Hello, I recently put together some linear actuators from OpenBuilds that came with the NEMA 17 stepper motor. I did this in an effort to start learning how all this works (I am completely new to all this). My basic question goes like this: On the motor specs it says that the motor can operate at 12-24VDC volts with a peak current of 1.68A/phase. The thing is that I measured the resistance of the stepper motor coils (per phase) and it measured 2.5 ohms. Now, from basic electricity, if I apply 12 volts to the motor with 2.5 ohms of coil resistance I would end up with a current of 4.8 amps. This is far more than the allowable peak current of 1.68 amps. With 24 volts I end up with double the current which just makes matters even worse. So how is this supposed to work? How can the motor be rated for a voltages that it really can’t handle because with a voltage that high, the resulting amps will essentially fry the motor? Thanks.
12-24v PSU > Stepper Driver > Stepper motor The driver converts PSU voltage to what the motor needs (a fixed current setpoint, so automatically adjusts voltage to suit. But needs "extra" voltage to work correctly)
Thank you, More context: As I experiment, I am currently trying to drive the stepper motor using an Adrafruit driver board (Adafruit Motor/Stepper/Servo Shield for Arduino v2 Kit). For this to somewhat work, I have to limit my PSU voltage to about 3 volts (outputting around 1.4 amps), anything greater than that and bad things start to happen. But with that voltage the motor feels anemic. Given the resistance of the motor coils, limiting the voltage to 3 volts actually makes sense. I can only guess that no matter what controller I use, at the end of the day, the controller will need to limit the motor input voltage to around 3 volts, but man, based on my experiments, under those conditions, the motor is just weak, I can stop it just by pinching my fingers on the motor gear. Still not sure what am I missing.... Thanks.
Use a decent driver like a DQ542MA It does it all for you! Will have way more power than an H-Bridge based driver - thats all on/off - no microstepping, no intelligence, no current monitoring, no chopper, nothing!
Thank you, I will give the DQ542MA a try. Given that you guys don't sell the driver (I was hoping you did), Any chance you could provide me with link from a reputable vendor (one that you guys recommend) to buy this from? I just don't want to buy some cheap clone from some bogus vendor and end up with a driver that does not work correctly and end up running into all kinds of issues. Thanks.
Generally anything from StepperOnline is solid and reliable. Digital Stepper Driver 1.0-4.5A 18-50VDC for Nema 17, 23, 24 Stepper Motor - DM542T|STEPPERONLINE (omc-stepperonline.com).
Thank you for your recommendation, I ended up getting one of those stepper motor drivers and that made all the difference. Assuming this question is not out of scope for this forum, do you guys know why the PUL, DIR, ENA etc have both positive and negative terminals exposed? I am only asking because normally I would have expected for the driver to just have an exposed positive terminal and the negative / common polarity to be wired internally and not exposed as a terminal. I guess I am curious as to what problem is the stepper driver trying to solve by exposing both the positive and negative terminals. Thanks.
For flexibility in setup, can be operated in pull up + or down - for control.. for example by default Arduinos digital control "pull to ground" so you would have all the pos wires in parallel and the neg would be the control lead. Cheers Gary
The inputs are opto-isolated so that there is no electrical connection between the controller and the internal circuitry of the driver. The LEDs within the opto-isolators have two legs and these are what comes out on the step/dir/en +/- terminals. To do that (^^^), the driver and the controller would need to share the same circuit, which is generally undesirable.
