About the Inductor Energy Calculator
The Inductor Energy Storage Calculator finds how much energy is stored in an inductor's magnetic field when it's carrying a steady current. It's the electrical counterpart to a capacitor energy calculation, useful for anyone sizing chokes, transformers, or energy storage components in a circuit. Because the relationship depends on current squared, the calculator also shows how sensitive stored energy is to changes in operating current, something worth checking when sizing a component for an application like a boost converter or flyback transformer.
How It Works
Enter the inductor's inductance in millihenries and the current flowing through it in amps. The calculator converts inductance to henries, applies the standard magnetic energy formula, and reports the stored energy in millijoules.
Formula & Methodology
Convert the inductance from millihenries to henries by dividing by 1000. Square the current value, multiply by the inductance in henries, then multiply by one-half to get energy in joules. Multiply by 1000 to express the result in millijoules, which is a more readable scale for typical small inductors. As a quick hand check, an inductor rated at 220 mH carrying 1.5 A stores 0.5 x 0.22 x 1.5^2 = 0.2475 J, or 247.5 mJ.
Examples
Power inductor at rated current
A 100 mH inductor carrying 2 A of steady current stores energy = 0.5 x 0.1 x 2^2 = 0.2 J, shown as 200 mJ.
Small signal inductor
A small 10 mH inductor carrying 0.5 A stores energy = 0.5 x 0.01 x 0.5^2 = 0.00125 J, shown as 1.25 mJ.
Advantages
- Handles the millihenry-to-henry unit conversion automatically, so inputs can be entered in the units typically printed on inductor datasheets.
- Makes the squared relationship between current and stored energy immediately visible by comparing results at different current levels.
- Useful alongside a capacitor energy calculation for comparing how much energy different reactive components, coils versus capacitors, can store side by side in the same circuit design.
Common Mistakes
- Entering inductance directly in henries when the field expects millihenries, which would produce a result 1000 times too large.
- Assuming energy scales linearly with current, since the formula's squared current term means a modest current increase produces a much larger jump in stored energy.
- Treating stored magnetic energy as available instantly, in practice an inductor releases this energy over time as current decays, governed by the circuit's time constant.
Edge Cases to Watch For
- Because current is squared, doubling current quadruples stored energy, a detail worth checking if you're comparing two different operating currents for the same inductor.
- The calculator accepts any numeric inductance and current without a positivity check, so a negative current still returns a positive energy value since it's squared, matching the real physics.
- This formula gives the energy stored at a steady current, it doesn't account for the time it takes current to ramp up to that level, which depends separately on the circuit's resistance and applied voltage.
- The formula doesn't factor in a real inductor's core saturation limit, past a manufacturer's rated maximum current, additional current no longer stores energy in proportion to I squared because the magnetic core stops behaving linearly.
Common Use Cases
- Electronics students and hobbyists working through magnetic energy storage problems.
- Circuit designers estimating energy storage in chokes or inductive components for power supply design.
- Engineers comparing inductors and capacitors as energy storage elements in a given application.