How fast to run a motor with a VFD?

[TheGreenMachine]

I am powering a 3hp motor on my knee mill with a Teco VFD. Currently the HZ is set to a maximum of 120hz, as far as I can tell it runs just fine but I don't know what to look for. My question is how high can I take the motor? What problems can I encounter with the motor taking it higher? (I am not taking it above what the spindle is rated for)

[chich2]

I run a VFD on my two 3hp (2.2Kw) motors on my knee mill and have set my max frequency to 100Hz I have accidentally run one motor at 400hz without load and I'm counting myfelf VERY lucky the motor didn't fly to pieces!!!! WAY too fast. What motors are you you running on your machine.
If you look at my thread:
http://www.cnczone.com/forums/showth...=25895&page=16 Post 188 you will see I changed my motors. They were designed for up to 60Hz but run comfortable at 100Hz. Even 120Hz would probably be the fastest I'd go but cant see myself going over 100hz.
To answer your question though, It will come down to motor rotor ballancing, bearing speed and load, and motor cooling to name a few. On small motors like 3hp you will find the same bearings in a 4 pole (1450RPM @ 50hz) as what is in a 2 pole (2900RPM @ 50hz) motors. Don't run a 2 pole motor at more than name plate frequency without doing some real good homework.

Hope this has been of some help,
Chich

[mactec54]

TheGreenMachine

120Hz is fine & normal for either 4 pole or 2 pole, both handle the 120 Hz, You don't want to go above 120Hz unless you have a inverter duty motor

[Al_The_Man]

The VFD's I have installed for 4 pole motors I have not yet had a problem at 120hz, but I would not suggest going over that, even the motor manufacturers have reserved rpm ratings for vector rated motors even.
2 pole motors should not be used much over 60hz.
A couple of criteria are bearings and rotor balance.
Here is a tech sheet from baldor.
http://net.grundfos.com/doc/webnet/b...-%20Baldor.pdf
Al.