Inductor Energy: A Coil Current Stores Energy Before Switching Opens

Keep joules and watts distinct

For a constant-inductance model, stored magnetic energy is ½LI². Steady resistive dissipation belongs to a separate resistance term. Primary reference: inductor energy.

Stored energy describes a state at a stated current. Power describes a rate of energy transfer. A coil wattage alone therefore does not tell the reviewer how much energy its selected inductance model contains when switching opens.

A fictional coil calculation

Assume an idealized inductance of 0.20 H carrying 0.50 A. Its stored energy is 0.5×0.20×0.50² = 0.025 J. At 1.0 A with the same inductance, that energy becomes 0.10 J. Doubling current quadruples this modeled energy.

If a separate winding resistance is 10 Ω, resistive dissipation at 0.50 A is 2.5 W. Multiplying that power by a 10 s hold gives 25 J of resistive energy over the interval. It is not the 0.025 J magnetic energy snapshot. These invented values describe no installed HM coil.

Ask where the energy goes

List inductance condition, current history, winding resistance and the event of interest. A changing armature position or magnetic saturation can invalidate a constant-L approximation.

A switch-off assessment also needs the actual recirculation or clamp path and device limits. Record that as a separate review item instead of selecting suppression from this energy figure alone. The useful outcome is a budget that distinguishes stored energy, ongoing heating and subsequent energy transfer.

Customer Questions

Primary References

These references support the technical principles discussed in this guide. The worked examples and review questions are educational.

• Primary reference: inductor energy