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RL time constant calculator

Calculates the RL time constant, current rise and decay, stored inductor energy, and the switch-off voltage spike with clamp comparison.

Enter a coil and its supply to time it.

tau = L/R sets everything here: the current climbs toward V/R along the same 63.2, 86.5, 99.3 percent ladder a capacitor follows, and decays along the mirror. The stored energy is half L I squared. The kickback figure is L times the current change over your switch-off time, which is an order-of-magnitude estimate, not a prediction: it assumes constant inductance, ignores saturation, and assumes the interruption is clean. Real coils arc, real switches avalanche, motor windings push back with their own EMF. If you are switching an inductive load for real, have the suppression design checked by a qualified engineer.
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