Fwd: Re: [Amps] Silly Inductor Question

[Will Matney]

On Mon, 7 Feb 2005 21:11:44 -0800, Dan Levin <djl at andlev.com> wrote:

> Suppose that I want an inductor of 5 mH that will handle 1500 watts into  
> a
> 3:1 SWR from 1.8 to 30 Mhz (to build an L network antenna tuner, at the
> output of a solid state amplifier, say).
>
> 12 turns on a T-400A-2 powdered iron core will give me something like  
> 5.2 uH
> at a maximum flux density of 70 gauss at 500 volts at 1.8 Mhz (with no DC
> current flowing).  70 gauss is acceptable at 1.8 Mhz (and it gets better
> relative to the spec as you get higher in frequency).  Fine, I'm a happy
> camper.
>
> Now suppose that I want an inductor of .5 mH, all else the same.  4  
> turns on
> the same core gets me .58 mH, close enough - but the flux density is now
> 210, well beyond acceptable limits.  Things get worse for smaller  
> inductors
> - the flux density goes through the roof for just 1 or 2 turns.
>
> I can't buy a bigger core easily - so what do I do?  Is my only option an
> air core inductor (which I then have to shield...)?  It seems more likely
> that I am being dense, as usual :-)

All you need to do is stack the cores. Using two doubles the amount of
flux density it can handle. It's the same as multiplying the net core area
by 2.


>
> Thanks!
>
> 			***dan, K6IF
>
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Will



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