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Re: Inductor question
> From: Jim Fosse <jim.fosse-at-bdt-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Re: Inductor question
> >From: Mike McCarty <mmccarty-at-dnaco-dot-net>
> >To: tesla-at-pupman-dot-com
> >Subject: Re: Inductor question
> >
> [snip]
>
> >The permeability of different types of steel vary a lot from alloy to alloy.
> >A permeability of 5 is terrible. 99.9 % pure iron has a max permeability of
> >around 5000. The very best alloys for this kind of work have a high nickel
> >content and can reach permeabilitys of 800,000. I'd experiment with different
> >kinds of steel before you put too much work into winding a nice inductor.
> >
> [snip]
> >A co-worker and I were goofing around one day and wound a bunch of #10
> >THHN around a 3" PVC pipe. We jammed the wires into a wall outlet and
> >turned on the power. With a peak reading ammeter we pulled 60 amps
> >before the 20 amp breaker tripped a split second later. We took a piece
> >of heavy wall steel pipe and inserted it and we were able to hold the current
> >just under twenty amps.
>
> 60A/20A looks like 3 to me.
>
> Don't forget that this permeability of 5000 is in series with Air of
> permeability ~1.
>
> jim
Yes, since the magnetic path thrugh the steel is broken is it hard to tell the
actual permeability with such measurements. I was wrong in throwing the five out
there as an actual figure of permeability for the core he had.
The pipe I was using may have done better than than the threefold increase in
inductance, but the sixty amps I measured was the point at which the breaker
tripped, its hard to tell how much it could have drawn. Besides, this was an
example of a poor core material.
The main point I was trying to get across is that heat can be a big killer and
it would be worthwhile to test different core materials for heat buildup as well as
permeability before spending time and money based on what may be a poor
choice of core material.
-Mike McCarty