EMRFD Message Archive 4

Message Date From Subject
4 2006-07-10 12:42:39 Stan Use of power iron core and power question
This may be in the book, but i have not found it. But think it needs
to be in the book.

We use a lot of -2 and -6 material in our QRP rigs. But what size
should we use for the power developed (AC-RF) and DC flowing in the

Again we use a lot of T50 size, but at what power level should we move
to T106, etc.

Can anyone direct me to a table, equations, or web page on this topic?

Thanks, Stan
5 2006-07-10 20:04:47 Roger Hayward Re: Use of power iron core and power question
Hi Stan.

I'm going to try to answer this for you, although I'm afraid I might
be answering a slightly-different question.

I added the link to Amidon Associates web site to the group page
(www.amidoncorp.com) as well. These guys continue to be fantastic,
mainly because they will cater to hams (low quantity).

My intuition wants to say that power won't be an issue for these
cores. (Amidon's specifications make no mention of maximum fields
induced, etc.) I should qualify that with what I've seen. In
general, I believe the -2 and -6 cores are good for most-any power
level in the QRP range. I'd go out on a limb and say that even the
50W range should be fine.

The different sizes of each core will vary the inductance per turn
squared. The rule of thumb I've been taught (through my strict
upbringing, hi) was to pick a core which will have windings that
will (more or less) fill the core. In other words, a T50-2 would
have more than 3 windings on it, and probably less than 20
windings. If I need more turns than that, I'll choose a larger core
(and compute the inductance for that core).

It is a simple exercise (and a good one to do), to compute the
inductance per turn for both the -2 and -6 material, in all
diameters. This can be accomplished very quickly with a spreadsheet.

So I don't know if I've answered your question as best I could,
skirting the issue about power. Remember that the thinner gauge
wires will be resistive, so you'll get heat (I^2 * R) if there's too
much DC bias in the lines. But at <100W levels, I can't believe
that the cores would get upset at too much magnetic field.

(Anyone else want to join in
6 2006-07-10 20:36:21 Stan Re: Use of power iron core and power question
Thanks Roger, your intuition is very good for the T50-2. I cast a
wide net for information and one of the things that came back was
that micrometals has an application paper on their web site that
says the T50-2 is good for 49 watts and the T106 for over 200 watts.
Based on a 25 degree C rise in temperature.

So we are safe with our QRP and QRPp rigs. hi

I am working on a glowbug design using 5763s and want to use all
power iron cores for the RF coils. It appears that the T106 will
be over kill but should work great. I am designing a basic push-
pull LC stage for the final and was worried about the combined RF
and DC currents on the -2 material. I am also going to try using
RF-174 for the output link and use its shield as a Faraday shield
with just one end grounded.

Anyhow that's my play project with the powered iron.

Cheers, Stan ak0b
7 2006-07-11 07:38:02 John Levreault Re: Use of power iron core and power question
There was an article in _QEX_ for 3/95, reprinted in the original _QRP
Power_ (starting on page 2-20) written by Zack Lau that discussed power
limits of toroids.

In addition, he's got 5 pages of Q data for toroidal chokes over a wide
range of values.

I think this article might be helpful. Let me know if you need a copy.

de John NB1I

11 2006-07-12 10:53:39 Chuck Re: Use of power iron core and power question -- W1FB's Info Flux
Stan and All,

Another source that might be useful is in "W1FB's Design Notebook"

On page 84 he describes the requirements and calculations needed to
prevent exceeding flux density of cores.

The equation he gives is: B(max) = Erms x 10^8 / 4.44fNAe Gauss

B(max) is maximum core flux density, Erms is the AC or RF Voltage, Ae
is the equivalent area of the magnetic path in cm^2, f is the
frequency in Hz and N is the number of inductor turns.

The book is copyrighted so permission would be needed to reproduce the

He, W1FB, also mentions another of his books: "Ferromagnetic Core
Design and Application Handbook" 1981 Prentice-Hall, Inc.