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3 phase to single phase conversion 1
- Thread starter mushroom
- Start date
jbartos
Electrical
- Jan 15, 2000
- 6,440
Suggestion: Generally, any motor can be rewired for some feasible other motor; however, the following may be questioned:
1. Cost
2. Rewired motor parameters
3. Quality of rewiring. It is often somewhat inferior to the originally manufactured motor/product.
1. Cost
2. Rewired motor parameters
3. Quality of rewiring. It is often somewhat inferior to the originally manufactured motor/product.
Assuming the electric motor is not too big (max. 3 Hp?) and 3 phase Y motor for 415 V, I think it's possible to do so by the use of a capacitor.
The connection should be than:
Phase L1 (215 V) -> U terminal on electric motor;
Neutral -> V terminal on electric motor;
Capacitor -> V terminal on electric motor;
Capacitor -> W terminal on electric motor.
Rotating direction can be changed by changing terminal connection U with W.
The required capacity of the capacitor to be used is depending on the electric motor power. (There are table for these values as a rule of thumb, but unfortunately not in my posession)
Note that this is will reduce the maximum motor power and start-up torque. It however might be a workable solution.
The connection should be than:
Phase L1 (215 V) -> U terminal on electric motor;
Neutral -> V terminal on electric motor;
Capacitor -> V terminal on electric motor;
Capacitor -> W terminal on electric motor.
Rotating direction can be changed by changing terminal connection U with W.
The required capacity of the capacitor to be used is depending on the electric motor power. (There are table for these values as a rule of thumb, but unfortunately not in my posession)
Note that this is will reduce the maximum motor power and start-up torque. It however might be a workable solution.
-
1
- #5
Look-up single phase to 3-phase conversion using a motor as a rotary converter. Take a look at this website:
You will probably need to "hand start" the motor, and your available power will be about 1/3, but if you insist, it can be done.
I have seen lots of 3-phase motors running off of 2 phases, with the 3rd phase created with capacitors. Not quite the same, but just a thought.
You will probably need to "hand start" the motor, and your available power will be about 1/3, but if you insist, it can be done.
I have seen lots of 3-phase motors running off of 2 phases, with the 3rd phase created with capacitors. Not quite the same, but just a thought.
There are several methods you could use for running your 3-phase motor from a single phase source. In order for any of them to be practical, it is important to know whether this motor can be re-connected for 240 VAC operation. If this is the case, then these are the options I am aware of:
1. "Single phasing"
2. Static phase convertor
3. V/F drive
4. Rotary phase convertor
"Single phasing"
This option is the cheap, quick, and dirty solution. It's disadvantages are that the motor will tend to run hotter and will not be able to safely operate at full power. It relies on the fact that a 3-phase motor will run with single phase power applied to two legs as long as it is turning fast enough when that power is applied. In order to get the motor started, you need to either use a starting capacitor or some sort of mechanical drive to get the motor turning. The starting circuit consists of a capacitor, a contactor, and a timer. To start the motor, you apply single phase power to two legs of the motor and, at the same time, connect the capacitor between one of the powered legs and the unpowered leg. After the motor gets up to speed, you disconnect the capacitor (this is what the timer and the contactor are for). A mechanical method of starting the motor could be a simple as wrapping a rope around the shaft and giving it a pull just before you press the start button. A more reliable method is to couple a small single phase motor to the 3-phase motor and set up a timer to remove power from the starting motor after the 3-phase motor is running. It is important to note, that if you are starting the motor mechanically, you should wait until the motor is turning before you apply power to it. If you apply the power first, you would have a very difficult time turning the motor shaft.
Static Phase Convertor
This device "generates" power for the third leg of the motor using capacitors to produce a phase shift. They are available from commercial suppliers and are relatively inexpensive. They produce better performance the the "single phasing" method but you still have to derate the motor somewhat. Also, the size of the phase convertor has to be matched to the motor size and they tend to work best in applications where the motor load doesn't vary widely.
V/F Drive
Some variable frequency drives are rated to operate on single phase input power. Often the drive needs to be oversized in this application. You would have to contact the drive manufacturer to know for sure. The V/F drive would cost somewhat more than the first two options, but it offers many extra features including variable speed, current limiting, and controlled acceleration rate.
Rotary Phase Convertor
This is basically a 3-phase motor set up to run off single phase power either using the first or the second method described above. The motor then "generates" the third leg. An advantage to this device is that is more tolerant of varying load than a static phase convertor. These devices are available commercially but they are somewhat more expensive then the static phase convertors--probably on a par with the V/F drive.
As a side note:
I have a friend who is running a machine shop in a rural area using a cast off 40 Hp 3-phase motor as a rotary phase convertor. The motor is started using a starting capacitor as described above. In the power it produces, the phases are not perfectly balanced, but it works well enough for the equipment he is using. His equipment ranges from a large lathe with a 30 Hp motor to a small CNC mill with a 3 Hp spindle motor.
1. "Single phasing"
2. Static phase convertor
3. V/F drive
4. Rotary phase convertor
"Single phasing"
This option is the cheap, quick, and dirty solution. It's disadvantages are that the motor will tend to run hotter and will not be able to safely operate at full power. It relies on the fact that a 3-phase motor will run with single phase power applied to two legs as long as it is turning fast enough when that power is applied. In order to get the motor started, you need to either use a starting capacitor or some sort of mechanical drive to get the motor turning. The starting circuit consists of a capacitor, a contactor, and a timer. To start the motor, you apply single phase power to two legs of the motor and, at the same time, connect the capacitor between one of the powered legs and the unpowered leg. After the motor gets up to speed, you disconnect the capacitor (this is what the timer and the contactor are for). A mechanical method of starting the motor could be a simple as wrapping a rope around the shaft and giving it a pull just before you press the start button. A more reliable method is to couple a small single phase motor to the 3-phase motor and set up a timer to remove power from the starting motor after the 3-phase motor is running. It is important to note, that if you are starting the motor mechanically, you should wait until the motor is turning before you apply power to it. If you apply the power first, you would have a very difficult time turning the motor shaft.
Static Phase Convertor
This device "generates" power for the third leg of the motor using capacitors to produce a phase shift. They are available from commercial suppliers and are relatively inexpensive. They produce better performance the the "single phasing" method but you still have to derate the motor somewhat. Also, the size of the phase convertor has to be matched to the motor size and they tend to work best in applications where the motor load doesn't vary widely.
V/F Drive
Some variable frequency drives are rated to operate on single phase input power. Often the drive needs to be oversized in this application. You would have to contact the drive manufacturer to know for sure. The V/F drive would cost somewhat more than the first two options, but it offers many extra features including variable speed, current limiting, and controlled acceleration rate.
Rotary Phase Convertor
This is basically a 3-phase motor set up to run off single phase power either using the first or the second method described above. The motor then "generates" the third leg. An advantage to this device is that is more tolerant of varying load than a static phase convertor. These devices are available commercially but they are somewhat more expensive then the static phase convertors--probably on a par with the V/F drive.
As a side note:
I have a friend who is running a machine shop in a rural area using a cast off 40 Hp 3-phase motor as a rotary phase convertor. The motor is started using a starting capacitor as described above. In the power it produces, the phases are not perfectly balanced, but it works well enough for the equipment he is using. His equipment ranges from a large lathe with a 30 Hp motor to a small CNC mill with a 3 Hp spindle motor.
jbartos
Electrical
- Jan 15, 2000
- 6,440
Suggestion to the previous posting marked ///\\V/F Drive
///AC motor drive could suffice.\\Some variable frequency drives are rated to operate on single phase input power. Often the drive needs to be oversized in this application. You would have to contact the drive manufacturer to know for sure. The V/F drive would cost somewhat more than the first two options, but it offers many extra features including variable speed, current limiting, and controlled acceleration rate.
///It is sufficient to rectify the AC to DC, and then invert the DC to 3-phase AC. Therefore, there is the AC (single phase) to DC to AC (three phase) energy conversion at fixed frequency. The variable frequency feature would be convenient for a speed control and soft start. If these two are not required, then the VFD will be unnecessary and more expensive.\\\
///AC motor drive could suffice.\\Some variable frequency drives are rated to operate on single phase input power. Often the drive needs to be oversized in this application. You would have to contact the drive manufacturer to know for sure. The V/F drive would cost somewhat more than the first two options, but it offers many extra features including variable speed, current limiting, and controlled acceleration rate.
///It is sufficient to rectify the AC to DC, and then invert the DC to 3-phase AC. Therefore, there is the AC (single phase) to DC to AC (three phase) energy conversion at fixed frequency. The variable frequency feature would be convenient for a speed control and soft start. If these two are not required, then the VFD will be unnecessary and more expensive.\\\
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