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

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

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