How much power do VFD controlled pump system use and what size generator do I need?

Many areas are subject to power outages and many folks are moving to an off grid lifestyle. We have other blogs that have helped homeowners that rely on their well to understand the factors around generator selection as well as the amount of power their traditional well equipment uses. This blog will focus on the power requirements of newer technology that is being integrated into modern well equipment.

Many modern pumps systems don’t just use a pump that turns on when the pressure is low and turn off when the pressure is high, they uses an advanced controller that monitors the system pressure and adjusts the speed of the pump to maintain constant pressure to your home or garden in spite of changing demand. These controllers are called constant pressure controllers, variable frequency drives or just referred to as “drives.” Sizing a generator for this type of system is NOT the same as for a traditional pump system! The generator requirements/recommendations for a traditional pump system are significantly different from those of the newer system that use VFD’s.

Modern pump controllers or “drives” typically have a display and the capability to program various motor parameters and the nominal system pressure that is required. If you don’t have any kind of display on your pump controller, then it is likely your pump equipment is using the traditional control box and pressure switch for operation. Check out this previous blog for information on power usage and generator sizing for traditional pump equipment. The data presented below is a generalization compiled from reviewing the requirements of Franklin Subdrive equipment in their AIM Manual on page 58, page 20 of the Franklin Subdrive Manual, as well as page 6 of the manual for the Pentek PID series of VFD’s developed for today’s modern pump systems. It is always recommended to know your specific equipment and manufacturers recommendations for that equipment when sizing the generator.

Franklin Water’s engineers pretty much sum up the size of a generator with this statement “Basic generator sizing for the Franklin Electric SubDrive/MonoDrive system is 1.5 times maximum input Watts consumed by the drive, rounded up to the next normal sized generator.” The engineers at Goulds give us similar adviceWith this in mind, err on the side of oversizing a generator and not undersizing!

Let’s lay out the data for the circuit breaker size and generator size required for you single phase 230 volt input VFD pump controller.

A 1/2 HP pump with a VFD controller will need a 15 Amp breaker and a 2 KW generate to operate properly.

A 3/4 HP pump with a VFD controller will need a 15 Amp breaker and a 3 KW generate to operate properly.

A 1 HP pump with a VFD controller will need a 15 Amp breaker and a 4 KW generate to operate properly.

A 1.5 HP pump with a VFD controller will need a 20 Amp breaker and a 5 KW generate to operate properly.

A 2 HP pump with a VFD controller will need a 25 Amp breaker and a 5 KW generate to operate properly.

A 3 HP pump with a VFD controller will need a 30 Amp breaker and a 6 KW generate to operate properly.

A 5 HP pump with a VFD controller will need a 50 Amp breaker and a 10 KW generate to operate properly.