How to choose a alternator? The difference between brushed and brushless alternators

1. Brushed alternator

   Key Components: Brushes (stationary) and slip rings (rotating with the rotor).  

   Working Principle: An external DC excitation power source (typically rectified from the generator’s output) supplies DC current to the 

   main rotor’s excitation winding via brushes pressing against the slip rings, creating a rotating magnetic field through this sliding contact.  

   Core Advantages: Cost-effective, straightforward design and manufacturing, relatively simple and low-cost maintenance and repair, 

   excellent low-speed torque performance, high torque output, strong instantaneous load-bearing capacity, and particularly effective in starting large motors.  

   Drawbacks: Brushes are mechanical wear parts that shorten over extended operation, requiring pressure adjustment or replacement. 

   Improper maintenance (e.g., uneven pressure, carbon buildup) can lead to poor contact, sparking, overheating, and even damage to the slip rings.

2. Brushless alternator

   Key Components: Coaxial exciter + rotating rectifier module.  

   Working Principle:  

   - The main rotor drives the rotor (armature) of an exciter mounted on the same shaft.  

   - An initial magnetic field generated by permanent magnets or a small excitation winding (pilot exciter) 

      induces three-phase AC current in the stator winding of the exciter.  

   - This three-phase AC is converted to DC by a rotating rectifier (a set of diodes) fixed on the main shaft.  

   - The DC power is directly supplied to the excitation winding of the main rotor, producing a strong magnetic field.  

   Core Advantages: Eliminates the conductive brushes of brushed generators, is largely maintenance-free, has low failure rates, 

   provides stable operation and voltage, offers long service life, generates minimal interference with radio equipment, operates quietly, 

   and is the standard and mainstream configuration in modern diesel generator sets. Widely used in data centers, hospitals, 

   communication base stations, high-end industrial applications, and other scenarios requiring high reliability and minimal maintenance.

Conclusion and Selection Recommendations 

For modern diesel generator sets, especially in applications such as primary power sources, backup power, 

or situations demanding high reliability, brushless generators are the absolute mainstream and preferred choice. 

Their advantages of being "maintenance-free and highly reliable" far outweigh their slightly higher initial cost.

Brushed generators are only considered when budgets are extremely limited and sufficient maintenance resources are available.

In summary: When purchasing or specifying a generator set, priority should be given to brushless generators, 

                     as they represent a more advanced, reliable, and lower lifecycle-cost technological direction.