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Problem getting proper current on powerSTEP eval boards

Question asked by mouser on Jan 24, 2018
Latest reply on Jan 24, 2018 by mouser

Hi, 

 

I am using NUCLEO-IHM03A1 eval boards on top of a Nucleo STM32F4IiREI to drive a NEMA23 stepper motor.

 

The motors are stalling at relatively low speeds with no additional load. I don't seem to be getting the required current to the phase windings even at slow step rates and when applying a load.

 

The manufacturer's torque graph is labelled as 3A 30V. I'm barely getting that using 50V supplied from lead acid batteries. The max current going into the eval board is 2.9A at 533 pps , half-step pulses.RMS input current drops half that value at 800pps.

 

The phase windings are spec'd as 1.6mH 3A ; 1 ohm wire resistance.

I calculate a nominal impedance of 8 ohm at 800 pps plus 1 ohm resistance, so I'd expect around 52/9, nearly 6A to each coil, not the 1.5A being pulled from the supply.

 

I'm using the chip with externally created pluses, not the internal motion commands so I'm setting TVAL_HOLD, rather than TVAL_RUN to control phase current.

 

At higher frequencies dropping TVAL_HOLD makes no difference until around TVAL_HOLD=0x11 , so clearly I am not getting up to the specified current in the windings.

 

Since the motor designed for 3A ; 2.9 is acceptable the problem is that this drops quickly with increasing speed and I'm not getting useful torque from the motor. From the inductance value, I would expect to get more current delivered to each phase using 50V.

 

Can anyone suggest how to optimise the chip params, or whether my problem lies elsewhere?

 

Thanks.

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