1
Comparison of Motors and Drives
Direct current drives have several advantages of over AC drives:
• DC drives utilize a much simpler controller design
• One power conversion stage and no power storage elements (capacitors)
• DC Drive has higher controller efficiency
• Direct current drives are typically 98% efficient
DC Drives benefit from high controller reliability and low maintenance due to a lone
power conversion module. Other advantages of DC motors include lower power line
harmonic contribution.
DC Drives advantages
• Need smaller line reactors
• Have compact controller design
• Have better overload and peak voltage characteristics
• Have low motor acoustical noise (AC drives have carrier noise)
• Easier troubleshooting and serviceability
AC Motors advantages
• No carbon brushes to replace
• No commutator to clean
• Low rotor inertia compared to the DC armature
• Up to 50 hp lower cost than DC Motors
The low initial cost of AC motors looks attractive in the short run; it becomes costly to
maintain because of unreliable power supply available in India. Carbon brush
replacement works out 70% cheaper than costly AC drive module replacement.
Ramson & Ramson, 13 Ramgopal Ind Est, Dr RP Road, Mulund( West) , Mumbai-80
Email: ramson.ramson@gmail.com , ramson@mail.com , Tel: 91 22 25617729

2
Suitable Applications for DC motors and DC Drives
Winders/Coilers:
Figure 1
DC motors offer superior characteristics at low speed for winder and coiler operation
and performance in winder applications maintaining tension at standstill is a very
important operation. DC motors offer a wide speed range at rated torque. On many
winder applications that run in an extended speed range a smaller horsepower DC
motor could run the same job as a larger horsepower AC motor.
Extruding:
Figure 2
Extrusion is a price competitive industry. DC drives offers economical solutions for
Extrusion applications.
References
http://www.scribd.com/doc/6358001/Basics-Of-DC-Drives (23 Nov 2008)
Pharmaceutical Extrusion Technology By Isaac Ghebre-Sellassie, Charles Martin (page
375)
Ramson & Ramson, 13 Ramgopal Ind Est, Dr RP Road, Mulund( West) , Mumbai-80
Email: ramson.ramson@gmail.com , ramson@mail.com , Tel: 91 22 25617729