Full Torque at Zero Speed
Full Torque at Zero Speed
(OP)
I am using a nord 20hp gearmotor with a Siemens MM440 invertor in a hoist application.(With encoder feedback and resistor for regen) The system can lift 9000 lbs at over 8 inches per second in normal operating mode. When is comes to holding the load at close to zero speed, it can only handle 5000-6000 lbs before the platform looses control.
(Specs - Gearmotor Torque 13000 in lbs at 97 rpm)
Question:
Shoudn't the system be able to generate full torque at zero speed. (I am using encoder feedback for closed loop vector)
Is the motor undersized? I do not want to put blame on the invertor supplier if it is a motor problem. The VFD specs claim that my config can produce full torque at zero speed. (200% for a small period of Time)
Thanks
(Specs - Gearmotor Torque 13000 in lbs at 97 rpm)
Question:
Shoudn't the system be able to generate full torque at zero speed. (I am using encoder feedback for closed loop vector)
Is the motor undersized? I do not want to put blame on the invertor supplier if it is a motor problem. The VFD specs claim that my config can produce full torque at zero speed. (200% for a small period of Time)
Thanks





RE: Full Torque at Zero Speed
Also, check to see if the drive has a parameter for "allowable speed variations per XXXX" or something like that. I think its intent is to allow for backlash.
RE: Full Torque at Zero Speed
Just thinking out loud of possible problems:
- To obtain zero speed the motor has to be able to exactly match the load torque. Sounds like that will require sophisticated control.
- If you reduce sync speed you also have to reduce voltage which reduces torque.
- At zero speed there will be high current and zero cooling. This results in motor heating very rapidly.
- Rapid heating will increase rotor resistance which has dramatic effect on the torque speed curve and can further complicate the control problem.
- Heating can also damage the motor.
Let me repeat I am not that familiar with this type of application.
RE: Full Torque at Zero Speed
-ojay-
Jay Lehrbach
www.eCycle.com
RE: Full Torque at Zero Speed
For electricpete, this is done all the time in crane and hoist applications now. Good quality Closed Loop Vector Drives have what is called a "Torque Proving" algorithm (maybe by another name) which serves to ensure that the motor does in fact match the load torque requirements prior to releasing the mechanical holding brake. The motors are designed for this use, having independently powered cooling fans so that they get full air flow regardless of rotor speed. I worked on crane systems at Boeing where we lifted and held 747s and 777s with 4 20HP vector drives. If you drop one of those babies, run to the nearest Tibetan monestary to hide for the rest of your life!
Quando Omni Flunkus Moritati
RE: Full Torque at Zero Speed
RE: Full Torque at Zero Speed