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 (V) (V)

Required number input.

Coil Resistance (Ω) (Ω)

Required number input.

Calculate DC contactor-coil steady current from applied voltage and DC coil resistance; do not use this for AC inrush or inductive impedance. 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]

Coil Current (A) (A)

The resulting coil current (a) returned as a number.

• Compact electronics formulas omit some combination of tolerances, temperature drift, bandwidth, loading, parasitics, noise spectrum, nonlinearity, clipping, calibration, layout, and device-specific limits. Typical datasheet values are not guaranteed limits.
• 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 Power

  Calculate DC relay-coil electrical power as applied voltage squared divided by coil resistance; AC impedance is outside this model.

• Dc Motor Armature Current

  Calculate DC motor armature current from applied voltage, back EMF, and winding resistance using the steady-state armature equation.

• Battery Internal Impedance

  Estimate DC battery internal resistance from the voltage drop between two load-current operating points measured over a short interval.