Use this electronics calculation for a first-pass component, converter, signal, motor, or sensor estimate when the stated operating conditions and units match the device data.

Coil inductance (mH)

Inductance of the relay coil.

Coil resistance (Ω)

DC resistance of the relay coil.

Pickup voltage (V)

Voltage at which the relay must pick up.

Supply voltage (V)

Applied supply voltage.

Estimate how long an RL relay coil takes to reach its pickup voltage from the L/R time constant. The tool evaluates the supplied inputs together and returns the named outputs below; it does not infer omitted operating conditions or change the units shown.^[1]

Operate time (ms)

Estimated time for coil current to reach pickup.

• Relay timing, coil power, inductance, and bounce depend on coil voltage, temperature, driver, suppression network, mechanical load, contact material, current, and aging. Contact ratings differ for AC, DC, resistive, inductive, and inrush loads.
• Use finite inputs in the displayed units and preserve more precision than the final presentation requires. Independently verify safety-critical, financial, compliance, or production decisions.

Check the result against the current datasheet and worst-case operating corners, then verify the circuit or measurement with simulation and bench testing where failure matters.

• Relay Coil Inductance

  Calculate relay-coil inductance from measured coil resistance and RL electrical time constant using L=Rτ; contact mechanics are not included.

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