Another Motor star/delta conundrum

I have a question for any boffins out there that can possibly help me. I am running two PLC controlled motors via mitsubishi FR520 inverters, both are 0.5 HP, identical make (ABB), specification and interter settings. Both are attached to 10:1 gearboxes which each drive a belt between two identically sized pulleys. (Both systems are physically separate and identical mechanically). With it being a fairly low torque application I wired both motors in star. Both inverters showed a running current of 0.3A. All nice, however on testing the torque of each motor (by pressing fingers to the belts). One could not be stalled by hand and the other could be quite easily. On testing the voltage of each phase at each motor, they were all identical. What am I missing that could cause this difference in output torque? (To get around the problem I had to change one motor to delta configuration, but this brings the current up to 0.7A and runs the motor hotter than I would like (about 40 degrees C)). Any ideas, or have I missed something obvious?

Can distance be a factor, wire size?

Are you positive you wired them both the same..retrace and recheck your steps.

See if that motor does it without a load...may be a bad motor.

Just do the basic troubleshooting. Swap motors and see if the problem stays with the motor or stays with the circuit. Proceed in the direction it points to.
Roger

Check the drive parameter; Stall Prevention Operation Level
Should be set the same for both motors.

Wiring a motor star or delta is not an arbitrary decision. The motor nameplate will indicate the design voltage in star and also the design voltage in delta. You MUST pick the one that matches the supply voltage if you expect the motor to perform properly.

The supply voltage to the drive will normally be close to one of the motor nameplate voltages. Enter the motor data into the drive using the nameplate data which corresponds to the voltage you are running on.

As mentioned above, first swap the motors to see if the problem follows the motor. If it doesn't, it is almost certain that some parameter is different between the two drives or the input signals are not the same. Better double check them.

If the problem follows the motor and they are wired the same, clearly, one motor is bad. If you chose the star connection (low voltage) and then ran the motor on the higher voltage, you likely damaged the motor.

I concur with DickDV in that the motor should be wired for the voltage it will run at. However, the Star connection is for the higher voltage and running a motor connected for a higher voltage on a lower voltage is not likely to damage it unless the load was large enough to draw excessive current.

Vic is correct and I was wrong. Star is for higher voltage and delta for lower.

Wired for low voltage and running on high voltage will be destructive. Wired for high voltage and running on low will not cause damage unless the slip get so high that the amps become destructive as Vic mentions. Also, if wired for high voltage and running on low voltage, there will be very low torque output from the motor.