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Will a vfd work?

Rooster35236

Plastic
Joined
Jan 7, 2020
I have an older industrial sewing machine that is ran by a 3 phase clutch motor, but only have single phase power coming in. Under normal circumstances I would just swap out the motor with a single phase servo motor and be done with it. This machine came with a controller that can do a host of things, Needle positioner, automatic thread cutting, programmable stitching etc.

We would really like to have the full features of this machine, as a bit of a electrical novice I thought a vfd would do the trick as the motor it rated 220v/550w/2.1a which is under 1hp. What I was told in the sewing forums was that because the controller has a speed control a vfd would not work? I was thinking setting the vfd to fixed voltage but will that not work?

I only have 120/20a running there now but if needed I can run a 220 line to feed the machine.

The path that it takes right now is power into a fuse box out to the clutch motor which then feeds into the controller. Normally without a controller the pedal pulls down on the actuator lever and engages the clutch, with this one the pedal pulls down and engages an actuator on the controller. I do not see any markings on the controller besides a switch to change voltage 190/208/220/240

Here are some photos:

https://cdn.shopify.com/s/files/1/0026/0525/2672/files/20200105_180026.jpg?v=1578295749

https://cdn.shopify.com/s/files/1/0026/0525/2672/files/20200105_180253.jpg?v=1578295747

https://cdn.shopify.com/s/files/1/0026/0525/2672/files/20200105_174819.jpg?v=1578295746

https://cdn.shopify.com/s/files/1/0026/0525/2672/files/20200105_174523.jpg?v=1578295746

https://cdn.shopify.com/s/files/1/0026/0525/2672/files/20200105_174749.jpg?v=1578295743

Is this something that is possible without getting into the thousands?

Thanks in advance
 
Last edited:
It is a bit difficult to determine what you have.

It looks as if incoming power is 3 phase. And the motor definitely is. The question is whether there is already an inverter (VFD) in there, which is furnishing varable speed 3 phase.

I assume there is the usual foot pedal control for speed, in which case there should be a VFD in it.

It is possible (ask Singer) that the thing will actually run on single phase input, since the internal VFD (assuming there is one) simply converts the incoming 3 phase to DC, and then the VFD "re-makes" the 3 phase to run the motor, varying the frequency to control speed.

If that will work, then there is no issue.

If not, then you may need to "feed it" 3 phase, which can be done with a VFD, yes, just as you suspected, by setting it to a constant voltage/frequency. The VFD may have to be larger, because rectifying AC to DC takes current in a way that can cause a problem if the VFD used to supply it has too low a current capability. Look at the line fuses, that current or above is likely sufficient.

One can also use a 3 phase motor set up as a "Rotary phase converter" (RPC) and that can be somewhat more of a sure thing and often is less expensive if a used motor is obtained and the RPC locally built. They can also be bought ready-to-go.

I would suggest still paying attention to the line current, and going to 1.5x that number for the RPC rating.
 
The VFD does not output sinusoidal 3 phase, the output is a series of many DC pulses that simulate an AC wave. It is unlikely that your controller will run correctly under these circumstances and most likely there is a transformer to provide DC to the controller circuit and whatever else. These are designed to operate off of a true 60 Hz sinusoidal wave. It may result in failure of the transformer/controller and good luck trying to find a replacement, I could find no posted information on it. If you had a schematic that would be beneficial. I am guessing the vintage of the machine is 60-70's, given that VFD's are circa 1980's onward, it probably uses some other form of motor speed control. If you had a schematic, could isolate the control circuits to run on single phase, used a VFD to directly operate just the sewing motor, and incorporate all that into the current controller it could work. A static converter would significantly reduce the main motor's power, there are some posted discussions, but probably a poor choice.
 
I am struggling with a similar issue supplying power to an industrial sewing machine. Did this problem ever get resolved here with a VFD set to constant voltage/frequency? Are there other options for supplying 3ph power to a sewing machine controller without industrial power?
Thanks!
 








 
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