This is popular subject here at Precision Electric. We receive emails and calls all the time for customers who have three phase equipment and need to operate this equipment from single phase power. Since most higher horsepower drives only accept three phase input power, many customers are left with little options or alternatives. However, we have a solution for these applications.
Before you derate your drive it is most important to ensure the drive you are using is properly suited for your application. The following are some basic guidlines to help you in determining whether or not your Variable Frequency Drive is suitable for your application:
- Gather motor nameplate data including horsepower (HP), current (Amps), motor voltage, input line voltage and power source phase.
- Determine which type of drive your application will require. The type will fall under the category of either Volts per Hertz (V/Hz), closed-loop vector, or open-loop vector (Sensorless Vector).
Heres how to derate a three phase drive for single phase power:
- Determine the motor horsepower and motor current
- Choose drive with a Horsepower higher than the Horsepower of the motor to compensate for the additional input current from the single phase power source.
The simplest formula used for these types of applications is:
The drive max current needs to be greater than that of the motor current. Take your motor current and multiply by 1.73. Then choose a drive that is rated at or higher than the revised current.
- Drive rated current > Motor Current Rating * 1.73
- Drive rated current > 27 Amps * 1.73
- Drive rated current > 46.71
Now it has been determined this example application will need a 230 VAC 3 phase Volts per Hertz (V/Hz) Variable Frequency Drive with an input current rated at or above 47.0 amps. This particular application would need a 15hp 240V three phase drive to operate on single phase power.