VFD Help Needed

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vocatexas

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I bought a VFD to run my South Bend lathe. It's got a 2 1/2 horsepower motor and I got to thinking that firing up a 40 hp RPC was just silly to run that small a motor. I ordered this VFD: https://www.ebay.com/itm/1414410659...,osub=osub,crd=crd,segname=segname,chnl=mkcid

Wow, what a link...

Anyway, I got the 220 circuit run to the lathe location yesterday. My electrician nephew wired the VFD to the lathe when he was here a couple of weeks ago, and I had him put a welder plug on the in-put side of the VFD so that if I ever wanted to move the lathe it wouldn't have to be un-wired and re-wired. I finally got the courage up to try powering it up today. It gives an error code that, according to the manual means it's receiving too much current. When I probe the wall outlet, my meter shows 244 volts. The VFD fan powers up for about two seconds, then stops and the display begins flashing.

Any ideas what I've done wrong here?
 
First off, is the VFD wired directly to the motor, or did you essentially plug the lathe into the VFD?
VFD’s are designed to have nothing between them and the motor. No switches, contactors, etc. It is possible that wired to an open switch, the vfd would report too much current as an erroneous message.

Second possible issue, you say it is a 2.5 hp motor. You have a 2hp vfd. It may see the starting current to that motor as too much. A vfd can be rated bigger than the motor, at least by a factor of two, but not smaller. (Actually it is the amperage rating, but hp follows amperage fairly closely). So you need a 3hp or 5 hp rated vfd.

The 220V vs 244V should be not be a problem.
 
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I'm sorry, I did say 2 1/2, it's actually 2 horsepower. There IS a drum switch on the lathe, but I have it in the 'forward' position and I took the handle off so it won't be moved. Long story, but that's the way I have it. Would simply having a closed switch cause a problem? I could understand if it was open. The lathe WAS running when I bought it. We simply disconnected it from a junction box and left all the remaining wiring alone.

I have another VFD set up the same way. That one is a 5 hp unit. Would it hurt to hook that one up to the lathe and try starting with it? I was under the impression that you wanted to size a VFD very close to the size of the motor it was going to run.
 
i'll bet if you were to go through the settings on the first vfd,
you would find the cause of the overcurrent error
 
Can you be more precise about the error? “Receiving too much current” doesn’t make sense. The VFD receives a voltage and may draw current from the wall. The motor draws current from the VFD.
 
Usually one would size the vfd a bit larger than the motor for example for a 2 hp motor you would want a 2.5 hp or larger vfd rating.
Having any switch in between the vfd and the motor is asking for trouble- if the switch gets bumped or one of the contacts decides to go slightly open circuit it can blow the vfd output stage- bad news since these things are not easily repairable
If you need to have the ability to reverse the motor you should do it at the vfd not by switching the motor leads
-Mark
 
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Many people have had the inexpensive off brand VFDs work fine, but often with them it does pay to heed @markba633csi's advice and oversize them. Not as much of an issue with name brand VFDs, but obviously you pay more for them. Hitachi and Teco seem to be common name choices.
 
There is more to installing the VFD than the physical wiring - Just in case you didn't correctly set up the VFD parameters. You didn't mention programming it, so in general, you need to set the current of the motor and one or two other parameters: I programmed all of my VFDs 5-6 years ago so I can't remember the others off-hand.. (I can check if you like)

The very most important setting is the motor current at 60Hz, found on the motor faceplate. This should help you avoid overcurrent errors.

Please don't leave the switch in-circuit. This is a mistake that will likely cause the destruction of one of you VFDs some day. There is no need to have it there - BUT - it is important to make the lead from the VFD to the motor as short as you can. The over-simplified explanation is that the VFD senses several parameters in the motor as it is turning, and long leads inductance, extra capacitiance from the leads, resistance from the switch can all play a part in the VFD not doing its 'best job'.

For cheaper VFDs and for lathes, it is really important to buy a much larger capacity VFD For it - at least 30% bigger, but 2X wouldn't hurt. (OK, perhaps the wallet)

I also have a RPC for my big lathe as buying a 15HP VFD for it would be a little pricey :tranquility:
 
A quick followup to the previous post: They say in the ad that it is for light-duty motors, and not for heavy duty motors. This may mean that the motor inrush current of the motor trying to overcome the inertia of the gears and chuck is too much for your inexpensive VFD.

If you move your 5HP VFD to your 2HP motor to test this, be sure to revise your motor current value.
 
I have not experienced any complications in using inexpensive vfd’s in 8 years of torture testing on everything from surface grinders to lathes to milling machines to tool grinders
Superstition often prevents trying new things
 
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