Drive stops all of a sudden without any indication.....






Many a times, dc motor stops all of a sudden, without giving any indication. On quite a few occasions, the motor starts running again without doing anything. This is, most of the time, due to poor electrical contact which “enables” the DC drive.  Normally a closed contact is used to “enable” the DC drive. If the contact resistance increases due to accumulation of dust, such observations are commonly seen. By putting the Electrical Power off, and doing resistance measurement of contact used for “enable” function of the drive, reveals the cause of the problem. Resistance values more than 1 or 2 ohms indicates that the contact condition is poor and is likely to show higher reisistance any time during operation. Cleaning the contact with “Electrical Contact Cleaner” or CTC ( Carbon Tetra Chloride ) solves this problem.

Since the drive is disabled when contact resistance is high, this does not blow fuses while the motor stars running on its own again. Reference is again routed through ramp circuit and motor does not experience jerks while restarting. Low values of Ramp acceleration timing may blow fuses in such situtations.






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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?