Trying to understand ground loop in a car

[david90]

I have an mp3 player in my car and i think it is having a ground loop issue. Whenever I plug it into my cig. lighter, I could hear a whining noise. The whining noise's pitch is proportional to the engine's RPM. I'm trying to fix and understand the problem because my background is electrical
http://img11.imageshack.us/img11/2213/drawing1tc.jpg

The picture above is a model of the the mp3 player and the ground loop. Is the model above accurate? Would the audio from the headphone have a whining noise that originates from the car's alternator? From my understand, the ground loop is caused by noise current flowing through Rground. Since the audio generator references the node @ Rground, the audio source picks up the noise and outputs it to the headphones.

 

[2milehi]

You could try and disconnect the alternator belt to see if the noise goes away, but I'd bet that you would still hear the noise. The wine that you are hearing is most likely from the ignition system. It could be from ignition plug wires that are starting to break down. There could be an ignition-coil capacitor that has gone south. You may need to install an ignition-coil capacitor to deal with the noise.

Can you try another MP3 player an see if the noise goes away?

 

[yungman]

You don't have a ground loop from the drawing. I don't believe it's ground loop problem. There only be two possible problem, first, the filtering of the 12V in the car is not good, or your mp3 does not do a good job in filtering the power supply noise.

If you just bought the mp3, return it and get another one and try it out before thinking about fixing anything.

 

[jim hardy]

Search on terms "Alternator Whine" . The noise more likely coming in on the power lead.

any electronics made for an automobile needs to filter its input power.
The car alternator might put out a hundred amps of rectified three phase which modulates the battery voltage. It is the responsibility of every device in the car to deal with it.
Radio Shack used to sell inline power filter - basically an inductor-capacitor combination.

If you're handy with tools you might be able to pillage the part from a junked car radio and mount it in a cellphone power plug, check thrift stores nearby.

 

[alphysicist]

I can provide some insights into the ground loop issue in your car. First, the model above is generally accurate in representing the components involved in the ground loop. The ground loop is indeed caused by noise current flowing through Rground, which is usually the car's chassis ground. This noise current can come from various sources such as the alternator, ignition system, or other electrical components in the car.

In your case, the whining noise you hear is likely originating from the car's alternator. This is because the alternator produces AC current that is converted to DC to power the car's electrical system. However, some AC noise can still leak into the DC system and cause the whining noise you hear in your headphones. This noise is then amplified by the audio source and outputted to your headphones.

To fix this issue, there are a few potential solutions you can try. One option is to use an isolator or filter in the power supply line to your mp3 player. This will help block the noise from reaching your audio source. Another option is to use a ground loop isolator, which essentially breaks the ground connection between the mp3 player and the car's electrical system. This can also help reduce the noise.

In terms of understanding the problem, it is important to note that ground loops can occur in any electrical system and are not limited to cars. They can be caused by various factors such as improper grounding, different ground potentials, or noise currents. It is important to properly isolate and mitigate these sources of noise to prevent ground loops from occurring.

I hope this information helps you better understand and solve the ground loop issue in your car. As a scientist, it is always important to approach problems with a systematic and analytical mindset, and I encourage you to continue exploring and learning about the underlying principles of electrical systems.