I want to calculate the weights that can be added to the dc motor for loading arrangement. So, how can I calculate this? I am using the motor with 24 volts DC, 6000 rpm No-Load current= 600 mA, Stall current= 30A max. What is the maximum weight that can be added?
Unless specifically identified as a brushless DC motor, a DC motor is usually assumed to be a a classical DC motor with a commutator. A DC motor of the size described is assumed to be a permanent-magnet DC (PMDC) motor unless information about a wound field is provided. The steady-state performance of a PMDC motor can be analyzed using the equivalent circuit shown below.
Va = Supply Voltage (24 volts) Ra = Armature resistance including brushes E - Back emf = N / Ks; N = Speed (RPM); Ks = Speed constant (RPM/Volt) Ia = Armature current (Amps)
V = Ia x Ra + E
At Stall: RPM = 0, E = 0, Va = Ia x Ra therefore Ra = 0.8 ohms
At No-Load: Va = Ia x Ra + E therefore E = 23.52 volts
N = 6000 RPM = Ea/Ks; Ks = 6000 / 23.52 = 255.1 RPM/volt
Electrical Input Power = Mechanical Output Power + Losses
Electrical Input Power (Watts) = V x Ia
Mechanical Output Power = Load Torque (Newton Meters) X Speed (RPM) x 0.1047
At No-Load: Torque = 0 so Output Power = 0 Input power = 0.6 x 24 = 14.4 watts Total losses = 14.4 watts. Losses in Ra = 0.6^2 x 0.8 = 0.288 watts. Total losses minus losses in Ra = mechanical losses = 14.112 watts. Assume the mechanical losses are due to bearing and brush friction and do not change with speed. Total friction losses = 14.112 W = Loss friction torque x 6000 x 0.1047. Total friction loss torque Mf = 0.0225 N-M.
Armature Power and Torque: Mechanical power developed in the armature before mechanical losses is P = Ia x E = Ia x N / Ks. The mechanical power developed is also the armature torque Ma x N x 0.1047 therefore 0.1047 x Ma x N = Ia x N / Ks.
Ma = Ia / (0.1047 x Ks) or
Ma = Ia x Km where Km = 1 / (0.1047 x 255.1) = 0.0374 N-m/amp
Stall torque is Km x stall current = 30 x 0.0374 = 1.12 N-m
The shaft torque, Ms, available to drive a load is the armature torque Ma, minus friction torque Mf. Ms = Ma - Mf.
In order to "calculate the weights that can be added to the dc motor for loading arrangement," it is necessary to determine the torque required from the motor shaft to move the weight in the required manner at the required speed. The torque available from the motor at any speed can be calculated from the motor analysis shown above. The continuous torque that the motor can provide without overheating can only be determined by testing the motor with the knowledge of the maximum allowable motor temperature. That information is normally provided by the motor manufacturer.