Stepper motor driving - Page 1
Forum section: electronics / projects

author: deephaven
author_rank: Frequent Contributor
timestamp: February 17, 2012, 01:17:11 pm
content: 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?

author: nessatse
author_rank: Regular Contributor
timestamp: February 17, 2012, 01:49:54 pm
content: 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.

author: deephaven
author_rank: Frequent Contributor
timestamp: February 17, 2012, 02:53:32 pm
content: Quote from: nessatse on February 17, 2012, 01:49:54 pmThanks 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?

author: PA3BNX
author_rank: Regular Contributor
timestamp: February 17, 2012, 06:46:50 pm
content: Hello Every Body,I use a series resistor with the stepper motor supplyWhen the stepper is standing still it must give the stepper motorvoltage.Wen the stepper is turning fast then the voltage goes up.So you keep very easy more torxI use 5 volt steppers on a 12 volt Supply with onebig 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 vb6onhttp://www.pi4wag.nl/index.php/winstepper

author: nessatse
author_rank: Regular Contributor
timestamp: February 17, 2012, 08:10:46 pm
content: Quote from: deephaven on February 17, 2012, 02:53:32 pmStepper 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.

author: Rufus
author_rank: Super Contributor
timestamp: February 17, 2012, 09:33:19 pm
content: Quote from: nessatse on February 17, 2012, 08:10:46 pmWay back that is how it was done. I have seen stepper drives with a big box full of fan cooled resistors.

author: deephaven
author_rank: Frequent Contributor
timestamp: February 17, 2012, 09:52:36 pm
content: 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.

author: electrode
author_rank: Regular Contributor
timestamp: February 17, 2012, 09:56:27 pm
content: 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 theRepRap stepper motor page, and settled on the Texas Instruments DRV8811, though the HSSOP28 package is a pain. There are other options there.

author: deephaven
author_rank: Frequent Contributor
timestamp: February 17, 2012, 10:29:03 pm
content: Quote from: electrode on February 17, 2012, 09:56:27 pmElectrode, that is a mine of information, many thanks for the link.