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I am currently working on a project that involves 6x NEMA 23 stepper motors, rated at 2.8A - 2.5V each.

I have been doing extensive research on what drivers and power supply I should use. From my knowledge, I have decided to use a 10A, 12V Switching Power Supply, and to use the L298N Stepper motor drivers. I just require confirmation that the parts I have chosen will all work properly together - any guidance would be appreciated.

The data sheet for the Motor: RS Pro Hybrid, Permanent Magnet Stepper Motor 0.9°, 1.26nm, 2.5 V, 2.8 A, 4 Wires

The data sheet for the Driver: L298 DUAL FULL-BRIDGE DRIVER

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  • \$\begingroup\$ how did you arrive at that power supply rating? Seems wrong, but we might be missing some restriction that contributed to your decision that 10A is enough. So: Please explain how you've decided! \$\endgroup\$ – Marcus Müller Jan 28 '18 at 16:22
  • \$\begingroup\$ I was under the assumption that in practice, you would never run a stepper motor at its rated current, and that reducing the current will proportionally the holding torque... therefore I felt 10A would be OK. If this is wrong please let me know :) I am also only ever gonna have 3 motors running at a time. \$\endgroup\$ – james Jan 28 '18 at 16:34
  • \$\begingroup\$ I believe today L298 is the worst choice. It's a probably 20 years old ic showing over 5V voltage drop at the current you are going to use. It's popularity among Arduino & Sparkfun communities is something I really cannot understand. Many many newer ic can do much better (L6203 is the first that comes into my mind) \$\endgroup\$ – carloc Jan 28 '18 at 17:22
  • \$\begingroup\$ @carloc I can't really be as harsh on the L298 as you are, but: 20 years? hahahaha, that thing has an ST datasheet from 2000 (so it's at least 17 years old, if there was no further info) with pictures in it that look like they're from the late 70s or early 80s. sooo.. off by 20 years. \$\endgroup\$ – Marcus Müller Jan 28 '18 at 17:38
  • \$\begingroup\$ For a one time app I have always use a stepper motor driver For $20 it is way cheaper than re-inventing the wheel. \$\endgroup\$ – lakeweb Jan 28 '18 at 17:40
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Your choices will certainly work, but only if you are careful. If you don't pay attention to the details, you will cause the power supply to go into current limit, with bad consequences for system performance.

First, your choice of driver is fine. With a 4A/phase capability, you should have no problems on that count.

Now, about the motors. The first thing you need to realize is that the 2.8 A limit applies to each winding, so it's perfectly possible to draw 5.6 A in normal operation. Since you will be running as many as 3 motors at a time, your current draw will be as high as 16.8 amps.

Is this a problem? Not necessarily. The question comes down to how much torque (and therefore current) you need. You must have noticed that you cannot apply 12 volts to the motor for any length of time, since this will provide 12 V/0.9 ohms per phase, or 13.2 amps once the inductive effects has settled out. Instead, you'll need to create (or buy, they're cheap) a constant-current driver. Commercial units use PWM controlled by feedback from a current sense resistor (which you'll notice on the L298 data sheet). In the process of building or using such a circuit, you can set the current to pretty much any level you want.

So, if you set your current levels to 1.5 A per phase, you'll draw 3 amps per motor, and 3 motors will only draw 9 amps. Of course, this will only give you half the torque you expect. How much do you need?

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  • \$\begingroup\$ Hi, thank you for the quick response. I only require roughly 1 kg-in (247 mN-m), which surely should not be a problem with the NEMA 23 motors I have chosen. My main priority is high speed with high accuracy. Would you suggest shifting my power supply to a higher current? Also, I did not fully understand what you meant by the constant current driver, would I need to source one or does the L298 already do this for me? Thank you. \$\endgroup\$ – james Jan 28 '18 at 17:22
  • \$\begingroup\$ An L298 can be used in a chopping current-mode driver, but is not itself one, as it lacks the control circuit. The L297 it was sometimes used with back in its era contained that along with the step sequencer. For a high speed application you may even need more than 12v - depends on how much torque falloff you can tolerate, and also if your controller implements smoothly profiled acceleration. \$\endgroup\$ – Chris Stratton Jan 28 '18 at 19:26
  • \$\begingroup\$ @james - as an example of a stepper controller, see ebay.com/itm/… Note that I am not actually recommending this particular unit, but it's an example of what you can get for very little money. Of course, reliability may not be the best (you get what you pay for, caveat emptor, etc) but it's cheap to find a controller which will deal with all your concerns. If you set the motor currents to 1.5 A/phase, 10 amps is all you need. Otherwise, bigger supply. \$\endgroup\$ – WhatRoughBeast Jan 28 '18 at 22:32
  • \$\begingroup\$ @james - Also, keep in mind that the L298 has a big voltage drop, as Chris Stratton pointed out. Worst case is 5 volts at 2 amps (page 3 bottom of data sheet). With 2 channels, this means the the L298 will dissipate about 20 watts per motor (!) at this current, and something like 30 watts at 2.8 amps. This will require a much larger heat sink than you are accustomed to, or you will Let The Magic Smoke Out. Google the phrase. And big heat sinks, in addition to being big and heavy, are expensive. But you can do what you want with an L298. Like I say, you need to pay attention to details. \$\endgroup\$ – WhatRoughBeast Jan 28 '18 at 22:38
  • \$\begingroup\$ @james - And motor power dissipation can be a problem. At full current, the motor will dissipate 14 watts. If the motor is mounted in a metal frame this should be no problem, since the metal will conduct heat away (although then you need to consider the overall heat transfer of the frame). If you're thinking wood or some other, easier to work, material, they usually don't conduct heat well, and you can get in trouble that way. Pay attention to details. \$\endgroup\$ – WhatRoughBeast Jan 28 '18 at 22:44

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