Nichrome coil calculation
How to Calculate a Nichrome Coil
In thermal elements of electric appliances, the coil is usually wound "by eye". The required number of turns and heating temperature is selected after switching on the mains. This not only wastes time, but also the nichrome filament. If you read the table below, you can make a preliminary calculation for the voltage of 220 V with the known specific resistance of nichrome = 1.12 Ohm-mm2/m. The table allows you to determine the winding length "turn to turn", taking into account the thickness of the filament and the diameter of the rod on which the coil is wound. The length of the wire under voltage 127V is recalculated using a mathematical proportion.
The notation in the table is: D - rod diameter, mm; L - spiral length, cm.
| NiCr 0.2 mm dia. | diameter of nichrome 0,2 mm | diameter of nichrome 0,3 mm | diameter of nichrome 0,3 mm | nichrome 0,4 mm dia. | nichrome 0.4 mm dia. | nichrome 0.5 mm dia. | nichrome 0.5 mm dia. | nichrome 0.6 mm dia. | nichrome 0.6 mm dia. | nichrome 0.7 mm dia. | nichrome 0.7 mm dia. | nichrome 0.8 mm dia. | nichrome 0.8 mm dia. | nichrome 0.9 mm dia. | nichrome 0.9 mm dia. | nichrome 1.0 mm diameter | 1.0 mm diameter nichrome |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| D | L | D | L | D | L | D | L | D | L | D | L | D | L | D | L | D | L |
| 1,5 | 49 | 1,5 | 59 | 1,5 | 77 | 2 | 64 | 2 | 76 | 2 | 84 | 3 | 68 | 3 | 78 | 3 | 75 |
| 2 | 30 | 2 | 43 | 2 | 68 | 3 | 46 | 3 | 53 | 3 | 62 | 4 | 54 | 4 | 72 | 4 | 63 |
| 3 | 21 | 3 | 30 | 3 | 40 | 4 | 36 | 4 | 40 | 4 | 49 | 5 | 46 | 6 | 68 | 5 | 54 |
| 4 | 16 | 4 | 22 | 4 | 28 | 5 | 30 | 5 | 33 | 5 | 40 | 6 | 40 | 8 | 52 | 6 | 48 |
| 5 | 13 | 5 | 18 | 5 | 24 | 6 | 26 | 6 | 30 | 6 | 34 | 8 | 31 | 8 | 33 | ||
| 6 | 20 | 8 | 22 | 8 | 26 | 10 | 24 | 10 | 30 | ||||||||
| 10 | 22 |
For example, it is necessary to determine the winding length of a 0.5 mm nichrome wire on a rod Ø 5 mm for voltage 127 Volts. The table shows that the length of such a wire for 220 Volts = 30 cm. Then follows the arithmetic proportion: 220 V - 30 cm 127 V - X cm, then: X =127x30 / 220 = 18 cm. Having wound the wire, connect it to the mains and make sure that everything is correct. For closed spirals, increase the winding length by one-third of the value given in the table. (V. DOROGOV Modelist-Constructor, 1986)
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