Block diagram of a typical DC drive...














Some experience of working on DC drives is being shared here. Actually, many of the observations made during the process of troubleshooting have to be really "felt" by the troubleshooter and it is difficult to find a "ready to eat" answer here. However, some clues can always be taken from these observations.

Over years, technology has changed substantially, but I am sure, there are many industries still depending on old equipment and trying to continue using it for some reason or other. With advent of the technology in the drive systems, repairs on "component level" also has reduced to a great extent, but the suggestions here can still be useful to many. ( This refers mainly to analog dc drives with discrete circuit components )


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Block Diagram



Ramp Circuit


Speed Amplifier


Current Amplifier


 Firing Circuit


Power Circuit


Types of DC drives 



 Checking Thyristor


Voltage feedback Vs Tacho feedback


Current Limit


Constant HP & constant Torque


Field Weakening


Using CRO 



Motor runs at full speed


Fuses Blow


Hunting in speed


Motor gives jerks


Belts vibrate


Speed control not satisfactory 



Speed drops on load


Motor overheats


Sparking on commutator


DC drives and Power Factor


Your comments and suggestions 


Drive stops all of a sudden 


Motor not able to drive the load


DC to DC isolation


 Motor or Drive?