Electric Motor Torque Calculator

The amazing electric motor torque calculator indicates the relationship between motor speed, power, and torque. Are you looking to determine how much torque you can get at a specific rotational speed? Then keep reading. We will discuss how an electric motor works and indicate formulas to calculate its torque. We also define, exclusively for alternate current, what is electrical motor slip.

It is easy to determine whether the electric motor is working correctly, but few choose to know how they work. Keep reading; you are about to become one of the selected ones.

In case you think you have not seen an electric motor, you have one in the water pump of your house or your living room fan. Electric motors are everywhere, converting electrical energy into mechanical energy, making a shaft rotate. We have two main types of electrical motors:

• AC electrical motor: These work with alternating current. Alternating current has the characteristic of periodically reversing current direction and magnitude over time. Such a feature makes it perfect for creating alternating magnetic fields that rotate the motor.

• DC electrical motor: This type works with direct current. We call the armature its rotatory part and the stator its stationary part. The stator contains magnets that build a magnetic field that covers the armature. On the other side, we have the armature, which is energized by the DC power. The electrical flow through the armature creates an electromagnetic field. The interaction between the electromagnetic field and the stator magnetic field makes the armature rotate.

If you are wondering which cable size to use for your new electrical motor, you can check our set of wire size calculators. We have a specific set of tools for DC and AC motors.

In both cases described above, the shaft rotates with a certain angular speed, producing torque. We can use such torque to rotate driven equipment like impellers in water pumps. In other words, electric motor torque is the amount of rotational force the motor develops.

In both types of electrical motors, torque depends on the intensity of the magnetic fluxes inside the motor; however, their speed and torque relation are different. In direct current, a high-torque electric motor will rotate considerably slower than at other loads. You can see this in the figure below:

That is why the phrase: "high torque low-speed electric motor" is mostly related to DC motors. On the other hand, AC electric motor experiences its maximum torque at a specific rotating speed. Engineers call such torque breakdown torque. Check it in the next picture:

In the above picture, note the "slip" text in the x-axis next to 100% speed. Slip is a value that only applies to alternate current motors. It represents the difference between synchronous velocity (the rotating speed of the magnetic field inside the motor) and the shaft speed. Our powerful electric motor torque calculator can also calculate it. Here you can see its formula:

Slip is an important value since it indicates how much less speed you get running the electric motor compared to its synchronous velocity. From the graph, you can notice that maximum torque (breakdown torque) appears at a specific slip value which is data that manufacturers provide. See the catalog of a famous manufacturer of electrical motors.

Independently of the current source, there is one main formula that relates shaft revolutions per minute, torque, and power:

where:

• $T$ — Torque: also referred to as electric motor torque, represents the amount of rotational force that the motor develops;
• $P$ — Power: indicates the output power that can be used from the shaft; and
• $\rm rpm$ — Motor speed: Measures the rotation speed of the shaft.

In AC electric motors, we have two rotation speeds: synchronous speed or magnetic field speed and real rotation speed:

• $\rm rpm_{synch}$ — Synchronous revolutions per minute: Indicates the rotational speed of the magnetic field. It is controlled by the voltage frequency and the number of electric motor poles.
• $\rm rpm_{load}$ — Motor speed with load: Represents the real rotation speed when the motor is under load. It is less than the synchronous speed.

Synchronous revolutions per minute can be calculated as follows:

where:

• $f$ — Supply frequency: indicates the supply voltage frequency; and
• $p$ — Number of poles: Represents the number of permanent magnet poles for the rotating rotor. A paired set of magnets with north and south represents two poles.

The electric motor torque calculator includes a feature where, by adding the maximum slip, you can get the operating rotating speed or vice versa. In other words, if you add the motor operating speed, you obtain the slip. Such a feature helps determine whether the motor is operating at its maximum torque or not.