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Old 6th March 2012, 02:09 PM   #1
maurycy is offline maurycy  United States
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Default Question about trafo

I have trafo that was pulled from a working environment. Unfortunately, I have forgot to mark which wire is in and which wire is out. Is there any danger in trying to connect one side and measure the output on the other side? I know the specs on the trafo so this way I could determine which side is which.

Here is a picture of this trafo: picture

Weird thing is that thicker wire is soldered to a thinner wound wire and on the other side is the other way around (thinner wire soldered to thicker wound wire).

Thanks.
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Old 6th March 2012, 02:33 PM   #2
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Safest way to test which is the input and which is the output is with a DMM.

Measure the resistance of the two windings. The primary will be the Higher resistance (approx 400 Ohms or so). The secondary will be much lower resistance.
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Old 6th March 2012, 02:56 PM   #3
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Originally Posted by KatieandDad View Post
Measure the resistance of the two windings. The primary will be the Higher resistance (approx 400 Ohms or so). The secondary will be much lower resistance.
But it can be and vice versa (secondary will be the Higher resistance and primary will be lower resistance)!!! And this case is possible and is found in practice.

To achieve a fair test would be to have an auto-transformer or adjustable power transformer. Then check the thickness of the transformer windings and charged with auto-transformer on all those windings so current density of no more than 3A/mm2. Measure the voltage applied to the winding when current density reached those 3A/mmp. Perform this test for each winding and note voltages. These are voltage transformer windings.
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Old 6th March 2012, 03:00 PM   #4
maurycy is offline maurycy  United States
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Thanks for replies. What can happen if I put 110V thru the output terminals of the trafo? Will I destroy it? There is a 50/50 chance I will get it right the first time.
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Old 6th March 2012, 03:02 PM   #5
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Read carefully what I said above.
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Old 6th March 2012, 03:03 PM   #6
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Originally Posted by donpetru View Post
But it can be and vice versa (secondary will be the Higher resistance and primary will be lower resistance)!!! And this case is possible and is found in practice.

To achieve a fair test would be to have an auto-transformer or adjustable power transformer. Then check the thickness of the transformer windings and charged with auto-transformer on all those windings so current density of no more than 3A/mm2. Measure the voltage applied to the winding when current density reached those 3A/mmp. Perform this test for each winding and note voltages. These are voltage transformer windings.

Unlikely, this is just a trafo from a Wallmart wall brick.
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Old 6th March 2012, 03:04 PM   #7
maurycy is offline maurycy  United States
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Read carefully what I said above.
Problem is that I do not have adjustable power transformer. All I have is a DMM.

The trafo was pulled from a power adapter for Verizon DSL box.
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Old 6th March 2012, 03:05 PM   #8
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Thanks for replies. What can happen if I put 110V thru the output terminals of the trafo? Will I destroy it? There is a 50/50 chance I will get it right the first time.

Can you confirm that the trafo does have separate Primary and Secondary.

It looks like a standard trafo.
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Old 6th March 2012, 03:07 PM   #9
maurycy is offline maurycy  United States
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Originally Posted by KatieandDad View Post
Can you confirm that the trafo does have separate Primary and Secondary.

It looks like a standard trafo.
There are two wires going in and two wires going out. This is AC to AC so I do not even have to worry about polarity on the input, correct?
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Old 6th March 2012, 03:10 PM   #10
AndrewT is offline AndrewT  Scotland
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Build up a light bulb tester.
It will stop you blowing up your transformer, even if you wire it up incorrectly and save you from the non explosion.
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