# Choosing power supply for nema17 stepper motor

Hi,

I have the following motor:

And the following driver:

I’ve red a lot about stepper, not sure I understood everything, but it seems that I can power this motor using any voltage I want and the actual voltage limit comes from the driver.

The driver works with 8 - 45 volts.

What I don’t understand is what is the minimum and the optimal power supply needed ?
Is a 12v 1A power supply from an old router will power it (without any load) ?
Should I buy 24v power supply ? if so, how much current should it support ? I guess there is no need for more than 2.2A as the driver can’t cope with higher current.
And If that is the case, to get the maximum torque should I look for a 45V power supply ?

I’d really appreciate if someone could clarify this things
Thanks

No, the current limit comes from the driver, the supply limits the voltage. The max stationary torque is completely independent of supply voltage.

The lower the voltage the lower the top speed.

Since the motor is a low impedance one (the impedance isn't given, but the 1.5A current rating implies around 1.5 to 2 ohms), a lower supply voltage is going to work (12V for instance).

If you want best performance, a higher supply voltage will be better though. This means more torque at speed as well as more speed. Stepper motor torque falls off dramatically with speed, completely unlike DC motors.

Note that the current the driver takes from the supply is different from the current it gives to the motor, and can be substantially less in fact. The driver is a power converter, not a linear regulator. I'd suggest about 10W in for a NEMA17 stepper driver (NEMA17 motors about usually about 5W, and you need to allow for loses too). You might want to increase that 10W with higher voltage supplies as more mechnical power can be developed with a higher voltage driver and that requires more input power.

Hi MarkT,

So when you are saying it needs about 10W, it means that 24V and 0.5A will be enough ?

tautau123: So when you are saying it needs about 10W, it means that 24V and 0.5A will be enough ?

That should be OK. Put a big capacitor across the motor power supply to handle short term high-current draws.

These links may be of interest Stepper Motor Basics Simple Stepper Code

...R

The only thing I still don't get is where the 10W came from ?

If the motor can take up to 1.7Amp and the driver can push up to 45V, isn't it 1.7*45 =~ 60W ?

You were mentioning a 12V 1A supply...

Most of the power into a stepper just goes to generating heat, the mechanical work is much more limited than you might imagine (much less than an equivalent sized DC motor for instance).

Yes, with a high supply voltage and driving a stepper fast you will pull more power from the supply, but the inductance of the motor will be fighting this.

I was mentioning 12V 1A as an example. Should I buy 12v power supply ? or 24 ? or 36 ? The more merrier ?

So I've said that the speed and torque at speed depend on supply voltage, but only you know what speed you are looking for - you've not indicated anything about it, nor what you are trying to actually do...

I'm sorry, I'll clarify.

I need a full rotation every 2 seconds, meaning 0.5 rpm. With maximum torque I can get.

tautau123: If the motor can take up to 1.7Amp and the driver can push up to 45V, isn't it 1.7*45 =~ 60W ?

The link to the motor data does not provide a lot of information. If you measure the resistance of the motor coils you will probably find that the 1.7 amps can be supplied with just 2 or 3v (OHM's law) so the wattage would be that voltage multiplied by the current. For example if it was 2v and 1.7A that would mean 3.4 watts.

The voltage of the stepper motor power supply is not relevant for calculating the motor power.

...R

Robin2: The link to the motor data does not provide a lot of information. If you measure the resistance of the motor coils you will probably find that the 1.7 amps can be supplied with just 2 or 3v (OHM's law) so the wattage would be that voltage multiplied by the current. For example if it was 2v and 1.7A that would mean 3.4 watts.

The voltage of the stepper motor power supply is not relevant for calculating the motor power.

...R

I understand, So you suggest that in order to calculate the power the motor needs instead of using P = I * V, use P = I ^ 2 * R

The data sheet ( http://datasheetcafe.databank.netdna-cdn.com/wp-content/uploads/2016/04/17HS4401-datasheet-pdf.gif ) says it is 1.5OHM so the wattage is : 1.7 * 1.7 * 1.5 = 4.33W

I'm still not sure if providing 12V vs 24V vs 36V will do any difference in terms of torque ? (assuming all power suppliers can provide enough current)

tautau123: I understand, So you suggest that in order to calculate the power the motor needs instead of using P = I * V, use P = I ^ 2 * R

I * V and I^2 * R give the same answer. Otherwise OHM's position in the physics firmament will need to be reconsidered :)

I'm still not sure if providing 12V vs 24V vs 36V will do any difference in terms of torque ? (assuming all power suppliers can provide enough current)

Using a higher voltage enables the motor to maintain its torque at higher speeds. It will have no effect at low speeds. When the stepper driver turns on a coil it takes some time for the current to reach its limit. If that time is long compared to the interval between steps then the coil may only be at full current for a short proportion of the step. Using a higher voltage causes the current limit to be reached more quickly.

The better motor manufacturers produce graphs showing how torque is affected by speed and voltage. It would be worth browsing to find some just to get a sense of how stepper motors perform. The numbers may not match your motor but the general behaviour will be the same.

...R

Robin2: I * V and I^2 * R give the same answer. Otherwise OHM's position in the physics firmament will need to be reconsidered :)

Using a higher voltage enables the motor to maintain its torque at higher speeds. It will have no effect at low speeds. When the stepper driver turns on a coil it takes some time for the current to reach its limit. If that time is long compared to the interval between steps then the coil may only be at full current for a short proportion of the step. Using a higher voltage causes the current limit to be reached more quickly.

The better motor manufacturers produce graphs showing how torque is affected by speed and voltage. It would be worth browsing to find some just to get a sense of how stepper motors perform. The numbers may not match your motor but the general behaviour will be the same.

...R

Great, thanks. I guess single rotation every two seconds considered low :)

tautau123:
I’m sorry, I’ll clarify.

I need a full rotation every 2 seconds, meaning 0.5 rpm.
With maximum torque I can get.

Check your math, 1 rotation per 2 seconds is 30 RPM. 0.5 rpm is 1 rotation every 120 seconds.

Paul

I also don't know how to choose cnc power supply as you. Hope some one can give me some suggestion:

Jamiedyce: Hope some one can give me some suggestion:

According to your link the driver needs a power supply between 18v and 30v DC. I suspect any power supply in that range will be fine. Just make sure it can supply at least 2 amps. If you want the motor to operate at higher speeds then use a power supply with a voltage nearer the high end.

If you need more help with your project I suggest you start your own Topic.

I am going to use arduino uno, CNC shield with a4988 driver. I am going to use 2 stepper motors. My stepper motor specification says that 17 amps per phase for this. How much power supply i want to use......? 12v 2amps or 12v 4amps or suggest me power supply for this setup

Noormd786: I am going to use arduino uno, CNC shield with a4988 driver. I am going to use 2 stepper motors. My stepper motor specification says that 17 amps per phase for this. How much power supply i want to use......? 12v 2amps or 12v 4amps or suggest me power supply for this setup

I strongly suspect that that should be 1.7 amps per phase.

Unfortunately an A4988 is not really capable of delivering that much current - it will likely overheat and shut down to protect itself. A DRV8825 driver would be just about suitable. If you want to use the A4988 I suggest you set the current limit to 1.4 amps which will, of course, not get the full torque from the motor.

To work out the size of power supply needed we also need to know the nominal voltage of the stepper motor so we an calculate its power requirement in watts. For example (and this is just a guess for illustration) if the nominal voltage is 3.6v then the wattage will be 3.6 * 1.7 = 6.12 watts. For two motors you would need 12 watts - call it 20 watts to allow for inefficiencies. A 12v 2amp power supply provides 24 watts so it should be sufficient. BUT you need to re-do the calculation with the data for your motor rather than my guess.

This topic seems to have wandered a little bit with a small amount of guesswork from some of the new people.

Simple rule of thumb.

Check your CNC shield as some are 12 volt and some are 24 volt and some are even 36 volt. Let that be your guide to choosing the voltage.

When it comes to required amps my own recommendation is a minimum 10 amps but more if you can afford it. Reason here is that I often want to add something to my CNC setup and having those extra amps means I dont have to worry if I am getting close to any limits. It also means that the PSU will generally be running less than its maximum.

You can always add a buck convertor to any of the PSU's spare outputs if you want a different voltage for extra bits. the buck convertors allow you save space as they are a lot smaller than the main PSU and I use them with my 36 volt psu to also give me 5V, 12V for extra items such as relays so that the shield does not have to supply that voltage and I only have to worry about triggering the extra items.

Buck convertors come in various aperages too so in choosing them select something that again has the extra capacity to meet your needs. eg. "Oh I need an extra 12 volt 500 mA for item X" then choose a buck convertor that is twice that or larger still.