Discussion in 'General Electronics Chat' started by wes, Feb 19, 2011.

1. wes Thread Starter Active Member

Aug 24, 2007
242
2
Hi, I was just reading Mutual inductance and basic operation

and what got me a little confused is this part

"Magneto-motive force is produced any time electrons move through a wire. Usually, this mmf is accompanied by magnetic flux, in accordance with the mmf=ΦR “magnetic Ohm's Law” equation. In this case, though, additional flux is not permitted, so the only way the secondary coil's mmf may exist is if a counteracting mmf is generated by the primary coil, of equal magnitude and opposite phase. Indeed, this is what happens, an alternating current forming in the primary coil -- 180' out of phase with the secondary coil's current -- to generate this counteracting mmf and prevent additional core flux. Polarity marks and current direction arrows have been added to the illustration to clarify phase relations: (Figure below) "

also

"If you find this process a bit confusing, do not worry. Transformer dynamics is a complex subject. What is important to understand is this: when an AC voltage is applied to the primary coil, it creates a magnetic flux in the core, which induces AC voltage in the secondary coil in-phase with the source voltage. Any current drawn through the secondary coil to power a load induces a corresponding current in the primary coil, drawing current from the source. "

What get's me a little confused is the part about the secondary current inducing a current 180' out phase with the secondary.

You see I have always thought the way it works is as follows.

The primary current induces voltage in secondary, Secondary voltage causes current, current is out of phase with primary current by 180', the magnetic flux in the core decreases, primary current decreases and field collapses back inducing back-emf but because the secondary decreased flux, less voltage is induced in primary causing higher current flow.

I always thought the action of the secondary affecting primary current was delayed until the primary field collapsed back inducing voltage. IS that wrong?

If what i read is true then does that mean the primary actually has two currents running through it?

2. wes Thread Starter Active Member

Aug 24, 2007
242
2
well seeing as no one is answering this, I guess either nobody knows or this is just a stupid question, lol. I reread again and I am pretty sure it is correct that the Primary actually has two current's, the magnetizing current and then the load current caused by the secondary.

If somebody could at least reassure me that this is true or wrong then I would feel alot better. Because as of now, I am still not totally sure.

I have to admit though, if it is true then this make's a lot more sense then the energy being alternately absorbed and returned to the primary coil circuit, because with that, there would be delays of when the primary feels the load and such. With this it is nearly instantaneous for intents and purposes. There is actually about a delay of 83 picoseconds for every inch between them.

3. wes Thread Starter Active Member

Aug 24, 2007
242
2
Never mind I am retarded, lol, what I said before was incorrect sorta.

4. marshallf3 Well-Known Member

Jul 26, 2010
2,358
201
Naw, you'll get an answer, be patient, this forum is just a side hobby for a lot of us as most of us have jobs or are not addicted to the internet.

In the meantime: http://en.wikipedia.org/wiki/Transformer is a good primer unless you're dealing with three phase or RF.

We'll fill you with info as time goes by.

wes likes this.