[sdiy] Transformer question

[Czech Martin]

It is not very efficient.

Remeber that the induced voltage in a loop is proportional
to d/dt B.

And B is u*H. (u is often nonlinear and not isotrop).
Now, H is given by the amperes and windings
in the other loop. There is some limit that you can not exceed.
The only way to increase B is to increase u, the magnetic
material constant.

this aspect was missing in the replies I saw.
The magnetic core will guide the flux lines, that is true.
But the other effect is, that the magnetic core material
has about 500 - 100000 higer u then air or vacuum.

So, building an "air core" transformer is double inefficient.
Lot's of stray flux und low B/H ratio.
This is tending towards radio, very lossy, but good enough
for communictaion. But usually not for power transfer.
However, there are exceptions when the circuit to supply has 
the lowest possible consumption also an air core transformer
can be sufficient.

m.c.

> -----Original Message-----
> From: owner-synth-diy at dropmix.xs4all.nl
> [mailto:owner-synth-diy at dropmix.xs4all.nl]On Behalf Of Bert
> Schiettecatte
> Sent: Donnerstag, 22. Juli 2004 17:25
> To: synth-diy at dropmix.xs4all.nl
> Subject: RE: [sdiy] Transformer question
> 
> 
> Mmm.. I am wondering now whether I could implement my transformer by
> creating 2 PCBs with spiral inductors and bringing the PCBs close to
> each other. I wonder how efficient that would be and up to 
> what distance
> that would work..
> 
> bert
> 
> -----Original Message-----
> From: jhaible at debitel.net [mailto:jhaible at debitel.net] 
> Sent: donderdag 22 juli 2004 16:37
> To: Bert Schiettecatte
> Cc: synth-diy at dropmix.xs4all.nl
> Subject: RE: [sdiy] Transformer question
> 
> 
> > Thanks for the info. Why does the core have to be sheets of iron 
> > seperated by an insulating material, and not a solid core?
> 
> 
> You need a ferromagnetic material to make a path of low magnetic
> impedance in order to direct the magnetic field the way you want 
> it to go (i.e. from your primary to secondary winding, without much
> stray field). 
> You want to avoid eddy currents (i.e. the ferromagnetic 
> material acting
> like secondary windings of low electric impedance), so you 
> either use a
> ferrite (not electrically conducting), or lamination (thin layers of
> material, that is electrically cunducting as well as magnetically,
> separated by thin layers of insulation to avoid the material forming
> closed loops above a certain size for the electric current.)
> 
> JH.
> 
> 
> 
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