You don't lose torque with a FVD. Period. A three phase motor develops full rated torque at full load amps whether its on a VFD or across the line.
Is the three phase motor connected for 230 Volts? A three phase motor connected for 460 volts will develop less 1/4 its rated torque if run on 230 volts.
Have you read the book that comes with it? Have you set the parameters to suit your particular application? Most VFD's come with default settings that include very slow acceleration lasting 10 seconds or more. The motor seems like it's slowly building up to speed because of heavy load whereas it's actually following its over-conservative default programming. The accel can be adjusted to any value but I prefer 2 seconds or so.
Are you using the existing speed changing correctly. A motor develops its rated power at 60 Hz at full motor torque. Halve the frequency and you halve the RPM but still at full rated torque. At 15 Hz you get 1/4 the rated motor HP still at full motor torque and so on in proportion to nearly zero HZ. It may seem like the motor is "losing torque" but the problem is misapplied physics not motor torque - that and pervasive motor-head perversion of technical terms: "torgue" is not power.
If you wish to take full HP cuts you HAVE to use the belt speeds or the gear changes to keep the motor at or near 60 Hz. Light cuts you can use whatever VFD and mechanical speed setting that works but if you want stock removal you have to use the mechanical reduction to keep the motor in its sweet spot..
And you HAVE to use a three phase motor with a VFD; it will not work with a single phase motor.
Maybe I'm being impatient. If so, I'm sorry but a good VFD whose parameters are set correctly and run with a good appropriately sized three phase motor connected for the rated voltage cannot fail to function properly.
Something is wrong.and there's a 99% chance it aint the VFD itself.
No. You de rate your 3 phase motor by 1/3. You should know this going in. If you need 2 h.p. you purchase a 3 h.p. v.f.d. and motor. I run my 14x40 on a teco 2 h.p drive and 2 h.p. motor with that I dont have any problems. O.P. look in your drive and see if you can increase the torque out put. I dont know where mine is set and I cant check for a few days, sorry.
Randy, three phase motors run from a VFD run to full nameplate ratings. The VFD put s out sine coded PWM to the motor leads leading the motor to think its running from clean three phase. Thus the motor develops full power.