Hello there,
There is no way that i know of for most transformers because the windings are usually
varnished. This means you cant even unwind the
windings in most cases. The transformers
are usually dipped in varnish and then
baked in an oven to dry the varnish. This
makes the windings stick together so they
dont vibrate and also makes the whole
structure more thermally conductive.
You can sometimes add windings however, if
you can find room inside the core. You have
to wrap the new windings around the center part
of the core also.
I've taken several transformers apart by
cutting the windings off with a hacksaw.
Although it's not an easy task, you can
then wind your own turns around the core.
Before you do this though, it would be a
good idea to get an estimate of the
number of turns on the primary and the
typical driving voltage so you can estimate
your Bmax for the transformer so you can
determine how many turns you will need for
a given application.
I can tell you before you start though, plan
on spending LOTS of hours doing something like
this. I doubt it is worth it really, unless
you have a very pressing application or
something.
On the other hand, adding turns isnt that hard
as long as there is room in the core window.
It might help if you stated what you are trying to
do with this.
Good luck with your LED circuits,
Al