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From: "Klaus Vestergaard Kragelund"
Subject: Re: Strange behaviour - core saturation puzzle
Date: Sun, 19 Jan 2003 16:46:47 +0100
X-Newsreader: Microsoft Outlook Express 6.00.2800.1106
Organization: TDC Internet
"Winfield Hill" wrote in message
> email@example.com wrote...
> > 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?
> - Win
The test current is applied perhaps 10 times a second and lasting only for
about 40us. So self warming should not occur. Furthermore the coil has a
good thermal contact to a temperature regulation device to set the needed
temperature. The end result of the test is to show the current saturation
level dependance versus temperature of the coil (at higher temperature the
saturation level decreases significantly)
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