Troubleshooting VFD drives can be cost prohibited when it impacts maximum throughput. Evaluating the situation and knowing when to call a professional is critical when equipment becomes problematic. Troubleshooting VFD drives takes time and time is money if customer demands cannot be met due to VFD problems. In this day and age it’s simply unacceptable to lose throughput over an equipment issue. For these reasons, manufacturers stock spare drives in the storeroom to prevent troubleshooting VFD drives during production hours.
Connections
Checking connections is a step many people miss or do incorrectly when troubleshooting VFD drives. Heat cycles and mechanical vibration can lead to sub-standard connections, as can standard preventative maintenance practices. Reusing torque screws is not a good idea, and further tightening an already tight connection can ruin the connection. Bad connections eventually lead to arcing. Arcing at the VFD input could result in nuisance over voltage faults, clearing of input fuses, or damage to protective components. Arcing at the VFD output could result in over-current faults or even damage to the power components.
Loose connections can cause erratic operation. For example, a loose START/STOP signal wire can cause uncontrollable VFD starting and stopping. A loose speed reference wire can cause the drive speed to fluctuate, resulting in scrap, machine damage, or personnel injury.
Diode and IGBT
There are a number of methods to test the input and output power sections of a VFD, and this step is essential prior to applying power to the VFD unit. If for any reason there is a short on the input side or output side of the VFD, further damage can be caused to the unit if power is applied to it.
For this reason, Precision Electric uses meters to properly test the input and output power sections of the VFD prior to applying power to the actual unit. If a short is found, 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 offered to the customer.
Power Up
If the input and output power sections test healthy when troubleshooting VFD drives, Precision Electric will power up the drives and perform amp reading and output frequency tests. Precision Electric prefers to slowly increase power voltage to the VFD until the rated input voltage of the VFD is achieved.
Depending on whether or not the VFD provides a display will determine what further action(s) will be taken. If display is unavailable, dis-assembly and diagnosis of the internal power supply of the control section of the VFD is likely necessary to further evaluate cause of failure, establish cost and lead time for a repair and replacement.
Run Motor
If the previous tests pass while troubleshooting VFD drives, performing a basic jog function of the VFD with a simple template program is suggested. Often when a VFD comes into our facility, we make sure to backup whatever program is currently stored in the VFD prior to installing a template program to perform a basic jog function. This ensures a backup copy of the program can be installed after the repair is complete.
The best method for backing up depends on the brand of drive, but after it has been backed up, the VFD is reset to factory defaults through the keypad. Then the technician will commission a basic start, stop and job application; or, closed loop if an encoder is present. If the motor will not run, it will be necessary to check the output voltages and current ratings going to the motor to see if the VFD is functioning properly to rotate the motor.
Contact Customer
At this point we have determined the cause of failure, estimated lead time and cost of the VFD repair. If the VFD tested good, then further underlying issues are communicated to the customer. This is when Precision Electric will gather application specific information from the customer to establish whether or not it may be an outside issue associated with the system such as, 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.
Send Service Tech
If the VFD tests good, then it may be necessary to send a field service technician on site to establish cause of failure. Field service technicians should be trained to troubleshoot any issue ranging from troubleshooting VFD drives, onsite repair, to advanced robotics, PLCs and more. Field technicians should also be trained and experienced enough to establish cause of failure and come up with solutions onsite, or, as quick as possible.
Troubleshooting VFD drives should be taken with extreme caution. Troubleshooting VFD drives should only be performed by technicians who have required training and experience to work with electrical equipment. Precision Electric strongly recommends consulting an expert in the field when troubleshooting VFD drives. Many VFD controllers have an internal DC bus that retains a charge after power has been cut to the drive, and as a result, electrocution may occur if parts are touched before the capacitors are discharged. Technicians troubleshooting VFD drives must always take extra precautions to ensure proper safety measures are taken, or injury or even death may occur.
Precision Electric has been troubleshooting VFD drives since 1984. Precision Electric offers free repair quotes and free replacement quotes for VFD drives other industrial related equipment. Call us today at 574-256-1000
