Hey all,
I just picked up a DoAll Model C-4 horizontal bandsaw today from a place thats downsizing. I bought it for $200 and it looks really really nice. Ill post pictures soon.
My problem is the motor...its a three phase motor, with 1100RPM and a 5/8" shaft. I want to try an keep the 1100 RPM to keep the variable speed selection chart on the machine accurate. Ive only been able to find one motor that fits this criteria and is single phase. It was from Grainger and was over $400.
Im wondering if theres any place out there that people know of that sell used motors possibly? Maybe I should check my local phonebook? Also, DoAll has a box about 12"x12" with all the contactors and wiring going into it. I was told I could leave everything alone, and that my new input power would just go on L1 and L2...then the way its wired now will work...and Ill end up with two outputs on L1 and L2 going to the motor. Basically, leave everything alone the way it is, and leave out the third leg. Does this sound right? Could it really be that easy?

Thanks in advance for any help!
Kyle Curley

You can get a small electronic phase converter for around 100.00. I ran a 16" vertical Do All on one for years. It was a Cedarburg brand, good for 1-3 hp motor, works just fine even though you do lose some hp. If you change the motor the contactors should all work as you were told. 1100 rpm motors are expensive and hard to find used.

Thanks Moonlight. I think Ive decided on a convertor, but now I need to figure out which one or how big of one I need. They list them by HP ratings, but I was told I want one a little bigger than any motor Im going to start with it. Id say the MAXIMUM size motor Id start that was 2 HP, probably not even that. So, Im thinking about going with a 3HP convertor. Company on ebay sells them for $299. Any ideas?
Thanks!

That saw is standard with a 3/4 hp, 208/230/460 volt motor. Make certain that the motor is wired for low voltage - there should be a connection diagram on the motor plate.

The least expensive method for converting 1ph to 3ph on a small motor is a VFD.

http://dealerselectric.com/item.asp?PID=417

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Barry Milton

Wow thanks Barry! The guy I work for said a friend of his had a little device about the size of a thermostat on his wall, that he ran his mill and lathe off of. Im guessing this is what he was talking about. Are they rated for different horsepower or no? I'll have to do some searching for info on them before I buy one.
Whats the disadvantage to the VFD when compared to a phase converter?
Thanks again!


Kyle

None that I'm aware of, Kyle. They can function as a phase converter & that may be all you use it for. They can also add features to the saw like soft start, instant stop & variable speeds with each step pulley range.

Yes they are. Most companies make a 1/2 hp drive (which is too small for your motor) and the next size up is 1 hp. Even though that drive is slightly over sized, you'll set the drive up so that it is correct for the 3/4 hp motor, which allows the drive to function as a motor overload protector.

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Barry Milton

Kyle-

You noted that your existing 3-phase motor is rated 1100rpm.

If you go looking, you shouldn't find ANY 3-phase 60hz AC synchronous motors to run at 1100rpm.

That's because 1100 is not evenly divisible by 60hz. What you have is a 1200rpm motor (1200rpm /60hz = 20)... that when LOADED, reaches it's rated power capacity when "SLIP" equates to a 1100rpm shaft speed.

All AC synchronous motors operate at a speed relative to the input frequency, divided by the number of poles wound into the motor... hence, motors are 1200, 1800, and 3600rpm. You'll see them rated based on slip to 1150rpm, 1725rpm, and 3750rpm, or thereabouts.

As for the numbers in your speed chart being accurate, they're already inaccurate, so changing to a motor with 1200rpm shaft-speed-rating wouldn't cause a major change in saw performance or cutting calculations.

That being said, Barry's right- a VFD would be an excellent solution for this application. Another thing you'd find useful, is putting a speed indication on the machine.

There's many ways of doing it, but one of the slickest and cheapest ways, is to stop by your local bicycle shop and buy an inexpensive bicycle computer. Mess around with the calibration factor so that your indication yields a number that's easily transposable to a suitable blade speed. Instant speed DRO, and it even comes with elapsed time, distance travelled, and a wireless heart-rate monitor!!!

"My problem is the motor...its a three phase motor, with 1100RPM and a 5/8" shaft. I want to try an keep the 1100 RPM to keep the variable speed selection chart on the machine accurate. Ive only been able to find one motor that fits this criteria and is single phase. It was from Grainger and was over $400."

If you are handy with electricals, you can convert your 1200 rpm (synchronous speed)/1100 rpm (at fully rated HP) six-pole, three-phase motor into a single-phase capacitor start/capacitor run motor.

Basically, this boils down to isolating the so-called "star point" of the three-phase motor, and bringing-out T10, T11 and T12, and thereafter implementing a so-called H.A.S.-type static converter.

With such a conversion there is no loss of HP, and even a 230/460 volt motor may be handled with the same type of conversion.

The details are in the Monarch Forum archives, which consists of a reference to the Steelman patent, and to the Steelman Electric Service installation guide, and of a discussion of the same.

In most cases, the motor's control system can be retained.

If you really feel the need for 1100 rpm get a VFD and one of these http://www.controlres.com/labstrobe.php Works nice!
You can set it up and vary the speed and get it exact. Ya gotta have a real need if you go this far though.

peters star point
http://www.practicalmachinist.com/vb...teelman+patent

I just bought the same model saw, but wasn't quite lucky enough to pay only $200. Still a better price than a brand new imprted 7x12 saw though. I still have an extra 3ph plug left- I'll probably use that one for the saw, but if not I'll definitely go with a VFD as a lot of guys here have been saying.

I 2nd Barry suggestion

I run my lathe using the 3HP version of Teco VFDs and I love it I can vary the spindle speed from 1 rpm to above 1,800 RPM and anything between. It will accept single phase or 3 phase input and gibe you 3 phase power to your motor great little devices.

Marci

I looked on ebay and found a GE Fuji AF-300 Mini 1hp rated single phase to 3phase VFD for $111.55 shipped. Item #360206984668. The drive is rated for 5 amps, and the motor on our saw draws 3.2 max.