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Motor Efficiency

Motor efficiency, abbreviated as ηm (Greek symbol eta), a dimensionless number, is the ratio of useful mechanical power output to the electrical power input in an electric motor.  It measures how effectively an electric motor converts electrical energy into mechanical work or output power.  Motor efficiency is important to consider when evaluating the performance and energy consumption of electric motors.  In an ideal situation, where there are no losses, the efficiency would be 100%.  However, real world motors always have some level of losses due to factors such as resistance in the windings, friction, and other mechanical losses.  These losses result in a reduction of the overall efficiency of the motor.

Efficiency matters because more efficient motors consume less energy to achieve the same level of mechanical output, leading to reduced energy costs and lower environmental impact.  When selecting a motor for a specific application, choosing a motor with higher efficiency can result in long term energy savings and improved overall system performance.

 

 Motor Efficiency Formula

ηm=PoutPin100     (Motor Efficiency)

Pout=ηmPin100

Pin=Pout100ηm

Symbol English Metric
ηm  (Greek symbol eta) = Motor Efficiency dimensionless dimensionless
Pout = Output Power W kgm2/s3
Pin = Input Power W kgm2/s3

 

Single Phase Motor Efficiency Formula

  • Single phase motor efficiency is the measure of how effectively a single phase motor converts electrical energy into mechanical energy.

ηm=746PoutIVPF     (Single Phase Motor Efficiency)

Pout=ηmIVPF746

I=746PoutηmVPF

V=746PoutηmIPF

PF=746PoutηmIV 

Symbol English Metric
ηm  (Greek symbol eta) = Motor Efficiency dimensionless dimensionless
Pout = Output Power W kgm2/s3
I = Current A C/s
V = Voltage V kgm2/s3A
PF = Power Factor dimensionless dimensionless

 

 Three Phase Motor Efficiency Formula

  • Three phase motor efficiency is the percentage of input electrical power that a three phase motor converts into usable mechanical power.

ηm=746Pout1.732IVPF     (Three Phase Motor Efficiency)

Pout=ηm1.732IVPF746

I=746Poutηm1.732VPF

V=746Poutηm1.732IPF

PF=ηm1.732IV746Pout

Symbol English Metric
ηm  (Greek symbol eta) = Motor Efficiency dimensionless dimensionless
Pout = Output Power W kgm2/s3
I = Current A C/s
V = Voltage V kgm2/s3A
PF = Power Factor dimensionless dimensionless

   

Motor Efficiency Formulas

V = Voltage  -  I = Amps  -  PF = Power Factor  -  η = Efficiency  -  HP = Horsepower

To Find Direct Curren Alternating Current
Single Phase Two Phase Four Wire Three Phase
Efficienty 746HPVI 746HPVIPF - 746HP1.732VIPF

 

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