How do you calculate torque from voltage in an electric motor?

Electrical
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How do you calculate torque from voltage in an electric motor?

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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