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Audio feedback with 12vDC to 120vAC inverter in car

Discussion in 'Power Electronics' started by Bradleydof, Jan 16, 2020.

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  1. Bradleydof

    Bradleydof

    3
    0
    Jan 16, 2020
    I have an inverter that I use to charge my phone and I play music from that phone as well I'm my car. I connect the phone with a direct audio patch cable using the headphone jack. This causes some feedback to be produced from the speakers. I am unable to figure out why this happens and how to do stop it. Any help you can provide me is appreciated. Thanks in advance!
    Brad
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    10,025
    2,138
    Nov 17, 2011
    Welcome to EP, Bradley.
    I see at least two ways for the distortion to find its way into your audio system:
    1. Your inverter may generate excessive noise.
    2. You create a grond loop via battery - inverter - phone - audio input - radio - battery. This loop is large and easily picks up noise.

    question: What do you mean by "inverter"? In the context of power delivery the name "inverter" is usually uses short for power inverter, a device that converts DC to AC.
    You wouldn't need such a device here. A simple 12 V to 5 V regulator, typically available as a plug for the cigarette lighter, will suffice.

    In your current setup a ground loop isolator may help. Google "3,5 mm Car Audio Ground Loop Noise Isolator".

    Cheers,

    Harald
     
  3. Bradleydof

    Bradleydof

    3
    0
    Jan 16, 2020
    Yes, it is a 12v DC to 120v AC converter. I use this because it is what I have available. I charge multiple things from the same setup with different USB cables. When I have available cash I will buy a Quick Charge 3.0 compatible cigarette lighter adapter. But for now this is what I have and was hoping I might be able to purchase a cheap component from Radio Shack to solve the issue. I'm going to search for a wiring diagram for a 3.5mm ground loop isolator and see if I can put one together cheaply. Any advice on that?

    Thanks for the quick response on the forum!
     
  4. Harald Kapp

    Harald Kapp Moderator Moderator

    10,025
    2,138
    Nov 17, 2011
    So you go from 12 V to 120 V and back to 5 V. Rather inefficient. But if that's what you have at hand...
    A car adapter with 2 ports is available on e.g. Amazon for as little as 3 $, a tad more for one with (hopefully) higher quality.
    13 $ for an adapter with 4 ports.
     
  5. Bradleydof

    Bradleydof

    3
    0
    Jan 16, 2020
    I agree that this is not the most efficient arrangememt. It started as a method of charging my laptop and just ended up being what it is because it's what I had lying around to charge my devices. I will get the appropriate adapter soon. I was just being curious about why there was noise on the line only when the power was connected and not on the battery. I wasn't that I needed to continue this insane 12vDC to 120vAC to 5vDC conversion but that I wanted to understant what was going on and how I could fix it. I'm a naturally curious person.

    Now I get what is happening and with what you have told me I should be able to continue the research and understand how this is possible and what exactly the solution does to prevent this. I appreciate your taking the time to satisfy my curiosity and teach me something. Thank you so much!
     
  6. bertus

    bertus Moderator

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    Nov 8, 2019
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