# RPM, Magnetic Strength and Coils ?

Discussion in 'Electronic Basics' started by [email protected], Feb 5, 2006.

1. ### Guest

What is the formula that determines the power output one would expect
to get by rotating a magnet within a coil ? Say I have a coil with 100
wraps and a magnet at 1 Gauss and I rotate that magnet at 1000 rpm
within the coil... what will be my power (voltage and amp/watt) output
?

1. IF I KEEP ALL THE SAME:
But double the MAGNETIC GAUSS (to 2 GAUSS) how much more power output
can I expect ?

2. IF I KEEP ALL THE SAME:
But double the RPM of the magnet (to 2000 RPM) within the coil, how
much more power output can I expect ?

3. IF I KEEP ALL THE SAME:
But double the coil (to 200 wraps), how much more power output can I
expect ?

I'm trying to understand the ratio and relationship (in power output)
between RPM, Magnetic Strength and Coils.

Thanks,
J.

2. ### Guest

Just as in other cases SIZE MATTERS!!

3. ### Guest

Thanks CBarn -- Can you formulate how "SIZE MATTERS" in regards to my
questions ? An Atom contains the smallest particles known, for not
exist atoms there would be no "size" -- nothing greater than "the
nothingness" -- therefore I propose that it's the tiny that matter, for
without them there would be nothing bigger.

4. ### Bob MonsenGuest

Faraday's law of induction points out that you can get a *voltage* if you
change the magnetic flux through a coil. The formula is

V = N * dF/dt

where F is the magnetic flux in webers, and N is the number of turns in
the coil. Unfortunately, you can't directly relate gauss to webers
unless you know the geometry of the situation.

So, given my shaky understanding of the subject, I believe that you can't
know the power with the information given for several reasons:

voltage cannot be related to power without knowing the impedance.

You don't know the rate of change of magnetic flux, because we can't
calculate the flux without knowing the geometry.

That being said, you can see that if you double the magnetic flux density,
then the rate of change of flux as the coil rotates will double. This
means that the induced voltage will double, and since power is related to
the square of voltage, the power transferred will quadruple.

Doubling the RPM will also double the rate of change of flux, causing the
same result.

Doubling N will again double the voltage, causing the same result...

--
Regards,
Bob Monsen

appears to me (whether rightly or wrongly) that direct arguments
against christianity & theism produce hardly any effect on the public;
& freedom of thought is best promoted by the gradual illumination of
therefore, been always my object to avoid writing on religion, & I
have confined myself to science. I may, however, have been unduly
biassed by the pain which it would give some members of my family, if
I aided in any way direct attacks on religion"
-- Charles Darwin

Thanks Bob

6. ### Rich GriseGuest

. ;-)

What you're talking about is indistinguishable from magic - there is no
formula, it's by-guess-and-by-gosh, and the people who have been making
motors and generators for centuries now keep their tools and techniques
a closely guarded secret.

Good Luck!
Rich