Regulator for Dynamo Machines

Tesla's regulators for dynamo-electric machines, patented in 1886 including U.S. Patent 336,961, employed auxiliary brushes and shunt connections to automatically stabilize output current and voltage. In series-wound dynamos, a third brush tapped an intermediate point on the field coils, shunting excess energy to prevent overload as demand varied. By adjusting brush positions relative to the commutator—manually or automatically—the regulator balanced excitation, maintaining consistent performance irrespective of load fluctuations or frictional losses.

These early patents demonstrated Tesla's mastery of self-regulating systems, facilitating stable power in arc lighting and early grids. The "third brush" method enhanced self-excitation in high-resistance fields, improving startup and operation. Foundational to automatic voltage regulation, they influenced generator controls in power plants. Today, similar principles appear in automotive alternators and stabilizers, ensuring reliable electricity supply in varying conditions.