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Control Techniques Variable Speed Drives
Control Techniques Variable Speed Drives
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Can I save energy by applying a VSD to an existing motor?
Yes, particularly if you have a centrifugal fan or pump load. If you know the duty cycle of the application you can quickly calculate your payback period using a simple software utility downloadable from
What is the recommended shelf life?
Proper storage would be temperatures less than 122 degrees F and greater than -40 degrees F. After two years of storage the DC capacitors may need to be reformed.
When should I install AC Line Reactors?
Input line reactors may reduce the risk of drive damage due to supply imbalances and severe disturbances. They may also reduce the amount of electrical noise that a drive generates back to the power line. There are several factors that affect this decision.
Can I operate a VSD at high altitude?
Yes, however de-rating of 1% per 330ft above 3,300 ft above sea level to compensate for the reduced air density is required.
What is the maximum temperature that a VSD can operate?
For best conditions a VSD should operate between 32 to 104 degrees Fahrenheit. It may be necessary to include heaters below 32 degrees F in order to reduce problems caused by condensation. If temperatures exceed 104 degrees Fahrenheit de-rating of the drive may be necessary.
Can I run multiple motors from a single VSD?
Yes, but the drive needs to be sized for the combined motor full load current ratings of all the connected motors and individual motor protection needs to be provided. In addition a drive output filter may be required depending upon distance between the drive and motors and the number of motors. Check with Emerson Application Engineering.
Can I operate a single-phase motor off a VSD?
No, a single-phase motor is not designed to operate from a VSD. It is possible to connect a single-phase input to some VSD models, which in turn control three-phase motors. Check with Emerson Application Engineering.
I have a 10hp motor; can I select a VSD based on the hp rating only?
The best way to size a VSD is to obtain the motor full load amp rating (FLA) and nameplate voltage rating and select a drive that has sufficient ampere capacity at the rated motor voltage.
I have read the manual and I still need help, who do I call?
Emerson has a global network of drive and application centers to support you. In North America, the technical support line number is 1- 800-533-0031 Ext. 302
How do I add custom features to my application?
Depending on the drive you can typically add memory devices and create custom applications on board without having to purchase a PLC or Process Controller in many cases.
What is the best way to record my drive configuration?
Emerson drive parameters can be copied onto a physical plug in memory device or to a PC using a communications cable. The drive software is downloadable at no charge from
What is the difference between an Inverter and a VSD?
Nothing, there are many names and acronyms that are used for electronic variable speed drives. These include VSD (variable speed drive), VFD (variable frequency drive), ASD (adjustable speed drive), AFD, Inverter and just Drive.
Can I extend the speed range of the motor above 60Hz?
Yes, but with caution. The load characteristics of a centrifugal fan or pump inherently increase sharply above rated speed. If you increase the maximum speed to say 66Hz (10%) this will result in an increase in load horsepower of 33%. This may well exceed the capacity of the motor or cause nuisance VSD tripping.
Can I connect a VSD to any existing three-phase motor?
No, the motor insulation must be adequately rated for VSD use. If in doubt you can either contact the motor manufacturer or Control Techniques can supply a motor filter. For example US Electric Motors provide an application note that explains which of their motors can be used on a VSD supply and what application constraints apply. Check out
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