At the heart of the machines we use in our daily lives and in industry mostly lie electric motors. Whether it's a conveyor belt in a factory, a heavy-duty crane, or the washing machine in our home, the system's operation depends on the twisting force, or "torque," produced by the electric motor. For electrical engineers, automation technicians, or electronics hobbyists, selecting the right electric motor comes down to establishing the connection between the motor's power (kW), the torque it produces (Nm), and its operating speed (RPM).
In this article, we will examine the torque characteristics of electric motors, explain how industrial motor calculations are done with examples, and discuss the role of our Tork Devir Güç Hesaplama in this process.
Why is Torque Important in Electric Motors?
There is a fundamental behavioral difference between internal combustion engines (gasoline/diesel) and electric motors. A gasoline engine needs its RPM to rise to a certain level (e.g., 3000 RPM) to produce its maximum torque. However, electric motors (especially AC Induction or DC Brushless motors) can deliver their maximum torque even at near-zero RPM (at the moment of startup).
The importance of torque in electric motors becomes apparent in the following scenarios:
- Startup (Breakaway) Moment: Imagine you are designing an elevator or crane system. A massive initial push (starting torque) is required for the cabin to start moving from a standstill with its load. If the selected motor's torque is insufficient, the motor will draw excessive current trying to turn, overheat, and trip the thermal breakers, locking the system.
- Continuous Load (Nominal Torque): This is the torque value the motor can continuously sustain at the RPM indicated on its nameplate. It is necessary to overcome the friction or workload encountered while the system is running.
In short, while the motor's power (kW) determines how fast the work will be done, the torque (Nm) determines whether that work can be done at all (whether the load can be moved).
Torque and Power (kW) Calculation in Motor Selection
When a motor is selected in the industry, the "Nominal Torque" and "Rotational Speed (RPM)" required by the system are usually calculated first. Then, the "Power (kW)" of the motor that will provide these values is determined.
In electric motors, mechanical output power is a direct function of Torque and RPM. The industry standard formula used in the International System of Units (SI) is:
Power (kW) = (Torque (Nm) × RPM) / 9548.8
If you are in the design phase of a factory setup and have the Torque and RPM values required to turn a specific load, you can instantly find out how many kW the motor you will install on the panel should be using this formula.
Example Project Calculation
Let's say a packaging machine's main shaft you designed for a factory requires 150 Nm of torque to turn, and you want this shaft to rotate at 1000 revolutions per minute (1000 RPM). What should the minimum power of the electric motor driving this system be?
Let's apply the formula:
Power (kW) = (150 Nm × 1000 RPM) / 9548.8
Power (kW) ≈ 15.7 kW
So, you need a motor of at least 15.7 kW for this system. When ordering from a catalog, choosing a higher standard value like an 18.5 kW or 22 kW motor will allow you to leave a safety margin from an engineering perspective.
To perform such calculations without bothering with pen and paper or a manual calculator, you can use our Tork Devir Güç Hesaplama. The calculator instantly provides the exact kW or HP value without any margin for human error.
The Effect of Gearboxes on Torque
Electric motors typically rotate at high speeds like 1500 RPM or 3000 RPM. However, industrial machines (like conveyor belts) require much lower speeds (e.g., 50 RPM) and much higher torques. In this case, a "Gearbox" (reducer) is connected to the motor's output.
While gearboxes reduce speed, they increase torque by exactly that ratio (excluding friction losses). The motor's power (kW) is constant at the gearbox input and output!
Example:
We have a 5 kW motor rotating at 1500 RPM. (When we calculate with our tool, this motor's torque is ~31.8 Nm).
We connected a gearbox with a 1:30 ratio to this motor.
- New RPM = 1500 / 30 = 50 RPM.
- Power = 5 kW (Constant).
When we enter the new speed (50 RPM) and Power (5 kW) values into our Tork Devir Güç Hesaplama and click "Calculate Torque," we see that we obtain a massive 954.8 Nm of torque at the output of the system. This is mechanical advantage!
Frequently Asked Questions (FAQ)
1. Torque is not listed on the motor nameplate; how can I find it?
Standard electric motor nameplates usually do not list Torque (Nm); instead, they list Power (kW) and Speed (RPM). To find the torque, you can enter these two values into our calculator tool and learn the nominal torque in seconds.
2. Where does the 9548.8 constant in the formula come from?
This constant number comes from unit conversions (minutes to seconds, watts to kilowatts) and the number Pi (π) in the angular velocity calculation. The exact value is $30,000 / \pi$, which corresponds to approximately 9549.
3. Can I calculate torque by entering Voltage and Amperage?
Voltage (V) and Amperage (I) are used to calculate the "Electrical Power" drawn by the electric motor (P = V × I). After finding the electrical power, you can find the mechanical power (kW) at the shaft output by factoring in the motor's efficiency (Cos φ and η). You can then enter this kW value into our calculator tool to reach the torque.
4. Is there a torque difference between 50 Hz and 60 Hz?
Frequency (Hz) directly affects the motor's RPM. A motor turns faster on a 60 Hz grid. Because the power remains constant, as the frequency increases, the RPM increases, and according to the formula, the nominal torque at the motor shaft decreases.
Instead of wasting time with math while designing electric drive systems, you can speed up your projects by using our Tork Devir Güç Hesaplama right away.
