The GS4 drive can control multiple motors three different basic ways and via two additional modes which are a combination of the basic modes. In Time circulation mode, the drive controls up to 8 motors, one at a time. It sequentially cycles through the pump motors to keep the run time and wear of the motors evenly distributed which extends the service life of your system and saves you time and money. Quantity Control and Quantity Cycle allow you to control multiple motors at the same time so the system can keep up with increasing demand. Quantity Control typically has one motor that is sized to meet the average or typical demand. And it’s powered directly by the GS4 Drive. The GS4 drive then uses its relay outputs to control contactors so it can add pumping capacity as demand increases. This mode can add up to 8 additional motors that are strictly line powered while the original motor is controlled by the drive. Quantity Cycle mode is similar in that it adds motors as demand increases, but each motor can be drive powered. The nice thing about that is as demand increases, each motor is spun up under drive control and then switched over to line power so the dive can spin up the next motor - which means you can control how fast each motor comes up to speed and therefore control the wear and tear on all the motors, which saves you money in the long run. The quantity control mode simpy hits the additional motors with full line power each time they are powered up – which is more stressful on the motors than bringing them up under drive control. The last motor stays under drive control so there is no need for that last contactor. The catch with Quantity Cycle is now it takes two drive outputs to control each motor so you’re are limited to controlling 4 motors total. Both Quantity Control and Quantity Cycle modes monitor the drives output frequency to decide when it is time to add or remove a motor. So, you would typically have the motor trying to maintain some system setpoint – maybe keeping a tank filled to a certain level with a level sensor as the feedback to the drive’s PID. As the demand increases the first motor will eventually reach a frequency that you specify – usually the motors rated frequency - which tells the Quantity Control or Cycle modes it’s time to add in another motor to help meet that demand. The beauty of that is you don’t have to buy a single big expensive motor and big expansive drive just to meet the infrequent worse case system load. You can buy a less expensive motor and less expensive drive to meet a more moderate or typical demand, and supplement that with additional inexpensive smaller motors that the drive can automatically bring on-line as the need arises. This reduces both your initial expense and your long-term maintenance expenses. Win-Win. You can also use the Time Circulation mode with Quantity Cycle and Quantity Control modes so you can even out the motor wear in those modes too! Click here to learn more about GS4 Drives. Click here to learn about AutomationDirect’s free support options and click here to subscribe to AutomationDirect’s free YouTube channel so you will be notified when we publish new videos.