Do they make single phase VFD's

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ritelec

ritelec

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Hello all....
never thought of it.........

I've installed 3 phase motors which ran back to control panels with vfd's.......

I relocated a single phase house well pump control panel which appeared to have a vfd.........


Just read that VFD's will only work on 3 phase motor..............??? any truth in this statement........

Is a variable frequency drive the same as a variable speed drive....???
 
Yep........... reason I asked is cause I thought they make them for single phase................
didn't give it much thought..............
as I'm looking around, I'm only locating single phase to three phase inverters,,, and misc.....
but no single phase vfd's.....
will continue............
not life threatening...... just curious......
 
Motor must be three phase

Motor must be three phase

They may have used a three phase motor, and a single phase supplied drive. A inverter or VFD will convert your input power to DC, then output a chopped three phase sine wave. The rectifier works better with three phase but for a small motor single phase is fine.
Hope this helps
 
It is possible to vary the speed of a single phase motor by varying the frequency as a general rule, but the problem with many higher torque single phase motors is there is usually a governor assembly that will kick in the starting winding and/or starting capacitors when the speed drops below a certain level, making the motor itself not all that usable for a variable speed application. In the case of PSC and shaded pole motors there are less costly simple ways of varying the speed of those motors than the VFD route, but those motors are typically only available up to about 1-2 hp max.

There are single phase VFD's for single phase applications - usually somewhat specific OEM type products. Submersible well pumps is one that I am familiar with, look into Franklin's "monodrive" or Berkley's "intellidrive". But those are kind of designed for a specific motor and not for general purpose use.
 
They certainly do make single phase variable frequency power sources, but I don't know how common these would be for running motors.

The problem is that a single phase of AC doesn't provide any sort of directionality. Something in the single phase motor must create a rotating magnetic field...or the motor must not actually depend on the AC for rotation at all. (For example, a brush commutated 'universal' motor depends on the brush positioning to produce the rotation, and will work with DC or low frequency AC.
The problem is that if you have a single phase AC motor, you need to do something to create a sense of rotation in the motor itself.

Most single phase AC motors use reactive elements of one sort or another to create an out of phase component, which when added to the supply AC produces a rotating magnetic field. This could be in the form of capacitors feeding out of phase motor windings, or in the form of 'shading coils' built into the stator. But something is creating an out of phase AC to produce rotation. These reactive elements are frequency dependant, making frequency control of such a single phase motor much more difficult.

Now some single phase motors are speed controlled using some sort of voltage regulation. I am thinking of the speed control used for things like fans, which are little more than dimmers. A VFD could also function (with appropriate logic) essentially as a dimmer or fixed frequency variable voltage supply. So it is _possible_ to control a single phase motor with a VFD like device. Perhaps due to economies of scale, a manufacturer is actually using small VFDs in this fashion. There are other tricks out there, eg replacing the capacitor connection with one of the phase outputs of the VFD...but I don't know if any manufacturer implements this....there are a huge number of theoretical possibilities, not all of which are practical.

The most common method of using VFDs and single phase is to have a single phase input to the VFD, but then three phase output to a three phase motor. The VFD becomes the system that creates the rotation.

-Jon
 
ritelec said:
Is a variable frequency drive the same as a variable speed drive....???
Click to expand...

How technical do you want to get and how far back into history do you want to go?
For the most part these are now simply marketing terms, kind of like loadcenters and panelboards.

A controller is the 'smarts' only, while a drive is is the controller + the driven element/motor. Controllers are usually sold as single items, while Drives are usually sold as packages or matched sets.

At one time speed control was obtained through mechanical means like 'belts and pulleys', then along came electronics. So, for awhile Adjustable Speed Drives (ASD) were used to describe brute force devices and Variable Speed Drives (VSD) described the fancy electronic ones, like servos.
For the most part, the first successful variable speed controllers varied speed by 'chopping' voltage or current these competed with mechanical devices so it was not uncommon to hear them called Adjustable. Eventually someone figured out out a way to vary the frequency thus creating the Adjustable Frequency Controller (AFC).
As the frequency control got better, these AFCs were able to move into the world dominated by servo drives, so the industry started calling them VFDs.
 
Last edited:
ritelec said:
Hello all....
never thought of it.........

I've installed 3 phase motors which ran back to control panels with vfd's.......

I relocated a single phase house well pump control panel which appeared to have a vfd.........


Just read that VFD's will only work on 3 phase motor..............??? any truth in this statement........

Is a variable frequency drive the same as a variable speed drive....???
Click to expand...

What you have is likely a packaged system with a 3 phase submersible pump and a control panel that includes a VFD. The VFD also handles the phase conversion. All the major submersible pump companies offer these systems now. There are some advantages to this setup as opposed to the old way of using a single phase motor which required a controller with a start cap and potential relay and a separate start lead to the motor. It also allows for a smaller required expansion tank and better overall performance.
 
VFD = Variable Frequency Drive, maybe Vacuum Fluorescent Display, occasionally if you mix those two up, it means Volunteer Fire Department.
AFD = Adjustable Frequency Drive, same thing.

VSD = Variable SPEED drive, could be a VFD, could be a DC drive, could even be a mechanical (Reeves) drive or an Eddy Current Clutch. Bottom line, the term VSD is not specific, VFD is. ASD is the same thing as VSD, Adjustable vs Variable.

A VFD uses line power as a raw material to make DC, it doesn't care if it's single phase, 3 phase, ABC rotation or CAB rotation. The output is 3 phase for the most part. But with single phase feeding a 3 phase motor, the incoming current increases by the sq. rt. of 3. Below 5HP at 230V, most VFDs on the market are sized for the additional power input capability to be used on single phase supplies. 5HP 230V and above, and 480V, most drives can be fed with single phase if the VFD size is 2X the motor size (but always size by FLA, not HP). A few drives cannot have their Phase Loss Protection disabled, making them unsuitable for this. Check your manual for a way to disable Phase Loss. If you don't see it, you can't use it for phase conversion.

There are a few versions of VFDs that work on only TWO versions of single phase motors, PSC (Permanent Split Capacitor) and Shaded Pole. Shaded pole motors can be speed controlled with voltage only, i.e. rheostat, which is a quantum leap cheaper. PSC motors are only good for lot torque applications like pumps and fans. Single Phase output VFDs are significantly more expensive than those tor 3 phase motors, so it only makes sense if you cannot replace the motor.
 
ritelec said:
Just read that VFD's will only work on 3 phase motor..............??? any truth in this statement........
Click to expand...
Generally speaking you need a 3-phase motor to be able to use a VFD. However it is possible to run such a system from single phase power. A VFD with a single-phase output intended to operate a single-phase motor is a rare bird indeed.

Most VFDs convert the incoming power to DC, so they don't really care about phasing. In many cases you can simply use a 3-phase VFD on single phase, but you will need to upsize it to compensate for the fact that you're only feeding 2 of the three inputs: http://www.dartcontrols.com/wp-content/uploads/2012/01/De-Rating-VFD-for-Single-Phase-Power.pdf
 
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