Re: will my house burn down?

On Nov 19, 10:55 am, John Popelish <jpopel...@xxxxxxxx> wrote:
Mark wrote:
putting a diode in series with the secondary does NOT push the core
towards saturation.. The PRIMARY still has AC on it and the
magnitizing current that flows in the primary keeps the core
centered.

(snip)

If the primary winding has zero resistance, then the voltage
might remain pure AC, but this is not the case, especially
for small transformers.

Loading the secondary with DC also loads the primary with
DC, and that produces a voltage drop on half of the half
cycles that is not there during the other half. That
current drops voltage across the primary resistance, and
that drop is subtracted from from the line voltage for those
half cycles. This effect definitely unbalances the AC
applied to the winding, and walks the core toward saturation.

snip

Hmmm OK that's a good point. Let me think about it.

It's interesting therefore to note that the core is actually stressed
more (and may approch saturation) during the 1/2 cycle that the diode
is NOT conducting and the primary voltage is therefore higher.

So I'm thinking that if the core starts to saturate when the diode is
off, the primary current will increase during the "off" 1/2 cycle,
until the primary voltage drops to reaches some equalibrium.....it's
hard to predict which combination of conditions ends up with more heat
in the transformer.....

Very interesting question... maybe time for someone to make some
measurments...

Mark



.

Relevant Pages

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  • Re: DC magnetisation of transfromers and chokes.
    ... Afe is the core area in sq. ... one has to limit ac Bmax to 0.6T ... What would you regard as saturation problems? ... you consider voltage rather than current. ...
    (rec.audio.tubes)
  • Re: will my house burn down?
    ... Loading the secondary with DC also loads the primary with DC, and that produces a voltage drop on half of the half cycles that is not there during the other half. ... This effect definitely unbalances the AC applied to the winding, and walks the core toward saturation. ...
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