need large 1ph motor

I am looking for a large (7.5-10HP) 240V single phase motor to drive
a 15KW 3PH alternator to make real 3PH power for my workshop.
Anyone know a source in the chicago area?
I already have 3 phase converters in the shop and I like them for
specific applications but I need more 3ph power for grinders and
things that don't need VS. I already have the alternator so I might
as well use it for something useful.
chuck
Reply to
Charles A. Sherwood
Loading thread data ...
Charles
Have you determined the alternator's shaft RPM required for 60 Hz?
And, since I have never seen a used (affordable) single phase motor bigger than 10 HP, I wonder if you could consider getting a hugh (maybe 30 HP) old (cheap) 3 phase motor and drive it with single phase.
Jerry
Reply to
Jerry Martes
How about an engine?
Reply to
John Manders
Been there done that. All I need is a enough 3PH power to run a 2HP motor. A 5HP drive motor might be enough but I would rather have a 7.5
chuck
Reply to
Charles A. Sherwood
Charles sez: "I already have the alternator so I might as well use it for something useful."
Not likely! A 7.5 HP single-phase motor would take full load current of aprox. 31 amps at 240 volts. That 7.5 HP motor could realistically be expected to drive the alternator to generate only about 3.5 to 5 HP which is far shy of the 15 KW (20 HP) output capability of your alternator. Larger 240-volt, single-phase motors are hard to find because of the size of the branch circuit required. A 7.5 HP single-phase motor is about the practical maximum.
Bob Swinney
Reply to
Robert Swinney
5 hp should be plenty assuming you are not trying to accelerate a huge alternator rotor on start up.
Bear in mine that the alternator output freq. is going to be less than 60 Hz by the same percentage that the motor runs below synchronous speed. This should not be a problem for tool motors except that they will be down on power by roughly the same percentage that they are down on speed.
Randy
Reply to
Randal O'Brian
Why not make a rotary phase converter? It should do the job just fine.
Steve Smith
Charles A. Sherwood wrote:
Reply to
Steve Smith
It probably would, but I an alternator will have better phase balance. chuck
Reply to
Charles A. Sherwood
Yes it is not possible to drive the alternator to full power,but I would be satified with enough power to run a couple 2HP motors.
This alternator has a 100lb rotor so I expect it will provide adequate surge power to start or instant reverse any motor I would use on a machine tool.
chuck
Reply to
Charles A. Sherwood
You should get a gas engine and run your alternator with that. It's unlikely normal house electrical power can supply what you're thinking. I figure the same thing for compressed air, by the way. If I ever have to do sandblasting or jackhammering I'm just planning to rent a huge compressor and be done with it.
Grant
Charles A. Sherwood wrote:
Reply to
Grant Erwin
No, it would not be possible to drive a 15 KW alternator to anywhere near full power with only a 7.5 HP motor.
Bob Swinney
Reply to
Robert Swinney
Belt drive 'em and build the "slip" into the ratio. To accellerate the heavy armature rotor on startup you want the old repulsion start motor (the one with brushes that lift when the motor comes up to speed)
I have a nice one sitting in my shed here in Ontario - not sure what HP but it weighs about 200 lbs. (Century Electric)
Reply to
nospam.clare.nce
Clare
Is there a marking on the alternator that indicates the frequency out if it with some standard RPM?
The torque to rotate an alternator is less than that required to start up an air compressor. I suspect that almost any induction motor would spin-up that 200 pound alternator if it was powerfull enough to overcome the total "windage" and bearing losses. Granted, it might take 20 or 30 seconds for a marginally small motor to get up to operating RPM, but the torque required to rotate an alternator is small compared to things like air compressors.
If frequency control of the 3 phase voltage is important, a synchronous motor can be used to drive the alternator. That way, the output RPM doesnt vary as much with changing loads.
Jerry
Reply to
Jerry Martes
Jerry,
What you wrote seems to say an alternator makes free power! I think you know better than that! An alternator's input will require at least 1-1/2 times the power it is putting out.
Bob Swinney
Reply to
Robert Swinney
Bob
I couldnt find the place where I suggested the alternator power was free. I meant to imply that alternators can be spun up with a common induction motor. I would think that an old (maybe free) 3 phase 10 HP motor could easily spin up an alternator and keep it running when the alternator was loaded by 2 motors 2 HP each. I think that if I had plans to spin a 15 KW alternator with a single phase motor, I look around for a used 30 HP 3 phase motor and run it on single phase. I occasionally see 30 HP motors in the trash but have never had need for something that big.
Jerry
compressors.
synchronous
Reply to
Jerry Martes
Hey Chuck,
I betcha you'll have a hard time finding a single phase 220VAC motor over 5HP. Have you considered a multi-motor drive? Say three motors at 5HP each, belt driven on a common input shaft of the 3 phase alternator, such that if you run one only, and need more power, that you cut-in another one or two. Slipping V-belts should work. I think I'd try one on a direct drive to the alternator, and the other two mounted like a reverse pyramid stack above the first, but belt drive.
Take care.
Brian Lawson, Bothwell, Ontario. XXXXXXXXXXXXXXXXXXXXXXXXX
Reply to
Brian Lawson
I never said it was. I said it is NOT possible.
Reply to
Charles A. Sherwood
Right on, Jerry. I didn't mean to insult your intelligence with my statement - I just wanted to clear the point of any possible confusion. Yeah. I heartily concur that a large 3-phase motor would be the way to go. No doubt about that. It would be much easier to find a large 3-phase motor than a single-phase one of the same rating. Make that -- practically impossible to get a single-phase motor of greater than 10 HP.
The original poster seemed to be afraid of rotary phase converters which is why this thread got started. He will almost have to build a rotary phase converter (better if he did) in order to start and run a large 3-phase motor on single-phase power.
message
Reply to
Robert Swinney
On Thu, 22 Jul 2004 22:37:57 -0500, "Robert Swinney" vaguely proposed a theory ......and in reply I say!:
remove ns from my header address to reply via email
Spun up is different from powered. It's not the milk and honey we hate. It's having it rammed down our throats.
Reply to
Old Nick
Those (single phase motors above a couple of hp) are available.
Problem is, they're not common so they won't go for free. They probably will command a premium even when bought new because they sell so few.
Three phase motor, of, say, 7 hp, with some capacitors and a potential relay to start it?
Jim
================================================== please reply to: JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com ==================================================
Reply to
jim rozen

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.