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#172755 - 12/25/07 06:00 PM Motor help
Obsaleet Offline
Member

Registered: 04/05/03
Posts: 361
Loc: Pa
Hi,
Merry X-mass!
I have a question concerning a motor I have been asked to make run. It has been sitting in an old mill for some years and is in good condition. It has supposedly run. I am not sure but thid may be bad info as the motor is 220v 3Phase and the mill has single phase. The motor is as follows: 220v 3phase, 1150 rpm, 5hp, 12.2a. GE model # 68A2 Form C, Type KT-946 6 5 1200. I do some work with motors but its not a strong point. Can I make this thing work without a phase converter? what will it do to the amperage?
Any help would be appreciated!


Thanks!
Ob
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#172763 - 12/26/07 06:30 AM Re: Motor help [Re: Obsaleet]
ghost307 Offline
Member

Registered: 05/09/05
Posts: 876
Loc: Chicago Illinois USA
The guts of 3-phase motors are different that those of single phase ones.
A motor designed to start and run on 3-phase power takes advantage of the 'rotating magnetic field' that can be created by the motor windings. Single phase power is incapable of creating that effect.
That being said, the motor could feasibly run on the single phase, but it would not be able to start. If you found a way to spin the motor fast enough to get it to run, it might keep spinning, but there would be such a current imbalance between the windings that you might well end up overheating the windings and damaging them.
I'd avoid hooking the motor up to the single phase; when it eventually failed, I'd end up getting blamed for it and have to buy a new one out of my own pocket.
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#172767 - 12/26/07 09:01 AM Re: Motor help [Re: ghost307]
gfretwell Online   content

Member

Registered: 07/20/04
Posts: 9012
Loc: Estero,Fl,usa
There is a trick with a capacitor to add the 3d leg to a 3p motor on single phase but it is not a very efficient operation.
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#172772 - 12/26/07 11:34 AM Re: Motor help [Re: gfretwell]
ausador Offline
Member

Registered: 03/26/07
Posts: 49
Loc: Central Florida
Obsaleet, It would be pointless for you to try to make a five HP three phase motor run in a single phase enviroment. The attempt would require either an "add-a-phase" or a VFD, either of which are much costlier than any five HP motor I know of.

The only reason I know for attempting this is if the motor is part of a fairly expensive peice of listed equipment. If that is the case then you need to tell the owner in no uncertain terms what you will need to do to install it properly.

If that is not the case buy a new motor, it will be a lot cheaper.

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#172777 - 12/26/07 03:04 PM Re: Motor help [Re: Obsaleet]
Obsaleet Offline
Member

Registered: 04/05/03
Posts: 361
Loc: Pa
Thanks Guys! I knew there was a trick but was not sure of its practicality. I will just get a new motor and go from there. Thanks again!


Ob
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#172809 - 12/27/07 08:48 AM Re: Motor help [Re: Obsaleet]
JValdes Offline
Member

Registered: 06/03/07
Posts: 308
Loc: South Carolina
Obsaleet, Don't buy a new motor yet. A motor at 1200 RPM, 230 volt single phase, TEFC on 215T frame can be purchased for about $550.00. Motors at 1200 rpm are the next most expensive except for 900 rpm which is very uncommon. But available.

The VFD (drive) will have to go to 7.5 Hp for derating single phase. You can get the drive for about $550.00.

As you can see you now have a choice. You have to ask yourself a couple of questions.

Do you want speed control?
Do you want controlled starting?
If so you should buy the VFD.

If you don't need any of the above, then just buy the single phase motor.
Check http://www.automationdirect for prices on drives and motors. These folks have very good prices as they have no overhead. All orders are web orders. They do have a tech support team. The prices I gave you are from http://www.wegelectric.com Also a good price at great quality.
Another thing to consider is the existing motor. Can it run on an inverter (VFD). Does it have 1600 volt magnet wire in it. Does it have class H insulation. It is possible to kill that existing motor with a VFD as the output from the VFD is not a true sign wave. So be careful if you go with the VFD. Might have a motor shop check it out, or give all the nameplate information here and I can check on it.

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#172825 - 12/27/07 02:56 PM Re: Motor help [Re: JValdes]
ausador Offline
Member

Registered: 03/26/07
Posts: 49
Loc: Central Florida
JValdes so perhaps he can buy a VFD for approximately the same price as the motor in question, (but I doubt it). What you have not discussed is the time to locate and size a VFD, the labor and materials to install it. The permitting required to do a new installation as opposed to the non-permitted motor swap,(in theory). Whether the person in question is capable of doing the math to size the VFD or if he needs to pay an engineer to do it for him. Also probably a few more items I have not thought of....

You are talking to people you do not know on the internet, please give the simplest and most correct answer possible. Neither I, this site, nor you I am sure wants to be sued for giving bad or hard to follow advice. In this case the answer is simple and obvious, unless the motor is part of a larger and listed assembly then junk and replace it. If it is part of a listed assembly then he needs to get engineering supervision and alter the listing. Adding a VFD to control a motor within a listed assembly will violate and obliviate it's listing as surely as replaceing the motor will.

You are placeing yourself on thin ice by giving the kind of advice you just gave and a lawyer will have a feild-day with it. Don't put yourself or the site in that position. If you are confident that you are talking to a professional then offer the full range of your experience and knowledge, but be aware that they still might blame/sue you. If you are talking to an unknown???....well use your best judgement but keep it as simple as you can.....

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#172828 - 12/27/07 04:34 PM Re: Motor help [Re: ausador]
Elviscat Offline
Member

Registered: 08/13/05
Posts: 214
Loc: Seattle Washington USA
how 'bout a rotary phase convertor? I realise it's not the most efficient, but it's kind of a pita to find a 5 hp 1 phase motor at close to 1200 revs, and the convertor'd be about $500 (about 7.5 hp which'd give him about the right output) which is probably less than a new motor with similar specs. It really depends on the situation. what are the tolerences they need? will just about any 5 hp motor do? is this application speed/rpm dependant? does it need a specific frame size that this motor needs? if so a phase convertor is a good option, imo, if they just need an approx. 5hp motor with 1000-1500 or so rev output it'd probably be better to trash the old motor.

plus, hey these things are a breeze to hook up, way simpler than a VFD. and if it's a pretty light-duty app he could even get a static phase convertor (capacitor) which are pretty cheap (but with poor efficiency)

-Will

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#172834 - 12/27/07 05:40 PM Re: Motor help [Re: Elviscat]
Obsaleet Offline
Member

Registered: 04/05/03
Posts: 361
Loc: Pa
This motor is for an old mill. I mean belt driven old. The water wheel has been removed and was functional into the early 1980's using electric motors. Somewhere after that but between the 80s and 1993 the service was upgraded to 400A single phase. Now the non-profit group that owns it has found someone that can make some of it work. Not for real just for show. So I am taking what you have said and will probably try to see if perhaps a smaller motor will suffice. I was trying to stay awy from a phase converter as they tend to be noisy etc. I have never seen or worked with a static phase converter? Is that cost effective?

Ob
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#172836 - 12/27/07 06:01 PM Re: Motor help [Re: Obsaleet]
gfretwell Online   content

Member

Registered: 07/20/04
Posts: 9012
Loc: Estero,Fl,usa
If you just want to see the wheels go round the capacitor trick will work. I would start with about 20mfd and tune it with your clamp on.
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