> I have a circuit mounted on a fan, doing about 3000 rpm. This circu=
it has
to be powered with 5v, 30 mA. I can't use brushes because they slow d=
own the
fan too much.
I tried to make an "open transformer": an open coil (not rotating) wi=
th a
smaller coil with iron core inside it (not touching the other coil, a=
nd
rotating).
Both coils have ~30 windings.
Using 50 Hz 5v 500 mA at the primary side,=C2 only 300 mV shows up at=
 th
secondary side with short-circuit current of 1 mA.
Should I use a higher frequency, or just make the coils larger with m=
ore
windings?
(or is this never gonna work and you have a better idea?)
>

Magnetic induction, as you are using, can definitely be made to work.=
 A
ferrite core for both with as closed as possible a magnetic path woul=
d help.
Resonating the receiver will also help markedly.

BUT it may be easier to simply use a fixed magnet and rotate a coil p=
ast it
to generate voltage.



        Russell McMahon

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