Yet Another VFD Question...

[Greg Ketell]

Several people have asked why 220v doesn't use a "common" line. Textual descriptions don't do it for me so I thought I would give a visual version.

If you take the Blue line as "Hot", or "Line" and the x-axis as "common" or "neutral", this is how 120v AC (Alternating Current) works. The voltage on the "Hot" swings from 120v to -120 and the power produced is the difference between that and the "common", which is always at zero volts. When the Line peaks at 120v you get 120v, when it dips to -120v you get -120v. (sorry, that is obvious but you will understand why I needed it in just a second).
AC-110v.PNG


This is how 220v AC works. The red line is "Line-1", and the blue line is "Line-2", and the x-axis is Neutral. Notice that Line-1 and Line-2 are always exactly out of phase with each other. Because they ARE out of phase and because you only hook up Line-1 and Line-2 you now have the situation where your power produced is the difference between them, when line-1 is at 120v line-2 will be at -120v and the power produced is the difference which is 220v.

AC-220v.PNG


So, 120v uses one hot and one neutral. 220v uses 2 hots working in opposition and neutral is not needed. 440v uses 3 hots.
Which is why manual says you don't use neutral but you hook up L1, L2, L3 and the footnote also said that the device had to be used for 220v or 440v.


Just in case someone doesn't understand how the VFD makes the motor spin at different speeds...

The motor is driven by the "wave" in the power. At 120v it is driving one side of a magnet, at -120v it is driving the other side of the magnet: Push-Pull-Push-Pull. In the simplest case, one cycle of the electrical wave makes one revolution of the motor.

So if you have a "Variable Frequency" drive, you can make the electrical wave come in faster or slower which turns the motor faster or slower. In the graph below, the blue line is "normal" (60Hz in North America so in our simple example: 60RPM), the red line is twice as fast (120RPM), and the orange line is 6 times as fast (360RPM).

Freq-Drive.PNG

I hope this helps.
GK

[David Reed]

David
i have followed this somewhat chaotic thread and without commenting on the VFD wiring and function, thus further muddling the waters, I noticed terminology used which has added to the confusion (some of which has been clarified). Neutral is not the same as ground in function and purpose. They are both at earth or ground (that being zero) potential and often joined inside the electrical panel but serve different purposes. This somewhat sloppy use is seen clearly in the YouTube video and perhaps one more source for confusion.
Just sayin
D

[David C. Roseman]

Several people have asked why 220v doesn't use a "common" line. Textual descriptions don't do it for me so I thought I would give a visual version.
[snip]

Greg, very nice way to present this, and great graphics!

David

[David DeCristoforo]

First off, thanx again for all the inout. I too am hoping that the VFD is not "fried". I do wonder about how it would protect against whatever it needs to protect against without there being some kind of reset option, something else I did not find either on the device itself or in the documentation. One way or the other the basic problem has been the lack of power at the output terminals. Could this have been caused by the incorrect input connection? Did the unit instantly go into limbo because the second hot wire was connected to L2 instead of L3? If some protection kicked in, what is that protection? How does the unit protect itself? And how is that "reset"? The tech support person I was on the phone with did not suggest any way to reset the unit. Maybe "resetting" the device can only be done by a "qualified technician"? I guess I'll have to wait until the unit gets inspected before I have definitive answers. The unit is scheduled for delivery on Wednesday and it will probably take them at least a couple of days to "get to it". So maybe by the end of next week I'll find out the status. In the meantime, I've got lots to keep me busy and I still have the issue of the motor not being the "right one" for this VFD. So I am looking again for a good used 3hp motor and this time, I'll be sure to check the nomenclature plate before I buy it!