Re: Current Limiting and Impedence

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Jim Lux <jimlux@xxxxxxxxxxxxx>

At 09:41 AM 5/10/2005, Tesla list wrote:
> Original poster: "Malcolm Watts" <m.j.watts@xxxxxxxxxxxx>
>
> Hi Paul,
>           Whatever rods you purchase for the core, they have to have
> a very small x-sectional area. They should also not retain much if
> any magnetism after being de-energized (check with a magnet) or they
> will have large hysteresis losses resulting in lots of heating.
> Silicon steel such as used in transformer cores is preferred if you
> can get them.
>
> Malcolm
>
> On 9 May 2005, at 20:25, Tesla list wrote:
>
> > Original poster: "Paul B. Brodie" <pbbrodie@xxxxxxxxxxxxx>
> >
> > Gerry,
> > When I was in Home Depot the other day looking for polyurethane, I
> > noticed a bin full of all thread that also had many sizes of
> > unthreaded steel rod as well. While going through some of the rods it
> >

Searching back through the archives, maybe 5 or 6 years ago, there was a 
fairly long discussion about improvised core materials. I seem to remember 
that wire coat hangers were proposed. The diameter is a bit large (few mm), 
but they're fairly "soft" both mechanically and magnetically, and they are 
already varnished, and, are available very cheaply (as in free if you 
scrounge).

I'm not a magnetics guy, but maybe someone could come up with a quick and 
dirty "what's the effect of using diameter x" equation?  I assume that 
things like the material mu and the material resistivity would factor into 
it, but we could probably make some sort of rough and ready approximation:
iron conductivity is 10 m/(ohm mm2), mild steel is given as 7.7  (Cu is 58)

cast iron mu = 77 (relative to free space!)
steel casting  2690 (P1.0 = 3.6W/kg)  (I think mild steel is in this category)
alloyed dynamo steel 2240 ( P 1.0 = 1.3 W/kg)

P1.0 >> core losses per unit mass at f=50Hz and induction of 1.0T

So, these numbers (for loss) are for the hysteresis losses.  I assume the 
eddy current losses would be in addition.