winding your own transformer

To: "'Tesla List'" <tesla-at-pupman-dot-com>
Subject: winding your own transformer
From: Tesla List <tesla-at-stic-dot-net>
Date: Fri, 6 Feb 1998 01:20:22 -0600
Approved: tesla-at-stic-dot-net


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From:  Harri Suomalainen [SMTP:haba-at-cc.hut.fi]
Sent:  Thursday, February 05, 1998 1:32 PM
To:  tesla-at-pupman-dot-com
Subject:  Re: winding your own transformer

>Toroidal?? Hmmm.. the pic I saw looked like the typical square
shaped
>transformer.. are they build from multipule cores? And what material
would
>I want for this thing? 

Toroidal cores are not good for PSU-type applications. The reason
behind this is simple: core shape will make it totally protected by
winding. This includes thermal insulation. Double-E cores are much
better and much more common for power supplys.

>> configuration or possibly a current driven inverter operating
>> at approximately 300 kHz.  As far as the windings being Cu
>> foil - yes they need to be foil based on the guesstimation that
>> this transformer is operating at 300 kHz and using a fairly high
>> current with the necessity of having a low impedance as possible.

I definately disagree. Winding a few thinner wires for a bundle will
do equally well or better. Copper foil windings have no way of making
the proximity effect less severe. Both do have lots of surface area
which is important due to skin effect. Litz will also do naturally.
Copper
foil is also nasty thing to be wound. Using copper foil with toroids
is
definately not nice.

>I had a reply on here about winding the coils in two parts, each
would the
>opposite direction from the other with the center tap being the
inside
>connection of both sides and the two parts wound in opposite
directions. I
>assume since I'm dealing with bare copper here I need some kind of
>turn-to-turn insulation. And something for the primary-to-secondary
>windings. 

Bifilar winding is a must for push-pull. That means you wind two
wires side
by side. Then you form the center-tap by connecting different ends of
two
windings togeather. That is needed for minimizing leakage inductance
between the two windings.



--
Harri Suomalainen     mailto:haba-at-cc.hut.fi

We have phone numbers, why would we need IP-numbers? - a person in a
bus