Go Down

Topic: Choosing power supply for nema17 stepper motor (Read 2118 times) previous topic - next topic

tautau123

Hi,

I have the following motor:
https://www.aliexpress.com/item/CE-certification-1pcs-4-lead-Nema17-Stepper-Motor-42-motor-Nema-17-motor-42BYGH-1-7A/32377416566.html?spm=a2g0s.9042311.0.0.27424c4dVKqosl

And the following driver:
https://www.aliexpress.com/item/3D-Printer-StepStick-DRV8825-Stepper-Motor-Driver-Carrier-Reprap-4-layer-PCB-RAMPS-replace-A4988/32618856994.html?spm=a2g0s.9042311.0.0.27424c4d5Fugeg

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

MarkT

#1
Oct 10, 2018, 01:20 am Last Edit: Oct 10, 2018, 01:22 am by MarkT
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.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

tautau123

Hi MarkT,

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

Robin2

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
Two or three hours spent thinking and reading documentation solves most programming problems.

tautau123

Thanks for the answer,

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 ?


MarkT

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 will NOT respond to personal messages, I WILL delete them, use the forum please ]

tautau123

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

MarkT

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 will NOT respond to personal messages, I WILL delete them, use the forum please ]

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.

Robin2

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
Two or three hours spent thinking and reading documentation solves most programming problems.

tautau123

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)

Robin2

#11
Oct 10, 2018, 06:18 pm Last Edit: Oct 10, 2018, 06:25 pm by Robin2
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 :)

Quote
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
Two or three hours spent thinking and reading documentation solves most programming problems.

tautau123

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 :)

Paul_KD7HB

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

Go Up