VFD Speed Controller

VFD Speed Controller

A VFD speed controller is also known as a variable frequency drive, variable speed drive, adjustable frequency drive, VFD or, aninverter.

A VFD speed controller is asolid state electric motor control system, designed to control the speed of an electric motor. A VFD speed controller can reduce energy costsup to 50% by speed reduction on electric motorswhere the full speed of the electric motor is not needed. VFD speed controller functions allow an AC electric motor to only operate when needed, which allows an electric motor to last longer.Technology has allowed VFDs to reduce in cost and physical size, and has improved performance through advances in semiconductor switching devices, simulation, control techniques, control hardware, and software.

Approximately one third of electrical energy in the world is supplied by electric motors in fixed-speed centrifugal pump, fan, and air compressor applications. These fixed-speed applications do not usually require full load speed of the electric motor theyre operating. By installing a VFD speed controller to these applications, electric motor speeds are reduced and power costs can be reduced by 50% or more.Properly applied VFD speed controllers withelectric motorswill also significantly reduce energycosts for variable torque loads such as fans, blowers, and pumps.Blowers are often used with dampers to control air flow that operate either manually or automatically. When dampers are closed, 50% of the electric motor current will drop to approximately 60% of full load nameplate current. By utilizing VFD speed controllersin blower applications, the current draw of the motor will be reduced 30% for every 10% drop in speed. Electric motors controlled by VFD speed controllersat 50% speed will draw approximately 20% of the electric motor full load current.

VFD speed controllersare also used on rotating equipment toreduce amperage spikes upon start up of large electric motors.Adjusting the acceleration and deceleration time of electric motors can extend the lifespan of an electric motor. Using a drive on an electric motor provides the ability to increase or decrease the frequent starting and stopping of an AC electric motor. Limiting the starting and stopping of a motor, and controlling the ramp up and ramp down speed of amotor, allows for decreased wear and extended lifetime of the motor. VFD speed controllers are used in AC servo systems, air compressors, conveyor systems, lathes, mills, plastic extrusion, slitter lines, bottlers, packaging lines, pharmaceutical production, food processing, HVAC systems, waste water treatment systems, submersible pumps, fans, blowers, and many more electric motor applications.

To learn more about VFD speed controllers, or, for drive repair and replacement quotes, contact Precision Electric, Inc.

How We Repair AC Motor Speed Controllers Or VFDs Professionally

We repair and warranty all major AC and DC Motor Speed Controllers, feel free to call now at 1-877-625-2402 for a free quote or fill out the Digital AC or DC Drive Quote Request Form. For those of you looking to repair the drive yourselves, our procedure for professional repair is listed below.

The industrial electronics repair industry is one that should be taken with extreme caution. For those who do not have the required training or experience to work with electrical equipment, it is strongly recommended you consult an expert in the field when repairing equipment such as AC Motor Speed Controllers.

Many AC Motor Speed Controllers have an internal DC bus that retains a charge after power has been cut to the drive, as a result, just because line power is cut off from the equipment, it does not necessarily mean it is safe to work with. You must always take extra precautions to ensure proper safety measures are taken and injury or even death do not occur.

Precision Electric has spent years working with electrical components and AC Motor Speed Controllers as well as standard DC and Servo Motor Speed Controllers. The troubleshooting techniques for each brand of drive can be unique, but the overall structure of troubleshooting always remains the same. The ultimate goal when repairing an AC Motor Speed Controller is to diagnose, repair and re-commission the unit as quickly as possible, so there are some steps that should be taken before anydis assemblyeven takes place.

Here are all of the steps illustrating how Precision Electric repairs AC motor speed controllers professionally and quickly:

Step 1: Take Notes

This is often a subject that is passed by many individuals who are attempting to repair industrial equipment. When a unit first hits our bench we make note of many important aspects of the equipment including, but not limited too:

    1. Manufacturer
    2. Serial Number
    3. Reason for Service
    4. Urgency (Rush Overtime or Standard)
    5. Visual Inspection of External Device

Step 2: Conduct Diode and IGBT Tests

There are a number of methods to test the input and output power section of a drive, and this step is essential prior to applying power to the unit. If for any reason there is a short on the input side or output side of the drive, further damage can be caused to the unit if power is applied to it.

For this reason, we use a meter to properly test the input and output power sections of the drive prior to applying any power to the actual unit. If a short is found, quite often the unit can be disassembled and the cause of the short can be diagnosed and quoted for repair. If the repair is too costly, then a replacement is recommended.

Step 3: Power The Unit

If the input and output power sections of the AC Motor Speed Controller test healthy, then now is the time to power the unit up to see what we get. It is at this point that all of the safety precautions must be taken to ensure death or injury do not occur. On our test bench, we prefer to slowly increase the voltage to the unit until the rated input voltage of the drive is achieved.

Depending on whether or not the drive gives us a display will determine what further action will be taken. If no display is available, dis assembly and diagnosis of the internal power supply of the control section of the drive is likely necessary to further evaluate cause of failure and establish a quotation.

Step 4: Run A Motor

If the previous three tests have passed, then it is time to run a basic jog function of the drive with a simple template program. Often when a drive comes into our facility, we make sure to backup whatever program is currently stored in the drive prior to inputting a template program and running a test procedure. This ensure we have a backup copy of the program.

The best method for backing up depends on the brand of drive, but after it has been backed up, we typically will either reset the AC motor speed controller to factory defaults through the keypad and recommission a basic start, stop and job application or closed loop if an encoder is involved. If the motor will not run, it will be necessary to check the output voltages and current rating going to the motor to see if the AC motor speed controller is “firing” properly to move the motor.

Step 5: Contact The Customer

Usually at this point we have established some failure in the unit, if for some reason there seems to be no issues at this point further communication with the customer is often necessary.

At this point we will gather application specific information from the customer to establish whether or not it may be some outside issue associated with the system including, but not limited to, PLC communications, faulty IO, bad wiring or even bad cabling. There is no single way to do this step, as it really depends on a wide variety of variables.

Step 6: Send a Tech

If the customer cannot establish failure on any other aspect of the machine and the drive appears to test fine, then it may be necessary to send a field service technician on site to establish cause of failure.

Our field service techs are trained to troubleshoot any issue ranging from standard AC Motor Speed Controllers to advanced robotics and PLCs. They are trained to establish cause of failure as quick as possible.


Precision Electric has used these techniques over the past 20 years to establish one of the best reputations for the industrial service industry. These methods for testing AC motor speed controllers have been well established and have resulted in the repair or replacement of thousands of industrial AC motor speed controllers.