Ideal Transformer

Can you provide some context for this?

Hello PeterR

Have a look here: http://en.wikipedia.org/wiki/Transformer

Kind Regards....

For a toroidal transformer the turns are always whole numbers, the ratio can of course be any fractional number.

But for a C core, an EI core etc... you can wind half turns or any fractional number you like, within reason! So the ratio can be any multiple you want and 1.73 : 1 is perfectly feasible...

Just wind 173 turns and then wind 100 turns. the ratio is 1.73:1 !!

John

Of course, you're right about getting any ratio.

But to make it clear for newbies, the number of turns on each winding is an integer (the wire either goes around the core's leg or it doesn't, the path back to complete the circuit doesn't matter). ffeJ

E-Man,

I wish you could post this is every EE classroom in the world. I keep running into people who think the number of turns on a torroid is somehow different from the number of wires that go through the hole. Hurrah for you!

On the EIs, I've wound half turns, but never other fractions. Do you have to use loose coupling (maybe a large air gap) to get that? Or, can you just use different leg areas?

Do you mean real rather than imaginary? It could have no real value in that sense unless the device was purely reactive, an impossibility.

If you will say what you mean, you'll get a better answer.

Thanks.

Where T_p=T_s=0

Hi,

If you woulk like to have a regulating transformer to control active and reactive power flow, then the ratio will have a magnitude and angle.

Regards

How a transformer actually performs is based on many factors, frequency, input type, loading etc... but in general the turns ratio is always exact in an ideal transformer; power in = power out. In the real world however parasitic resistance and capacitance alter the performance. Proximity and skin effect also alter performance. Magnetizing inductance stores and releases energy, often in a way that is not ideal for the circuit function. Transformers can very very complex in operation and which factors are most critical varies with the application specifics and transformer design.

To further muddy the waters (I love to do that), for small numbers of turns, on a low permeability torroidal core, almost any ratio is physically possible (the ideal ratio is, of course, the division of integers). When doing railway signalling circuits, I've wound many transformers that had ratios like 1.87 etc. Note this is the actual ratio not the ideal one.

I hope I'm not getting off track with more talk on fractional turns ratio. As stated earlier, with certain core geometries (e.g EE, EI, Cut-Core, etc) it is fairly easy to get half turns by using a vertically oriented bobbin and having your start and stop for the same winding on opposite sides.

Two other methods; neither of which are generally advisable are to wind a turn around an outer leg of an E (please note that this will drive the core assymetrically) and the other is for specialized or modified cores (such as those which might have a hole drilled through the exact center (or off center for different ratios). This latter is very dangerous in cores with high drive signals because proximity effects can cause major issues.