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.

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

Posting from Google? See http://cfaj.freeshell.org/google/

Tim W. wrote, "Ferrite cores usually have higher permitivity, which
means more
inductance for the same number of winds."

Presumably he means permeability.

You should be able to find both downloadable programs and web applets
which let you find the inductance for a given number of turns, for a
core of particular dimensions and permeability. Using that info, you
can go back to permeability if you measure the dimensions and an
inductance with a known number of turns.

There are also fairly standard color codes for powdered iron toroids,
though, as they say, your mileage may vary. But in general if you find
a permeability below about 50, it's very likely a powdered iron core,
and above that it's much more likely to be ferrite.

You can find some good core info at the Amidon Associates web site, or
at least could the last time I looked. A Google search should turn up
lots of other references.

Cheers,
Tom

K7ITM wrote:

Tim W. wrote, "Ferrite cores usually have higher permitivity, which
means more
inductance for the same number of winds."

Presumably he means permeability.

Yes, he did. They may have more permitivity, as well, but since they're
rarely touted as a dielectric it doesn't make much difference.

You should be able to find both downloadable programs and web applets
which let you find the inductance for a given number of turns, for a
core of particular dimensions and permeability. Using that info, you
can go back to permeability if you measure the dimensions and an
inductance with a known number of turns.

There are also fairly standard color codes for powdered iron toroids,
though, as they say, your mileage may vary. But in general if you find
a permeability below about 50, it's very likely a powdered iron core,
and above that it's much more likely to be ferrite.

AFAIK the color codes vary by company. There is probably overlap, but I
don't think it's "standard".

You can find some good core info at the Amidon Associates web site, or
at least could the last time I looked. A Google search should turn up
lots of other references.

Cheers,
Tom



--

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

Posting from Google? See http://cfaj.freeshell.org/google/

Tim Wescott kirjoitti:


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.

Hi

The great advantage of ferrite materials is just what you said - more
inductance for the same number of winds.
In this way high Q coils can be done. A good example is direction
finding receiver with ferrite rod antenna for magnetical field component
of fox transmitter.

I agree that saturation can be a problem in higher power levells
Anyhow good high power baluns are made with toroids and filament chokes
with ferrite rods for grounded grid linears ( Yes- they are not tuned
resonant circuits )

73, Risto OH2BT