Convert a 3 Phase Motor to Single Phase
3 Phase Motor Conversion Options: Single Phase Rotary Phase Converter, Electric Motors and VFD Variable Frequency Drives.© By: Dave Rongey
Power Supply Options for a 3 Phase Motor
Electrical Question: I have a German woodworking machine that is powered by a 380 V 3 phase motor rated at 3KW 50 HZ 6.3 Amps. I have been making inquiries as to how to power this motor from a 240 V single phase supply, and I would welcome any advice on the options that I believe I have.
- The machine came with a separate transformer. The primary is rated at 3 phase 220V, 9.73 amps and the secondary is rated at 3phase 380V, 5.32amps. 50-60 HZ The woodworking machine was purchased in Germany and so I would assume that this transformer was purchased when the machine was moved to the US.
- The first opinion I received was to pull 480V and feed it into a 5KW VFD. I would then be able to limit the voltage to 380 V and dial the frequency to 50HZ. Can I pull 480V from a domestic type 240V panel? Would a 480 V 5 KW VFD be something of a custom drive and be expensive?
- Second option would be to rewire the transformer to a single phase transformer to change 240V single phase feed to 380V single phase. This would then feed a 5KW VDF to change the supply to 380V 3 Phase. Would this be possible and safe?
- Third option would be to run 240V single phase from the panel to a 5KW VFD converting the supply to 240V 3 phase 50 HZ then using the transformer change up the supply to 380V, 3phase 50HZ.
- Fourth option would be a rotary phase converter. this would work but I would not be able to adjust the HZ to match the motor.
- I would like to use a VFD as I can change the frequency to match the motor. Also I understand that the hard start will not be an issue as with a rotary phase converter. However I am unsure of the best place to put the VFD, before the transformer or after it? Any potential problem with where the VFD goes?
- If the transformer can be rewired to single phase will there be any change it it’s properties or performance?
I know just enough about this subject to be dangerous. I will be using a qualified electrician. Any help would be gratefully appreciated. Thank you for taking the time.
This electrical wiring question came from Martin, in Upperville, Virginia.
Thanks for your electrical wiring question Martin.
3 Phase Motor Conversion Options
To make a decision about how to convert a machine to work with a different voltage and phase it would be good to identify all options and then determine the best conversion process.
The Machine to be Converted
- Are the electrical functions of the machine limited to the motor only and a Start Stop switch, or are there other components or electronic components that require power?
- If the motor is the only electrical device that is to be powered then we can focus on the cost of replacing the motor with one of the same specifications, but with the available power at the location where the machine will be installed.
Rotary Phase Converter
- A rotary phase converter is definitely an option that should be considered, and may not be as expensive as replacing the motor.
- I have personally installed such equipment to power up commercial three phase motors when the power was limited to single phase.
Electric Motors and VFD Variable Frequency Drives
- My experience with Variable Frequency Drives has been with industrial applications where energy savings was the primary objective.
- The VFD units that were installed were used to control the speed of large motors, thereby reducing energy consumption.
- A typical VFD is costly and may not be practical for an individual application such as this, especially when the goal is power conversion, not energy savings.
Electrical Power Motor Conversion Summary
- It may be more practical and economical to replace the motor, provided a motor with the same specifications and frame can be located.
- A rotary phase converter can be a reliable option when the secondary power output will match the required power specifications of the equipment.
IMPORTANT: Warranty and Manufacture Support
- I would highly recommend consulting the manufacturer to see if they have a power conversion unit available, or what their recommendation would be.
- Keep in mind that altering the equipment OEM specifications will most likely void the warranty.
- Typically when equipment fails and a manufacture representative is contacted the first thing they will inquire about is how the equipment was installed and if the power supply matches the specifications as stated in the Owners and Installation Manual which is supplied with the machine.
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