Small Variable Frequency Drive

[BrianR]

I have a 1.5HP 3ph variable speed motor drive from a varaible frequency drive to give about 10:1 speed range. What is the speed / torque characteristic common to this setup.

 

[acmotorengineer]

With an AC induction motor with squirrel cage rotor, self cooled -- Variable Torque.

With an AC induction motor with squirrel cage rotor, external fan cooled -- Constant Torque.

With an AC induction motor with squirrel cage rotor, intermittant duty -- Constant HP.

... etc ... etc ...

 

[BrianR]

Thanks for that. This one is probably the 1st as it's on a wood lathe.

 

[jbartos]

Suggestion: Since there are different principles of Variable Speed Drives, it may be a good idea to check with its manufacturer for correct application settings.

 

[ElektranMan]

My application experience has shown me that with a standard volts/hertz drive, the torque produced by the motor will drop off exponentially at about 17 HZ. If you need to run slower, you may need to get a drive capable of open loop vector or a vector drive which with encoder feedback will allow you to run to zero speed with full torque.

 

[jbartos]

Suggestion: The very slow loaded motor run may need a special cooling.

 

[jOmega]

Lathes are constant HP applications; not constant torque.

Check motor manufacturer for minimum operating speed on inverter power for a lathe application.

I.E. Marathon Electric makes a BlackMax motor that is capable of 1000:1 constant torque..... They also make Blue max motors rated for 20:1 and 10:1 constant torque speed ranges w/o requiring auxiliary cooling. Their inverter motors, such as those stated above, are often closer to a NEMA design A than a design B motor speed-torque curve. They have a stiffer speed-torque characteristic, and because of less copper in the slots, are able to produce the torque with less heat (copper losses) ...

Back to application, ... lathe mfgr can give you either curves of data points or curves that show HP vs speed requirements.

That will be the determinent when discussing the application with the motor manufacturer.

 

[BrianR]

Thanks for these comments. I'll go back to the motor manufacturer for the curves.

 

[jbartos]

Suggestion: Also, the variable frequency drive characteristic curves might be useful to have. There may also be some application notes available.

 

[jOmega]

JB,

Can you give me a reference to "Variable Frequency Drive Characteristic Curves" .. I'd like to see to what you are referring.

Thanks.