Need advice on noise in 12v supply

[Bruce]

I am hooking up a Raspberry Pi to play music for the boat but have noise in the signal whenever it is powered from the boat. If I draw power from an external source there is no noise, only minimal static.

Previously I experienced similar noise using a Fusion Bluetooth adapter and a Sabrent AirPlay adapter. The Pi introduces the lowest noise of the three.

In the video below I start with the Pi running from a USB battery pack and there is no noise. Then I plug it into the boat and the noise starts. Then I unplug and the noise goes away. Finally I replug and the noise is back.

I either need to replace my USB power supply with one that will filter the noise or filter the noise before the power supply. The Pi will be powered from a USB power supply inside the console. I used the one on the dash for the video. The in console power supply is connected to the stereos power leads.

I appreciate your advice.

@David Analog, do you have any tips?

 

[farrelltravis]

I can't offer too much help, but a ferrite bead might solve the problem.

https://www.google.com/webhp?source...ion=1&espv=2&ie=UTF-8#q=ferrite+bead&tbm=shop

 

[ArmyChief]

@Bruce ,

I would like to put a scope on the positive and negative. However. I'm guessing the SMPS used by your dash USB jack is the issue.

Replacing that with a better 12v->5v jack is your best bet. I post conversion filter could be designed (I don't think I e ever sent one) to plug onto the end of your USB cable.

Ferrite beads are used on cables for noise.

 

[ArmyChief]

@Bruce , @farrelltravis might have a cheap resolution. Look at this post:

http://pointsforpilots.blogspot.com/2013/06/radio-interference-of-12v-ipad-charger.html?m=1

Large ferrite bead fixed there noise.

 

[farrelltravis]

When he said "filter", that is exactly what a ferrite bead does for power cords.

 

[farrelltravis]

Chances are, too, that @Bruce wouldn't even have to buy one. If you have some old "wall warts" laying around you could grab one off of it and try it.

 

[ArmyChief]

Yup, good idea.

 

[Bruce]

@farrelltravis, off of it or out of it. Very happy to try anything that I have laying around.

The USB outlet in the video is the Blue Seas FCC certified model that the pilots discuss using.

My current thinking is to order a 12v filter for the power supply and a ground loop isolator for the RCA cable.

Could I install the ferrite bead on the power wire before the the USB supply?

 

[farrelltravis]

Look for any old cord you have laying around that has something that looks like this on it. That is a ferrite bead. Take it off the old cord and put it on the cord at issue and see if that solves your problem.

 

[ArmyChief]

@Bruce ,

In my field I teach to not guess....test. Hence my earlier statements about scoping. If the engine was not running, the odds that the 12v source is the noise issue are minimum. I was unaware a RCA was attached.

The raspberry PI is powered by 5VDC USB?

Since it doesn't make a noise when powered from the USB battery. My our issue is either the SMPS in the blue seas jack and/or the differences between 12v battery ground and the ground output of the USB jack.

 

[ArmyChief]

Or, if you have a USB cable with the head on it...just use that to power the PI

 

[ArmyChief]

The raspberry PI use a microUSB to power?

6' USB A to 5-pin USB Mini-B Cable w/Ferrite Bead (Black) https://www.amazon.com/dp/B001M58H1G/ref=cm_sw_r_awd_Z3bJvbTZJSME5

 

[Bruce]

I found a ferrite on a wall wart and cut it off to experiment with. I removed the panel where the BlueSeas USB supply is installed and disconnected the wires from the back.

The hum remained when I disconnected the positive. So there must be RF or a loop on the ground. Experimenting further I found that a small amount of noise is introduced when the positive alone is connected but the majority of the noise comes from the ground.

I connected the ferrite ahead of the BlueSeas USB power supply and found that the hum remained.

 

[Bruce]

@internationalmarinemike, do you have any advice?

 

[David Analog]

When you have a source device, like a phone or other, that displays no noise when operating on battery power but suddenly yields noise when operating on a power supply which in turn is fed by the boat, then you have a voltage traveling down the signal ground.
That which is intended to shield the signal from noise is now the noise transmitter. Kind of the fox watching the hen house.
So what is usually done is to interrupt the ground shield with an isolation transformer, such as those found in a ground loop isolator. I don't normally care for the device because it treats the symptom and leaves the original cause intact. But in this scenario it is often unavoidable. Worth a try.

 

[Julian]

@Bruce Is your fridge the source?

 

[Bruce]

So what is usually done is to interrupt the ground shield with an isolation transformer, such as those found in a ground loop isolator. I don't normally care for the device because it treats the symptom and leaves the original cause intact. But in this scenario it is often unavoidable. Worth a try.

David, this PAC SNI-1 Noise Isolator has good reviews on Amazon and Crutchfield. Would you try it or can you recommend something better?

I would use it with two 1.5' shielded RCA cables.

Do you think that this Pyramid NS12 12 Amp InLine Noise Suppressor would do any good? I believe I have confirmed that the hum is coming from the ground. Can I install any kind of filter on the ground?

Thanks

 

[Bruce]

@Bruce Is your fridge the source?

That is a real possibility and one that I have long suspected. But the fridge stays.

 

[farrelltravis]

I found a ferrite on a wall wart and cut it off to experiment with. I removed the panel where the BlueSeas USB supply is installed and disconnected the wires from the back.

The hum remained when I disconnected the positive. So there must be RF or a loop on the ground. Experimenting further I found that a small amount of noise is introduced when the positive alone is connected but the majority of the noise comes from the ground.

I connected the ferrite ahead of the BlueSeas USB power supply and found that the hum remained.

Was worth a shot. Sorry that didn't work for you.

 

[Bruce]

Was worth a shot. Sorry that didn't work for you.

I appreciate the suggestion!