stepper motor not delivering expected torque.

Hello,
We have a NEMA-23 a stepper motor from there: http://www.homeshopcnc.com/page3.html
270 oz/in Model # RHT23-270 rated at 2.48 V and 4 amps.
and we are using a stepper driver FT-3 from there:
http://www.stepperworld.com /
the FT-3 driver works for unipolar motor, so I am really expecting 1.35 Nm (190 oz-in) torque for the motor mentionned above. Yet, when we implement this solution ( a power supply of 5 V and resistors of .6 Ohms), we barely get 1/10th of that torque. What are we doing wrong ?
Jake.
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A couple of points. 1. A stepper motors torque is rated while it is stopped. The faster it turns the less torque it has because the coils can't charge fast enough. 2. The higher the voltage of the power supply, then faster the motors will turn with more torque BUT you may need ballast resistors in the 50-75 watt range if you wanted to use a 24VDC power supply. Dan

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Dan, Thank you,
I understand for the torque curve showing a decreasing slope, so that indeed when it turns, the motor cannot have the max holding torque. Yet, we are talking about relatively slow speed. Irrespective I see you point.
Now to the second one, what do you mean we need to ballast resistors: increase resistor size ? If so I can show my calculation so that everybody can get a lesson out of our initiation in this realm :-)
Jake.
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Do you have a current reading from your powersupply? Lots of supplies have current limits. Be sure you're really getting 5V at 4A before jumping to conclusions.
--
Randy M. Dumse

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