[Amps] Silly Inductor Question

[Angel Vilaseca]

You can stack some cores, but maybe a more elegant solution would be to
cut a small gap with a fret saw into the core. That would interrupt the
magnetic path and prevent saturation. Fill the gap with a drop of glue.
Now to obtain .5 mH it will take much more than just one or two turns.
To know how many, you will need some way of measuring inductance. Add
windings until you reach your target value.

Angel Vilaseca HB9SLV

Dan Levin 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 :-)
> 
> Thanks!
> 
>                         ***dan, K6IF
> 
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