Howard wrote:

I can't find the answers to these in the books and I've wondered about them
for years.
When winding a coil on a standard (say 1/4") former with ferrite or iron
dust core, should the secondary be wound adjacent to the "hot" end of the
primary or the earthy end? Also, should the earthy end of the secondary be
adjacent to the primary hot end or earthy end?
What's the difference between dust iron and ferrite cores and can you tell
the difference by just looking at them?
Thanks. Howard.


Usually you would wind the secondary on the ground end of the primary,
because you'll get less capacitive coupling from the primary to the
secondary. The direction of the secondary probably matters much less.

Iron dust cores are made with various different iron compounds ground to
dust and bound in a matrix of some sort of plastic (they probably use
epoxy or phenol, but I don't really know). Ferrite cores are made with
various different ceramics that include iron. The surface of ferrite
cores usually look more solid, less porous. Iron cores can be scratched
or cut with steel tools. The ferrite cores I've used are quite hard.

Just knowing that a core is iron or ferrite won't help you much, because
there's a whole bunch of different mixes of each.

Ferrite cores usually have higher permitivity, which means more
inductance for the same number of winds. They also usually saturate
quicker, which means that they aren't as good for resonant circuits or
for filters.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

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