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From: Winfield Hill
Subject: Re: Strange behaviour - core saturation puzzle
Date: 16 Jan 2003 08:11:44 -0800
Organization: Rowland Institute
X-Newsreader: Direct Read News 4.20
> I've been doing some common-mode coil saturation tests:
> One side of the coil is shorted and on the other side a DC voltage is
> applied. The current ramps linear up until the core saturates at which
> point the coil di/dt will rise significantly due to the reduced
> permeability. Taking the data from the scope - doing some number
> crunshing will allow me to plot the inductance as a function of the
> coil current.
> My problem is that the test is done perhaps once a second and the
> saturation current reaches some level - lets say 10amps. But if I
> increase the frequency of the test - the saturation level moves down
> to perhaps 8 amps. Does anyone have an explanation for this?
> I've allready checked the current when the ramp starts - and it is
> zero - so there is no energy stored in advance. Moreover I have a
> flyback diode accross the coil to absorbe the flyback voltage.
> Perhaps some flux imbalance from the hystersis curve?
Klaus, have you checked, is the core temperature going up?
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