[sdiy] How to predict a transformer's current capability?

[John L Marshall]

Mounting holes are cool. The gap of concern is across the magnetic path.
Typical power transformers have primary and secondary winding on a single
bobbin. E-laminations are alternated through each end of the bobbin and then
meet an I-lamination. There is one magnetic path through the windings and
two magnetic paths around the outside where the mounting holes are. Least
flux densitiy in the corners of the rectangular core.

----- Original Message -----
From: Jaco Sloof <jacosloof at yahoo.com>
To: SynthDIYmailinglist <synth-diy at dropmix.xs4all.nl>
Sent: Monday, December 24, 2001 11:42 AM
Subject: Re: [sdiy] How to predict a transformer's current capability?


> Hmm, gaps in the core...
>
> This concerns me a little bit, because:
>
> I'm still constructing my power supply, and
> the transformer HAS gaps, as in; mounting holes to screw it
> to the chassis, THROUGH the core...
>
> Is this Bad?
> (hole diameter is 4.5 mm, that on each corner thus 4 holes...)
>
> Rrrrr, i'm getting saturating shivers here, with lots a background
> noise...
>
> --- harry bissell <paia2720 at yahoo.com> wrote:
> > You should be able to detect core saturation by
> > watching the current very carefully... as saturation
> > approaches the current increases very quickly... a
> > knee
> > similar to diode conduction (but going the other
> > way...
> > bigger!)
> >
> > Another way is to use a "telephone pickup coil" to
> > listen to the hum (flux leakage) around the
> > transformer. When the core saturates, the magnetic
> > field will grow in the air surrounding the core.
> >
> > This will also identify transformers that by design
> > or mistake, have substantial gaps in the core (usually
> > a bad thing...)
> >
> > H^) harry
>
>
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