An inductor (coil) resists changes in current. When you're driving current through it and suddenly stop, the coil doesn't just go quiet — it generates a voltage spike in the opposite direction, trying to keep the current flowing. This is back-EMF (electromotive force), and it's a direct consequence of Faraday's law of induction.
The voltage spike can be much higher than the original driving voltage. A 12V circuit driving a coil can produce back-EMF spikes of hundreds of volts. This is how car ignition coils work: a 12V battery pulse through a coil creates a 20,000V+ spike that fires the spark plug.
Why it matters for Open Energy
Back-EMF represents energy that was stored in the coil's magnetic field being released. In a conventional circuit, this energy is dissipated — it gets absorbed by a flyback diode or snubber circuit to protect the switching transistor.
Several Open Energy experiments ask: what if you capture that energy instead of wasting it? The Back-EMF Energy Recovery Circuit experiment builds a recovery path that routes the back-EMF spike into a storage capacitor, then measures how much energy comes back compared to how much went in.
This connects directly to pulsed excitation — pulsed drive produces back-EMF on every cycle. If the recovery is efficient enough, each cycle returns more energy than a simple analysis predicts.