How do you calculate torque from voltage in an electric motor?
To compute torque from voltage in an electric motor, various parameters must be considered, including the motor’s electrical & mechanical properties. The link between voltage, current, & torque is indirect, requiring an understanding of the motor’s characteristics and performance curve.
Here’s a step-by-step guide:
Step 1: Identify Motor Specifications
Obtain the following motor characteristics from the datasheet.
- The motor constant (Kt) is commonly measured in Nm/A.
- Motor Resistance (R)
- Motor back EMF constant (Ke)
- The no-load speed (ω) and current (I) are both zero.
Step 2: Determine the Operating Conditions
Determine the motor’s operating voltage (V) and current (I). The formula for estimating the current is as follows:
I = (V−Eb) / R
The rear EMF (Eb) is proportional to motor speed (ω).
Eb = Ke . ω
Step 3: Calculate the Back EMF
To calculate the back EMF (Eb), use the known motor speed (ω).
Eb = Ke . ω
Step 4: Calculate Current Input the back EMF into Current Formula
U = (V-Ke.ω)/R
Step 5: Calculate Torque
Finally, use the motor constant (Kt) to determine the torque (𝜏).
τ = K t x (I −I 0 )
Optimized calculation for DC motors:
For a DC motor, you can simplify the torque calculation by keeping the motor constant and assuming insignificant no-load current:
τ = K t x I