# "Least worst" effect on motors of home 3-phase options



## kd1yt (Oct 1, 2014)

I'm the new owner of a nicely kept Cincinatti Toolmaster 1-B milling machine, and, soon, after completing "round two" of moving big stuff, a nice old Leblond 14 inch lathe that was originally lineshaft-driven, but at some point had a motor drive fitted.

I only have single phase power, so I will need to put in place some means of feeding both with three phase.

I already have on hand a couple of very sizeable 3-ph industrial motors, and a magnetic start switch, so the path of least financial resistance would be to wire up an idler-motor-type rotary converter.

From what I understand, idler-motor RPCs supply less than ideally balanced phases and voltages, in ways that are not entirely great for the powered equipment.

The less initially frugal path would be to get a VFD that is adequate to run either machine (I don't need to run more than one at a time) but from what I have been reading, VFDs have their own downsides, especially for older motors, in the way of electrical 'artifacts' introduced by the high speed switching/ synthesized waveforms, and that can take their own toll on motor insulation and bearings, especially on older motors that were not built with VFDs in mind. I do seem to find that putting a reactor between the VFD and driven load may mollify some of those wear and tear factors from a VFD (not sure if that is partial or full remediation of those wear and tear factors), and it seems like the reactors can be found surprisingly cheaply on ebay, etc.

Either way, while my budget is very finite, I don't want to cut corners in a way that would zorch the motor in either the Toolmaster or the Leblond, or I could quickly find myself with headaches and costs that cripple my ability to begin to use and learn about this equipment.

Thanks in advance for any experience and wisdom that you can share...


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## MADJACK (Oct 1, 2014)

I have a rotary phase converter in my shop. I used a motor I had and was researching the building of one when I found a premade setup on ebay. I don't remember the seller, but here are several similar ones.

Mine runs very smooth & quiet compared to some others I've heard. I power my mill and lathe with it, Been using it for a few years with no ill effects

here's a few I found searching ...

http://www.ebay.com/itm/5-HP-ROTARY...607?pt=LH_DefaultDomain_0&hash=item45fa633b0f

http://www.ebay.com/itm/5-Hp-phase-...507?pt=LH_DefaultDomain_0&hash=item2c8c9f7543

http://www.ebay.com/itm/5hp-rotary-...800?pt=LH_DefaultDomain_0&hash=item3f3cef7d58


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## CluelessNewB (Oct 1, 2014)

I currently have 4 machines with VFD's and none of the motors are "VFD rated".  All are 1970s vintage or older.  I do not run the speeds below about 50% of rated speed or above 150% of rated speed.  It's all hobby usage for me so I don't run machines all day long.   I have had zero problems.   The oldest motor is on the metal lathe, that is mid 1940's vintage.  The newest is probably my wood shaper late 1970s vintage.   My wood jointer, early 70's vintage has probably had the most continuous use running about 10 hours one day, that was running at rated speed.      

The wires between the motors and the VFD's are all rather short, typically 3ft or less.

Just because I haven't had problems doesn't mean that none exist (absence of evidence doesn't imply evidence of absence) but I haven't found much evidence on the web of problems using older motors with VFD's except in continuous use situations like fans and pumps with long wire runs between the VFD's and the motors.  For me it was worth the minor risk.


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## rdhem2 (Oct 8, 2014)

I have been installing VFDs since the days of soft start controllers and even though they warn of impending possible disaster by connecting to an older motor I have never seen it happen.  Usually the drive trips out early when there is a problem to SAVE the motor.  They are so much more sensitive to faults then a standard eutectic overload block.
VFDs are the only way to go, in my opinion, if you can put together the combination that works for you.


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## hermetic (Oct 8, 2014)

The major problems with using VFD's on older motors is cooling. With a TEFC (totally enclosed fan cooled) motor the cooling efficiency drops rapidly as the motor is slowed below its rated speed, and there is not a lot you can do about it, you need to blow cool air on the outside of the motor.. With an open frame motor you can fit an extra blower type fan to push cool air through the motor, so no problem. If in doubt, use the vfd at standard frequency so that the motor runs at its full speed, and use the machine gears and belts to change speeds. Beware of running older lathes, especially plain bearings at more than the maximum speed of the fastes gear, you risk wrecking the bearings and possibly even bursting the chuck with increased centrifugal force.
Phil.


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## Ulma Doctor (Oct 8, 2014)

VFD's are getting pretty cheap now but a RPC will do the same job, just less efficiently.
to echo others sentiments if you use the vfd at 60hz you won't cause damage to even the oldest motor.

the damage comes from overspeeding or underspeeding the motor with a frequency it's not designed to run at which generates great amounts of heat which in turn raises the motor's temperature creating ideal conditions for thermal failure.

if you are interested in a cheap,reliable RPC you can check out my design or others designs to get you going pretty cheap
click the link below for those interested.

http://www.hobby-machinist.com/showthread.php/12712-Rpc-simple-design-unbalanced


lmk if i can answer any questions. i'm always happy to help out.
mike)


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