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Message from discussion Mystery transformer
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Don Pearce  
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 More options Oct 29 2012, 1:29 pm
Newsgroups: rec.audio.tubes
From: s...@spam.com (Don Pearce)
Date: Mon, 29 Oct 2012 17:29:55 GMT
Local: Mon, Oct 29 2012 1:29 pm
Subject: Re: Mystery transformer
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On Mon, 29 Oct 2012 17:05:25 +0100, "GRe"

<mynamespacedbyd...@xs4all.nl> wrote:

>"Don Pearce"

>> Could you explain these tests in a little more detail? I'm not sure
>> why the inductance appears to be dependent on the voltage.

>It's due to hysteresis losses of ferromagnetic materials like the lamination
>in transformers.

>Take f.e. a mains transformer and measure the current trough the primary,
>while the secondary is open:

>1) at mains voltage, f.e. 230Vac
>2) at about 1/10 of the first, f.e. 24Vac.

>Calculate Z from Vac/Iac and XL from Sqrt(Z^2 - Rdc^2).
>Than calculate L from XL/(2.pi.f)
>Usually Rdc can be ignored, so XL practically equals Z.

>3) you will find two quite different figures for the inductance.

>Gio

But in your numbers, the inductance is increasing as the voltage
increases. At higher voltage, the current should be higher, so the
core would be more saturated, so the inductance should decrease, not
increase. I think maybe you need to check your calculations.

d


 
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