Hi, I am pretty new to these particular devices and I'm looking for a power supply for my NEMA17 Stepper Motor. Any recommendations are appreciated.
Thanks
Alias_33:
I'm looking for a power supply for my NEMA17 Stepper Motor.
My understanding is that the NEMA numbers relate to the physical dimensions of steppers, and don't indicate the electrical characteristics. So you would need to give more details.....
Here are the electrical specifications for my particular stepper motor:
Phase: 2
Current / Phase: 1.7 amps
Rated voltage: 2.55V
Phase resistance: 1.5 ohm
Phase inductance: 2.8 mH
I am pretty new to all of this.
Well there you go: for a power supply you need to go for one that exceeds the volts and amps listed there.
Have a look at this example from the tutorial.
use a 5 volt PSU and keep the PWM below 60
Are you driving the stepper motor with a stepper driver? For example the Pololu A4988 Pololu - A4988 Stepper Motor Driver Carrier which I have allows you to set the maximum current and then supply the motor with a much higher voltage to get it to move faster. The A4988 needs forced cooling for currents in excess of 1amp and the max is 2amps so I'm not sure if it is suitable for your motor. I presume other driver boards have similar features.
...R
Yes I have a stepper motor driver. This is the one I will be using; http://www.oddwires.com/l298n-dual-h-bridge-dc-stepper-motor-controller-module-for-arduino/. So I have an arduino mega and I want to know if I plug a 5V external power supply into the jack on the arduino board itself (not the usb) can I then run the stepper motor using my driver board connected to the 5V pin on the arduino board. Or would I have to wire the external 5V power supply directly to the motor driver board and then to the motor?
Alias_33:
Here are the electrical specifications for my particular stepper motor:
Rated voltage: 2.55V
shooter:
use a 5 volt PSU and keep the PWM below 60
That would only be for a dc motor wouldn't it, not a stepper? (And even then, it would still supply 5v in the on phases, only giving 2.5 on average, to control speed.) I think this stepper needs a 2.5v supply.
Then there's a bit of a problem: the driver board says it needs a drive voltage of 5v and up. In fact it contradicts itself: in the bulleted features in the description it says 5v; in the note at the bottom it says 7.
In any event, the answer to this question....
Or would I have to wire the external 5V power supply directly to the motor driver board and then to the motor?
..... is Yes, even if 5v was the required voltage.
But with the motor being rated for 2.5 I think you'll need a 2.5v supply.
You can use PWM to control the current through a stepper motor -- that is exactly what the newer motor driver chips like the A4988 do. Boards based on those chips are far more convenient to use than the L298-based drivers because of this feature.
I would strongly recommend ditching the L298 board, in favor of a newer board, because with 2.55 volt motors, you will need large, heat dissipating resistors to drop that portion of the power supply voltage that the motor coils do not. Look up L/R stepper motor control to learn more.
The newer motor drivers are far easier to use, offer current control and automatic step or microstep generation with only two inputs (Step and Dir) as opposed to four inputs and full step only for the L298 board. I have used Pololu's drivers and they work very well. The DRV8825 can handle 1.5 amps/coil with no extra cooling or heat sink and up to 2.2 amps/coil with cooling. It should work well for your application. Pololu - DRV8825 Stepper Motor Driver Carrier, High Current
Your power supply has to easily supply enough current for both coils at the same time, so about 4 amps minimum.
Ah ok, thanks for that.
But am I right in saying that with PWM, the problem of the peak voltage being too high (5v vs 2.5) would be an issue, since the voltage is still 5 in the on-times?
As it happens anyway, that 298 based board can't drive a 2.5v motor it seems, since it has a minimum of 5v (or 7 as it also says, which I suppose allows for the 2v minimum loss in a 298).
Look, I'm really just trying to get it working for learning purposes. I am brand new to the arduino stuff as I have said and I am trying to experiment with different things just to gain some general knowledge about these electronics. I am not interested in getting a different driver board as I do not have any immediate projects in mind for the motor. I have also read a little bit about the stepper motors in general. People run up to 10 times the rated voltage (~25V) to increase the speed of the stepper motor. There are even torque charts provided by manufacturers that map the torque of the motors vs voltage up to voltages roughly 10 times that of the rated voltage. That makes sense considering the board I have, the L298N, provides a driving voltage of 5-35V with a maximum amperage of 2amps. I do appreciate the help and from everyone but that being said I am now more confused by the previous comments.
I can't comment on it running at 25v, or even at 5.
If you do run it at 5, definitely don't take that 5v from the Arduino pin, take it from an external source.
There is an inherent voltage drop of almost 2v in a 298: so it could be that if you put 5 in, you'll only get just over 3 out anyway and perhaps the 2.5v motor will be happy with that.
On that page you linked to, if you didn't see it already, I noticed there's an Arduino sketch in the Product Documents tab.
Yeah I would definitely not try to power it using the 5V pin on the arduino. I know for sure that it will not provide the amps needed for the motor. To JimboZA: have you used these sorts of stepper motors before? If so maybe you can suggest an external power supply that I can connect to my L298N driver board. I really do think they are capable of being run at the higher voltages (at least from what I have read) just as long as the amps do not exceed what the motor is rated for which in my case is 1.7 amps. Feel free to correct me if I'm wrong. I'm just trying to learn here.
My experience with steppers is very limited, so rather take the other guys' advice on that voltage thing!
You cannot exceed EITHER the rated winding current or the rated winding voltage in a steady state situation. The motor will overheat.
If you want to use a higher voltage power supply and the L298, then you must put a suitable resistor in series with each winding. You also need a motor power supply that is capable of delivering more than the total current required by the two windings.
The low-voltage high-current steppers that are commonly available were not designed to be used by motor drivers like the L298. They were designed to be used by chopper motor drivers that use a current sense resistor to set the chopper PWM rate.
If you just want to learn, it is a lot easier to work with 5V or 12V steppers!
I'd double-check that this alleged 2.55 V rating is not actually 25.5 volts.
A 2.5 volt stepper motor sounds ridiculous to me.
Those low voltage motors are kind of ridiculous! However, there are lots of them and they can be found pretty cheaply. This is probably what the OP has: http://www.aliexpress.com/item/Nema-17-stepper-motor-with-motor-Length-40mm-1-7A-2-55V-4-Lead-Wire/456770611.html
This one is rated at 3.4 V, for only US$ 6.99! http://www.ebay.com/itm/CNC-Nema17-Stepper-Motor-2-Phase-DC3-4V-1-7A-48oz-in-4-Lead-1-8Degree-220g-cm-/151026187358?pt=LH_DefaultDomain_0&hash=item2329dcbc5e
Here is how to choose the winding resistor for such motors:
R = (motor power supply voltage - 1.8 - coil voltage)/(maximum steady state coil current in amps)
For 12 V PS and 2.55 V, 1.7 A winding, use R = 7.65/1.7 = 4.5 ohms. Larger is OK.
The resistor must be able to dissipate a lot of heat, RI^2. In this case, 4.5(1.7)^2 = 13 watts, so use a 20 watt resistor.
jremington, I am just trying to get it to work with what I've got at the moment. I am not interested in buying any different equipment except for the power supply for the motor. I need to be able to work with what I have, which is why I have all of these questions.
Also I do think the stepper motor is rated for 2.55V and not 25.5V.
It is sounding like I'm a bit in over my head here. I really don't know anything about stepper motors. If anyone could help me get my stepper motor up and running with the equipment I have and recommend a power supply to purchase (an actual model of power supply that I could search for and purchase).
My understanding of stepper motor current and voltage is like this...
The specifications list the voltage which will produce the maximum allowable current on a continuous basis using the usual Ohms law formula v = I R.
However a stepper motor doesn't work with a continuous voltage or current, rather the power is continuously switched from one coil to another to make the motor move. In that situation the inductance of the coils starts to interfere and it takes a small but measurable delay between supplying power and the current reaching its maximum. If you want the motor to run fast that delay becomes a problem. The solution is to supply the power at a much higher voltage which reduces the delay but, of course, it also means that the maximum current will be exceeded and the motor may (probably will) be damaged. The smart stepper controllers (like the A4988) are designed to use a high voltage to allow the current to reach its maximum as quickly as possible and then (using PWM) to prevent the current from rising further. There is a preset potentiometer on the Pololu A4988 board that allows you to set the maximum current.
If you don't want to use a driver board that has the current limiting feature then you must ensure that the maximum voltage coming out of the driver board (remember there will probably be a voltage drop in the driver electronics) matches the specification for your motor.
You may be able to control the output voltage by feeding a PWM signal to the driver board - but this will make things complicated and will require experiment to determine the right duty cycle. The driver board that the OP referred to requires more connections from the Arduino than an 4988 board and I don't know how the PWM should be applied. (Obviously it is not necessary with the A4988 as it is looked after on the board itself). My guess is that the makers of the L298 board assumed that you would use an input voltage that matches your motor (or vice versa), but the L298 board needs a minimum of 5v on the power input.
...R
Edit to add...
Thinking more about this it seems to me that, due to the nature of stepper motors, you can only really learn about them properly with a "proper" current limiting stepper driver board.
...R
Alias_33:
jremington, I am just trying to get it to work with what I've got at the moment. I am not interested in buying any different equipment except for the power supply for the motor. I need to be able to work with what I have, which is why I have all of these questions.
..
It is sounding like I'm a bit in over my head here. I really don't know anything about stepper motors. If anyone could help me get my stepper motor up and running with the equipment I have and recommend a power supply to purchase (an actual model of power supply that I could search for and purchase).
I told you what you need to do, but you didn't bother to read it. Use your L298 driver and ANY power supply that can supply 5 volts or greater (needed for the L298) at 4 amps of current or greater. But the circuit won't work unless you choose an appropriate series resistor for the windings. Without it, the L298 driver will overheat and shut down in seconds.
The reason that you are in this situation is that you went out and bought incompatible hardware without doing the necessary background reading or following someone else's successful example. Here is a great overview on stepper motors, but I'm guessing that you won't read that either: http://homepage.cs.uiowa.edu/~jones/step/