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12vdc ground isolation

Martin Beukes

Oct 21, 2015
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Hi there,

I have two modules running off a single battery (12vdc). A audio amplifier and a usb charger. I need to isolate the supply to the usb charger to break a ground loop. How would i go about this?

Many Thanks,
Martin
 

Martaine2005

May 12, 2015
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Hi Martin,
What makes you think it's a ground loop? It's a DC battery.
You probably just have a bad connection or two.. Check all your connections.

EDIT: How have you wired all this together?

From another Martin
 

Martin Beukes

Oct 21, 2015
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Hey there,

The audio comes from an Android device. In the device the ground is common. To check the loop I cut the audio ground. Without the charger connected, no audio, wish wasn't a shock. If I connect the USB charger, audio returns. But there is some harmonics from the charger. Also if a separate charger (separate feed to the amp) is used, then there is noharmonics from the charger and the group less audio line does not work (as one would expect)

Did some research on dc ìsolation and it looks a bit beyond my abilities at the moment. Hence the cry for help.

Thanks,
Martin
 

Martaine2005

May 12, 2015
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Hi Martin,
You can use a 1:1 ratio transformer on each channel output from phone to input of amp.
I personally use these on my mobile sound system.

But it is more than likely that the charger is interfering. You can try and use a heavier gauge cable connecting amp to charger 'common' or try and locate one of these.. Called a ground loop isolator.
http://www.amazon.co.uk/Ground-isolator-audio-noise-removal-Black/dp/B000KHBU1G
upload_2015-10-21_13-19-30.jpeg
Martin
 
Last edited:

Martin Beukes

Oct 21, 2015
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This unfortunately doesn't work. The ground loop is cause by the charger. The USB and audio jack in the android device is common. I have tried using a 470 OHM resister on the ground feed to the charger, and 2 different designs of chargers. The only solution that removes the interference has been power supply isolator. The problem is that in the compleated unit there needs to be a 12vdc backup battery. Hence the question. Any thoughts?

Sorry for being a pain.
 

Martaine2005

May 12, 2015
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Martin,
Can you tell me how it's connected?
Is the android phablet connected to the head unit AUX via 3.5 jacks?
And is the charger a 12v car cigarette charger?
Also, is the noise constant or go away when playing music?

Martin
 

Martin Beukes

Oct 21, 2015
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In essence yes. That is when the charger causes the hum.

If I use an accredited charger or different powersupply on the charger, no hum.
 

Martaine2005

May 12, 2015
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Ok, why not use the recommended charger then?

The isolator I linked to before will definitely work. It has a 1:1 transformer inside. You can buy them with 3.5 jacks too.


images

Martin
 

Martin Beukes

Oct 21, 2015
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As I mentioned before, both modules need to run off battery power. Multiple batteries are too expensive. The audio isolator would not work as the system is grounding through the USB ground. I phisically removed the audio ground and it still plays with the USB plugged in.
 

BobK

Jan 5, 2010
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If you expect any more help, you will have to show us a schematic. Your last statement does not make any sense. You cannot have isolated grounds using only 1 power source.

Bob
 

Martaine2005

May 12, 2015
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I think you are missing the point Martin.
Every item or device on a vehicle have the same common chassis ground.
It is the 'noise being amplified that is causing the issue.
The isolator will work between the audio out and audio in.

Martin
 

Martin Beukes

Oct 21, 2015
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I am not sure how a schematic helps or how to put ot together. And needless to say an audio isolater did not work and the grounding issue is though the USB charger.

The actual question:
I know that you can isolate ground and live in an ac supply by using 1:1 transformers. Is the same possible in dc using an ic or the like?
 

Martin Beukes

Oct 21, 2015
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Thanks for you time.

I have tried the audio isolater, with no success. I will find another solution.
Thanks
 

Martaine2005

May 12, 2015
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The other solution is the recommended charger that didn't cause problems.
You tried 470 ohm resistors. That is not an audio isolator.
They should have been 10 to 100 ohm. But that wouldn't have worked either.
Hope you sort it.
Can you tell us how you sorted it when you do please?

Martin
 

Martin Beukes

Oct 21, 2015
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Using an ac charger is not an option. 2 separate dc supplies is t either.

I found an isolater.....

Meanwell pda-30a-12

More expensive than I would like. But groundloop is gone as soon as I use it to isolate the USB charger.

Thanks for the help guys.
 
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