Aboutcleggsan Expertise All technical areas of Electronics Engineering.
Experience BSEE, MBA, Design, R&D, University Research.
Senior Life Member of IEEE. Life Fellow of AES.
Organizations IEEE, Consumer Electronics Society, Audio Engineering Society.
Broad teaching experience; work experience mostly in consumer electronics and conversion from analog to digital technologies. Pioneer in digital audio at all levels.
Question What is a free firing thyristor? how do you check for one ? and if there is such a thing what sort of fault would it cause in a converter drive for D.C. Motors ?
Answer A thyristor, or SCR (Silicon Controlled Rectifier), is a diode that has an input to control when the diode becomes conductive. A good diagram and explanation is found at:
It is most likely used as part of the control circuitry in the motor drive system. Suppose you are using an AC source of power to feed current to the dc motor and the SCR is used to help rectify the ac AND control the level of dc to the fields, then if the thyristor failed you would lose dc feed to the motor windings.
Testing is best done by just replacing it with a new one as they are not so expensive (Unless you are using it in a very large power system). You can test the thyristor itself with an ohmmeter by placing the positive terminal on the anode and the negative on the cathode side of the unit; then alternatively touch the control lead to the anode and cathode.
