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Thread: Low Voltage Problem?? Not blowing fuses

  1. Question Low Voltage Problem?? Not blowing fuses

    Hi Guys,

    I've been running an aftermarket DVD unit in my Mazda 6 (06 model) for over 6 months now and just the other day i decided to add a DVB-T TV tuner to the unit. I soon realized that i had a low voltage issue, as the unit did not want to open at all.

    So i went back to square one and unplugged all the wires of the DVB-T tuner, although the DVD unit still did not want to open.

    So i decided to check the voltages i was getting while the unit was connected. i was surprised to find between Battery (+) to ground i was sitting on 3.4V & when i went between ACC - Ground i was sitting on 8.2V.

    When the DVD unit is Unplugged i get 12.03V on the ACC to Ground and Battery (+) to ground.

    Does anyone know what i could be experiencing to get such low voltages when the unit is connected? I retested the DVD unit to make sure it still works and i was able to get it to operate when i ran a temporary cable from the battery.

    Anyone here have some knowledge in auto electronics that could possibly help me understand what could be wrong?

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    Quote Originally Posted by kowalczyk View Post
    Hi Guys,

    I've been running an aftermarket DVD unit in my Mazda 6 (06 model) for over 6 months now and just the other day i decided to add a DVB-T TV tuner to the unit. I soon realized that i had a low voltage issue, as the unit did not want to open at all.

    So i went back to square one and unplugged all the wires of the DVB-T tuner, although the DVD unit still did not want to open.

    So i decided to check the voltages i was getting while the unit was connected. i was surprised to find between Battery (+) to ground i was sitting on 3.4V & when i went between ACC - Ground i was sitting on 8.2V.

    When the DVD unit is Unplugged i get 12.03V on the ACC to Ground and Battery (+) to ground.

    Does anyone know what i could be experiencing to get such low voltages when the unit is connected? I retested the DVD unit to make sure it still works and i was able to get it to operate when i ran a temporary cable from the battery.

    Anyone here have some knowledge in auto electronics that could possibly help me understand what could be wrong?
    Battery and Acc should be closer to 12V. That you have such low voltages suggests you have greater current draw than the cabling you have utilized can support. Heavier gauge power wires can help. Problem I had that prompted me to install battery isolation and reserve battery was having computer interfaces shut down when electric windows hit top. For a moment they draw excess current and that causes voltage drop which in turn causes electronics to shut down.

    In a nutshell you can have excess current draw cause voltage drop without blowing fuses because there's sufficient resistance in your power wiring to prevent amps rising above the fuse rating.

    Try double-ing up on power cable. You can have this happen on Acc and not Batt because (a) batt has higher voltage (there are voltage drops between the batt and Acc) to start with and (b) greater current supply capacity than the Acc rail, so the voltage drop is not as severe when attached to battery.

    You could also have a DC offset form of ground loop between the DVB-T unit and the DVD unit, and this could potentially lead to voltage drop and burning components out.

    Try heavier gauge power and get a multimeter onto the power cable at the supply end of the cable as well as the appliance end of the cable and check it for consistency before attaching devices. You want to make sure that the 12V rail at the supply for the DVB-T and the DVD unit are equal - shouldn't differ by mopre than points of a V. If they do it suggests there's resistance, possibly in a dry joint or a cable connection you may have spliced in for the DVB-T.
    Last edited by Nexus; 11-12-2011 at 09:46 PM.
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  3. Default

    Quote Originally Posted by Nexus View Post
    Battery and Acc should be closer to 12V. That you have such low voltages suggests you have greater current draw than the cabling you have utilized can support. Heavier gauge power wires can help. Problem I had that prompted me to install battery isolation and reserve battery was having computer interfaces shut down when electric windows hit top. For a moment they draw excess current and that causes voltage drop which in turn causes electronics to shut down.

    In a nutshell you can have excess current draw cause voltage drop without blowing fuses because there's sufficient resistance in your power wiring to prevent amps rising above the fuse rating.

    Try double-ing up on power cable. You can have this happen on Acc and not Batt because (a) batt has higher voltage (there are voltage drops between the batt and Acc) to start with and (b) greater current supply capacity than the Acc rail, so the voltage drop is not as severe when attached to battery.

    You could also have a DC offset form of ground loop between the DVB-T unit and the DVD unit, and this could potentially lead to voltage drop and burning components out.

    Try heavier gauge power and get a multimeter onto the power cable at the supply end of the cable as well as the appliance end of the cable and check it for consistency before attaching devices. You want to make sure that the 12V rail at the supply for the DVB-T and the DVD unit are equal - shouldn't differ by mopre than points of a V. If they do it suggests there's resistance, possibly in a dry joint or a cable connection you may have spliced in for the DVB-T.
    Thanks, I've actually managed to trace the problem back to the cd stacker itself. I've got 12v on that batt Positive input when under load. Although, when tested the output batt positive voltage under load I am getting 3.4V.

    I decided to unplug it to see if I could see any fuses in the unit. But now when I've connected it back up again I get a message on the screen that there are no discs web the whole unit is stacked with cd's. Is there a way I could possible reset the unit?

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