A 220V 8 kW Dc motor takes 4A at no load when running at 700

A 220V, 8 kW Dc motor takes 4A at no load when running at 700 rpm. The armature resistance at standstill gives drop of 6 V across armature terminals when 10A were passed through it. Calculate (a) speed on load (b) torque (c) efficiency. A12V, 24W, 500 rpm DC motor is connected to DC/DC chopper to control its speed using PWM of frequency 10KHz. If Ra = 0.5 Ohm and the efficiency = 80%, Find The motor constant The developed torque The no load speed The duty cycle of the chopper to reach 300 rpm If you are using Arduino to produce the PWM, show the connection of the necessary circuit with the Arduino and write a code to produce the PWM or this case

Solution

Ea = Eb + ia * Ra
Eb = 220 - 4*.2 = 219.2 V
w = Eb/Kb ==> Kb = 219.2/700 = 0.313 V/rpm
at no load, current through armature is 0(assuming no losses)
Eb = 220V
w = Eb/Kb = 220 / 0.313 = 702.55 rpm
no load speed = 702.55 rpm