Author Topic: Stepper motor driving  (Read 8529 times)

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Offline deephavenTopic starter

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Stepper motor driving
« on: February 17, 2012, 01:17:11 pm »
I am using the old and established L297/L298 chip combination to drive a stepper motor. This provides two H drivers to the two respective stepper motor windings. If I step at around 500 steps/second it runs fine, but if I reduce the step rate to around 120, the power consumed goes right up and the L298 gets very hot. What would be the cause of such rise in consumption?

Another point, if I want some holding torque when it's stationary, is it acceptable to keep a (reduced) current flowing through the windings?
 

Offline nessatse

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Re: Stepper motor driving
« Reply #1 on: February 17, 2012, 01:49:54 pm »
At high step rates you are probably not getting a lot of current through the windings of your motor due to the inductance, so you dissipation will be lower.  At lower step rates there is more time for the current to build up, hence more power dissipated.  What is you motor drive voltage?   The L298 is really old technology, you should be looking at something a bit more modern, preferably with a chopper drive to limit current .  Perhaps look at one of the Allegro chips.


It is standard practice to use a reduced holding current, but once again, without a proper chopper drive to limit current, you are likely to burn something out, or at least reduce its lifetime.
 

Offline deephavenTopic starter

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Re: Stepper motor driving
« Reply #2 on: February 17, 2012, 02:53:32 pm »
At high step rates you are probably not getting a lot of current through the windings of your motor due to the inductance, so you dissipation will be lower.  At lower step rates there is more time for the current to build up, hence more power dissipated.  What is you motor drive voltage?   The L298 is really old technology, you should be looking at something a bit more modern, preferably with a chopper drive to limit current .  Perhaps look at one of the Allegro chips.


It is standard practice to use a reduced holding current, but once again, without a proper chopper drive to limit current, you are likely to burn something out, or at least reduce its lifetime.

Thanks for your reply, nessatse. I was using a board I made some then years ago. It runs off 12V. So thinking about torque, is the torque correspondingly higher at low speeds because the current is allowed to rise to a higher value? If this is the case, would it be normal to limit the current (through PWM) at lower speeds to keep the torque at the same level?
 

Offline PA3BNX

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Re: Stepper motor driving
« Reply #3 on: February 17, 2012, 06:46:50 pm »
Hello Every Body,


I use a series resistor with the stepper motor supply

When the stepper is standing still it must give the stepper motor
voltage.

Wen the stepper is turning fast then the voltage goes up.

So you keep very easy more torx

I use 5 volt steppers on a 12 volt Supply with one
big power resistor in series.

I have also build it with a lm200 power supply.

With that you can easy set the max current and max voltage.

Take a look at my WinStepper software in vb6

on

http://www.pi4wag.nl/index.php/winstepper
Greetings,

Lodewijk

Credo:

Home brew projects:
Build/Design  with minimum hardware
and maximal software.
 

Offline nessatse

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Re: Stepper motor driving
« Reply #4 on: February 17, 2012, 08:10:46 pm »

Thanks for your reply, nessatse. I was using a board I made some then years ago. It runs off 12V. So thinking about torque, is the torque correspondingly higher at low speeds because the current is allowed to rise to a higher value? If this is the case, would it be normal to limit the current (through PWM) at lower speeds to keep the torque at the same level?


Stepper motor torque essentially drops to zero as speed increases, so there is no reason I can think of why you would want to reduce the low speed torque to compensate.  For most application you would probably want as much torque as possible.  Usually a high drive voltage (40V and up) us used to get decent torque at higher speeds.  This must of course be done in conjunction with a chopper drive (i.e. PWM)  in order to limit the current appropriately.  Using resistors to limit current is not really an option for anything but very low power applications.

 

Offline Rufus

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Re: Stepper motor driving
« Reply #5 on: February 17, 2012, 09:33:19 pm »
Using resistors to limit current is not really an option for anything but very low power applications.

Way back that is how it was done. I have seen stepper drives with a big box full of fan cooled resistors.
 
 

Offline deephavenTopic starter

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Re: Stepper motor driving
« Reply #6 on: February 17, 2012, 09:52:36 pm »
Thanks for the replies. I had a look at the Allegro chips and it they have amazing capabilities compared with the L298 I was using. I would like to investigate micro-stepping as noise is a real issue for me and that may be a way of reducing it as my speed requirement is quite low.
 

Offline electrode

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Re: Stepper motor driving
« Reply #7 on: February 17, 2012, 09:56:27 pm »
I'm actually working on a stepper motor project myself at the moment. Unless your motor is rated at exactly 12V (ie max current = 12/coil resistance), simple H bridge drivers, such as L293/298 are useless. The big resistor idea is antiquated, as you're either wasting power or choking the motor.

I came across the RepRap stepper motor page, and settled on the Texas Instruments DRV8811, though the HSSOP28 package is a pain. There are other options there.
 

Offline deephavenTopic starter

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Re: Stepper motor driving
« Reply #8 on: February 17, 2012, 10:29:03 pm »
I'm actually working on a stepper motor project myself at the moment. Unless your motor is rated at exactly 12V (ie max current = 12/coil resistance), simple H bridge drivers, such as L293/298 are useless. The big resistor idea is antiquated, as you're either wasting power or choking the motor.

I came across the RepRap stepper motor page, and settled on the Texas Instruments DRV8811, though the HSSOP28 package is a pain. There are other options there.

Electrode, that is a mine of information, many thanks for the link.
 


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