Calculate inductor voltage spike, inductance, current change, or time from three known values using L, ΔI, and Δt with unit support.

Inductor Voltage Spike Calculator

Enter any 3 values to calculate the missing variable

Related Calculators

Inductor Voltage Spike Formula

The calculator uses the inductor voltage relationship between inductance, change in current, and the time over which that current changes.

V = L * (ΔI / Δt)
  • V = inductor voltage spike, in volts (V)
  • L = inductance, in henrys (H)
  • ΔI = change in current, in amperes (A)
  • Δt = change in time, in seconds (s)

If you leave voltage blank, the calculator solves for the inductor voltage spike:

V = L * (ΔI / Δt)

If you leave inductance blank, it rearranges the same formula:

L = V / (ΔI / Δt)

If you leave change in current blank, it solves for current change:

ΔI = (V * Δt) / L

If you leave change in time blank, it solves for switching or transition time:

Δt = (L * ΔI) / V

The calculator converts all entries to base units before calculating: volts, henrys, amperes, and seconds. It then converts the result back to the unit selected for the missing value.

Common Unit Conversions for Inductor Spike Calculations

Use these conversions to check whether your inputs are in the expected scale.

Quantity Unit Base unit conversion
Voltage 1 kV 1000 V
Inductance 1 mH 0.001 H
Inductance 1 kH 1000 H
Current 1 mA 0.001 A
Current 1 kA 1000 A
Time 1 ms 0.001 s
Time 1 min 60 s

How Transition Time Affects Voltage Spike

For the same inductance and current change, a shorter transition time creates a higher voltage spike.

Inductance Change in Current Change in Time Voltage Spike
10 mH 2 A 100 ms 0.2 V
10 mH 2 A 10 ms 2 V
10 mH 2 A 1 ms 20 V
10 mH 2 A 0.1 ms 200 V

Example Problems

Example 1: Calculate the voltage spike

You have an inductance of 50 mH, a current change of 3 A, and a time change of 2 ms.

Convert units first:

  • 50 mH = 0.05 H
  • 2 ms = 0.002 s
V = 0.05 * (3 / 0.002)
V = 75 V

The inductor voltage spike is 75 V.

Example 2: Calculate the change in time

You have a voltage spike of 120 V, an inductance of 20 mH, and a current change of 6 A.

Convert inductance first:

  • 20 mH = 0.02 H
Δt = (0.02 * 6) / 120
Δt = 0.001 s

The change in time is 0.001 s, or 1 ms.

FAQ

Why does an inductor create a voltage spike?

An inductor resists changes in current. When current through the inductor changes quickly, the inductor generates voltage in response. The faster the current changes, the larger the voltage can be. This is why switching off a coil, relay, solenoid, or motor winding can produce a sharp voltage spike.

Does the formula include polarity?

The calculator gives the magnitude of the voltage spike using V = L × ΔI / Δt. In circuit analysis, the full inductor voltage law can include a polarity sign depending on the chosen current direction and voltage reference. For sizing or estimating spike magnitude, the positive value is usually the useful result.

Why does a smaller time value produce a much larger spike?

The voltage is proportional to the rate of current change. If the same current change happens in one tenth of the time, the voltage spike becomes ten times larger. This is why very fast switching events can create high transient voltages even with relatively small inductors.