Re: De-Rating '400hz' Variacs

On Wed, 15 May 1996 13:08:36 -0600, Tesla List
<tesla-at-poodle.pupman-dot-com>, you wrote:

> The size of the three cores are about 5" in diameter, 2" hole, and and 
> about 1.25" thick.  They came off a 10A 400Hz 3 phase variac.  I haven't
> put them in any circuit, so I haven't had any break downs yet :-).
> I have no idea about the inductance.  If you can tell me how to measure
> it using a signal generator, frequency counter, oscilloscope, and/or
> a VOM, I'll try it.
> Chip

	V = I * Z, put the core and a sense resistor in series, apply
a voltage across them with your signal gen. measure the applied
voltage  and the voltage across the sense resistor. 

Knowing the voltage across the sense resistor and it's value. 
   Isense = Vsense / Rsense

Since the resistor and core are in series, their current is the same.

Given the applied voltage and the network current, if the r is small
compared to the Z of the toroid, the V = I * Z formula works.

Then work backwards from Z = 2 * pi * F * L, to get L.