Learn how to choose a VFD for a motor based on voltage, current, load type and control requirements. Compare RENLE RNB1000, RNB2000 and RNB5000 VFDs.
Choosing the right variable frequency drive is important for motor performance, reliability and operating cost. However, many buyers still select a VFD only according to motor power.
In fact, how to choose a VFD for a motor depends on several factors, including motor voltage, rated current, load type, starting torque and control requirements.
For distributors and industrial buyers, the following steps can make VFD selection much easier.
1. Check the Motor Nameplate
The first step in understanding how to choose a VFD for a motor is to check the motor nameplate.
Important information includes:
- Motor power, kW or HP
- Rated voltage
- Rated current
- Rated frequency
- Motor type
- Rated speed
Among these parameters, motor rated current is especially important.
A VFD should not be selected based on motor kW alone. The VFD rated output current should also meet or exceed the motor rated current.
For example, if you have a 55 kW motor, you should also check its actual rated current before selecting the drive.
2. Identify the Motor Load
Different loads require different VFD performance.
Pumps and Fans
Centrifugal pumps, fans and blowers are usually variable-torque loads.
For these applications, a general-purpose VFD is often sufficient.
Recommended VFD: RENLE RNB1000
The RNB1000 is suitable for common industrial applications such as pumps, fans, packaging machines and material-handling equipment.
View RENLE RNB1000 Low Voltage VFD
Conveyors, Mixers and Compressors
These applications may require stronger torque and better speed control.
Recommended VFD: RENLE RNB2000
The RNB2000 supports more advanced vector control and can be used with both asynchronous motors and permanent magnet synchronous motors.
View RENLE RNB2000 VFD
High-Performance Applications
For applications requiring high starting torque, accurate speed control or stronger low-speed performance, a high-performance vector VFD is more suitable.
Recommended VFD: RENLE RNB5000
The RNB5000 is designed for more demanding motor-control applications requiring advanced torque and speed performance.
View RENLE RNB5000 Vector VFD
3. Match the VFD Voltage
Another important point in learning how to select a VFD for a motor is the matching of voltage.
The VFD must be matched to the power supply and motor voltage.
Low voltage motor systems typically consist of:
- 220 to 240 V
- 380-415 VAC
- 440–480 V
Medium voltage VFDs are required for 3 kV, 6 kV, 10 kV or other medium voltage systems driving larger industrial motors.
4. Check the VFD Rated Current
A simple VFD sizing rule is:
VFD rated output current ≥ motor rated current.
This is especially important for applications with:
- Heavy starting loads
- Frequent acceleration
- High starting torque
- Continuous full-load operation
For demanding applications, buyers should also check the VFD overload capacity instead of considering only the kW rating.
5. Choose the Right Control Method
When deciding how to choose a VFD for a motor, control performance also matters.
V/F control is suitable for many standard pumps, fans and simple machinery.
Sensorless vector control provides better low-speed torque and is suitable for conveyors, mixers and more demanding equipment.
Closed-loop vector control is normally used where accurate speed or torque control is required.
This is why two motors with the same power rating may require different VFD models.
| Application | Recommended VFD |
| Pumps and fans | RNB1000 |
| General industrial machinery | RNB1000 |
| Conveyors and mixers | RNB2000 |
| Compressors and demanding loads | RNB2000 |
| High-performance torque control | RNB5000 |
| Medium-voltage motors | RNHV |
For example, a 75 kW centrifugal pump may be suitable for the RNB1000 series.
However, a 75 kW conveyor requiring high starting torque may be better matched with RNB2000 or RNB5000.
Therefore, how to choose a VFD for a motor should always depend on the actual application, not only motor power.
What Information Should You Send for VFD Selection?
To receive a more accurate VFD recommendation, provide:
- Motor power
- Motor voltage
- Motor rated current
- Motor type
- Application
- Load type
- Starting torque requirement
- Operating environment
With this information, the VFD supplier can recommend a more suitable model and configuration.
FAQ: How to Choose a VFD for a Motor
Can I select a VFD only by motor kW?
No. Motor power is only the starting point. Motor current, voltage, load type and overload requirements should also be considered.
Which VFD is suitable for pumps and fans?
For standard low-voltage pumps and fans, the RENLE RNB1000 is a practical option.
Which VFD is suitable for high starting torque?
For applications requiring stronger torque performance, RENLE RNB2000 or RNB5000 can be considered.
