Electric motor efficiency & Torque speed relationship for a D.C motor
By DarthVader
Date: 2024-02-03
Topic: 205 see comments
Post views: 659
Motor efficiency
To calculate the efficiency η of a motor, first the power input P in and the useful power output P out must be calculated. The power input can be calculated if the electrical conditions are known, using:
Pin = IV
where I is the current and V is the voltage. Power has the SI unit watt (W). The power output can be calculated by considering the useful work that is done on the shaft of the motor. If the turning force τ, or torque, on the shaft turns the shaft through an angle θ, then the work done is τθ, where θ has units of radians. This work done is over time, therefore the power is the rate of doing work, given by:
Pout = τω
where ω is the angular speed in rad s-1
The motor efficiency η is the ratio of power output to power input and can be expressed as:
η = Pout / Pin
Torque speed relationship for a D.C motor
The equation relating torque to rotation speed for a d.c motor is:
τ = τs − (τs / ωn)ω
where:
τs = stall torque of the motor
ωn = no-load speed of the motor
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