Wire
SWG |
Dia ins. |
Dia mm |
Resistance ohms/1000yds |
Current rating |
Turns per linear inch (ECW) |
Nearest AWG |
10 |
0.128 | 3.25 | 1.866 |
15 |
7.48 |
8 |
12 |
0.104 | 2.64 | 2.826 |
10 |
9.09 |
10 |
14 |
0.080 | 2.03 | 7.776 |
6 |
11.78 |
12 |
16 |
0.064 | 1.63 | 3.5 |
14.8 |
14 |
|
18 |
0.048 | 1.22 | 13.27 |
2 |
19.7 |
17 |
20 |
0.036 | 0.92 | 23.59 |
1.2 |
26 |
19 |
22 |
0.028 | 0.71 | 38.99 |
0.7 |
33 |
21 |
24 |
0.022 |
0.56 | 63.16 |
0.45 |
41.6 |
23 |
26 |
0.018 |
0.46 | 94.4 |
0.3 |
50.2 |
25 |
28 |
0.0148 | 0.38 | 139.6 |
0.2 |
61 |
27 |
30 |
0.0124 |
0.305 |
199 |
0.1 |
72.5 |
28 |
32 |
0.0108 |
0.27 | 262 |
0.1 |
82.7 |
30 |
34 |
0.0092 |
0.229 |
361 |
0.075 |
97 |
32 |
36 |
0.0076 |
0.178 |
529 |
0.05 |
116 |
34 |
38 |
0.0060 |
0.15 | 849 |
0.03 |
145 |
36 |
40 |
0.0048 |
0.016 |
1327 |
0.02 |
178 |
38 |
Note the current rating has been rounded down slightly to give a wider range of safety, so there will be slight differences from other published tables. Additionaly the figures for turns per linear inch are approximations as there will be some variation in thickness of the insulation, and hand winding will not produce the density of windings of a commercially wound coil.
Relative Resistivity
Material |
Resistance Compared to Copper |
Aluminium (pure) |
1.60 |
Brass |
3.7 - 4.90 |
Cadmium |
4.40 |
Chromium |
1.80 |
Copper (hard drawn) |
1.03 |
Copper (annealed) |
1.00 |
Gold |
1.40 |
Iron (pure) |
5.68 |
Lead |
12.80 |
Nickel |
5.10 |
Phosphor bronze |
2.8 - 5.40 |
Silver |
0.94 |
Steel |
7.6 - 12.70 |
Tin |
6.70 |
Zinc |
3.40 |
Dielectric Constants and Breakdown Voltages
Material |
Dielectric Constant | Puncture Voltage |
Air |
1.0 |
21 |
Alumina (99.5%) |
9.0 |
100 |
Bakelite |
4.4 |
300 |
Bakelite (mica filled) |
4.7 |
325 - 375 |
Cellulose acetate |
3.3 - 3.9 |
250 - 600 |
Formica |
4.6 - 4.9 |
450 |
Glass, window |
7.6 - 8.0 |
200 - 250 |
Glass, Pyrex |
4.8 |
335 |
Mica, ruby |
5.4 |
3800 - 5600 |
Mycalex |
7.4 |
250 |
Paper |
3.0 |
200 |
Perspex (Plexiglas) |
2.8 |
990 |
Polythene |
2.3 |
1200 |
Polystyrene, unmodified |
2.6 |
500 - 700 |
Porcelain |
5.1 - 5.9 |
40 - 100 |
Quartz, fused |
3.8 |
1000 |
Steatite, low loss |
5.8 |
150 - 315 |
Teflon |
2.1 |
1000 - 2000 |
Epoxy fibreglass G10 |
4.5 |
15000 |
The term dielectric constant is a misnomer, as this property is frequency dependent. In the above table the value is taken at 1MHz.
Dielectric strength in the above table is measured in volts per mil (V/0.001") at 50Hz. In Tesla and other pulse operation the dielectric is stressed at a far higher level, and allowance must be made for this, a factor of at least 2 should be used as a bare minimum.
Ferrite Toroids
Physical Properties |
||||||||
| Core size | OD | ID | H | Ae | Ie | Ve | As | Aw |
| FT-23 | 0.230 | 0.120 | 0.060 | 0.00330 | 0.529 | 0.00174 | 0.1264 | 0.01121 |
| FT-37 | 0.370 | 0.187 | 0.125 | 0.01175 | 0.846 | 0.00994 | 0.3860 | 0.02750 |
| FT-50 | 0.500 | 0.281 | 0.188 | 0.02060 | 1.190 | 0.02450 | 0.7300 | 0.06200 |
| FT-82 | 0.825 | 0.520 | 0.250 | 0.03810 | 2.070 | 0.07890 | 1.7000 | 0.21200 |
| FT-114 | 1.142 | 0.748 | 0.295 | 0.05810 | 2.920 | 0.16950 | 2.9200 | 0.43900 |
Above dimensions are in inches
| OD - Outer Diameter | Ae - Effective magnetic cross-sectional area (in)2 |
| ID - Inner Diameter | Ie - Effective magnetic path length |
| H - Height | Ve - Effective magnetic volume (in)3 |
| Aw - Total window area (in|)2 | As - Surface area exposed for cooling (in)2 |
Magnetic Properties |
||||||
| Property | Unit | 63-mix | 61-mix | 43-mix | 72-mix | 75-mix |
| Initial permitivity (”i) | 40 | 125 | 950 | 2000 | 5000 | |
| Maximum permitivity (”m) | 125 | 450 | 3000 | 3500 | 8000 | |
| Saturation flux density @ 13 Oersted | Gauss | 1850 | 2350 | 2750 | 3500 | 3900 |
| Residual flux density | Gauss | 750 | 1200 | 1200 | 1500 | 1250 |
| Curie temperature | șC | 500 | 300 | 130 | 150 | 160 |
| Volume resistivity | ohm/cm | 1 x 108 | 1 x 108 | 1 x 105 | 1 x 102 | 5 x 102 |
| Optimum frequency range | MHz | 15-25 | 0.2-10 | 0.01-1 | 0.001-1 | 0.001-1 |
| Specific gravity | 4.7 | 4.7 | 4.5 | 4.8 | 4.8 | |
| Loss factor | 1/”o | 9.0 x 10-5 @ 25MHz | 2.2 x 10-5 @ 2.5MHz | 2.5 x 10-5 @ 0.2MHz | 9.0 x 10-6 @ 0.1MHz | 5.0 x 10-6 @ 0.1MHz |
| Coercive force | Oersted | 2.40 | 1.60 | 0.30 | 0.18 | 0.18 |
| Temperature coefficient of (”i) | %/șC 20-70șC | 0.10 | 0.10 | 0.20 | 0.60 | |
AL Chart (mH per 1000 turns) |
|||||
| Core size | 63-mix | 61-mix | 43-mix | 72-mix | 75-mix |
| ” = 40 | ” = 125 | ” = 950 | ” = 2000 | ” = 5000 | |
| FT-23 | 7.9 | 24.8 | 189.0 | 396.0 | 990.0 |
| FT-37 | 17.7 | 55.3 | 420.0 | 884.0 | 2210.0 |
| FT-50 | 22.0 | 68.0 | 523.0 | 1100.0 | 2750.0 |
| FT-82 | 23.4 | 73.3 | 557.0 | 1172.0 | 2930.0 |
| FT114 | 25.4 | 79.3 | 603.0 | 1268.0 | 3170.0 |
The above data are for Amidon Associates ferrite cores.
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