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The Best Way to Reduce Motor Energy Costs

The Best Way to Reduce Motor Energy Costs

To Save Motor Energy Costs, Slow it Down

Variable frequency drives (VFD) are components that convert incoming AC power to accurately control motor torque, speed, and in some cases position.  Typically managing 3 phase induction motors, some drives can now control 3 phase permanent magnet brushless DC motors (PMDC) as well.  VFD’s are used in many applications today including industrial, agricultural, building automation, water/wastewater treatment and more.

A VFD converts its incoming power, a fixed voltage and frequency, to a variable voltage and frequency, which in turn can be used to manage motor speed.

In cases where these motors are running directly connected to AC power and at rated load, motors run at a known speed (based on AC frequency).  This speed is determined by the number of electrical poles in the motor.


In applications where motors run without a VFD, they are simply on or off, meaning they run at rated speed or they are not rotating at all.  Many people think that managing on time verses off time is a sensible way to control power consumption. Makes sense, right?  Not so fast!

In this case, the term “not so fast!” has significant meaning.  In simple terms, the speed at which a motor is running in some of these applications has a tremendous impact on energy consumption.  And it is not just proportional to motor speed – a motor driven pump operating at a base speed of 3450 rpm that requires 2000 watts may see the power requirements drop to 250 watts when run at ½ speed, or 1725rpm.  That is an 87.5% reduction in power!

Lower Motor Speeds will Reduce Energy Consumption Significantly


Many applications do not need the motor to run at full speed all of the time.  In fact, it some cases it may be beneficial to run the motor continuously at a lower speed rather than occasionally at high speed.

An easy to understand example is a motor driven pool pump.  (Understand that many pool pumps are single phase, but running them at variable speed has a similar power saving result).  In the case of a pool pump, water turnover rate through the filter system is key (along with chemical balance) to keep the water clear and clean.  Most filtration systems instruct the user to control the pump so that it turns over the total number of gallons in the pool at least once in a 24 hour period.  As a result, most people determine how many hours the pump must be on (running at full speed) to turn the water over in that 24 hour period.  What if the pump runs slower for a longer period of time?  You will get the same water cleaning results for less money. In fact, it is often better for cleaning as the circulation system helps pull debris from the pool while it is running.  And while the pump may be running slower for a longer period of time, there may be significant savings in power consumption.

Quickly Realize Cost Savings

The return on investment (ROI) can be significant, and the cost of a VFD can normally be recouped very quickly (in a matter of months).  We can run calculations that will very accurately measure the power consumption and cost savings a VFD may offer.  Contact AMMC today today to get started!