Three Phase Motors – What to do?
WBGoodwin
| Posted in Power Tools and Machinery on
Hi,
I just picked up two older Delta woodworking machines, a Unisaw and a Lathe with a 36 inch bed. Both are in very good condition, but have three phase motors. Since my shop is at home and I don’t have three phase power, I need to do something in order to put them to work.
I guess my two options are a phase converter or get new motors. I would rather go with the motors, but am not sure where to get good motors at a fair price.
Does anyone have a suggestion for any type of effective resolution to this problem?
Bill G
Replies
Is there a shop within a reasonable distance from you that repairs and rewinds electric motors? Or are they all sent to China? You could probably get a good deal on a trade-in or swap for those 3-phase motors.
I've been dealing with this stuff for years. A VFD from http://www.factorymation.com is your best bet.
Are you suggesting a phase converter or a new motor from this company?
A VFD is a converter!!!
It's under AC drives
http://www.factorymation.com/s.nl;jsessionid=0a0107431f43f1c3d06d6c674a9c9c8dfbca2add09fb.e3eTaxiPc3mTe34Pa38Ta38Mb3z0?sc=2&category=11
Call the tech to get the proper sized AC Drive/VFD
If you lathe is a step pulley model, the VFD will give infinitely variable speeds with a dial. All the lathe companies are using VFD technology now.
Unisaw motor have an odd frame siuze meaning the mounting bracket in unique to a Unisaw. The Jet cabinet saw was a clone of the Uni and a special mounting bracket can be used to mount a stadard motor to a Jet or Uni. You can modify the switch and change the heaters on the mag switch for a Uni. With a VFD the VFD becomes the switch. A VFD will allow soft start, breaking and varible speed.
A VFD will also allow you to double the motors rpm so it has some real plusses depending on the application.
A rotary conver will run multiple machines but no bells and whistles.
A static will give 2/3's the power but an unbalanced static isn't as good for the motor on the long term.
Edited 9/8/2008 2:41 pm ET by RickL
Edited 9/8/2008 3:18 pm ET by RickL
I called the company and they said that these inverters are designed to adapt 3 phase motors to single phase. Since I have a two horsepower motor on the unisaw, their inverter would cost me $145.00. They are said to be 98% efficient and as you mentioned, they can also provide variable speed. I would not need this on the saw, but would be nice on the lathe, since it is a step pulley design.
This looks to be a very good option at this point, but perhaps other members will have interesting suggestions as well.
Thank you, Bill G
Since you didn't give enough info and now you mention it's only 2 hp on the Unisaw I'd recommend you get a new single phase motor, 3 hp, which is more than enough instead of the VFD. As I mentioned before Jet has an adapter bracket to allow a standard motor to be used or one could be made. Probably cheaper to get a motor designed for the saw.
There's usually a source for motors in the back of WoodShop News. I used to be an independent Delta tech and still am a service tech for machines so I know all the options.
RickL
Thanks for the advice, I am going to continue to look for motors. Used is fine if they are in good shape. However at $145.00 for the VFD, this is also a reasonable option. The concern for me with the VFD is that they need clean environment because of their internal cooling fan. I would need to mount it in a filtered housing.
Bill G
RickL advise on getting a VFD would be the least costly. You can get Unisaw motors on eBay and from other sources. The motor will not be cheap because of the special pivoting mount. Woodworker's Supply has Marathon motors from $320 to $447 for a Unisaw. I do not know what motor you need for the lathe but it should be less expensive.
Life is what happens to you when you're making other plans .
"Life is not a success only journey." Dr. Phil
Bill G, I used to own a big 24" MiniMax planer, and a big 16" MiniMax jointer. They both had three phase motors but had been wired at the factory with a second capacitor that was used to start the motor. The way I understand it, which isn't very well, once a 3 phase motor is started, it can run on single phase. You don't have the same horsepower but it was still plenty for what I was doing. I had to have some work done once on the planer. I got a electric motor expert to come out and replace one of the capacitors. He said he had never seen that set up before, but was able to get it running again. It's was better than having a converter, I've been down that road as well. Bill
I suspect you don't really understand what you have. You are sort of describing a static converter without the timer which activates the capacitor to start the windings. There's a lot more to this than your description. I've made up rotary converters using this to start the slave motor. Instead of a timer, I manually hold a momentary switch to engage the capacitor.
A balanced static converter is better...
http://home.att.net/~waterfront-woods/
All I know is that the 3ph motor had two capacitors, one to start and one to run. they were both about the same size. And you are right, I don't understand it, at all. You might get a better idea of what I'm talking about if you call up MiniMax and ask to speak to a technician. I now have a different machine, so this was all in the past.
I had purchased a used Powermatic 66 with a 5 hp 3 ph. Contacted my local electrical contractor and he installed a phase converter. The converter lowered the hp to 3.25+-/220. The saw has been operational for 4yrs now with no problems and no lack of hp. The cost +- 225$ 4 yrs ago. Cheapest route at the time.
Rick, one advantage of the Variable Frequency Drive that you did not mention is that the VFW can provide for automatic braking of the saw blade when the switch is turned off. I opted for the VFW for the safety factor of automatic blade stopping on my Powermatic.
Many, many issues ago FWW featured an article for using a slave 3 phase motor as a converter. It featured an auxilary motor to start the slave motor. (I hope that I am using the term"slave motor" correctly) My son uses this system to run the 3 phase motor on his old Bridgeport milling machine but his slave motor is delta wound and thus does not need an auxiilary motor to start it running.
BJ
Gardening, cooking and woodworking in South'n Murlyn'
Bee Jay, You must have missed it, but RickL wrote <A VFD will allow soft start, breaking and varible speed.> I am not sure, but when I got some help from a very good electrician on one VFD that I used, I think I recall him saying that some of the older motors are not real compatible with these systems. Since it is a 2hp, I would take this to be a really old saw, and would check with someone with a lot of knowledge on the subject before buying one for a motor that might ruin the VFD or the motor. I am also kinda leaning toward advising just getting a new motor, for not so much more money.
Keith, when he mentioned it was a 2 hp motor I suggested he go with a replacement motor. If it was a 5 hp a balanced static would be plenty to use. A 3 hp would be fine with a rotary or a VFD. Even a 2 hp would probably be fine with a rotary or a VFD but folks think they always need more. 2 hp doesn't necessarily means it's older. Maybe it's really one of those contractor saws with the full base. People often confuse those with a Unisaw.
Yep, I did miss it. Thanks. It seems clear to me that Rickl really knows his stuff with Variable Frequency Drives.
BJGardening, cooking and woodworking in South'n Murlyn'
He must be using a static converter or a capacitor with a momentary switch to get his slave motor (the basics of a rotary converter). A small fractional HP secondary motor is another option to start a slave motor converter. The metal working guys are much more adept and eloquent on home made phase converters. Unfortunately there is no laymans site for the woodworker explaining the ins and outs of phase converting in very simple language. Everytime I see the subject mentionened it gets more confused by well meaning folks.
A small fractional single phase motor was used as the starting set up in the FWW article I mentioned. DS does not have another motor to start his slave running. In fact the slave motor is lying in a pile of wires at the base of the mill. Capacitor possibly, but no momentary switch. His explaination is that because the slave 3 phase was delta wound instead on Y wound it will start turning on its own when plugged into single phase 220V. I wonder if i missed something. You've got me curious.
You are so on target about discussions confusing the issue.
BJ
Gardening, cooking and woodworking in South'n Murlyn'
Edited 9/12/2008 11:28 pm ET by BeeJay
That was a static converter he installed which would give reduced HP. Perfectly fine solution for the application but such vague info will just confuse the masses.
A text book that explains how the three phase is supposed to work that I have found very useful is called Electrical/Electronic Systems. I think I got it at Grangers some time ago. The book is buried right now or I would post the ISBN.
As I understand it converters are a bad idea. Too much lost energy. (the heat and the fan that was mentioned is one indication of loss through heat. The 98% efficiency mentioned may be a manipulation of the facts by the supplier) The whole point of the three phase is cheep power. Best to stick with single phase for single phase and three phase for three phase.
Splitting up the single phase you loose the "punch" and the current flows faster and you get heat. A happy motor running in its efficiency/load range has a back emf that keeps the current flow in check. Or some such. It has been a long time and I don't have the book in front of me. Interestingly it is a bad idea to run too large a motor under a light load for the same reason.
Here's a "green" idea: open an arobics gym at your place. When the ladies show up to ride the exercise "spin" cycles and the stair steppers etc. rig it so they produce three phase. They will power your shop, you can sell the excess power back to the city (hey people do it all the time with solar collecters) and they will pay YOU for the use of the exercise equipment !
As Red Green says I'm pullin' for ya. We are all in this together.
Edited 9/13/2008 5:10 am by roc
Edited 9/13/2008 5:23 am by roc
Edited 9/13/2008 5:27 am by roc
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