View Full Version : VFD Application Question

05-22-2013, 03:45 PM
I have a 3/4 hp 3 ph motor on my Standard Modern 10"Utilathe. It is controlled by a 1 hp VFD. I want to up the power, and ideally a 1 hp motor is what I need. HOWEVER, I found a couple of 1 1/2 hp motors for free.
The question is, can I run the larger motor with the 1 hp VFD? I realise that if I loaded the motor down, it would probably fry something, but this is a HOBBY lathe, not a production shop. Also, the guy using it is the guy who paid for it!:)
I suppose, if the answer is "no way," then I have to buy a higher-rated VFD. That would probably mean that I would have to move both motor and controller to my old Logan, which would not be a bad idea. HOWEVER it would be REALLY neat to do all this for FREE!

Forrest Addy
05-22-2013, 03:52 PM
Yeah, probably. The larger motor will have a lower impedencew than the VFD is designed for. The control may not like it. OTH it may work if you can fool it into thinking the connected motor is 1 1/2 HP. Max the parameter setting for FLA etc and see what happens.

Sorry for the "it depends" response but it really does. Free motor? Doesn't cost much to try it.

1 1/2 HP is perfect for a VFD equipped drill press. Plenty of oomph for driving taps at 15 Hz where the reversal is nearly instantaneous.

05-22-2013, 05:21 PM
As a general rule the limiting factor is current, it will work as long as you do not push it, a 1.5hp should not 'fry' anything, just don't push it to the max, it will go into current limit condition.

05-22-2013, 08:34 PM
The VFD can be set to max out at it's rated capacity and a larger motor run at that setting without harm to either the motor or VFD. Nordic made a tread mill that was advertised as having a five horse motor. The controller was a nice private label VFD that was good for 1 hp. The power cord was 110-120V single phase. The five hp rating was correct if run at 380V and 200Hz, conditions the motors only saw in the test lab to determine maximum possible power output.

05-22-2013, 09:22 PM
Like the others said, it should work. Before you tear anything apart you should find the "frame number" of both motors so that you can make any adapters that might be needed. You should also find the VFD parameters that set the limits for full load amps as well as starting amps to ensure that it will limit the VFD output rather than shut down. An unexpected shutt down can be a real hassle while you are turning something.


05-22-2013, 10:38 PM
As above, but also your startup current. Limit your acceleration and you "should" be ok. Much of it will depend on the actual vfd model.

05-22-2013, 11:17 PM
Thanks a lot for your information. I will pick the motors up tomorrow. They were removed from a pair of fan/coil units and are most probably North American make. Incidentally, I have previously suggested, on this forum, that mechanical contractors are a good source of inexpensive motors. These are from a contractor, (and friend,) and they were going to the scrap dealer. The dealer has an "elecrtic motor rate" that is a bit more than iron, but not much. If the pair weighed 80 pounds, then he might get $16.00.

05-23-2013, 12:20 AM
'limit your acceleration' - I was going to suggest to use a soft-start function if the vfd has it, but that is about the same thing.