Uploaded December 2024 | Updated September 2026, 2 weeks ago
Cheap & Easy inductor from a plastic Singer sewing machine bobbin. I went with a scatter weave, which seems to have pushed my wire length values up by a third. But it will also produce a cleaner (lower capacitance) coil.
WHY? I'm thinking about how to make a small, cheap, easy to build pocket crystal radio.
MATERIALS & CALCULATIONS & RESOURCES
Singer Bobbin (plastic) 8mm x 7mm (20.5mm sides; 6.2mm hole)
0.22mm = 30 AWG
0.227mm = 31 AWG
--------------------------
https://www.circuits.dk/multilayer-air-core-inductor/
There are 2 wire sizes to allow you to compare how that impacts the results.
Inductance (L): 512 uH
Coil Inner Diameter (d=2*r1): 8 mm
Coil Length (l): 7 mm
Wire Gauge: 30 AWG
Number of Turns (N): 240 turns
Turns per Layer: 25.28 turns/layer
Number of Layers: 9.49 layers
Coil Outer Diameter (D): 13.54 mm (fits in the 20.5 spool)
Wire Diameter: 0.28 mm
Wire Length: 7.8 meters
DC Resistance (R): 2.64 Ω (at 20°C)
---------------------
Inductance (L): 512 uH
Coil Inner Diameter (d=2*r1): 8 mm
Coil Length (l): 7 mm
Wire Gauge: 31 AWG
Number of Turns (N): 247 turns
Turns per Layer: 28.12 turns/layer
Number of Layers: 8.78 layers
Coil Outer Diameter (D): 12.48 mm (fits in the 20.5 spool)
Wire Diameter: 0.25 mm
Wire Length: 7.71 meters
DC Resistance (R): 3.31 Ω (at 20°C)
https://www.circuits.dk/calculator_multi_layer_aircore.htm
pronine.ca/multind.htm
66pacific.com/calculators/coil-inductance-calculator.aspxSelf-inductance Calculator
teslascientific.com/products/coil-inductance-calculator
Cheap & Easy inductor from a plastic Singer sewing machine bobbin. I went with a scatter weave, which seems to have pushed my wire length values up by a third. But it will also produce a cleaner (lower capacitance) coil.
WHY? I'm thinking about how to make a small, cheap, easy to build pocket crystal radio.
MATERIALS & CALCULATIONS & RESOURCES
Singer Bobbin (plastic) 8mm x 7mm (20.5mm sides; 6.2mm hole)
0.22mm = 30 AWG
0.227mm = 31 AWG
--------------------------
https://www.circuits.dk/multilayer-air-core-inductor/
There are 2 wire sizes to allow you to compare how that impacts the results.
Inductance (L): 512 uH
Coil Inner Diameter (d=2*r1): 8 mm
Coil Length (l): 7 mm
Wire Gauge: 30 AWG
Number of Turns (N): 240 turns
Turns per Layer: 25.28 turns/layer
Number of Layers: 9.49 layers
Coil Outer Diameter (D): 13.54 mm (fits in the 20.5 spool)
Wire Diameter: 0.28 mm
Wire Length: 7.8 meters
DC Resistance (R): 2.64 Ω (at 20°C)
---------------------
Inductance (L): 512 uH
Coil Inner Diameter (d=2*r1): 8 mm
Coil Length (l): 7 mm
Wire Gauge: 31 AWG
Number of Turns (N): 247 turns
Turns per Layer: 28.12 turns/layer
Number of Layers: 8.78 layers
Coil Outer Diameter (D): 12.48 mm (fits in the 20.5 spool)
Wire Diameter: 0.25 mm
Wire Length: 7.71 meters
DC Resistance (R): 3.31 Ω (at 20°C)
https://www.circuits.dk/calculator_multi_layer_aircore.htm
pronine.ca/multind.htm
66pacific.com/calculators/coil-inductance-calculator.aspxSelf-inductance Calculator
teslascientific.com/products/coil-inductance-calculator
