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Re: Coil Formers.
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To: tesla-at-grendel.objinc-dot-com
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Subject: Re: Coil Formers.
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From: "Malcolm Watts" <MALCOLM-at-directorate.wnp.ac.nz>
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Date: Sun, 17 Dec 1995 12:38:42 +1200
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>Received: from rata.vuw.ac.nz (root-at-rata.vuw.ac.nz [130.195.2.11]) by uucp-1.csn-dot-net (8.6.12/8.6.12) with ESMTP id QAA04634 for <tesla-at-grendel.objinc-dot-com>; Sat, 16 Dec 1995 16:05:28 -0700
COIL MEASUREMENTS
*****************
(a) Coils of varying h/d ratio. (frequencies in kHz)
NB - frequency has been rounded to the nearest 1kHz so the tables could
be fitted in a reasonable space.
COIL1 | SPHERE | TOROID
| NO TERM | |
Height| | 0.7" | 7.0" | 0.7" | 7.0" | 17.3"
---------------------------------------------------------------------------
h/d | f Q | f Q | f Q | f Q | f Q | f Q
---------------------------------------------------------------------------
5 | 190 351 | 159 300 | 149 317 | 179 299 | 128 290 | 121 269
4 | 224 393 | 184 347 | 172 318 | 152 292 | 146 316 | 138 286
3 | 276 389 | 221 356 | 205 341 | 178 301 | 171 323 | 163 291
2 | 367 353 | 284 326 | 262 339 | 222 288 | 216 322 | 207 283
1 | 600 285 | 438 267 | 401 299 | 330 233 | 327 261 | 316 256
0.56 | 890 182 | 644 220 | 587 243 | 476 208 | 477 227 | 465 226
---------------------------------------------------------------------------
h/d = 4 with bottom turn 13" off floor : f = 222, Q = 363
h/d | 0.56 | 1 | 2 | 3 | 4 | 5
L (mH)| 4.02 | 9.0 | 20.75 | 33.2 | 45.6 | 57.45
COIL2 | SPHERE | TOROID
| NO TERM | |
Height| | 0.7" | 7.0" | 0.7" | 7.0" | 17.3"
---------------------------------------------------------------------------
h/d | f Q | f Q | f Q | f Q | f Q | f Q
---------------------------------------------------------------------------
5 | 186 286 | 169 232 | 145 227 | 176 234 | 125 204 | 118 178
4 | 220 329 | 205 233 | 168 258 | 149 225 | 142 225 | 135 204
3 | 274 351 | 216 292 | 201 275 | 174 232 | 168 243 | 160 231
2 | 371 399 | 280 325 | 259 307 | 219 237 | 213 266 | 204 239
1 | 605 451 | 433 336 | 397 325 | 326 237 | 323 271 | 312 256
0.56 | 899 392 | 632 353 | 577 326 | 467 253 | 467 279 | 456 274
---------------------------------------------------------------------------
h/d = 3 with bottom mounted 13" off floor : f = 272, Q = 339
h/d | 0.56 | 1 | 2 | 3 | 4 | 5
L (mH)| 4.2 | 9.05 | 20.7 | 33.1 | | 56.6
NOTES: I forgot to get inductance reading for h/d=4 for Coil 2 :(
: A reality check on Coil 2 (h/d=1) Q reveals that the resonant
frequency measured is within 1% of that calculated using the
measured inductance and Medhurst's self-capacitance formula.
The Q gives an AC resistance of around 75 Ohms including the
generator and coax and strap used to feed the coil. The clear
message is : If you are using 100 Ohms+ in series with your
coils to measure them, you are not doing them justice.
: One final note; I only recorded the data at the time of measurement
and did not calculate BW and Q so my judgement would not be
clouded by seeing the results. I consider the results to be
entirely consistent with well established theory. On the basis
of these results, I have wound two coils on these formers for
powered use, one close-wound using 0.9mm wire and one spaced
using 0.56mm wire with a wire/pitch ratio of about 0.5.