The primary difference between brushless and brush generators lies in their method for transferring DC power from the exciting current to the generator's magnetic fields. According to EmergencyPower.com, generators produce current by moving an exciter, or mobile electromagnet, against the field generated by a stator, or stationary, electromagnet. This distorts the field and generates an electric current.
The current requires that both electromagnets be imbued with an exciter current in the form of a DC feed. The exciter hardware rotates within the generator and transfers that energy to the magnets. Where the two designs differ is at the point of DC transfer to the stator and exciter. A brush system employs rotating brushes to build up a static charge that can then be transferred to static slip rings that are kept in contact with the brushes, according to EmergencyPower.com.
A brushless generator, in contrast, typically uses a solid-state rectifier assembly in place of the brushes and rings. This assembly contains no moving parts. This is important, as it makes the system more reliable and less prone to mechanical breakdown, jamming or seizing as a result of obstructions in the casing. Instead, a continuing charge is built up by transferring a portion of the generator's AC charge back into the exciter.