951
                                      • New Zealand

                                      #19
                                      Re: Car stereo USB question

                                      I think that guy is some kind of spammer probably... well he kinda sounds like one anyway.

                                      Then again if he's the same guy as http://forum.lowyat.net/user/beggarmaster2000 then maybe not..
                                      Last edited by Agent24; 06-19-2011, 04:25 PM.
                                      "Tantalum for the brave, Solid Aluminium for the wise, Wet Electrolytic for the adventurous"
                                      -David VanHorn

                                      Comment

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