Re: Transformer basics

In a message dated 96-02-27 22:13:16 EST, tesla-at-grendel.objinc-dot-com writes:

>My questions are, has anybody wound their own before and if so could you
>me any practical advice such as ball park core weight for a 2-3 KVA xfrmr,
>practical dimensions obtained and how the H.V. winding was wound for good 
>insulation i.e. is it nessacery to varnish impregnate the windings ect.
>I have some calculations for determining core weight ect. But were taken
>a book published in 1950's and has probably been far exceeded by modern 
>silicone irons used in cores ect. In fact i checked  a couple of 440-240
>power transformers and their weight was a little over two thirds the value 
>calculated for the weight of the iron core alone(and this was the total
>weight including copper and frames).
>Ian Hopley ---->  i_hopley-at-wintermute.co.uk


I have rewound old transformers before, but for low voltage (battery chargers
and brute force power supplies) not for high voltage.  Since I did not have
access to new cores, I searched surplus outlets, junkyards, etc. to find one
with the kva rating that I needed.  Then I unwound all the secondaries and
counted the turns on some to calculate the turns per volt.  Then wound on the
appropriate secondary wire.  I would think you could find an old 2 or 3 kva
transformer and do the same thing, only with a lot more wire of a smaller
gauge.  I don't think you need to do anything special like layering
insulation between windings.  When you unpot neon sign transformers, they
just have miles of fine wire wound on layer after layer.  I would give the
finished product a good varnishing - or submerge it in oil.

Ed Sonderman