RSA Bardo | Home Page
RSA Bardo | Home Page
Infra Red Thermography : Infra Red Surveys
Send Email
RSA Bardo | Home
RSA Bardo| Services
RSA Bardo| Services
RSA Bardo| Services
RSA Bardo| Services
RSA Bardo| Services
RSA Bardo| Support
RSA Bardo | Contact

Soft Starters

We are frequently asked, what the difference is between a variable speed drive and a soft starter?

The difference is the speed that the motor can run when at full speed.

With a soft start starter, the motor is reduced when voltage is started; and then when the motor is at full speed, or a timing circuit has timed out, a running by-pass contractor pulls in and the motor continues to run at full base speed.

With a VSD (Variable Speed Drive) or VFD (Variable Frequency Drive), the motor will soft start, and you can vary the speed of the motor by varying the output frequency from the VSD or VFD. 

So, if you don’t need to vary the speed of the motor, once the motor is up to speed, then the correct solution is a soft start starter for that motor. If the process requires the motor speed to vary at any time, the correct solution is a VSD / VFD. 

The cost for a soft start starter is much less than a VSD or VFD.

A common question when deciding between a soft starter or a drive is, which one to select?
The purpose of this web page is to show similarities and differences between the soft starter and the drive.
When comparing the two devices, you should be able to pick the best device for the application. Many comparisons are done using Smart Motor Controllers (SMCs) and AC variable frequency drives (VFDs).

While the question is simple, the answer is not. If you examine the function and purpose of the soft starter and drive, the answer becomes clearer. Generally, the application determines the best fit. Common questions to ask are:
• Does the application need full torque at zero speed?
• Does the application need speed control once the motor is at speed?
• Does the application need constant torque?
• Does the application need precise starting and stopping times?
• Is space a consideration?

Soft Starters
• Applications with low or medium starting torque
• Lightly loaded applications
• Little or no speed control during run mode
• Reduce mechanical wear and damage to system
• Controlling inrush
• Power monitoring

AC Drives
• Single-phase applications on certain drives
• Speed control and system efficiencies operating at reduced speeds during the run mode
• Applications with high starting torque
• Continuous feedback for critical position control
• Holding rotor at zero speed
• Reduce mechanical wear and damage to system

Efficiency Soft Starter Soft starters can achieve up to 99.5…99.9% efficiency. Typically, less than 1V is dropped across an SCR.

Efficiency is dependent upon the size of the soft starter and the 3-phase voltage applied. After the starting process is complete, a soft start with integrated bypass, as with the SMC-3 and SMC Flex, pulls in an internal bypass contactor. The SCRs are no longer firing and all running current is across the contacts maintaining or improving efficiency.

When operating at full speed and properly loaded, soft starters are more efficient than VFDs.

Contact Rob Bardo for more information.

Soft Starter

Bardo | Terms and Conditions
RSA Bardo | Services RSA Bardo | Products
RSA Bardo| Support
RSA Bardo | Contact
Click to send Email