How to determine what is the primary and secondary winding of the transformer??

jeraldson25

Joined Feb 6, 2008
1
help me about my problem plzzz.. HOW TO DETERMINE WHAT IS THE PRIMARY WINDING AND SECONDARY WINDING OF THE DEVICE OR TRANSFORMER.. AND HOW CAN I KNOW WHERE THE PRIMARY AND SECONDARY WINDING CAN FOUND..

SgtWookie

Joined Jul 17, 2007
22,210
help me about my problem plzzz.. HOW TO DETERMINE WHAT IS THE PRIMARY WINDING AND SECONDARY WINDING OF THE DEVICE OR TRANSFORMER.. AND HOW CAN I KNOW WHERE THE PRIMARY AND SECONDARY WINDING CAN FOUND..
Jeraldson25,
What you have done is considered "hijacking" a topic, by injecting a query into an existing topic that is not a reply to the original poster's question. This can cause a great deal of confusion, and is therefore strongly discouraged.

Transformers exchange AC voltage for AC current, period.
The lower-voltage higher-current side can generally be determined by a physically larger wire gauge.

Where the windings can be found depends upon the physical construction of the transformer.

thingmaker3

Joined May 16, 2005
5,084
Jeraldson25,
What you have done is considered "hijacking" a topic, by injecting a query into an existing topic that is not a reply to the original poster's question. This can cause a great deal of confusion, and is therefore strongly discouraged.
And so the question now has its very own thread.

Here is a far more eloquent description of transformers than I could ever hope to write: http://ludens.cl/Electron/Magnet.html

james7701

Joined Jan 5, 2016
37
The side the has the applied voltage is usually the primary (mostly the left side) and the output is the secondary (mostly the right side)

Joined Jan 15, 2015
5,513
The side the has the applied voltage is usually the primary (mostly the left side) and the output is the secondary (mostly the right side)

Ron

JSCV

Joined Oct 3, 2015
23
The side the has the applied voltage is usually the primary (mostly the left side) and the output is the secondary (mostly the right side)
What happens when you rotate the transformer 180 degrees ?
Giving sides of a transformer is not usefull.

Measuring coil resistances can give you a clue. There could also be a label on it indicating primairy and secondary.

Tonyr1084

Joined Sep 24, 2015
4,738
The side the has the applied voltage is usually the primary (mostly the left side) and the output is the secondary (mostly the right side)
This may be generally considered true mostly on schematics. But there are a number of problems with this description. Some transformers are in sealed bodies where you can't see one coil from the other. Most often - BUT NOT ALWAYS - when you have a sealed transformer the primary side is typically - BUT NOT ALWAYS - black and white wires. Secondary wires may be different colors or they may be (for instance) two red wires. I have a sealed transformer with black and white as the primary input side, two red wires that are 10:1 (120 VAC to 12 VAC) and two yellow wires which are 50:1 (120 VAC to 2.4 VAC). I don't remember what that came out of - but - - - .

Center tapped transformers may have multiple leads. Usually - BUT NOT ALWAYS - the primary is just two wires. "Not Always" means I have a couple transformers in my lab that have inputs rated for 120 VAC and for 240 VAC. Commercial lighting may have 277 VAC inputs.

So how do you tell one side from the other on a simple 4 wire transformer? Resistance can give you a clue. The primary side (in a step down transformer) is typically a much finer wire and hence, much longer, with a higher resistance. The secondary side, lower voltage, higher amperage, is typically a much heavier wire, hence, much shorter, with lower resistance. Resistance is not always a good way to determine which side is which because some transformers are not meant to act as voltage transforming. What do I mean by that? Audio transformers - which I don't know how they work or why - also called "Line Matching" transformers (I think) are not intended for power supplies.

I mentioned black and white wires. That's not always true. Transformers built for use in countries (not the US) operate on a different color code. I think (and let me stress I THINK) brown and blue represent the input side of such transformers intended to work typically on 240 VAC line voltages.

Primary and Secondary are simply terms that don't specifically refer to which side is which. Primary typically means the input source side and secondary typically means the output side. But in truth a 2:1 transformer is nothing more than a transformer that takes an AC voltage on one side and turns it into another voltage on the other side. For instance a 2 to 1 may take 240 VAC and output 120 VAC. That very same transformer can take 120 VAC as an input and give you an output of 240 VAC. All depends on how you intend to use it.

Some transformers are considered "Isolation" transformers in that they don't change the voltage they just isolate the operating circuit from main voltage. These are 1 to 1 (1:1) transformers. They perform the task of providing the same voltage as an output as was taken in as a source voltage. This isolates the circuit from ground. I'm starting to get into an area where I'm not well versed, so I'm not going to be able to go into depth as to why you want an isolation transformer. Some of these isolation transformers have an additional coil and capacitor. These are called "Ferro-Resonant" transformers. They ARE isolation transformers but the ferro-resonant part of the transformer is intended to maintain a steady output while allowing the input to vary to some degree. Again, beyond any expertise I might like to believe I have.

But in answer to your question, the way I'd isolate the primary / secondary windings of a step down transformer is basic resistance. Again, primary should have higher resistance than the secondary.