VFD for rpm increase?

I've been running my 2 HP lathe and 1 1/2 HP mill/drill from 10 Hz to 90 Hz for some years, with no problems.
 
Wow. Lots of info.
I think I will keep it simple like Cooter mentioned. Might speed it up some but watch the spindle bearings.
Thanks for all tour input.


I too run 10 to 90 Hz. I do it not to exceed the spindle rated speeds, but so I don't have to constantly change the drive belt. The VFD plus back gear has gotten me the range I want without touching the belt. Now if I had a real heavy cut that required being towards the extremes of the VFD, I wouldn't hesitate to change belt positions. But I haven't needed to yet
 
you should be fine pushing the rpm a bit. I did find my vfd can slow the lath down quite fast which has caused the chuck to unscrew, so I've set my decelerate time to a fair bit longer than standard.
 
A line/load reactor between vfd and motor is easy way too solve spike issues for an older motor. Look for MTE on ebay,
 
A good quality modern Inverter Duty motor will safely run faster than any published specification might hint.
I have run a 1Hp, 2 Pole, Compact Frame, Electro Adda motor at up to 7000rpm for a couple of years in my bench top CNC mill without any issues at all.
I have run a 1Hp, 4 Pole TEE (Turkish made) motor in my Myford Super 7 at up to 3000rpm on a daily basis for over 5 years with no issues.

It's probably best to follow the data sheeps until you have enough experience to make your own decisions based upon experimentation though.
 
If motor is normally 1800 RPM at 60 hz you can potentially get it up to 3600 at 120 hz. Most VFDs can do this, I have my lathe set up this way.
If motor is already 3600 you probably don't want to push it any faster.
 
A VFD will only decrease the input frequency from 60Hz down to 0Hz. That will only make your lathe run slower.

Edit: I didn't know there were VFD's that push more than 60Hz. I love google sometimes. More rpm = less torque.

http://www.electriciantalk.com/f28/running-motor-vfd-past-its-hertz-rating-19715/

That's not true of my VFDs. They will run to at least 120 hz. I would not run my motors long at that rate, but I can double the speed according to the Tachometer. I usually do not go above 150 percent. I don't drop below 50 percent either, because the torque drops significantly. But between 30 and 90 hz all run well.

Randy
 
VFD's can run above the motor base speed no problem, although you will lose torque. Couple of things to watch for (as stated above) running a non-inverter duty rated motor at any speed with a VFD can damage the motor. VFD's generate high voltage spikes which can short between the windings (this is exacerbated the further away from the motor is from the VFD). Second, the motor bearings and mechanical structure of the windings are rated for a particular speed. Running beyond the rated speed can quickly degrade bearing, however going too fast can cause a catastrophic failure of the windings from centripetal force. I've seen that happen first hand. Inverter duty motors typically have a maximum speed on the name plate and have specially designed rotors to handle the higher speeds.

All said and done, you probably can push the top speed a little but don't go crazy.
 
going too fast can cause a catastrophic failure of the windings from centripetal force.

That's very interesting as none of my Induction Motors have rotor windings and I have yet to see one that does ;-)
Induction motor rotors are made in exactly the same way for 4 pole motors as for 2 pole motors and they don't fit different bearings for the same frame size in 2 & 4 pole motors.
Applying some engineering logic this strongly suggests that Inverter Duty 4 pole Induction Motors can be safely run at 200% of rated speed.
And that is indeed the case ;-)
 
That's very interesting as none of my Induction Motors have rotor windings and I have yet to see one that does ;-)
Induction motor rotors are made in exactly the same way for 4 pole motors as for 2 pole motors and they don't fit different bearings for the same frame size in 2 & 4 pole motors.
Applying some engineering logic this strongly suggests that Inverter Duty 4 pole Induction Motors can be safely run at 200% of rated speed.
And that is indeed the case ;-)

Depends on the motor... most induction motors are the “squirrel cage” type where the rotor is constructed with copper bars in a cage shape. Some motors like the ones in your washing machine as well as specialty high speed induction motors will have wrapped wire windings. Regardless I referred to them as windings. If you’d prefer, let’s use the word rotor. The same principles apply
 
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