I am working on a project where we want to run at a large range of speeds.
.03ft/min to 600ft/min. The motor I have runs a 12.5" dia drive drum.

Right now I am able to run the 600ft/min at 62Hz but the low range is where I am running into problems. I am using a 1000:1 vector motor and allen bradley 755 drive. In order to run the .03ft/min with my 10:1 gear reduction I need a output frequency of .003Hz. Is this even possible with a drive?
Has anyone ever run this large of range without secondary gearing?
Here are my motor specs.
Specifications: ZDVSM3661T
SPEC. NUMBER:
06H928X181Z1
CATALOG NUMBER:
ZDVSM3661T
FL AMPS:
8.2/4.1
BEARING-DRIVE-END:
6206
BEARING-OPP-DRIVE-END:
6206
BLOWER-AMPS:
--
BLOWER-HERTZ:
--
BLOWER-PHASE:
--
BLOWER-VOLTS:
--
DESIGN CODE:
B
DOE-CODE:
010A
FL EFFICIENCY:
89.5
FRAME:
182TC
HERTZ:
60
INSULATION-CLASS:
F
MAGNETIZING-CURRENT:
4.2/2.1
MAXIMUM-RPM:
5400
SPEED [rpm]:
1755
OUTPUT [hp]:
3 TE
PHASE:
3
RATING:
40C AMB-CONT
ROTOR-INERTIA:
0.3
SERIAL-NUMBER:
--
SERVICE FACTOR:
1.00
SLIP-HERTZ:
1.5
VOLTAGE:
230/460

What does slip-hertz mean? Does this mean the motor will slip under 1.5Hz? This is below the 1000:1 ratio. Should I not get full torque at .06Hz?

 

I haven't looked at all the issues, motor and VFD details, but .003hz is asking too much from a VFD, particularly without feedback, slip herz is slip frequency, the difference between the applied frequency and the actual rpm, an induction motor can never run at synchronism, a slip frequency is going to occur in order for induction to occur.
Max.

 

Thanks max. I am running with encoder. 1024ppr.
Is it a good idea to never run below the slip frequency for motor startup?

 

.003Hz is one electrical cycle every 5.6 minutes. Even if your VFD were capable of this, I doubt there would be any resultant motor movement. I think you will need quite a few multi-speed gearboxes to achieve such a wide range of speeds.

 

Thanks max. I am running with encoder. 1024ppr.
Is it a good idea to never run below the slip frequency for motor startup?

The slip or frequency difference is going to vary with load etc, e.g. a 60 hz induction motor, no VFD, at start up the slip freq. is naturally 60hz, and will decrease as the rotor catches up with the rotating field, with a VFD you have the option of programming the acceleration (maintain a lower slip freq).
As you may have found out, if you try to accell too fast (high slip freq), the VFD will trip the over current.
Max.