[How do I?] Single phase motor can i use a VFD

[jarhead]

Good morning folks,
I have a Grizzly knee mill that has a 2 HP single phase motor.
The mill uses step pulles and i would like to control the speeds with a VFD.

Is this a possibility? Can i gain anything by doing this?
The motor is currently running on a 20 AMP 220V circuit.

Here is the label on the motor. It has start and run capacitors.

Thanks, Joe

 

[RJSakowski]

There are many on this forum that would say no.

However, motor speed of an a.c induction motor id determined by the frequency of the driving voltage, whether it be three phase or single phase. There is no reason why an VFD couldn't be made for a single phase motor and in fact, there are multiple commercial units available.

A typical use for higher h.p. single phase VFD's is for fan motors and fans or blowers characteristically require a low low speed torque so there is some concern whether the available single phase VFD's can meet the needs of a mill or lathe. These motors are often split phase or permanent capacitor types.

Another concern is that most single phase induction motors require a start winding to ensure turning in the proper direction. This winding usually disengages once the motor speed reaches some preset rpm. Start windings typically see a fairly high current relative to the size of the winding which is acceptable due to the very short operating time. If they start circuit remains energized for an extended period of time, damage to the motor is a certainty. If using a vfd on such a motor, some means of defeating the the cutout switch would need to be used.

VFDs for Single Phase Applications - KEB

Single-phase applications require special consideration when applying a VFD. The VFD must be sized accordingly and a 3 phase motor must be used at the VFD output.

www.kebamerica.com

Can You Use a Variable Frequency Drive (VFD) on a Single Phase Motor?

While it is technically possible, it is not advisable to operate a single motor with a variable frequency drive. Read more about the disadvantages.

www.maderelectricinc.com

VFD’S for Single Phase Motors?

www.wolfautomation.com

Single Phase VFD, control speed for single phase motors | ATO.com

www.ato.com

I had entertained using a vfd on my single phase lathe motor before I finally elected to go with a PWM controlled brushed d.c. motor.

 

[mksj]

There are VFD's (ATO) for single phase motors, but they typically require you to remove the capacitors and connect the start winding directly to a VFD. I cannot see it working with a centrifugal switch. How well they work I do not know, as well as the constant torque ratio. Alternative would be to replace the current motor with a 3 phase version, keep the belt drive but probably only need to use two belt ratios. You can download the manual for this drive in the link below.

2 hp (1.5 kW) VFD, Single Phase Input & Output

Discounted 2 hp VFD, 1 phase for single phase AC motor, 220V - 240V 9.6 amps, brand new direct sale by manufacturer.

www.ato.com

 

[silence dogood]

Yes, it's possible. However, at lower speeds, you will proportionally lose power in relation to the speed. Which means less torque which the exact opposite of what you want for a lath. There is also possible overheating since the motor was design for a specific frequency.
There is another factor to consider. You have two engines of the same hp. The eight cylinders will naturally run much smoother than a four. This could also be said for three phase or PMW DC or a brushless DC compared to a single phase.
That said, there are single phase VFDs on the market, but I'm not familiar on how well this arrangement will work. So, I could be wrong.
Personally, I would use a different motor.

 

[jarhead]

Thanks all,

If i switched motors what would the recommendation be? I really dislike the belt changing routine.

 

[mksj]

You would need to measure up the motor specifications, it would appear that it is a metric frame motor so would need to know how it mounts as well as the shaft dimensions. Leeson, Marathon, Baldor do make metric versions 3 phase motors, there are others. One below is a 90L flange mount, you can pull the dimensions online the base may be to big, there is another version with a smaller base. Regular 1750 RPM (4P) motors can usually be run to 2X their base speed with no problem so usable speed range is probably 20-120 Hz. You can buy new metric frame Marathon motors from Zoro, they frequently have 20% off coupons and free shipping if you go directly to their website.

If you want a wider speed range then you may want to look at an inverter/vector style which usually have maximum RPM speeds in the 4-6K range. The stock pulley is probably not rated to that speed and also the shaft size would be different so would take some adapting. Some examples below, but impossible to say what will fit without pulling your current motor and looking at the mounting and shaft dimensions.

Marathon Electric 90LT17FH6519 Motor R398A 2HP D90LD 230V 460V 1745 Globetrotter

Marathon Electric 90LT17FH6519 Motor R398A 2HP D90LD 230V 460V 1745 Globetrotter | eBay

THIS IS A GENUINE OEM MARATHON ELECTRIC MOTOR! Speed :1745 RPM. Drive End Bearing Size :6205. Opp Drive End Bearing Size :6205. Motor Orientation :Horizontal. Electrical Type :Squirrel Cage Inverter Rated.

www.ebay.com

Marathon Motors 090Lt17fh6419 3-Phase General Purpose Motor, 2 Hp, 90L Frame

Marathon Motors 090Lt17fh6419 3-Phase General Purpose Motor, 2 Hp, 90L Frame, | eBay

Ambient Temp. 104 Degrees F, Motor Thermal Protection None, Duty Cycle Continuous, Ins. Class F, Motor Enclosure Design Totally Enclosed Fan-Cooled, Motor Shaft Rotation CW/CCW, Motor Mounting Type Face/Base, Motor Mounting Position Horizontal.

www.ebay.com

NEW MARATHON 145THFR5329AA 2 HP AC MOTOR 3Ø 230/460 VAC 1740 RPM 145TC TEFC

NEW MARATHON 145THFR5329AA 2 HP AC MOTOR 3Ø 230/460 VAC 1740 RPM 145TC TEFC | eBay

CAT#- 145THFR5329AA. NEW MARATHON. 230/460 VAC. 2 HP AC MOTOR. IT DOES NOT INCLUDE HAWAII, ALASKA, PUERTO RICO, GUAM, OR ANY OTHER US ISLAND TERRITORIES.

www.ebay.com

 

[jarhead]

Thank You MKSJ, very helpful