My Cure For THe Powermatic 3 Phase Blues

[John McClanahan]

I finally found a good table saw to replace my Craftsman contractor saw. Its a 1983 powermatic 66 with a 6 Ft. cast iron top and 5 HP 3 phase motor.

The 5 HP motor can be a problem. Plan A was to use a VFD as a phase converter, but VFDs that can support 1 phase in and 3 phase out top out at 3 HP for the most part.

Plan B, I didn't want to mess with a phase converter just to run my saw.

Plan C was to swap the motor for a 3 HP 1 phase motor. The problem is that the 5 HP motor has a 187C frame and a 3 HP motor has a 145C frame. So using a 3 HP motor would require buying a Powermatic motor mount for a 3 HP motor.

So, here is my plan D. I made these brackets to mount a T frame motor to the C frame mount. For now, my saw will be sporting a 1.5 HP Baldor motor. As a bonus, I can run it on house current. Later, I can always put a bigger motor on it.

I got it mounted up and one of the belts doesn't tighten as much as the other. When running, there was a bit of vibration, so I removed one of the belts. I didn't have a Nickel, so I used a Penny to test with, and it passed. Then I realized I didn't have the cast iron top on it to dampen the vibrations!

John

[david brum]

Did you say it has a 6 foot cast iron top? That's impressive!

I like your motor solution, although I just checked on the famous auction site and saw several 5 HP VDFs for around $300 new. You would still have to feed it 220v though.

[Larry Edgerton]

If you decide to get rid of that 5hp let me know, I could use a spare.

You will be happy with that saw, or at least I am with mine.

Larry

[John McClanahan]

David, I may have missed something, but what I was finding was the 5 HP VFDs required 3 phase input. There may be a Chinese exception to the rule, but I also found the Chinese VFDs to be a crapshoot on quality control. plus, I had this motor on hand, just waiting for a purpose.

Larry, I haven't decided what to do with the 5 HP motor and control yet. If I part with it, I will let you know.

John

[Homer Faucett]

Nice saw, and creative solution. Why not use a static phase converter? You'll only lose 1/3 of the hp, but that leaves you with more than 3 hp, and they run less than $100 for one that will handle a 5 hp motor. Not as snazzy as a VFD, but more cost effective and powerful than putting in a 3 hp motor.

[Chip Lindley]

Necessity IS the Mother of Invention! Great adapter bracket for using a "normal" motor on the PM66 C-face mount.

I know you are in "hawg heaven" after stepping up from a contractor saw, but a big cabinet saw of that caliber BEGS for at least 3hp! Every shop needs 230v power sooner or later! You might as well go for it!

[Rod Sheridan]

John, the 5HP motor will run just fine on a 3HP VFD with the VFD programmed to run a 3HP motor.

Your saw will then be a 3 HP saw.

Of course the 3 HP VFD will also accept a single phase input.

Regards, Rod.

[Noah Katz]

Plan C was to swap the motor for a 3 HP 1 phase motor.

If 3 HP is enough you could have gone with plan A.

[edit] oops, didn't see the previous post

[Kirk Poore]

187C? Odd, I didn't see that on this Baldor chart:
http://www.baldor.com/pdf/501_Catalog/BackCover.pdf

If it's a 184C, though, you would have been able to go with the 145TC frame motor--same bolt pattern and shaft size. Did you measure?

It'd still be cheaper to go with a 3hp VFD, though.

Kirk

[John McClanahan]

The 5 HP motor has a 184C mount. The 3 HP has a 145C mount, with a smaller bolt pattern(?) I think. The 145C and 184C are NEMA specs, based on motor horsepower.

After more research on VFDs, I have learned that I would need to "derate" the VFD. Basically, for single phase input, I would need to use a 7.5 HP VFD.

Rod and others mentioned using a 3 HP VFD. I'm guessing the VFD will limit the amp draw, preventing the VFD from being overloaded by the larger motor?? Help me out here!

I skipped the idea of a rotary phase converter, as I'm unsure of the total amp draw of the complete setup. I have limited power to my shop and don't want to have to turn stuff of before I start the saw.

Performance reviews that I found online for static converters wasn't very good, so I passed on that idea for now, but may revisit it later.

My modifications are bolt on, and removable. It gives me a chance to use the saw before dropping more money.

Thanks to everyone for advice on my saw buying decision!

John

[Peter Quinn]

[QUOTE=John McClanahan;1667253

I skipped the idea of a rotary phase converter, as I'm unsure of the total amp draw of the complete setup. I have limited power to my shop and don't want to have to turn stuff of before I start the saw.

John[/QUOTE]

That would be around 40A at 220V single phase line in to the phase convertor to run the 5HP motor effectively. I have a 5HP shaper, which is admittedly a much heavier load on the convertor than a TS by comparison, and 40A covers the shaper plus potential for a power feed simultaneously. I think 30A might run the TS sans power feed, depends on the rated amps at three phase of the original motor? You need to roughly double the single phase amps to provide the proper three phase power. My convertor is a 10HP, by which the company meant it has a 10HP three phase motor creating the third leg, not that it can start a 10HP load. You will run into some semantics here, where some companies claim "Our 5HP phase convertors actually provide 5HP...blah blah blah, yak yak yak.." Who cares? They have no magical formula for this, they include a 10HP slave motor and call it a 5HP convertor to make sizing simpler. The result is the same. You might be able to start and run a TS with a 7.5HP convertor as well, which should drop you down to the 30A 220 category.

To those well versed in the VFD technology, are you saying that you can start and run a 5HP three phase motor safely and effectively with a 3HP VFD, but that the potential work out put will simply be reduced to something more like a three HP motor? That is an interesting idea I hadn't heard before. This has no ill effects on the motor other than power loss? That would certainly make sense to me with a TS, not so much with a shaper or similar heavy load machine. 3HP is plenty for most TS applications IME.

[Noah Katz]

To those well versed in the VFD technology, are you saying that you can start and run a 5HP three phase motor safely and effectively with a 3HP VFD, but that the potential work out put will simply be reduced to something more like a three HP motor?

Pretty much.

You can set the FLA for the max rating of the VFD, and the acceleration ramp-up time to keep the starting current in check.

[Tom Stenzel]

[QUOTE=Peter Quinn;ll, which should drop you down to the 30A 220 category.

To those well versed in the VFD technology, are you saying that you can start and run a 5HP three phase motor safely and effectively with a 3HP VFD, but that the potential work out put will simply be reduced to something more like a three HP motor? That is an interesting idea I hadn't heard before. This has no ill effects on the motor other than power loss? That would certainly make sense to me with a TS, not so much with a shaper or similar heavy load machine. 3HP is plenty for most TS applications IME.[/QUOTE]

To put in visual terms, you can put 3 gallons in a 5 gallon bucket. When you use the bucket, remember what you can get only get out of it what you put into it!

The drive is then programmed to protect the drive, not the motor as the drive is the weak link.

The limitation to using single phase input to a drive is that 4 diodes do the AC to DC rectification instead of 6 diodes when 3 phase input power is used. Each diode has more current flow, causing the drive to be derating when one phase power is provided.


At work we have three 2000 kVA drives hooked to three 2500 hp motors, the drives are way undersized to run the motors at their rated capacity. The motors have taken it since 1991. Why undersize the drives? We couldn't expand the building and the larger size drive wouldn't fit. But that wasn't realized until after the motor and the pump had been spec'd out and ordered. Engineering at its finest. Still, it makes the capacity we need.



-Tom Stenzel

[david brum]

David, I may have missed something, but what I was finding was the 5 HP VFDs required 3 phase input. There may be a Chinese exception to the rule, but I also found the Chinese VFDs to be a crapshoot on quality control. plus, I had this motor on hand, just waiting for a purpose

PM sent on a Delta brand VDF. It's the same brand that appears on my Jet lathe.

[Kirk Poore]

The 5 HP motor has a 184C mount. The 3 HP has a 145C mount, with a smaller bolt pattern(?) I think. The 145C and 184C are NEMA specs, based on motor horsepower.

....
John

Actually, the 145TC and 184C (not the 184TC) have the same key dimensions for what you need. In the Baldor chart listed above, page 2, the key dimensions are AJ (bolt spacing), U (shaft size), and V (shaft length). These all match. Dimension N (distance from shaft end to motor case) is slightly less on the 145TC, but I don't think this would be critical in this situation.

I went from a 56C on my PM 65 to a 145TC, so I've done the same move, just in the other direction. If you don't go with the VFD, I think the motor replacement is the way to go. You might even be able to find a used motor, since 145TC seems to be a common size.

Kirk