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ZS6TMV > TECH 30.06.06 00:49l 352 Lines 17440 Bytes #999 (0) @ WW
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Read: OE5RCO DL1LCA DL8ZX GUEST
Subj: Toroid chart
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From: ZS6TMV@ZS0MEE.SRJ.GAU.ZAF.AF
To : TECH@WW
While I was looking for data on toroid cores, I came across the following.
It's described as an "oldie" so you may have seen it before and, upon
reading this, moan "Oh, not again..." But if it's new (and useful) to me
it may be so to someone else, so I just thought I'd share it.
====================[ cut ] =========================
TOROID INDUCTANCE CHARTS
Michael A. Czuhajewski WA8MCQ
7945 Citadel Drive
Severn, MD 21144
*****************************************************************
This article originally appeared in the QRP Quarterly for October
1992, page 9. Copyright 1992, Michael A. Czuhajewski. Non-commercial
reprinting or reposting permitted with proper credit.
*****************************************************************
This article is a "golden oldie", of sorts. I wrote the first version
in 1988 and have been trying, half-heartedly, since then to get it
into the QRP Quarterly. It's not that it's a bad article, just that
there were some substantial logistical problems in getting it from my
computer to the publishers typesetting computer, since I didn't own
an IBM compatible until 1991. Things started looking up when I got
volcano'ed out of the Philippines, had to abandon my TRS-80 computer
and buy a new one, this time an IBM compatible. Now I could send an
ASCII disk. And then Maryland Radio Center, the ham store where I
work, eventually upgraded to a '386 computer with laser printer, and
now I can submit camera-ready copy to the editor, totally eliminating
all middle-men. (My deepest thanks to MRC owner Jerry Johnson,
WA3WZF, for use of his computer.)
Now for the 397th rewrite of the text... Getting back into ham radio
in 1986 after an absence of over 15 years, I began poring over the
tremendous number of homebrew articles that I missed in the interim.
In comparing design features of various projects using toroids, I
often had to convert winding data to inductance or vice versa. At
other times, I found myself building something and didn't have the
exact size of core called for.
I got tired of hauling out the Amidon charts every time, hunting up
the formula and Al value, digging out the calculator and doing the
calculations. That seemed like a lot of unnecessary work,
reinventing the wheel each time (how often did I calculate the
inductance for 15 turns on a T50-2 core?), along with the ever
present possibility of making mistakes when applying the formulas.
It would be much quicker and simpler to refer to a chart and
instantly see that X turns on core Y gives Z microhenries, and how
many turns on another core would give approximately the same. The
obvious answer, then, was to write a BASIC program to compute and
print out, once and for all, the inductance per turn for a variety of
the most commonly used toroids. Amidon provides similar charts, but
only in multiples of ten turns. Mine are tailored to the coils and
cores most often used by QRPers.
USING THE CHARTS
Inductance for a given number of turns can be read directly from the
charts. When looking for the number of turns required to obtain a
specific inductance, simply choose the nearest inductance value from
the chart under the core(s) of interest and read across. (It is
assumed that you already know which core material is suitable for the
application at hand, having considered operating frequency, Q, etc.)
While I could have run off a second set of charts indexed by
inductance rather than turns, it would have been much larger and
would also have given results in fractions of turns, which are not
practical to implement on toroids. If a slightly different value of
inductance is required than that shown on the chart, the winding can
be compressed or expanded slightly.
I originally made charts for every core size within these 4
materials, which are the most commonly used types. It ran to 11
pages, but I quickly realized that only a small number of sizes were
used most of the time. (Do you remember the last time YOU used a
T157-2 core?) Also, most coils use a relatively small number of
turns, hence the cut-off at 35. In those relatively rare cases where
some other size or material is used, or more turns, you can consult
the published information, such as an Amidon flyer, and apply their
formulas.
I moved the output of the BASIC program over to the word processor
and dressed it up, including rounding off the values. There wasn't
much point in showing additional decimal places; it implied a degree
of precision that is unattainable in practice, as well as cluttering
up the charts. (If you put 21 turns on an FT50-43 core, can you
REALLY expect to get precisely 230.643 microhenries?) Anyone who has
ever used a toroid knows how variable the inductance is for a given
number of turns, depending on spacing of the turns as well as
variations in permeability between nominally identical cores. In one
of their catalogs, Micrometals (who makes the powdered iron cores
sold by Amidon) indicates that inductance tolerance, due to core to
core permeability variations, is plus or minus 5%
By the way, I've noticed over the years that under some circumstances
the published Al values seem to be little more than a general guide
to the actual inductances you'll get, and need to be taken with a
grain of salt. I've done a fair amount of experimenting with my
Boonton 260A Q meter, and notice that when I get to low values of
inductance the "apparent Al value" deviates from the published value.
This is most apparent with coils under one microhenry. The villains,
which become significant factors at low inductance values, are the
distributed capacitance of the coil, which makes the "apparent
inductance" appear larger than the "true inductance", and the lead
length. Even straight wire has finite inductance, and it adds up.
HOW MUCH WIRE TO USE?
Next, a different chart of great usefulness--how to figure out how
much wire you need to wind those coils. I originally had this
published in the October 1988 issue of the QRP Quarterly, and it's
time to resurrect it again. You have three choices when winding a
toroid: 1) cut off a random piece of wire which looks like it's long
enough and hope for the best; you'll end up wasting wire or saying
bad things when you run out of wire 5 turns before the end; 2) wind a
single turn with a piece of thread, measure it and multiply by the
number of turns you want; 3) look up the single turn length from the
chart below.
Since I didn't have all core sizes on hand to do the single turn
trick, I used the published dimensions from the Amidon flyer to
figure out the circumferences. I wound some sample coils, and things
didn't always work out right; the figures were the sum of dimensions,
but real wire has finite thickness, and I needed more. After
observing how much more wire was needed, from 7 to 13%, I settled on
a fudge factor of 15%, which should cover just about every case, and
that's built into the charts. On top of that, you also have to
provide extra wire for leads; I usually add two or three inches. If
you just cut the amount of wire shown, you'll end up with a coil that
just fits on the core but no wire left over to connect to your
circuit!
After the original publication, K3TKS pointed out to me that these
values are only good for single layer coils. They don't apply if you
do multiple layers (which we don't normally do in QRP building) or if
you wind bifilar, trifilar, etc; in those cases you're on your own,
but the chart gives a good starting point.
I hope these charts make life simpler for some of you homebrewers out
there; it certainly helps speed things up for me, and makes comparing
circuits and building much more enjoyable.
********************************************************************
Core types T25-2 T30-2 T37-2 T44-2 T50-2 T68-2
Al value 34 43 40 52 49 57
# of turns I n d u c t a n c e i n m i c r o h e n r i e s
1 .003 .004 .004 .005 .005 .006
2 .014 .017 .016 .021 .020 .023
3 .031 .039 .036 .047 .044 .051
4 .054 .069 .064 .083 .078 .091
5 .085 .108 .100 .130 .123 .143
6 .122 .155 .144 .187 .176 .205
7 .167 .211 .196 .255 .240 .279
8 .218 .275 .256 .333 .314 .365
9 .275 .348 .324 .421 .397 .462
10 .340 .430 .400 .520 .490 .570
11 .411 .520 .484 .629 .593 .690
12 .490 .619 .576 .749 .706 .821
13 .575 .727 .676 .879 .828 .963
14 .666 .843 .784 1.02 .960 1.12
15 .765 .968 .900 1.17 1.10 1.28
16 .870 1.10 1.02 1.33 1.25 1.46
17 .983 1.24 1.16 1.503 1.42 1.65
18 1.10 1.39 1.30 1.69 1.59 1.85
19 1.23 1.55 1.44 1.88 1.77 2.06
20 1.36 1.72 1.60 2.08 1.96 2.28
21 1.50 1.90 1.76 2.29 2.16 2.51
22 1.65 2.08 1.94 2.52 2.37 2.76
23 1.80 2.28 2.12 2.75 2.59 3.02
24 1.96 2.48 2.30 3.00 2.82 3.28
25 2.13 2.69 2.50 3.25 3.06 3.56
26 2.30 2.91 2.70 3.52 3.31 3.85
27 2.48 3.14 2.92 3.79 3.57 4.16
28 2.67 3.37 3.14 4.08 3.84 4.47
29 2.86 3.62 3.36 4.37 4.12 4.79
30 3.06 3.87 3.60 4.68 4.41 5.13
31 3.27 4.13 3.84 5.00 4.71 5.48
32 3.48 4.40 4.10 5.33 5.02 5.84
33 3.70 4.68 4.36 5.66 5.34 6.21
34 3.93 4.97 4.62 6.01 5.67 6.59
35 4.17 5.27 4.90 6.37 6.00 6.98
********************************************************************
Core T25-6 T30-6 T37-6 T44-6 T50-6 T68-6
types
Al values 27 36 30 42 40 47
# of turns I n d u c t a n c e i n m i c r o h e n r i e s
1 .003 .004 .003 .004 .004 .005
2 .011 .014 .012 .017 .016 .019
3 .024 .032 .027 .038 .036 .042
4 .043 .058 .048 .067 .064 .075
5 068 .090 .075 .105 .100 .118
6 .097 .130 .108 .151 .144 .169
7 .132 .176 .147 .206 .196 .230
8 .173 .230 .192 .269 .256 .301
9 .219 .292 .243 .340 .324 .381
10 .270 .360 .300 .420 .400 .470
11 .327 .436 .363 .508 .484 .569
12 .389 .518 .432 .605 .576 .677
13 .456 .608 .507 .710 .676 .794
14 .529 .706 .588 .823 .784 .921
15 .608 .810 .675 .945 .900 1.06
16 .691 .922 .768 1.08 1.02 1.20
17 .780 1.04 .867 1.21 1.16 1.36
18 .875 1.17 .972 1.36 1.30 1.52
19 .975 1.30 1.08 1.52 1.44 1.70
20 1.08 1.44 1.20 1.68 1.60 1.88
21 1.19 1.59 1.32 1.85 1.76 2.07
22 1.31 1.74 1.45 2.03 1.94 2.28
23 1.43 1.90 1.59 2.22 2.12 2.49
24 1.56 2.07 1.73 2.42 2.30 2.71
25 1.69 2.25 1.88 2.63 2.50 2.94
26 1.83 2.43 2.03 2.84 2.70 3.18
27 1.97 2.62 2.19 3.06 2.92 3.43
28 2.12 2.82 2.35 3.29 3.14 3.69
29 2.27 3.03 2.52 3.53 3.36 3.95
30 2.43 3.24 2.70 3.78 3.60 4.23
31 2.60 3.46 2.88 4.04 3.84 4.52
32 2.77 3.69 3.07 4.30 4.10 4.81
33 2.94 3.92 3.27 4.57 4.36 5.12
34 3.12 4.16 3.47 4.86 4.62 5.43
35 3.31 4.41 3.68 5.15 4.90 5.76
********************************************************************
Core types FT23-43 FT37-43 FT50-43 FT23-61 FT37-61 FT50-61
Al values 188 420 523 24.8 55.3 68
# of turns I n d u c t a n c e i n m i c r o h e n r i e s
1 .188 .420 .523 .025 .055 .068
2 .752 1.68 2.09 .099 .221 .272
3 1.69 3.78 4.71 .223 .498 .612
4 3.01 6.72 8.37 .397 .885 1.09
5 4.70 10.5 13.1 .620 1.38 1.70
6 6.77 15.1 18.8 .893 1.99 2.45
7 9.21 20.6 25.6 1.22 2.71 3.33
8 12.0 26.9 33.5 1.51 3.54 4.35
9 15.2 34.0 42.4 2.03 4.48 5.51
10 18.8 42.0 52.3 2.48 5.53 6.80
11 22.7 50.8 63.3 3.00 6.69 8.23
12 27.1 60.5 75.3 3.57 7.96 9.79
13 31.8 71.0 88.4 4.19 9.35 11.5
14 36.8 82.3 102 4.86 10.8 13.3
15 42.3 94.5 118 5.58 12.4 15.3
16 48.1 107 134 6.35 14.2 17.4
17 54.3 121 151 7.17 16.0 19.7
18 60.9 136 169 8.04 17.9 22.0
19 67.9 152 189 8.95 20.0 24.5
20 75.2 168 209 9.92 22.1 27.2
21 82.9 185 231 10.9 24.4 30.0
22 91.0 203 253 12.0 26.8 32.9
23 99.5 222 277 13.1 29.3 36.0
24 108 242 301 14.3 31.9 39.2
25 118 262 327 15.5 34.6 42.5
26 127 284 354 16.8 37.4 46.0
27 137 306 381 18.1 40.3 49.6
28 147 329 410 19.4 43.4 53.3
29 158 353 440 20.9 46.5 57.2
30 169 378 471 22.3 49.8 61.2
31 181 404 503 23.8 53.1 65.3
32 192 430 536 25.4 56.6 69.6
33 205 457 570 27.0 60.2 74.1
34 217 486 605 28.7 63.9 78.6
35 230 515 641 30.4 67.7 83.3
********************************************************************
Wire Length vs. Turns--
(Be sure to include a few extra inches for leads--lead length is NOT
included here!)
Size Inches per turn Size Inches per turn
FT23 .26 T37 .49
FT37 .5 T44 .61
FT50 .68 T50 .67
FT50A .79 T68 .8
FT50B 1.37 T80 .92
FT82 .93 T94 1.16
FT87A 1.53 T106 1.57
FT114 1.13 T130 1.6
FT114A 1.7 T157 2.02
FT140 1.73 T184 2.66
FT150 1.44 T200 2.13
FT150A 2.01 T200A 3.16
FT193 2.22 T225 2.24
FT193A 2.51 T225A 3.28
FT240 2.3 T300 2.39
T12 .19 T300A 3.54
T16 .23 T400 3.51
T20 .29 T400A 4.31
T25 .37 T500 4.28
T30 .47
[1995 note--that's not a typo--the list does go from FT82 to FT87A;
not sure why I didn't include FT87, and I'm too lazy to go back and
do the calculations for it :-) ]
--qrp--
Author: Mike Czuhajewski, user of the UniBoard System & abs.net
E-Mail: Mike.Czuhajewski@bbs.abs.net
The WB3FFV Amateur Radio BBS - Located in Baltimore, Maryland USA
Supporting the Amateur Radio Hobby, and TCP/IP InterNetworking
73 - Frank, ZS6TMV @ ZS0MEE
Message timed: 16:38 on 2006-Jun-27
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