Diodes are in effect switches which are used to allow electric current to flow in one direction only. They are used primarily for power supply operation. Rectifier diodes can handle higher current flow than regular diodes and are generally used in order to change alternating current into direct current. They are designed as discrete components or as integrated circuits and are usually fabricated from silicon. They are frequently characterised by a fairly large junction surface which results in high capacitance under reverse-bias conditions. In high voltage supplies two or more rectifier diodes may be connected in series in order to increase the peak inverse voltage rating of the combination.
Use of diodes in power generation
According to the principal of generation of alternating current, a magnetic field is required. To produce a magnetic field a diode disc assembly is used. This consists of rectifier diodes made up of an equal number of forward and reverse biased diodes. The self excited alternator has two sections, namely the exciter field and the main field. The alternator starts using the principle of residual magnetism but to maintain the generation of alternating current the main field windings or the rotor windings need to be magnetised. The alternating current which is produced by the exciter field is fed to the diode disc assembly and the rectified output is fed to the main field windings to magnetise it. When this field is rotated inside the stator the alternating current is induced in the armature windings.
Common causes of diode failure
The most common cause of diode failure is one shorted diode which is usually caused by over voltage or current which can be due to out of phase paralleling, a lightning strike or other abnormal transient. It can also occur if voltage is imposed on the terminals of a brushless generator while it is at rest. The effect of such a failure will be increase excitation and the exciter rotor or the voltage regulator may fail. Another reason to replace the diodes can be an open diode problem. This happens when, after a short, the diode burns open if no other failure occurs. Order from Generator Parts today to get your 330-25777 diode kit.