Transformer Mystery - Electronic Circuits Projects Diagrams Free

germaniohm · 16th July 2008, 08:53 AM

My problem is this. I have four 12v transformers working and they cause bad humming on an unrelated electronic device that I am using. The four transformers are 24 inches from the device that I am using. But the interesting thing about my problem is that if I remove two transformers, that is to say, if I pull two of them from the single surge protector/power tap that I have all four plugged into, the humming stops completely. If I add a third, the humming returns. If I plug a third transformer into a receptacle across the room, the humming returns. Can anyone please tell me WHY there is this two transfomer limit? I really need to have all four transformers working and my electronic device as well. Thank you.

mvs sarma · 16th July 2008, 09:05 AM

Welcome Germaniohm, to electro-tech-online.

Imagine each transformer having load of different power factor. The currents flowing will be at different phase angles. This causes the additional ripple that you hear, as I suppose. Please try adding a 2µF capacitor/400V ( in case of 230V supply) across each transformer. They would try to compensate for the Power Factor.

germaniohm · 16th July 2008, 06:27 PM

MVS SARMA:
How would I apply the 2 microfarads/400 volt capacitors to the transformer? Thank you.

mvs sarma · 16th July 2008, 07:44 PM

Quote:

Originally Posted by germaniohm

MVS SARMA:
How would I apply the 2 microfarads/400 volt capacitors to the transformer? Thank you.

Across the primary( parallel to primary)it is 2uF/400V AC capacitor and NOT electrolytic cap

germaniohm · 16th July 2008, 10:57 PM

MVS SARMA:
Thank You.
Do you mean:
1.Locate the primary (positive conductor) on said 12v transformer.
2.Sever the primary conductor and strip the insulation off the newly cut ends.
3.Solder the 2microfarads/400AC capacitor onto the primary conductor ends (according to polarity if there is one)
4.Tape the newly soldered wires with pvc tape to reinsulate the pimary conductor/2microfarads-400AC capacitor splice?
Thank You

JimB · 16th July 2008, 11:15 PM

Far too many unknowns here to make any diagnosis or suggested cure.

How big are the transformers, what is their power rating?

What is the electronic device which is humming?
In what way does it hum?
Does it have a loudspeaker which hums, or does it just make a noise?

What is the power supply to this place? Is it on the end of a long overloaded cable?

JimB

Sceadwian · 17th July 2008, 04:41 AM

I would say buy one 12 volt transformer that can supply power to the same devices as the current bank of four would be better. Adding more components to the existing setup is at best a stop gap measure, you're better off taking a broad look at exactly what you're trying to do and simplifying it as much as possible. So the first question I have to ask is why 4 12 volt transformers instead of one? If you need to have different devices on at seperate times run swithches after the transformer.

germaniohm · 18th July 2008, 09:59 PM

Sceadwian:
I was not aware that one 12v transformer could take the place of four 12v transformers. How is this done?

germaniohm · 18th July 2008, 10:23 PM

Quote:

Originally Posted by JimB

Far too many unknowns here to make any diagnosis or suggested cure.

How big are the transformers, what is their power rating?
There are 4 transformers that are 12 volts DC each and range from 300 to 500 milliamps.

What is the electronic device which is humming?
The device is called a "Listen Up" in the United States.

In what way does it hum?
Over my headphones.

Does it have a loudspeaker which hums, or does it just make a noise?
Headphones.

What is the power supply to this place? Is it on the end of a long overloaded cable?

I have a "DigiVue" video-camera card. It has a four camera capacity. I have my computer in my den which is in the rear most part of my house. All four cameras plus the "Listen Up" is located in the front of my house to watch the street as well as listen. My "Listen Up" is attached to a TRS stereo plug and uses the line intended for sound as of course there are three lines, one for the volts, one for the camera and one for the sound. Where the sound, volt and camera lines terminate in my den is where I have attached what is known as an "isolation transfomer" to the sound line to kill the aweful "DC hum" I've read it once described. On the other side of the "isolation transformer" I have attached by solder a TRS plug to plug into the "MICROPHONE" female plug which is on my "Xtreme" sound card. Everything works very well except for the hum.

JimB

I hope this is a sufficient explanation of what I have done.

ecerfoglio · 18th July 2008, 10:41 PM

Quote:

Originally Posted by germaniohm

..................................................
Where the sound, volt and camera lines terminate in my den is where I have attached what is known as an "isolation transfomer"
.................................................. .
hope this is a sufficient explanation of what I have done.

It may be that your audio isolation transformer is picking up the stray magnetic field from the power transformers.

You may try to increase the distance between the power and audio transformers (magnetic field decays with the square of the distance, so sometimes even a small distance increase - a couple of feet or half a meter - reduces the hum to unnoticeable levels).

Other thngs you may try:

>>> Enclose the isolation transformer in a steel enclosure to act as a "magnetic shield" - it ay even be an used food can, just be sure it is steel and not aluminium)

>>> Verify that the audio signal travels along screened cables, and that the screen is connected to ground at only one point (the ideal setup is a cable with a twisted pair for signal and return - even if the retirn wire is grounded - surrounded by a grounded screen.

ecerfoglio · 18th July 2008, 10:44 PM

Quote:

Originally Posted by germaniohm

Sceadwian:
I was not aware that one 12v transformer could take the place of four 12v transformers. How is this done?

You may use a bigger transformer instead of your four small ones.

If each of your transformers outputs 12 VDC @ 500 mA you may use a 12VDC 2A one to power your four cameras.

ste5442 · 18th July 2008, 11:17 PM

This could be caused by many things but if its a PFC issue then you will need to do the math to fix it.
Most devices need to go through radiated emmissions testing before going on sale so radiated noise is 'fairly' unlikely especially if its just a power supply 2 feet away.
Try a filtered multi-plug adaptor since I guess its conducted emmissions.
Alternatively (as mentioned above) try to shield the device to determine whether the interference is radiated or conducted.

S.

germaniohm · 18th July 2008, 11:29 PM

Quote:

Originally Posted by ecerfoglio

It may be that your audio isolation transformer is picking up the stray magnetic field from the power transformers.

You may try to increase the distance between the power and audio transformers (magnetic field decays with the square of the distance, so sometimes even a small distance increase - a couple of feet or half a meter - reduces the hum to unnoticeable levels).

Other thngs you may try:

>>> Enclose the isolation transformer in a steel enclosure to act as a "magnetic shield" - it ay even be an used food can, just be sure it is steel and not aluminium)

>>> Verify that the audio signal travels along screened cables, and that the screen is connected to ground at only one point (the ideal setup is a cable with a twisted pair for signal and return - even if the retirn wire is grounded - surrounded by a grounded screen.

May I asked what "screened" cables are? Connect to ground? How might one ground a two wire system? When I rewired my house I "bonded" all the copper water pipes and black iron gas pipes to a 10 foot grounding rod which I pounded into the ground. All my light fixtures and switches and receptacles are grounded. My cameras and "Listen Up" audio device are connected by the standard cable you buy at any electronics store. It's a single black wire that has camera, audio and power cable stuffed into a single wire that terminates in cheap red and white RCA connectors and a coaxial connector for a transformer. I did not mention a very important idiosyncracy and that is the buzzing disappears completely when ANY two transformers are plugged in. When a third transformer is plugged in the buzzing returns.

ecerfoglio · 19th July 2008, 12:24 AM

Quote:

Originally Posted by germaniohm

May I asked what "screened" cables are? Connect to ground? How might one ground a two wire system? When I rewired my house I "bonded" all the copper water pipes and black iron gas pipes to a 10 foot grounding rod which I pounded into the ground. All my light fixtures and switches and receptacles are grounded. My cameras and "Listen Up" audio device are connected by the standard cable you buy at any electronics store. It's a single black wire that has camera, audio and power cable stuffed into a single wire that terminates in cheap red and white RCA connectors and a coaxial connector for a transformer. I did not mention a very important idiosyncracy and that is the buzzing disappears completely when ANY two transformers are plugged in. When a third transformer is plugged in the buzzing returns.

"screened" cables are the ones that have an outer conductor (or shield, usually a wire mesh or else aluminium foil), arround the "active" conductors. Audio or video signal cables are usially screened ones.

Ground** is a relative term, if you have a 2 wire system your ground may be your computer case - you may connect the cable screens to the outer conductor of the RCA (or phone) plugs, or else to one of the screws that close the PC's case.

** (EDIT) I'm speaking of a signal ground, not a safety ground.

A safety ground must comply to your local codes.

germaniohm · 20th July 2008, 02:48 AM

Quote:

Originally Posted by ecerfoglio

"screened" cables are the ones that have an outer conductor (or shield, usually a wire mesh or else aluminium foil), arround the "active" conductors. Audio or video signal cables are usially screened ones.

Ground** is a relative term, if you have a 2 wire system your ground may be your computer case - you may connect the cable screens to the outer conductor of the RCA (or phone) plugs, or else to one of the screws that close the PC's case.

** (EDIT) I'm speaking of a signal ground, not a safety ground.

A safety ground must comply to your local codes.

Thanks for your answers. Are you familiar with the term "ATTENUATED"?? Would this be what you are referring to? I've never seen anything screened or aluminum foiled at the Radio Shack where I shop for my electronic hardware. But I have seen a few cables with the term "attenuated" printed on the label.

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16th July 2008, 08:53 AM	(permalink)
germaniohm	Transformer Mystery My problem is this. I have four 12v transformers working and they cause bad humming on an unrelated electronic device that I am using. The four transformers are 24 inches from the device that I am using. But the interesting thing about my problem is that if I remove two transformers, that is to say, if I pull two of them from the single surge protector/power tap that I have all four plugged into, the humming stops completely. If I add a third, the humming returns. If I plug a third transformer into a receptacle across the room, the humming returns. Can anyone please tell me WHY there is this two transfomer limit? I really need to have all four transformers working and my electronic device as well. Thank you.

16th July 2008, 09:05 AM	(permalink)
mvs sarma	Welcome Germaniohm, to electro-tech-online. Imagine each transformer having load of different power factor. The currents flowing will be at different phase angles. This causes the additional ripple that you hear, as I suppose. Please try adding a 2µF capacitor/400V ( in case of 230V supply) across each transformer. They would try to compensate for the Power Factor. __________________ Regards, Sarma.

16th July 2008, 06:27 PM	(permalink)
germaniohm	MVS SARMA: How would I apply the 2 microfarads/400 volt capacitors to the transformer? Thank you.

16th July 2008, 10:57 PM	(permalink)
germaniohm	MVS SARMA: Thank You. Do you mean: 1.Locate the primary (positive conductor) on said 12v transformer. 2.Sever the primary conductor and strip the insulation off the newly cut ends. 3.Solder the 2microfarads/400AC capacitor onto the primary conductor ends (according to polarity if there is one) 4.Tape the newly soldered wires with pvc tape to reinsulate the pimary conductor/2microfarads-400AC capacitor splice? Thank You

16th July 2008, 11:15 PM	(permalink)
JimB	Far too many unknowns here to make any diagnosis or suggested cure. How big are the transformers, what is their power rating? What is the electronic device which is humming? In what way does it hum? Does it have a loudspeaker which hums, or does it just make a noise? What is the power supply to this place? Is it on the end of a long overloaded cable? JimB __________________ Experience is directly proportional to the value of the equipment ruined.

17th July 2008, 04:41 AM	(permalink)
Sceadwian	I would say buy one 12 volt transformer that can supply power to the same devices as the current bank of four would be better. Adding more components to the existing setup is at best a stop gap measure, you're better off taking a broad look at exactly what you're trying to do and simplifying it as much as possible. So the first question I have to ask is why 4 12 volt transformers instead of one? If you need to have different devices on at seperate times run swithches after the transformer. __________________ "Because I be what I be. I would tell you what you want to know if I could, mum, but I be a cat, and no cat anywhere ever gave anyone a straight answer, har har."

18th July 2008, 09:59 PM	(permalink)
germaniohm	Sceadwian: I was not aware that one 12v transformer could take the place of four 12v transformers. How is this done?

18th July 2008, 11:17 PM	(permalink)
ste5442	This could be caused by many things but if its a PFC issue then you will need to do the math to fix it. Most devices need to go through radiated emmissions testing before going on sale so radiated noise is 'fairly' unlikely especially if its just a power supply 2 feet away. Try a filtered multi-plug adaptor since I guess its conducted emmissions. Alternatively (as mentioned above) try to shield the device to determine whether the interference is radiated or conducted. S. __________________ advert removed by moderator.