# A question on VFD's



## CNC Dude (Sep 30, 2013)

OK, more like a few questions on VFD's...

I see plenty of talk about VFD's and I know what they are (Variable Frequency Drive). I actually work on a motor drive design company and I know some of our designs are VFD's. I have never designed one myself, but maybe I should!

Anyway, the questions are these:

1. Can you use a VFD with any motor topology, or is it tied to one topology in particular? (e.g. single phase capacitor start, or capacitor run, AC induction, etc?)
2. Or is it for three phase motors?
3. Can I take any motor on any drill/lathe/mill and put a VFD on it?

OK, I realize this is pretty much the same question with a bunch of different flavors. Although my area of expertise is motor drives, I have never done much on the AC and high voltage fields, so am kind of ignorant on that area.


----------



## Kroll (Sep 30, 2013)

I work on vfd at work but I'm no expert,but they are only for 3phase motors.There are some motors that are lable on the name plate rated for vfd's,I think thats just a selling tool.VFD's for the most part will work on any 3phase motors that are rated at 60hz.At work all are 460 volts,in our little world at home in the work shop its either 110v/230v input w/230v 3phase output.Again I'm no expert so others opinion my vary---kroll


----------



## CluelessNewB (Sep 30, 2013)

For most machines like we have the answer is 3 phase only.

There are some VFD's for special applications of single phase but this is limited to motors that don't have speed dependent starting contacts.

See this thread from a couple of weeks ago.

http://www.hobby-machinist.com/showthread.php/17701-Just-a-thought-varible-question


----------



## Ray C (Sep 30, 2013)

For the purposes of this discussion, VFDs are for 3 phase motors.  There are some speed controllers that work on single phase motors but, is limited to certain types of motors -not employed with shop equipment.

When converting a machine to VFD, you will encounter problems if the original 3PH motor is two speed or, if there are other components in the machinery that needs to be powered off the incoming mains.  Machines without electronics are perfect candidates.   Even most of the new production lathes are fairly easy to convert as most of the accessory electronics can be run with a small separate line.  Sometimes, it's a little tricky to get all the safety switches and jog functionality to work properly but, it's not impossible nor is it rocket science -but it does require a basic understanding of simple circuits and switches.  I was able to convert my modern production lathe using all the existing components and just re-wiring a few things.

Finally, for our purposes, it's best to only convert machines that are 3 horsepower and under.  Larger motors can be converted but, the VFDs for 5, 7 and 10 HP motors are in the $700-1200 price range.

Ray



avayan said:


> OK, more like a few questions on VFD's...
> 
> I see plenty of talk about VFD's and I know what they are (Variable Frequency Drive). I actually work on a motor drive design company and I know some of our designs are VFD's. I have never designed one myself, but maybe I should!
> 
> ...


----------



## UncleRuss (Oct 2, 2013)

To be more exact, VFD's are for induction start, induction run motors.  They will operate on 50 Hz as that is what most of the world is.  The base cycles for operation are set via programming in the basic parameters section.  The VFD rating on a motor is not a selling point it is saying the motor insulation is rated for the high voltage spikes the drive puts out in normal operation.  A standard motor may last, maybe not.  A little run time will tell you real fast.  If the magic smoke comes out, oh well.  Good luck.

In this day and age VFDs are the only way to fly!  Now get that puppy working and flinging *SWARF*.

Wife told me once as she was admiring a newly made piece, made from brass fresh out of the lathe. 

Wife, "You made this?"  
Me,   "Yes on the lathe in the garage."
Wife, "WOW!  That's what that thing does."
Me,   "Well what did you think it did?"
Wife, "I thought all it did was go round and round and throw s**t all over the floor!"

Who'd a thunk it!!!!!!!!!!!!!!!!


----------

