Several years ago I purchased a used Unisaw at a county school auction. It has a 240V, 3 hp, three phase motor. In order to run it in my home shop on single phase power I needed a phase converter. I got to digging around and at a local scrap metal yard picked up a 5 hp. 3 phase motor and used it as the basis of a rotary phase converter. Over a month or so I worked out a starting system for the rotary converter motor so that all I had to do was throw a switch and the phase converter started. Then I could go to the tablesaw and start it. I also, at the same junk yard picked up a Cincinnati Fan 6" blower and built a cyclone and installed a dust collection system. The blower also had a three phase motor, 2 hp, so that fit in with the 5 hp rotary converter, 3 hp on the tablesaw and 2 hp on the blower. It worked well, very well. However it got to be a little annoying having to start the phase converter if I wanted to go over to my bandsaw or jointer and run them. I had to start the phase converter, start the dust collector and then use the tool. Through some of Terry Hatfield's work I found the guy on ebay who had the 2 hp single phase motors that work very well on a dust collector and at a very attractive price. I bought one. It had the correct C Face mounting but the motor shaft on the new motor was 7/8" and the motor shaft on my old three phase motor was 5/8". I had to take the impeller and have it remachined to fit the new motor shaft. Once that was done, I had the dust collector so that I didn't need to start a 5 hp motor in order to use it. Improvement, now I can go to any machine push a remote keychain type button and the DC runs.
The next issue was the rotary converter had to run for the table saw to start. If I was working on a project and using the tablesaw off an on over a couple of hours, I had two choices. Start a 5 hp rotary converter and leave it running the whole time or each time I needed the table saw, start the converter, start the table saw, cut, stop the table saw, stop the rotary converter. A real PITA.
I started reading up on Variable Frequency Drives. You can, if you choose the correct type, run a three phase motor on single phase current with a VFD. I started watching ebay again and found an Allen Bradly 1333 DAA VFD, used, taken out of a processing plant in running condition. A little research on line told me that that particular drive which is a 240V input drive, can take single phase current and produce three phase current. With 3 phase input it is rated at 10ph, with single phase input it is rated at 3hp. A perfect fit for my tablesaw. I bid and I got it for $71. The manual for this unit was last updated in 1988. But it works. I had done some temporary wiring of the unit to the tablesaw over the last week just to make sure that it worked as it should. The seller offered a 7 day return on it if it was not functioning properly. This past weekend I ran the permanent wiring and got it set up the way I wanted it.
Anyone out there who has seen a three phase machine and not bought it because of the electrical current issue? Passed up a great deal because what it would cost to get a single phase motor for a machine? This is the cure and it works wonderfully well. VFD's have all kinds of features that you can use to make running a motor very user friendly. For example. I have set the start sequence to take 2 seconds from pushing the on button till the motor reaches full RPM. This is like a soft start and doesn't make the shop lights go dim when I start the saw. The highest amperage I have seen the motor pull when starting is 6 amps. I have set the stop sequence to go from full RPM's to full dead stop in 1.5 seconds. No longer I have to wait for the blade to coast to a stop to change a set up or open her up to change the blade. I am no electrician but what this thing does is send short bursts of reverse current to brake the motor rotation. You can stop the motor rotation even faster by changing some settings but, I found that if you stop it too fast, the blade assembly wants to keep spinning while the motor is stopping and you get a little belt slip and a squeal, not much but a little. Playing around I stopped the blade rotation in one second. I think if I would make the belts a little tighter it would work without the squeak, but really see no point at this time in doing that.
I used the remote start contacts in the VFD to hook the normal start/stop switch on the saw. I even used a spare set of contacts in the VFD to put a little red light over the shop door. The light is on when the VFD is powered up, it is so quiet that you can't hear it running. It is just, hopefully, a reminder to me when leaving the shop, to turn the VFD off. When you turn it off the light goes out.
When the VFD is running and the saw isn't it draws 0.1 amps of power. It basically is like having a computer running, very little power usage. When the table saw is running it only draws the amperage that the motor normally would draw. In my case 3.4 amps with no load on the saw. No longer will I feel guilty about the rotary converter running while no work is being done.
This is the greatest thing since sliced bread.
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Originally Posted by Steve Clardy
