Recommendations
2017 - 07 - 28
Clicks: 0
Basic conceptsa. EMC, EMI and EMSElectromagnetic Compatibility (EMC) means the compatibility of products that are in the same electromagnetic environment (electric field and magnetic field). It has 2 ...
2017 - 07 - 28
Clicks: 0
Magnetic circuitThis article tries to introduce PMDC motor’s magnetic circuit by the most acquainted concepts. It also tries to introduce some characteristics and parameters of the motors by means of ...
2017 - 07 - 28
Clicks: 0
Basic conceptsMotor is an energy conversion device that converts electric energy into mechanical energy or mechanical energy into electric energy, using magnetic field as media.PMDC motor is an energy...
Electric potential, torque and energy equation

Electric potential, torque and energy equation
(1)  Electric potential (Figure 6)
From V=E+2△U+I*r we get E=V-2△U-I*r
Meanwhile E=KE*Φ*n(armature back EMF)
V: power supply voltage (Unit: V)
2△U: brush voltage drop (Unit: V)
I: armature current (Unit: A)
R: rotor resistance (Unit: Ω)
KE: EMF constant = Z/60 (for a 2-pole motor.
Z: number of conductors)
Φ: magnetic flux (Unit: Weber) = average magnetic flux density B * width of magnetic pole *effective length of rotor
N: speed (Unit: rpm)
(2)  Torque
TE=KTΦ*I（electromagnetic torque: N.M）                 KT: torque constant = Z/2π
Φ: magnetic flux (unit: Weber)                                  I: armature current (unit: A)
(3)  Relationship between power and torque：
P=T*n/97500        P: power（unit: W）        T: torque (unit: g.cm)        n: speed (unit: rpm)
When the unit of T is “N?m”, P=T*n/9.55（unit: W）
(4)  Energy equation(Figure 7):
P1=2△U*I+I2r+PE
PE=P2+PFe+Pmec
PE: electromagnetic power   P2: output power
Pmec: mechanical loss      PFe: iron loss
P2=P1-2△U*I-I2r-PFe-Pmec (unit: W)
Efficiency: η=P2/P1*100%
PFe+Pmec is also called no load power
P0=PFe+Pmec
PE=P2+P0 and TE=T2+T0

(5)  Energy transmission graph: (Figure 8)