Nichrome Wire and Heating Coil Calculation
Preliminary nichrome wire and coil calculation
A nichrome heating element is normally selected from the required voltage and power, the resistance per unit length of the chosen alloy and diameter, and the permitted surface loading. The table below is a historical preliminary guide, not a substitute for an electrical and thermal design check.
Basic calculation sequence
- Calculate target resistance using R = V² / P.
- Use certified resistivity data for the exact nichrome alloy and wire diameter.
- Calculate wire length, then check coil diameter, pitch, surface loading and operating temperature.
- Prototype and validate the element with appropriate electrical and thermal protection.
Resistance changes with temperature, while alloy, atmosphere, mounting and heat transfer affect service life. A table based on one assumed resistivity and voltage cannot cover every design.
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)
Related nichrome products
See the nichrome and FeCrAl alloy overview, Kh20N80 / Ni80Cr20 nichrome wire and nichrome heating coils.
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