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Building Transformer & flux density




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From:  Malcolm Watts [SMTP:MALCOLM-at-directorate.wnp.ac.nz]
Sent:  Sunday, June 14, 1998 7:40 PM
To:  Tesla List
Subject:  Re: Building Transformer & flux density

Hi Erik,

> Sent:  Friday, June 12, 1998 12:36 PM
> To:  tesla-at-pupman-dot-com
> Subject:  Building Transformer & flux density
> 
> Hi,
>     I am building a transformer for my tesla coil. =20
> I need to figure out the cross sectional area of the iron core. =20
> This would be related to max flux density in iron.
> 
> F stands for flux, A is area,=20
> f is frequency, N number of turns,
> B is magnetic field, V is voltage
> 
> F =3D B * A
> 
> now for a close packed coil using faradays law
> Emf =3D -d/dt * N * F
> 
> so if we substitute in for the flux F
> Emf =3D -d/dt * N * B * A
> 
> Which can be rewritten as
> V =3D f * N * B * A
> 
> Which can be rewritten as
> B =3D V / (f * N * A)
> 
> ok I measured a NST and a H&R transformer and found
> for NST B =3D 7.34 Tesla
> for H&R B =3D 5.86 Tesla
> 
> 5.86 and 7.34 Tesla seem kind of high to me.  Am I missing=20
> a factor or two?  Does this sound right?  Is all the physics good?

I seem to remember that for sinusoidal AC there is a factor of 4.44 
built into the denominator.

Malcolm