inductor core materials ferrite iron powder

[Doug Coulter]

Recent work with RF and "almost RF" has had me looking at various core materials...which I found some nice cheat sheets for, but not as pdf, so links here:

Ferrites:
https://www.fair-rite.com/materials/ (lots of these on amazon)

Iron powder:
https://www.micrometals.com/materials/pc

Happy winding...

[johnf]

both Fair-rite and Micrometals are some of the very original makers of these materials and most others copy what they do / or try to and give confusing data out as to the maerial properties.
type 43 and 61 for HF ferrites and type 0 type 2 type 5 for powedered iron

[Doug Coulter]

Yeah. I've been using 61 for this range (around a MHz) - least loss it seems. 43 seems to not quite work, too much permeability? Hysteresis loss? Gets real hot at any rate. Dunno.
I use type 2 iron when I can handle the turns count.
Type 77 or equivalent at the ultrasonic/switching supply range. I have some bars and Cs of that stuff, 1" sq cross section...nice for big power.

Type 61 seems a little rare and pricey, and I'd love to get a real amount of that stuff, as it looks like I'm about to do something like this:
http://w5jgv.com/4-400A_600M_amplifier/
Holy gonzo tank coil, batman!

[Doug Coulter]

A bit of interesting text I found on saturation of these guys. Might be a little over simple, but...seemed worth saving.

The crux of the problem is to avoid DC biasing the core far enough up on its
BH curve to approach flux saturation, at which point the (incremental)
permeability rapidly decreases. At this point and beyond your inductor becomes
a
resistor! The objective is to keep the values of B/H well below this point.

For the ferrites commonly used in RF work, the BH curves are very narrow and
almost rectangular. The onset of saturation is very close to "clipping", and
for the most popular materials (44,73,77,43) this point may be taken as 1 Oe
(call that Hmax). For HF above 10MHZ, type 61 is usually more preferable and
its
Hmax is 3Oe. This Hmax is the 'magic' number for this issue, and it is always
clearly stated in mfr. data.

Given Hmax, which will be 1Oe. almost always, the calculation of the maximum
DC bias current is simple: I=.8 x Hmax x length(cm). The last quantity is
simply the magnetic path length, which for a toroid is equal to the mean
diameter. It is always given in mfrs. specs for most geometries. So, for a .5"
toroid
(length=3cm) and 1Oe. the maximum current is simply .8 x 1 x 3=2.4A. (a/k/a
ampere-turns).

The parameters of magnetic materials are not precision quantities and are all
quite temperature/aging and process dependent compared to other materials.
Hence, it is foolish to attempt to make highly-precision calculations based on
them. In particular, the 'Hmax' value should be regarded as a (good)
approximation and one should not try to push the limit (e.g. aim for
Hmax=.95Oe. by
using as many turns of wire as possible.) A good practical rule used by me and
many that I know, is to stay below 50% of Hmax. This would be .5Oe for the
noted
materials. This will guarantee that your choke or coil will always be on the
lower portion of the BH curve where losses are lowest. Hence, the working rule
is simply: Imax=.5 x length(cm) A. or IOW 500ma. per cm. (For 61 material this
would be 1.5 amps/cm).

The value of length can be easily measured by eye if you don't have data
sheets. Just measure the mean diameter (half-way between the center hole and
the
OD) and calculate: length=PI x diameter. Mfrs. of binocular cores typically
don't give this number, but you can easily estimate it by visualizing the core
as
two side-by-side toroids with a little fill-in material. (This type of core
has no real benefit for ordinary chokes of this type and I recommend ordinary
toroids or pot-cores, but if you have 'em laying around, why not use 'em.)

The very highest frequency materials (e.g. 67 and 68) have loops that are not
nearly so rectangular, so it is not as feasible to summarize them with a
single, basic number (Hmax) as done above. For these materials, which are VERY
important at 30MHZ and above, you should consult the data sheet for each case.

73 and happy winding,
Eric von Valtier K8LV