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Audio feedback with 12vDC to 120vAC inverter in car

Bradleydof

Jan 16, 2020
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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
 

Harald Kapp

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Nov 17, 2011
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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
 

Bradleydof

Jan 16, 2020
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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!
 

Harald Kapp

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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.
 

Bradleydof

Jan 16, 2020
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Jan 16, 2020
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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!
 
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