inductance

Physical Properties of Coil

Calculate the physical and electrical properties of a wound coil on a bobbin.

The coil is the most recognizable form of an inductor. Both inductors and electromagnets consist of wires wound around a bobbin or core form, and the coiled wire is known as the winding. The center of the coil is referred to as the core.

Each individual loop of wire is called a turn. To prevent short-circuits between turns, the wire needs insulation such as plastic or enamel coating. Finally, to secure the winding, it is often wrapped around a coil form made of materials like plastic. In designing and constructing such a coil, it becomes necessary to estimate the cross-sectional area and resistance of the coil.

About This Calculator

This online electrical calculator helps you calculate the physical characteristics of a coil or material, including resistance, total wire length, and number of windings. The calculator assumes the wire to be copper when calculating resistance and voltage.

Understanding Physical Properties of a Coil

Property	Description
Stiffness	Increases with the fourth power of wire diameter $D_1$ , directly associated with wire density $G$ , and decreases with the cube of mean diameter $D_2$
Diameter ( $D_1$ )	Larger diameters contribute to increased stiffness and greater capacity to endure external pressures like compression and tension
Wire Density ( $G$ )	Greater wire density leads to coils with increased stiffness
Mean Diameter ( $D_2$ )	Demonstrates an inverse relationship with stiffness — smaller average diameters result in lower stiffness
Number of Wraps ( $n$ )	Inverse correlation with stiffness — fewer wraps per unit length corresponds to higher stiffness
Composition	Material type and quantity can impact physical characteristics — certain alloys may offer enhanced corrosion resistance or increased strength
Detachment Mechanism	The way the coil is disconnected, including mechanism type and materials used, can influence physical characteristics and operational effectiveness
Size	Larger coils often exhibit distinct properties compared to smaller counterparts
Shape	The curvature and orientation of the wire can influence physical characteristics and efficiency
Material Properties	Young's modulus, Poisson's ratio, and density of the material influence physical attributes and performance

Applications

Electrical Transformers
Magnetic Resonance Imaging (MRI) Machines
Solenoids
Antennas
Sensors

Conclusion

The performance and appropriateness of coils for diverse applications — including medical equipment, electrical components, and mechanical mechanisms — heavily rely on their inherent physical characteristics.

Formulas

$T = \frac{b_l}{d}$

$n = \frac{\text{Turns}}{T}$

$c_d = (2 \times n \times d) + b_d$

$r = \frac{n \times d + b_d}{2}$

$a = \pi r^2$

$L = \frac{2 \times \pi \times r \times n}{1000}$

$rpm = 0.0333 \times \frac{\left(\frac{0.812}{2}\right)^2}{\left(\frac{d}{2}\right)^2}$

$R = rpm \times L$

$V = R \times I$

$P = V \times I$

where:

$T$ = Turns per winding
$b_l$ = Length of Bobbin
$d$ = Wire Diameter
$n$ = Number of windings
$c_d$ = Outer diameter of the coil
$b_d$ = Diameter of Bobbin
$r$ = Radius of the middle of the coil
$a$ = Cross-sectional area
$L$ = Total Length
$rpm$ = Resistance per meter
$R$ = Resistance
$V$ = Voltage at Rated Current
$I$ = Current
$P$ = Power at Rated Current

Inputs

Wire Diameter(mm)

Diameter of the winding wire in millimetres

Number of Turns

Total number of turns in the coil

Bobbin Length(mm)

Winding length of the bobbin in millimetres

Bobbin Diameter(mm)

Inner diameter of the bobbin in millimetres

Current(A)

Rated current in amps

Results

⚠Wire diameter must be greater than zero

Turns per Winding—Number of turns that fit in one winding layer (bobbin length / wire diameter)

Number of Windings—Number of winding layers required to accommodate all turns

Coil Diameter—mmOuter diameter of the wound coil in millimetres

Cross Sectional Area—mm²Cross-sectional area of the wound coil in square millimetres

Total Length of Wire in Coil—mTotal wire length in the coil in metres

Resistance per Metre—Ω/mResistance per metre based on copper wire resistivity (reference diameter 0.812mm)

Resistance—ΩTotal DC resistance of the coil in ohms

Voltage at Rated Current—VVoltage across the coil at rated current in volts

Power at Rated Current—WPower dissipated at rated current in watts