3 Phase Motor On Single Phase

[weilertool]

Can anyone out there tell me or send me a wiring diagram on how to make a 3 phase motor run on single phase power? I know it can be done, I just don't know how. I greatly appreciate any help that can be given!!

[GGOSS]

This depends very much on the size of the motor and how it is internally wired.

 

Motors up to 2.2kW are generally designed for 400VAC star connection and come with 6 terminals. Through these terminals it is possible to reconfigure the wings for delta connection, which in affect means the motor is now suitable for 3-phase 230VAC in liue of 3-phase 400VAC. Using a single phase 230V input, 3-phase 230V output variable speed drive, it is then possible to start and control the speed of such a motor.

 

Hope the above helps.

 

Regards,

GGOSS

[jraef]

Can anyone out there tell me or send me a wiring diagram on how to make a 3 phase motor run on single phase power? I know it can be done, I just don't know how. I greatly appreciate any help that can be given!!

 

Technically, it can't be done without something added to create that 3rd phase, as GGOSS said. There are 'tricks" to doing it, but there are costs associated with those tricks.

 

If you need full power out of the motor, GGOSS' suggestion of using a VFD as a phase converter is the easiest and best solution. He probably didn't notice that you posted from the US, so don't get confused by his 400V stuff, it doesn't apply here. If you have 1 phase power we must assume you have 230V, line and motor. You didn't post the size, but up through 3HP most 230V VFDs will accept 1 phase input and provide 3 phase output without the need to derate. AC Tech even offers one that does that for 5HP, but generally at 5HP and above you can still do it, but you must derate the VFD by 50%. So if you have a 7-1/2HP motor, use a 15HP VFD. Even if you have no intention of varying the speed, this is the simplest method of running a 3 phase motor at full load from a 1 phase supply.

 

You can also use capacitors to create a "phantom" 3rd phase from the other 2. This may be what you have seen, but what you probably didn't know is that this severely robs the motor of power capacity. The motor runs severely unbalanced and has a lot of what are called "negative sequence currents" because of the 1 phase power and because the sine waves are 180 degrees apart on the 2 "real" phases, compared to being 120 degrees out on true 3 phase. Negative sequence current produces negative torque in the motor and causes heating without doing useful work, meaning that it will severely overheat under load. For this reason, you must derate the motor by at least 50%, some even say 66%. So that means if you have a 15HP motor, you had better not need more than 7-1/2 or even 5HP out of it if you are going to do this.

 

The other possibility is to buy a larger (2x) 3 phase motor and run it as an idler after starting it with capacitors as per above (the caps are then switched out). It will generate the 3rd leg for your motor. Still slightly unbalanced, but not as bad as above. This will likely cost you more than a VFD if you have only the one motor, but is a good choice if you have multiple 3 phase loads in the same area. Do a Google search on "Rotary Phase Converter" and "RPC design" for lots of circuit design examples.

 

There are also Static Phase Converters (SPC) out there that are either the capacitors I mentioned above in a re-packaged format, or a hybrid device that uses a PWM converter only for the 3rd phase (Google "Phase Perfect").

[AB2005]

Dear weilertool,

 

Sir Jraef has explained very well about demerits for running a three phase motor on single phase by using capacitors or VFD.

However, if you want to only check a three phase motor on single phase by using a cheaper way, purchase “Running Capacitor(s)” from your local market which often use in single phase motors (1KW = 65uf). Then hook your motor up as following method;

 

Line = U&Z

Neutral = V&X

Capacitor = Neutral and W&Y

 

But you should confirm first the voltage rating of your motor. This method is not appropriate such a load where starting torque is primary concerned.

Hope this will help you.

 

[Switch_639]

Dear weilertool,

 

Sir Jraef has explained very well about demerits for running a three phase motor on single phase by using capacitors or VFD.

However, if you want to only check a three phase motor on single phase by using a cheaper way, purchase “Running Capacitor(s)” from your local market which often use in single phase motors (1KW = 65uf). Then hook your motor up as following method;

 

Line = U&Z

Neutral = V&X

Capacitor = Neutral and W&Y

 

But you should confirm first the voltage rating of your motor. This method is not appropriate such a load where starting torque is primary concerned.

Hope this will help you.

 

say for 2KW, what would be the cap size? for every KW by how much will the cap size increase or decrease? or how does one calculate this?

 

[jdanger]

Greetings,

 

I have been running three phase motors on single phase for a time now. The way that I accomplish this is to add capacitors from one of the hot leads to the third lead of the three phase motor. It creates the phantom third hot lead. My formula for the capacitor is 15uf per horsepower. However, for starting the motor I have a momentary contact switch set up, just like the the before mentioned capacitors, except the starting capacitors are much, much larger. I first turn on the motor. It rotates slowly. Then I hit the momentary contact switch which brings online the starting caps. Then varoom. The motor takes off to it's normal operating speed. The largest motor that I've tried this trick on is a 7 1/2hp. If the motor is small enough then I don't need the start switch.

 

Hope that this information is helpful.

 

JD

[masterdamo]

hello there

 

Acording to my data sources if you put a capacitor between line 2 and line 3 that shall create a third phase then put L and N an line one and two but the motor will need a hand start in any direction