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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