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Pmdc motors
- 1. 1PERMANENT MAGNET KONGUNADUCOLEGE OF ENGINEEERING AND TECHNOLOGY PMDC MOTORS Content: Introduction to PMDC motors and types. Working principle Efficiency calculation with graph. References
- 2. 22 Permanent magnet (PM)DC motors Armature Permanent Magnets Brushes Commutator Coils PERMANENT MAGNET KONGUNADU COLEGE OF ENGINEEERING AND TECHNOLOGY
- 3. 3 PMDC motors –animation PERMANENT MAGNET KONGUNADU COLEGE OF ENGINEEERING AND TECHNOLOGY
- 4. 44 PMDC motors –components PERMANENT MAGNET KONGUNADU COLEGE OF ENGINEEERING AND TECHNOLOGY
- 5. 5 PMDC motors Stationary elementis a permanent magnet Have commutator and brushes to switch current direction in armature Limited in size (large magnets are expensive) Low cost, low power, battery operation Common in appliances, toys, RC Electric Toothbrush PERMANENT MAGNET KONGUNADU COLEGE OF ENGINEEERING AND TECHNOLOGY
- 6. 6 Other types ofDC motors • Wound Stator Stationary element is an electromagnet Connected in series or parallel with armature Commutator and brushes Can run on DC or AC current (universal motor) • Brushless No brushes to wear out or cause electrical noise More complicated to control Used in computer disc drives, fans shunt woundseries wound PERMANENT MAGNET KONGUNADU COLEGE OF ENGINEEERING AND TECHNOLOGY
- 7. 7 PMDC motors • TypicalUses: Small appliances, RC, often battery powered • Often used with position or velocity feedback (optical encoder or tachometer) • Reduction gear heads common • Easy to control: – Speed, Torque Input voltage • Size Range: Micro 0.5” L x 0.2”D (pager vibrator) <$1 Big 13”L x 4”D 2 HP $1000 RPM Torque V1 V2 >V1 PERMANENT MAGNET KONGUNADU COLEGE OF ENGINEEERING AND TECHNOLOGY
- 8. 8 Basic principle ofoperation – a wire in a magnetic field will be feel a sidewise force Conductor in a magnetic field: (Fleming’s Rule) N S B = magnetic flux density I = current Force = I L B F = force Permanent Magnet L = length of wire in the magnetic field )( BdLIdF PERMANENT MAGNET KONGUNADU COLEGE OF ENGINEEERING AND TECHNOLOGY
- 9. 9 In a motor,we have coils of wires, so the force becomes a moment For each turn of the coil: B F I Torque = 2rBIL r PERMANENT MAGNET KONGUNADU COLEGE OF ENGINEEERING AND TECHNOLOGY
- 10. 10 If you wantto get more torque out of motor: • Increase L – more coils, longer armature • Stronger magnetic field (B) – use stronger magnets (typical RC airplane motors use “rare earth” magnets) • Increase current (I) – increase input voltage • Increase armature diameter, (r) PERMANENT MAGNET KONGUNADU COLEGE OF ENGINEEERING AND TECHNOLOGY
- 11. 11 Typical PMDC motorperformance curves (available from the manufacturer, or by test) 𝑢 = 𝜔/𝜔 𝑀𝐴𝑋 𝑇 = 𝑇𝑆𝑇𝐴𝐿𝐿 1 − 𝑢 𝑖 = 𝑖 𝑆𝑇𝐴𝐿𝐿 + 𝑢 𝑖@𝑀𝐴𝑋 − 𝑖 𝑆𝑇𝐴𝐿𝐿 𝑃𝐼𝑁 = 𝑖 𝑉𝑃𝑂𝑈𝑇 = 𝑇 𝜔 𝜂 = 𝑃𝑂𝑈𝑇/𝑃𝐼𝑁 Speed (rpm) Efficiency Torque Current Power OutPower In 0 wMAX TSTALL iSTALL i@max Constant V PERMANENT MAGNET KONGUNADU COLEGE OF ENGINEEERING AND TECHNOLOGY
- 12. 12 Manufacturer’s data sheet PERMANENTMAGNET KONGUNADU COLEGE OF ENGINEEERING AND TECHNOLOGY
- 13. 13 RPM η Torque W Operates with max powerat this speed ½ No Load Speed No Load Speed Max Efficiency @ this speed What is your design objective - maximum power or maximum efficiency? PERMANENT MAGNET KONGUNADU COLEGE OF ENGINEEERING AND TECHNOLOGY
- 14. 14 To size themotor, we need to know what it is driving, i.e. the “load” curve Rotational Speed Torque 0.5 gpm 1 gpm 2 gpm 4 gpm 8 gpm Typical load curve for a pump and plumbing system, a fan load curve is similar PERMANENT MAGNET KONGUNADU COLEGE OF ENGINEEERING AND TECHNOLOGY
- 15. 15 The intersection ofthe load curve and the motor curve will determine the operating speed of the motor Rotational Speed Torque Load Larger Motor Motor A Motor A with 2:1 reduction PERMANENT MAGNET KONGUNADU COLEGE OF ENGINEEERING AND TECHNOLOGY
- 16. 16 Other concerns Motor Life: Internallosses (resulting in heat) ~ I2 This determines the maximum steady state current High temperature can demagnetize magnets, melt insulation Typical gear efficiency: 70-80% for each stage PERMANENT MAGNET KONGUNADU COLEGE OF ENGINEEERING AND TECHNOLOGY
- 17. 17 Conclusion: • PMDC types,working principal, torque equation and applcation is explained in detail with suitable diagrams.. • load curve and the motor curve will determine the operating speed of the motor also discussed. References: 1.P. C. Sen., ‘Principles of Electrical Machines and Power Electronics’, John Wiley & Sons, 1997. 2.P.S. Bimbhra, ‘Electrical Machinery’, Khanna Publishers, 2003. 3.S.Sarma & K.Pathak “Electric Machines”, Cengage Learning India (P) Ltd., Delhi, 2011. 4.U.A.Bakshi&M.N.Bakshi “Electric Machines-I”,Technical Publications,2015. 5.Other Web Sources PERMANENT MAGNET KONGUNADU COLEGE OF ENGINEEERING AND TECHNOLOGY