I know it is possible to wire up a 3-phase motor to run on single-phase using a capacitor in the motor circuit. Where must the capacitor be placed in the motor circuit and how do I determine the optimal size for the capacitor if all I know is the normal nameplate information for the motor?
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Running a 3-phase induction motor on single phase 3
- Thread starter vzylhj
- Start date
Hi,
This is a new thing for me!! Is it possible and can it be generalized to any size/speed motor? How about the reduction in torque in the single phase case?
As you are also aware,
1) A 3-phase motor develops its starting torque due to the rotating magnetic field of the input balanced 3-phase supply. Each coil correspond to each phase is physically separated by 120 electrical degrees whereas each coil of the same phase is separated by 180, 90 electrical degrees etc. depending on the number of poles(sync. speed)
2) A single phase motor does not develop its own starting torque, and hence to create a starting torque two separate windings (starting and running ) are physically separated by 90 electrical degrees. Also at the same time the currents in each winding are also spaced apart by 90 degrees to develop the maximum torque.
Therefore it is obvious that, to convert (1) to (2), you have to energize a set of two windings which are 90 degree apart. To my knowledge, I believe this is only possible on a 4 pole motor where the same phase coils are 90 degree apart. In that case the capacitor has to be connected to one set of windings chosen as starting. The sizing of the capacitor can be done by measuring each impedance of each winding and then determining the capacitance value for a 90 degree split using a basic phasor diagram.
I invite our friends to make their contributions to this interesting new thread!!!
Regards!
This is a new thing for me!! Is it possible and can it be generalized to any size/speed motor? How about the reduction in torque in the single phase case?
As you are also aware,
1) A 3-phase motor develops its starting torque due to the rotating magnetic field of the input balanced 3-phase supply. Each coil correspond to each phase is physically separated by 120 electrical degrees whereas each coil of the same phase is separated by 180, 90 electrical degrees etc. depending on the number of poles(sync. speed)
2) A single phase motor does not develop its own starting torque, and hence to create a starting torque two separate windings (starting and running ) are physically separated by 90 electrical degrees. Also at the same time the currents in each winding are also spaced apart by 90 degrees to develop the maximum torque.
Therefore it is obvious that, to convert (1) to (2), you have to energize a set of two windings which are 90 degree apart. To my knowledge, I believe this is only possible on a 4 pole motor where the same phase coils are 90 degree apart. In that case the capacitor has to be connected to one set of windings chosen as starting. The sizing of the capacitor can be done by measuring each impedance of each winding and then determining the capacitance value for a 90 degree split using a basic phasor diagram.
I invite our friends to make their contributions to this interesting new thread!!!
Regards!
landcruiserman
Electrical
hi i found this company on the net called faststarts ltd in new zealand website i think that they have cracked this problem, and mine to. regards
landcruiserman you have a typo on your link, it should be:
Having quickly read through their description, I'm not clear on what the advantage of running a 3-phase motor on their system rather than on a standard VFD designed to run off a single phase supply.
Having quickly read through their description, I'm not clear on what the advantage of running a 3-phase motor on their system rather than on a standard VFD designed to run off a single phase supply.
The easy way is to use a variable speed drive. There are many on the market designed for single phase input and three phase output. The only problem with this is thst the output voltage is determined by the input voltage, so you need a low voltage three phase motor.
Best regards,
Mark Empson
Best regards,
Mark Empson
Hello vzylhj,
Following on from the information posted by Marke, most motors of up to 2.2kW at 400VAC contain 230VAC windings.
For connection to 400VAC supplies, these windings must be configured in 'star' connection to ensure they are not over-voltaged.
When using this type of motor with a single phase input, 3 phase output VSD, the windings must be configured in 'Delta'.
Regards,
GGOSS
Following on from the information posted by Marke, most motors of up to 2.2kW at 400VAC contain 230VAC windings.
For connection to 400VAC supplies, these windings must be configured in 'star' connection to ensure they are not over-voltaged.
When using this type of motor with a single phase input, 3 phase output VSD, the windings must be configured in 'Delta'.
Regards,
GGOSS
jbartos
Electrical
- Jan 15, 2000
- 6,440
- 0
- 0
Suggestion: Essentially, a AC-DC-AC conversion can be applied. AC-DC will rectify the single phase power supply to DC. Then, it is a matter of DC-AC inverter. This conversion may have some marginal advantages than the VFD in a sense that additional three phase loads may be added since it works as a 3-phase power source. A reduced voltage or soft starter may be separate.
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1
- #9
Hi vzylhj
Rumor has it,that any 3ph motor will run on single ph power if you get it started.Connect a 1ph power (230volts)to Phases A and B of a 3 ph motor.Motor wil not run until capacitor/s are hooked up to the 3rd phase to produce a Phase shift.The size of the Caps will be dependent on the
expected load.Horse power rates will vary from 50 to 75% of the motor nameplate HP.Thre are other types of simple phase converters using Autoransformer and Capacitor also other connections that involves getting into the windings and spliting the phase connections from either a Y or Delta internal connection.I understand that manufactured for the specific load characteristics.If you want to do it yourself it may involve a lot trial and error.
GusD
Rumor has it,that any 3ph motor will run on single ph power if you get it started.Connect a 1ph power (230volts)to Phases A and B of a 3 ph motor.Motor wil not run until capacitor/s are hooked up to the 3rd phase to produce a Phase shift.The size of the Caps will be dependent on the
expected load.Horse power rates will vary from 50 to 75% of the motor nameplate HP.Thre are other types of simple phase converters using Autoransformer and Capacitor also other connections that involves getting into the windings and spliting the phase connections from either a Y or Delta internal connection.I understand that manufactured for the specific load characteristics.If you want to do it yourself it may involve a lot trial and error.
GusD
A VFD changes the Incoming the AC power to DC then back to AC. Almost any VFD will run on Single Phase in give 3 phase out. Just size the Drive 2x what the motor is rated for.
The motor should be at least 10-25% of the drive size depending on the drive. If it not some drives will give false loss of out put phase faults.
This is the easiest solution to your problem and will work. I like Yaskawa Drives which used to Magnetek. These drives without a doubt will work.
You can also buy phase converters from almost anywhere that go from single phase to 3 phase out. I think you can even get them from McMaster Carr.
Paul Thomas
The motor should be at least 10-25% of the drive size depending on the drive. If it not some drives will give false loss of out put phase faults.
This is the easiest solution to your problem and will work. I like Yaskawa Drives which used to Magnetek. These drives without a doubt will work.
You can also buy phase converters from almost anywhere that go from single phase to 3 phase out. I think you can even get them from McMaster Carr.
Paul Thomas
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- #11
I used to work for a small systems integrator that would routinely face this problem. We would have a system we were building a panel for that used 3 Phase motors, but we didn't have 3 phase in our building. One of the electicians worked out a method using an old 3 phase motor without the stator... don't ask me how it works, but you plug in single phase on the one side and out came 3 phase on the other. Obviously this isn't very efficient, but it allowed us to check out our panels before shipping to our customers.
There is a product that you can also purchase for this. The link is:
There is a product that you can also purchase for this. The link is:
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1
- #12
Hi:
I live in a rural area with severely attenuated utility services.
The local power co. wanted an exorbitant amount to bring in 3 ph power for a small molding operation I used to run.
So I was forced to “make” my own.
Three capacitors are needed, one electrolytic for starting, typically 70 – 100 mfd per hp and two running caps appx. 12 – 28 mfd / hp.
They are connected as follows; the running caps are connected from each side of the line to the “ghost” leg.
The starting cap (electrolytic) from one side of the line to the
Third, (ghost) leg through a momentary contact switch.
Power is applied through a suitable size line starter, and the
Momentary contact switch is closed until the motor comes up to full speed. Run caps must be oil filled, and can be “tweaked’ with a clamp-on ammeter to achieve the best balance conditions.
I routinely used this set up to start a 7.5 hp hydraulic pump
To operate my presses. The added benefit of doing this is that once the large motor was running, it would act as a generator for the third phase and you can start other three phase motors in your shop. Let me know if you require a diagram.
I live in a rural area with severely attenuated utility services.
The local power co. wanted an exorbitant amount to bring in 3 ph power for a small molding operation I used to run.
So I was forced to “make” my own.
Three capacitors are needed, one electrolytic for starting, typically 70 – 100 mfd per hp and two running caps appx. 12 – 28 mfd / hp.
They are connected as follows; the running caps are connected from each side of the line to the “ghost” leg.
The starting cap (electrolytic) from one side of the line to the
Third, (ghost) leg through a momentary contact switch.
Power is applied through a suitable size line starter, and the
Momentary contact switch is closed until the motor comes up to full speed. Run caps must be oil filled, and can be “tweaked’ with a clamp-on ammeter to achieve the best balance conditions.
I routinely used this set up to start a 7.5 hp hydraulic pump
To operate my presses. The added benefit of doing this is that once the large motor was running, it would act as a generator for the third phase and you can start other three phase motors in your shop. Let me know if you require a diagram.
RalphChristie
Electrical
jrjedi:
Something like this?
I do have an old paper (although I can't claim the origin of it) about the use of 3ph motors as single phase motors (50hz):
In special cases, three-phase motors can be used as single-phase motors, i.e.:
a) Manually started motors without capacitor. They do not start up by themselves but must be started by hand. The output is about 60% of the three-phase value. This type of service is only rarely used in practice.
It is essential that the motor be started immediately after the breaker has been closed. The motor will run in the direction in which it is started by hand.
b) Motor with running capacitor:
1)125V-delta/220V-star motor (star connection)
220V (L and N) on two legs and the cap between L and the gost leg.
For opposite direction, connect the cap on N and the gost leg.
2) 220V-delta/380V-star motor(delta connection)
220V (L and N) on two legs and the cap between L and the gost leg.
For opposite direction, connect the cap on N and the gost leg.
3) 125V-delta/220V-star motor (star connection)
220V (L and N) on two legs and the cap between L and N.
The motor delivers about 70 to 80% of the three-phase output, the starting torque being about 25 to 35% of the rated full-load torque available in operation as single-phase motor.
There is a diagram to obtain the cap rating:
X-axis = Power output P in operation as single phase machine (70 to 80% of three-phase output) in kW (max 1kW)
Y-axis = Capacitance C in micro-Farad (max 100micro-F)
For 1000 or 1500 rev/min the graph is almost a straight line with 0.2kW / 20micro-F a minimum and 1kW / 95micro-F a maximum.
For 3000 rev/min the graph is almost a straight line with 0.1kW / 10micro-F the minimum and 1kW / 80micro-F the maximum
For circuits 1 and 2, the cap must be rated for a continious service voltage equal to 1.15 times system voltage (for 220V systems at least 260V AC)
The cap rating required for circuit 3 is only 50% of that for circuits 1 and 2 at the same motor output and system voltage. The cap should be rated for a continious service voltage of 1.35 times the system voltage, i.e. for 320V AC continious in the case of 220V systems.
In the view of the cost of the capacitor circuit, economic use of the three-phase motors with a running cap for operation on a single-phase system is limeted to single-phase ratings of 1 to 2kW.
The low starting torque and poor acceleration characteristics limit the use of these motors to fan drives and light-starting drives.
For other system voltages, the capacitor rating varies inversly with the square of the system voltage.
I will try to trace the origin of the paper.
Regards
Ralph
Something like this?
I do have an old paper (although I can't claim the origin of it) about the use of 3ph motors as single phase motors (50hz):
In special cases, three-phase motors can be used as single-phase motors, i.e.:
a) Manually started motors without capacitor. They do not start up by themselves but must be started by hand. The output is about 60% of the three-phase value. This type of service is only rarely used in practice.
It is essential that the motor be started immediately after the breaker has been closed. The motor will run in the direction in which it is started by hand.
b) Motor with running capacitor:
1)125V-delta/220V-star motor (star connection)
220V (L and N) on two legs and the cap between L and the gost leg.
For opposite direction, connect the cap on N and the gost leg.
2) 220V-delta/380V-star motor(delta connection)
220V (L and N) on two legs and the cap between L and the gost leg.
For opposite direction, connect the cap on N and the gost leg.
3) 125V-delta/220V-star motor (star connection)
220V (L and N) on two legs and the cap between L and N.
The motor delivers about 70 to 80% of the three-phase output, the starting torque being about 25 to 35% of the rated full-load torque available in operation as single-phase motor.
There is a diagram to obtain the cap rating:
X-axis = Power output P in operation as single phase machine (70 to 80% of three-phase output) in kW (max 1kW)
Y-axis = Capacitance C in micro-Farad (max 100micro-F)
For 1000 or 1500 rev/min the graph is almost a straight line with 0.2kW / 20micro-F a minimum and 1kW / 95micro-F a maximum.
For 3000 rev/min the graph is almost a straight line with 0.1kW / 10micro-F the minimum and 1kW / 80micro-F the maximum
For circuits 1 and 2, the cap must be rated for a continious service voltage equal to 1.15 times system voltage (for 220V systems at least 260V AC)
The cap rating required for circuit 3 is only 50% of that for circuits 1 and 2 at the same motor output and system voltage. The cap should be rated for a continious service voltage of 1.35 times the system voltage, i.e. for 320V AC continious in the case of 220V systems.
In the view of the cost of the capacitor circuit, economic use of the three-phase motors with a running cap for operation on a single-phase system is limeted to single-phase ratings of 1 to 2kW.
The low starting torque and poor acceleration characteristics limit the use of these motors to fan drives and light-starting drives.
For other system voltages, the capacitor rating varies inversly with the square of the system voltage.
I will try to trace the origin of the paper.
Regards
Ralph
OnLineSystems
Electrical
To RalphChristie,
I agree with your quotes; but CAUTION[/color red] with the a) alternative (manual push), because:
1) until it is being pushed on, the motor sees short circuit currents of 6-10 times rated current levels in the energized windings (it will burn about as fast as a locked-rotor motor will take to burn).
2) I've shaken too many hands lacking a finger or two because of rotating machinery. The suggestion made by the reference sadly works; but this unsafe practice also dates the paper to older times.
A really good solution for many rural single phase applications is a written-pole-motor. (I tested one such beast extensively on a dynamometer). They definitely do work, even though their design is a bit puzzling. Here is the web adress of the manufacturer with whom I dealt years ago:
Greetings,
ew
I agree with your quotes; but CAUTION[/color red] with the a) alternative (manual push), because:
1) until it is being pushed on, the motor sees short circuit currents of 6-10 times rated current levels in the energized windings (it will burn about as fast as a locked-rotor motor will take to burn).
2) I've shaken too many hands lacking a finger or two because of rotating machinery. The suggestion made by the reference sadly works; but this unsafe practice also dates the paper to older times.
A really good solution for many rural single phase applications is a written-pole-motor. (I tested one such beast extensively on a dynamometer). They definitely do work, even though their design is a bit puzzling. Here is the web adress of the manufacturer with whom I dealt years ago:
Greetings,
ew
RalphChristie
Electrical
OnLineSystems:
You are correct in making these comments, and yes, I should have made sidenotes to show the possible dangers involved in doing it.
1.It is essential that the motor be started immediately after the breaker has been closed
I should have made a sidenote regarding the initial inrush current, although "immediately" state "at the moment of energizing"
2. I've just quote the paper to show that it can be done, although it is really an unsafe practice.
Thanks
Regards
Ralph
You are correct in making these comments, and yes, I should have made sidenotes to show the possible dangers involved in doing it.
1.It is essential that the motor be started immediately after the breaker has been closed
I should have made a sidenote regarding the initial inrush current, although "immediately" state "at the moment of energizing"
2. I've just quote the paper to show that it can be done, although it is really an unsafe practice.
Thanks
Regards
Ralph
Hello GGOSS,
You had said in previuos post.
"Following on from the information posted by Marke, most motors of up to 2.2kW at 400VAC contain 230VAC windings.
For connection to 400VAC supplies, these windings must be configured in 'star' connection to ensure they are not over-voltaged.
When using this type of motor with a single phase input, 3 phase output VSD, the windings must be configured in 'Delta'."
That being said. I have 3 phase input, hooking up to 440VAC with the motor possibly being more than 2.2KW. Does the star and delta connections need to be configured the same as said above. Would you know how to setup this type of motor? Also, might you know why on the cover would there be two delta connections and 2 star connections for 12 lead connection? One delta has ?, the other has ??. the same is for the star connections
Jrochte
You had said in previuos post.
"Following on from the information posted by Marke, most motors of up to 2.2kW at 400VAC contain 230VAC windings.
For connection to 400VAC supplies, these windings must be configured in 'star' connection to ensure they are not over-voltaged.
When using this type of motor with a single phase input, 3 phase output VSD, the windings must be configured in 'Delta'."
That being said. I have 3 phase input, hooking up to 440VAC with the motor possibly being more than 2.2KW. Does the star and delta connections need to be configured the same as said above. Would you know how to setup this type of motor? Also, might you know why on the cover would there be two delta connections and 2 star connections for 12 lead connection? One delta has ?, the other has ??. the same is for the star connections
Jrochte
There are some links - some of which are probably still good
at:
I also have extensive notes that I have not posted, but could.
There is also a link to a converter that has been in service
since I built it over a year ago. Works great.
<als>
at:
I also have extensive notes that I have not posted, but could.
There is also a link to a converter that has been in service
since I built it over a year ago. Works great.
<als>
Hello everyone..I have an Austrian-made Wintersteiger ski tuner in my garage, aquired from a local ski shop. In simple terms, it is a very large wet-belt sander with and large motor and a water pump. A single ski is placed over a long sanding belt turning one direction while a rubber coated feed wheel moves it across the moving belt. The water pump feeds water with coolant onto the sanding belt. I need info on how to get it running. It is a 3-phase unit and I have 220 to it's location. The numbers on the motor are: 3 x 208 - 220v 50/60HZ. It is out of the question to have the power company do anything for me. I have seen converters advertised for $130 to $200 and wonder if that's the answer. I've been told that 3-phase power is needed just to start it and that once started, it uses less power. If I haven't supplied enough information, please let me know via this site or my email address. I posted this message under Industrial because there was no posting for Garage Mechanic. Thanks for your help.....
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