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Can 3 Phase motor be changed to 1 Phase?


 
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Gwiz
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PostPosted: Sat Feb 09, 2008 6:46 pm    Post subject: Can 3 Phase motor be changed to 1 Phase? Reply to specific post Reply with quote

Can a 3 Phase motor be converted or rewound to run on one phase?
Thanks
James
 
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Charles (in GA)
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PostPosted: Sat Feb 09, 2008 6:50 pm    Post subject: Re: Can 3 Phase motor be changed to 1 Phase? Reply to specific post Reply with quote

No, it cannot.

Charles
 
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Gwiz
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PostPosted: Sat Feb 09, 2008 7:14 pm    Post subject: Does a VFD (variable frequency drive) have to match motor hp Reply to specific post Reply with quote

I've seen mention of VFD's converting single phase 230 volt to 3 phase. If I have a 5hp motor, do I need a 5hp VFD?
Anyone have any comment on their experience with VFD's for home use of 3 phase?
Thanks
James
 
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Gerald J.
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PostPosted: Sat Feb 09, 2008 8:13 pm    Post subject: Re: Can 3 Phase motor be changed to 1 Phase? Reply to specific post Reply with quote

Can't be rewound and deliver the same HP. A single phase motor is always considerably larger. And at 5 HP rewinding costs more than a new motor.

The modern way is a VFD and yes it needs to be a 5 HP VFD. It goes one better, by allowing speed control as well as the right VFD will run from single phase power.

Its also possible to rig up a capacitor rig to sorta make three phase, but you won't get full power out of the motor. There are also rotary phase converters, but they cost more than a 5 HP single phase motor.

The converters and VFD pay well for a special motor, but not for a standard motor where a single phase motor can be mounted, unless the three phase motor is nearly cost free and the only available single phase motor is at full price.

Gerald J.
 
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Bob
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PostPosted: Sun Feb 10, 2008 12:01 am    Post subject: Link to a GREAT Forum... Reply to specific post Reply with quote

Here's a link to a GREAT Forum about phase convertors and VFD's:
Practical Machinist

 
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Bus Driver
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PostPosted: Sun Feb 10, 2008 4:18 am    Post subject: Re: Does a VFD (variable frequency drive) have to match moto Reply to specific post Reply with quote

The 5HP rating of a VFD is for a 3-phase supply feeding a 3-phase motor. For single phase supply feeding a 3-phase motor, it is better to upsize the VFD. Use a 7.5HP VFD.
 
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David - OR
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PostPosted: Sun Feb 10, 2008 5:08 am    Post subject: Re: Does a VFD (variable frequency drive) have to match moto Reply to specific post Reply with quote

Speaking of homes use of VFDs

I use a 3HP VFD to run a 3 phase submersible pump for the well serving my home. Going that route allowed me to run a 27GPM 3HP pump with one modest size pressure tank instead of two or three large ones. I set the ramp time of the VFD to 3 seconds from 0 to 60 HZ when the pump starts -- this avoids the current surge normally associated with starting a large pump, and thus the pump does not have to run for two minutes to cool the windings of the motor. At the 3HP level, most VFDs can run off single phase without de-rating. The VFD cost less than the (required) single phase pump controller would have.

This setup has given me good service for over 5 years so far.
 
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Jon Hagen
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PostPosted: Sun Feb 10, 2008 7:32 am    Post subject: Re: Can 3 Phase motor be changed to 1 Phase? Reply to specific post Reply with quote

A totally stock 3 ph motor will run just fine on 1 ph at 2/3 of nameplate HP, it just wont start on 1 ph.
You can make them start on 1 ph by building a simple device using a starting cap and a manual or automatic starting switch.
The "control box" for a 1 ph 240 volt submersible well pump makes a great little converter box for cheap. all you need to do is adjust the cap size for the motor you intend to run.
My own expermenting has shown that a starting cap of about 150 MFD per nameplate HP of the motor will give the best starting torque.

I have a $10 junkyard 7.5 hp 3 ph motor on a grain auger that needs 5 hp 1 ph. I suspect this setup has moved in excess of a 1,000,000 bushels of grain in the last 20 years or so, to me thats not the perfect setup, but close enough for not much money.
 
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buickanddeere
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PostPosted: Sun Feb 10, 2008 8:42 am    Post subject: Re: Can 3 Phase motor be changed to 1 Phase? Reply to specific post Reply with quote

57.7% of nameplate HP, not 66.7% when running a three phase motor on single phase.

The largest single phase motor without getting into written pole motors is the two pole 15HP and four pole 16HP.

Good quality used variable frequency drives work well to run three phase motors on true three phase from single phase power. Many home & farm tinkerers are comfortable around VFD's however.
 
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Jon Hagen
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PostPosted: Sun Feb 10, 2008 9:28 am    Post subject: Re: Can 3 Phase motor be changed to 1 Phase? Reply to specific post Reply with quote

Thanks for the correction on 3 ph run as 1 ph motor capacity.

I have a very cheap source of used VFD's,mostly three ph, but know little about them. I would appreciate any link that would help walk me through understanding and using them. Possibly the link posted by Bob ? TIA
 
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JMS MN
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PostPosted: Sun Feb 10, 2008 12:43 pm    Post subject: Re: Can 3 Phase motor be changed to 1 Phase? Reply to specific post Reply with quote

No, but you can make a phase converter out of another 3 phase motor by running it on 220 and spinning it (only to start it) with a single phase motor. The converter generate the third leg elec that you need. I put mine on a wheeled cart, used a 110v 1hp on a hinge to spin the 3phase- can move it between three machines. Google for details and wiring diagrams. Lindsay Publications has plans as well.
 
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36 coupe
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PostPosted: Sun Feb 10, 2008 2:00 pm    Post subject: Re: Can 3 Phase motor be changed to 1 Phase? Reply to specific post Reply with quote

A large 3 phase motor can be started with a small single phase motor When the 3 phase motor is up to speed 240 v applied to the large motor will run the 3 phase motor.Fellow did this to run a 3 phase blower in his wood shop.I gave a friend a booklet on running 3 phase motors.He was able to build his own converter to run a large commercial meat saw with the info.Talked with a fellow in a small machine shop that ran many machine tools that were 3 phase.If you look at a rotary converter you will see a big 3 phase motor with the shaft cut off.
 
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Gerald J.
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PostPosted: Sun Feb 10, 2008 3:04 pm    Post subject: Re: Can 3 Phase motor be changed to 1 Phase? Reply to specific post Reply with quote

And you have a lot more vibration and a much larger current if you try to run it as a single phase motor at anywhere near its tag rating. I've been into too many burned up three phase motors from just a little unbalance to have any trust for one running on single phase. When the line voltage unbalance is 1% the line current unbalance is generally 6%. When the line voltage unbalance is 16%, one winding is running twice rated current and one is running no current. Smokesville.

Gerald J.
 
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Pycoed
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PostPosted: Mon Feb 11, 2008 2:54 pm    Post subject: Re: Does a VFD (variable frequency drive) have to match moto Reply to specific post Reply with quote

David - OR wrote:
(quoted from post at 15:08:19 02/10/0Cool Speaking of homes use of VFDs

I use a 3HP VFD to run a 3 phase submersible pump for the well serving my home. Going that route allowed me to run a 27GPM 3HP pump with one modest size pressure tank instead of two or three large ones. I set the ramp time of the VFD to 3 seconds from 0 to 60 HZ when the pump starts -- this avoids the current surge normally associated with starting a large pump, and thus the pump does not have to run for two minutes to cool the windings of the motor. At the 3HP level, most VFDs can run off single phase without de-rating. The VFD cost less than the (required) single phase pump controller would have.

This setup has given me good service for over 5 years so far.


Another vote for the VFDs. I had my milling machine running on single phase using capacitors to shift the phase, but there was heat, vibration & lack of power. I got a VFD from Ebay & boy what a difference. Since then I've even bought a 3 phase drill press which I retrofitted fitted with a VFD & now have a reversible tapping machine as well! Just bought another VFD to fit to my single phase lathe once I find the right 3 phase motor for that. VFDs rule!
 
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36 coupe
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PostPosted: Wed Feb 13, 2008 3:24 am    Post subject: Re: Can 3 Phase motor be changed to 1 Phase? Reply to specific post Reply with quote

A amp probe can check current in a few minutes.A friend sawed all the hardwood flooring for his house with a meat saw ,3 phase motor run on single phase.He built a capacitor converter.
 
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