Automatic Voltage Regulators
An automatic voltage regulator (AVR) holds a generating set’s output voltage steady by varying the current fed to the alternator’s exciter field. When output collapses, hunts, or drifts under load, the AVR, its sensing leads or the rotating rectifier are the first things to check.
The AVR is the most frequently replaced electrical component on a diesel generating set. It senses output voltage, compares it against a reference, and adjusts exciter field current to hold the set point — typically within ±0.5% across the load range.
Selecting the correct unit depends on the excitation method (self-excited or PMG), the sensing configuration (single- or three-phase), and the alternator frame. A half-wave regulator fitted to a PMG machine will not control correctly, so confirm the frame and winding before ordering.
Parts in this system
4 references listed. Prices quoted on enquiry.
Common questions
How do I know if my AVR has failed?
The classic symptoms are no output voltage on start-up despite the engine running at rated speed, output that hunts or oscillates under steady load, or voltage that climbs above the set point and trips over-voltage protection. Before replacing the AVR, confirm the rotating rectifier diodes and the sensing leads, because a failed diode presents almost identically.
What is the difference between an SX460 and an MX341?
The SX460 is a half-wave, self-excited regulator with single-phase sensing, used on smaller self-excited Stamford frames. The MX341 is designed for permanent magnet generator (PMG) excitation and offers three-phase sensing with better short-circuit performance. They are not interchangeable — the excitation system determines which one fits.
Can I fit a different brand of AVR?
Sometimes, but only where the excitation type, sensing voltage range, field resistance and output current rating all match. Cross-referencing by physical appearance or terminal count alone is unreliable. Send the alternator nameplate and we will confirm against the frame and winding.
Related systems
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