OT: speed control of stepper motor

Thanks a lot for a handfull of very usefull information .

I have a 10V, 3A reluctance type 3-phase synchronous stepping motor, 96steps/rev. It has 3 separate windings on stator each winding resistance is 2-ohms. I need to run it continously at a fixed speed and need a good torque as well.

One end of all the 3 windings is joined together and is connected to +10V. The other end of each winding is connected to a grounded MOSFET. Each winding also has a freewheeling diode connected across it.

Now i turn on MOSFET-1 for 5msec followed by a pulse train of 1:3 ratio for next 100msec. Next i stop these pulses at MOSFET-1 and apply a 5msec pulse at MOSFET-2 followed by a pulse train of 1:3 ratio for next 100msec. Similarly for MOSFET-3 and then back to MOSFET-1 and so on.

The motor steps nicely but it donot give sufficient torque and becomes heated up in few minutes.

Do you see where am i doing anything wrong ??

Thanks in advance.

rocknmoon@yahoo.com

Thanks a lot for a handfull of very usefull information .

I have a 10V, 3A reluctance type 3-phase synchronous stepping motor, 96steps/rev. It has 3 separate windings on stator each winding resistance is 2-ohms. I need to run it continously at a fixed speed and need a good torque as well.

One end of all the 3 windings is joined together and is connected to +10V. The other end of each winding is connected to a grounded MOSFET. Each winding also has a freewheeling diode connected across it.

Now i turn on MOSFET-1 for 5msec followed by a pulse train of 1:3 ratio for next 100msec. Next i stop these pulses at MOSFET-1 and apply a 5msec pulse at MOSFET-2 followed by a pulse train of 1:3 ratio for next 100msec. Similarly for MOSFET-3 and then back to MOSFET-1 and so on.

The motor steps nicely but it donot give sufficient torque and becomes heated up in few minutes.

Do you see where am i doing anything wrong ??

Thanks in advance.

rocknmoon@yahoo.com

The motor steps nicely but it donot give sufficient torque and becomes heated up in few minutes.

It is common for stepper motors to drive them with a very high current that after a short time (milliseconds - depending on motor) drops to a "holding current". This method gives more torque and less heat.

Erik

Whith Your MOSFET-swithes You don't have any real control about the current.
There are a lot of drivers for stepping motors on the market (Infineon, STM, or Ericsson) wich have half step or microstep mode will give You maximal torque.
The drivers provide an internal control loop for the current.
See on Ericsons website for applications and hints.

See:

http://www.cs.uiowa.edu/~jones/step/

This is a particularly good website on stepper motors.