Types of DC drives...






Senior Electrical Maintenance engineers above the age of forty or fifty sometimes find themselves outdated in their knowledge. With this background in mind an attempt is made here to describe certain concepts which one finds in old analog dc drives. Such drives are still in use in a large number of industries. Digital drives are different only in the manner in which these basic functions are achieved. Understanding these will help in solving many problems irrespective of the type of the drive. These details will help in better understanding of the subject which is otherwise learnt in bits and pieces by many over a period of time as they grow in industry.

Like any other classification, there are many ways in which the DC drives can be classified. Whatever may be the way, the main purpose is to divide and learn. i.e. learn the topic by breaking it down in small areas. Classification can be like...

-three phase or single phase

-analog or digital

-constant speed application or constant current application

-Semicontrolled or fullycontrolled etc.





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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?