What are Generator Diodes and What Do they Do?

Diodes are a small yet essential part of your diesel generator. A generator works by converting mechanical energy into electrical energy within an alternator. Inside the alternator, a magnetic field (moved by mechanical energy) transforms the mechanical energy into electrical energy.

What are Generator Diodes?

Diodes are devices placed within an electrical circuit to direct current. They allow current to move easily in one direction, but not in the other. When a diode is inserted into a circuit in a way that allows current to flow through the circuit, it is forward-biased, while when the diode blocks current from completing the circuit, it is reverse-biased. As explained by All About Circuits, “A diode may be thought of as like a switch: ‘closed’ when forward-biased and ‘open’ when reverse-biased.”

What Do Diodes Do in an Alternator?

Diodes are used within the process of rectification, or changing an AC flow into DC. This is possible because diodes only allow current to flow in one direction. AC, or alternating current, includes current flowing both forward and backward, creating a full sine wave. DC, or direct current, only moves in one direction. By blocking half of AC’s sine wave, diodes effectively morph the current into DC power.

This process is necessary for a generator’s alternator to work because the magnetic field relies on DC power. The AC output of the exciter must be transformed to DC power before it can be used to generate electrical energy. This process takes place within a genset’s automatic voltage regulator. The regulator matches the exciter’s output with the necessary power output, so the generator doesn’t produce more power than is necessary at the time. This helps keep components from wearing out, including generator diodes.

The diodes within an automatic voltage regulator are arranged in a collection called rectifier diodes. There are an equal number of forward- and reverse-biased diodes. This lets generators use both halves of AC’s sine wave. When the power is flowing in one direction, it goes through the forward-biased diodes. For the other half of the current’s sine wave, it flows through the reverse-based diodes. Together, the rectifier diodes let the magnetic field use all of the AC power to generate electricity, rather than just half of the AC power.