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

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.

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.

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.

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

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 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 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.

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.....

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

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

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.

I been told that back before rotary phase converters were available, a lot of old timers that lived out in the boonies would run three phase equipment in their wood shops by making a static synchronous phase generator using a second junk three phase motor and connecting one winding that was out of phase with the drive motors enough to create the third leg.
I have no idea if this is allowed anymore, or what it does for power factor, motor heating, etc., but met a guy from Vermont probably 15 years ago that did just this in his woodshop.
Since this was probably once a fairly common practice, maybe you could find an old timer industrial electrician in your area to help you hammer out the details to do it safely.

The static phase converters that I've used have a note on the door that the motor only develops 2/3 of it's rated h.p. if your 5 hp motor will only do as much work as a 3 hp, is it still worthwhile?

Phil,
My advice before you do anything with this motor, is dismantle it and have a good look at the seals,bearings and armature.
You say it has run before, but it is not clear when.
Bearing races can get distorted if left in the one place for any length of time, this can affect how well the armature turns within the narrow gap between the rotor and the stator and that gap is not that much.
To merely run the thing is inviting disaster.
The other thing that concerns me a tad, is that using an older type motor, the power factor of that motor isn't going to be that great, motors have improved considerably over the years.
The actual in-rush current would be a lot larger, than for a modern motor of the same rating.
Personally, I wouldn't use a phase converter on any motor unless it was the last resort, the reason for that being, converters have a habit of inducing harmonic currents into the lines supplying them.
What I would go for is a new motor and a Variable Frequency Drive, built for your voltage and load in mind.
No use mucking around, mate, it would save tears in the end.
Just my $0.02 worth.

Ausador....If what you say is true, knowone should give any advice on this forum. This is a discussion forum and knowone can be singled out for giving good information or bad information. It is what it is, a forum. Most of the members are proffesionals.

VFD's are no harder to program than connecting the motor. Some VFD's are challenging, but for most it is very simple. I have had many customers that were afraid to try VFD's. To show them how easy it is to set up, I told them I could teach anyone that spoke english and had fingers, could program the VFD to start, stop, ramp up and ramp down in a matter of minutes.
I have never failed with this approach. Also, I am more than happy to assist in programming here on this site. All I need is the brand and model number.

Regardless of your doubts it is a viable option that should be considered.



"Most Correct"????

That is strictly a matter of opinion.

Either replacing the motor or producing a third phase are 'correct' answers and I bet there are other correct options as well.



No, but advising to change the motor is no different from advising to produce a third phase. Either method can be done wrong and result in injury.




That is one opinion, John is also entitled to his.

In general I am a keep it simple guy and think VFDs are being overused but that is just my humble opinion.

Thanks Bob.