If Newton’s Third Law is “equal and opposite reaction”, then Lenz’s Law is “nature will actively attempt to ruin your day whenever magnetic fields change.”
🧲 The Physics of Spite
When you put 12V across a DC motor, current flows, magnetic fields build up, and the rotor spins. Great!
Except the moment the rotor spins, a copper wire is moving through a magnetic field. And what happens when a copper wire moves through a magnetic field? It becomes a generator.
And which way does that generated voltage (Back-EMF) point?
Directly backwards into your power supply.
As your motor spins faster (), the back-EMF grows larger (), until the net voltage driving current into the motor drops to near zero.
🏎️ Why Your Car Accelerates Hardest at 0 RPM
This is why an electric car (or a high-torque brushless DC motor) kicks your head back the second you touch the pedal at a red light, but tapers off at high speeds:
- At 0 RPM: Maximum current (), Maximum Torque ().
- At Top Speed: Almost zero current, zero torque left to accelerate.
Nature literally built a physical governor into electromagnetism. You don’t need a software speed limiter — Faraday and Lenz already programmed one into the fabric of space-time in 1834.
💥 The Flyback Diode (Or: How to stop inductors from killing your MOSFETs)
When you suddenly turn OFF a motor, the current wants to drop to zero instantly ().
Inductors HATE changing current:
If is massive, spikes to hundreds of Volts in nanoseconds. The inductor will literally generate a 300V spark across the silicon junction of your 30V MOSFET just to keep the current flowing.
That’s why every schematic I draw for Athera Motion Core has Schottky flyback diodes or active clamping — because inductors have anger management issues. ⚡