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VFD questions

DPittman

Ultra Member
Premium Member
A friend just recently purchased an old VOEST lathe that has a 440 volt, 3 phase, 5hp motor on it. Trouble is he does not have 3 phase in his shop.

I haven't yet found a VFD that puts out 3phase 440 volt. Do I need to just look harder or is that not a possibility with the vfds j find on Amazon?

Can a 440 volt be wired to run on 220 volt 3 phase?

Maybe finding a used 3 phase 220 volt motor might be a better solution?

Are rotary phase converters old technology that is replaced by vfds?
 

TorontoBuilder

Ultra Member
A friend just recently purchased an old VOEST lathe that has a 440 volt, 3 phase, 5hp motor on it. Trouble is he does not have 3 phase in his shop.

I haven't yet found a VFD that puts out 3phase 440 volt. Do I need to just look harder or is that not a possibility with the vfds j find on Amazon?

Can a 440 volt be wired to run on 220 volt 3 phase?

Maybe finding a used 3 phase 220 volt motor might be a better solution?

Are rotary phase converters old technology that is replaced by vfds?
you can run a 440 motor on 240 if your VFD has an option to change the base frequency..

you will get all the same performance characteristics as normal EXCEPT you wont get the max motor speed

This is how I'll be running my Colchester with a 440v motor

 

slow-poke

Ultra Member
Start by looking at the motor data plate, fairly common for motors to be reconfigurable for different voltages just by changing the connections inside the motor box, the motor plate will shown this if applicable. If not reconfigurable running at lower base frequency seems like a viable solution.
 
Yes step up VFD's are available, google it. Just remember a 8amp motor will require about double that on the supply when stepped up.
 

Bandit

Well-Known Member
I read the attachment, so why is the frequency down to only 29 hz from 50. I know very little about vfd's, just enough to be dangerous. We used them on nearly all the pumps and the blowers, centerfuge used 2 on it at the same time. We generally did not run motors below 30hz as cooling could start to suffer and some motors have plastic fans on them which can't take much heat. A few motors melted the fans.
Seems 220 single ph. to 380 3 ph. not to hard to find. 220 single ph. to 440 3 ph. and higher voltages harder to find. Also much more money. Finding makes that you can actually understand set up instructions also a pain.
Was trying to get a standard to be used, but the buck was talking to buy, then have to get someone in to setup/trouble shoot,cry about the buck.
 

TorontoBuilder

Ultra Member
I read the attachment, so why is the frequency down to only 29 hz from 50.

The frequency is reduced in the same proportion that the voltage is reduced (to match the output voltage of the inverter) so as to maintain the design torque of the motor.

If a VFD is just connected with the default base frequency (which is typically 60 hz) the motor will provide less torque at whatever rpm you run it at compared to either providing the full voltage or setting the base frequency to the reduced frequency
 

BaitMaster

Super User
Start by looking at the motor data plate, fairly common for motors to be reconfigurable for different voltages just by changing the connections inside the motor box, the motor plate will shown this if applicable. If not reconfigurable running at lower base frequency seems like a viable solution.

This is probably the easiest option. MOST 3ph AC motors that are rated for 440v (277/480VAC 3ph Nominal) are actually dual voltage motors, that if you look closely on the nameplate are rated for 220v (240v or 120/208VAC 3ph nominal). Simply rearranging motor terminations could fix that issue. Beware that any coils or transformers in the machine control are also set up for 440v and will need to be changed.
I read the attachment, so why is the frequency down to only 29 hz from 50. I know very little about vfd's, just enough to be dangerous. We used them on nearly all the pumps and the blowers, centerfuge used 2 on it at the same time. We generally did not run motors below 30hz as cooling could start to suffer and some motors have plastic fans on them which can't take much heat. A few motors melted the fans.

You can run half speed at half voltage safely as far as the windings are concerned, drives generally keep a volts/hertz ratio to slow down the motor and not cook the insulation. So 240v average at 30 ish hertz does make sense, and work.

The base frequency setting in the drives changes the volts/hertz ratio so the drive puts out full voltage at the 30 hertz.

However, you are 100% correct about running non inverter duty motors slower then rated speed and cooling being an issue. Because the centrifugal fan on the shaft of the motor runs at the same speed as the shaft, and it follows a centrifugal pump curve, airflow through the fan is about 1/4 of capacity compared to full speed, when the motor is running at half speed.

This is usually solved by having a fan powered seperately running at full speed all the time mounted to the motor instead of powering from the shaft.
 

TorontoBuilder

Ultra Member
This is probably the easiest option. MOST 3ph AC motors that are rated for 440v (277/480VAC 3ph Nominal) are actually dual voltage motors, that if you look closely on the nameplate are rated for 220v (240v or 120/208VAC 3ph nominal). Simply rearranging motor terminations could fix that issue. Beware that any coils or transformers in the machine control are also set up for 440v and will need to be changed.


You can run half speed at half voltage safely as far as the windings are concerned, drives generally keep a volts/hertz ratio to slow down the motor and not cook the insulation. So 240v average at 30 ish hertz does make sense, and work.

The base frequency setting in the drives changes the volts/hertz ratio so the drive puts out full voltage at the 30 hertz.

However, you are 100% correct about running non inverter duty motors slower then rated speed and cooling being an issue. Because the centrifugal fan on the shaft of the motor runs at the same speed as the shaft, and it follows a centrifugal pump curve, airflow through the fan is about 1/4 of capacity compared to full speed, when the motor is running at half speed.

This is usually solved by having a fan powered seperately running at full speed all the time mounted to the motor instead of powering from the shaft.

yep... but a 7.5hp motor running reduced speed (ie below adjusted base frequency) will require a lot of supplemental cooling. My cabinet lacks good options to provide additional cooling and I have a gearbox so I intend to run mine as a single speed motor until I install a new inverter duty 240 volt motor.
 

Bandit

Well-Known Member
What is an inverter duty motor? Dummist question is one not asked, and try to remember the answer so don't ask more then 3 times.
 

TorontoBuilder

Ultra Member
Digesting all that too, what's the amps doing when running at 30hz. increasing?
With pulse width modulation (PWM), the speed of the motor is controlled by varying the frequency and duty cycle of the pulse signal sent to the motor. The duty cycle is the percentage of time the pulse is on compared to the total time of the cycle. As the duty cycle is decreased, the speed of the motor is reduced.

When the duty cycle is decreased, the average voltage applied to the motor is also reduced. However, the relationship between the voltage and amperage is not linear, so the amperage drawn by the motor may not change in direct proportion to the voltage. In general, the amperage drawn by the motor will decrease as the speed decreases, but the exact relationship between voltage, amperage, and speed will depend on the specific motor and the load it is driving.

It is important to note that the PWM technique is used to control the speed of the motor while maintaining a constant torque. The first step when providing less voltage is to proportionally decrease the base frequency of the inverter. The new voltage and base frequency will cause the motor to draw a higher amperage so the inverter will typically require about double the motor's rated amperage.

If the using an inverter rated motor that allows for reduced speed beyond the reduction of the base frequency then the voltage and amperages will decrease while running at a lower speed, but caution should be exercised when operating a non-inverter duty motor below its rated voltage and frequency, as this can cause the motor to overheat, lose torque, and potentially damage the motor.
 

TorontoBuilder

Ultra Member
What is an inverter duty motor? Dummist question is one not asked, and try to remember the answer so don't ask more then 3 times.
An inverter duty rated motor is a type of motor that is specifically designed to be operated with variable frequency drives (VFDs) that are used to control the speed of the motor. Inverter duty motors are designed with special insulation systems that can withstand the high voltage spikes and harmonic distortion that are commonly associated with VFDs.

The insulation system of an inverter duty motor is designed to provide superior protection against voltage spikes and electrical noise that can damage the motor. The insulation material used in the motor windings is typically rated to withstand a higher voltage than standard motors, and it is also designed to dissipate heat more effectively. In addition, the motor's bearings and shaft are often designed to handle higher radial and axial loads that can be generated by VFDs.

Inverter duty motors are used in a variety of applications, including pumps, fans, conveyors, and other machinery that requires variable speed control. They are available in a range of sizes and power ratings, and they are typically more expensive than standard motors due to their specialized design and construction.
 

DPittman

Ultra Member
Premium Member
This is probably the easiest option. MOST 3ph AC motors that are rated for 440v (277/480VAC 3ph Nominal) are actually dual voltage motors, that if you look closely on the nameplate are rated for 220v (240v or 120/208VAC 3ph nominal). Simply rearranging motor terminations could fix that issue. Beware that any coils or transformers in the machine control are also set up for 440v and will need to be changed.
This sure would be easiest for sure. I only saw one spec plate on the lathe itself and not the motor and it stated 440 volt. I suppose it's very possible that the motor has been changed.
So hp/torque rating would not change if the motor was run at 220 instead of 440 volts?
 

BaitMaster

Super User
This sure would be easiest for sure. I only saw one spec plate on the lathe itself and not the motor and it stated 440 volt. I suppose it's very possible that the motor has been changed.
So hp/torque rating would not change if the motor was run at 220 instead of 440 volts?
HP/torque ratings stays the same. Should be fine :)
 

BaitMaster

Super User
An inverter duty rated motor is a type of motor that is specifically designed to be operated with variable frequency drives (VFDs) that are used to control the speed of the motor. Inverter duty motors are designed with special insulation systems that can withstand the high voltage spikes and harmonic distortion that are commonly associated with VFDs.

The insulation system of an inverter duty motor is designed to provide superior protection against voltage spikes and electrical noise that can damage the motor. The insulation material used in the motor windings is typically rated to withstand a higher voltage than standard motors, and it is also designed to dissipate heat more effectively. In addition, the motor's bearings and shaft are often designed to handle higher radial and axial loads that can be generated by VFDs.

Inverter duty motors are used in a variety of applications, including pumps, fans, conveyors, and other machinery that requires variable speed control. They are available in a range of sizes and power ratings, and they are typically more expensive than standard motors due to their specialized design and construction.

Bang on. The 3 differences I always remember are:

- Better cooling, separate fan or otherwise.

- Higher voltage rating on insulation, typically 1600v for 230/460 motors, and more coats of winding enamel to keep windings from moving.

- Insulated bearings to stop shaft arcing, and built to deal with more torque/load if the motor is rated for constant torque.

Smart folks on this forum.
 

Susquatch

Ultra Member
Administrator
Moderator
Premium Member
We generally did not run motors below 30hz as cooling could start to suffer and some motors have plastic fans on them which can't take much heat. A few motors melted the fans.

There are ways around this.

You can mount a separate fan on the end of the motor to keep the air flow up.

VFD Rated motors can also bring the rpm's way down. My mill motor is literally zero rated. In other words, full torque at zero rpm with no overheating worries. But my minimum setting is still 6Hz.

Edit - someday I will learn to read an entire thread before posting anything. I see now that @TorontoBuilder and @BaitMaster already covered much of what I said.
 
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slow-poke

Ultra Member
I have often wondered how long a non VFD rated motor will last when used with a VFD In a hobby like environment?

I found this post on another forum, post#20 is informative


I'm running a test, sample size one with my drill press, and an eBay "special" used motor (insulation class B) that was used in a commercial dryer for who knows how long?

It's been about two years and so far it's working fine, who knows maybe it will blow up tomorrow?
 
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