# Stepper motor voltage

#### Dritech

Joined Sep 21, 2011
869

#### donpetru

Joined Nov 14, 2008
185
Coil Resistance = 1.8 Ω and if use 12V supply, then amps windings will be lower and lower torque. And motor speed will be somewhat lower than usual.

#### Dritech

Joined Sep 21, 2011
869
Thanks for the reply. Is there a ratio related to the supply voltage and torque / speed?
For instance if I use half the recommended voltage (i.e. 12V) will I get half the speed and half the torque?

#### MikeML

Joined Oct 2, 2009
5,444
Last edited by a moderator:

#### THE_RB

Joined Feb 11, 2008
5,438
That motor is a 2.2A motor, it requires 2.2A through the coil(s) to make the correct operating torque.

It's resistance is 1.8 ohms, so to get the proper 2.2A in the coil requires 3.96 volts. (E = I*R)

The "24 volts" is just an industry recommendation for the driver operating voltage, it is pretty meaningless here. To properly drive that motor requires a constant current 2.2A driver, and you can run that from 80v, 24v or 12v as you like.

Running the driver from a lower voltage will make the motor run smoother (less vibration) but will limit the speed that it can move from one step to the next. Torque at low speeds or when holding will be the same, provided you supply 2.2A.

#### Dritech

Joined Sep 21, 2011
869
Thanks for the replies.

@THE RB, Can I use two LMD18245 drivers to drive this stepper? Also, how can I calculate the maximum speed of a stepper motor since it is never stated in the specs?

#### MikeML

Joined Oct 2, 2009
5,444
The max speed and acceleration has to be determined by trial and measurement after you hook the motor to its mechanical load. These depend mostly on the rotational inertia of the mechanical load.

#### THE_RB

Joined Feb 11, 2008
5,438
...
@THE RB, Can I use two LMD18245 drivers to drive this stepper? Also, how can I calculate the maximum speed of a stepper motor since it is never stated in the specs?
I'm not familiar with that driver. But you can get a lot of 2A or 3A bipolar stepper motor driver modules cheap on ebay or from Sparkfun or one fo the hobby electronics suppliers.

I personally suggest you get a microstepping driver, as this gives you better positioning resolution, quieter operation and more sophisticated features (like auto power reduction etc).

A 2.2A 3.96v motor has a low-ish inductance and will give pretty good speed. I'm using similar motors on my small CNC machine with a 35v PSU, and can get high accelerations and good reliable power up to about 10 revs per second.

#### THE_RB

Joined Feb 11, 2008
5,438
If that is a 20mm diameter 10mm lead ballscrew then the stepper motor should drive it.

But 12v is way too low for best performance. Ideally if you want good high speed perfromence you buy a good stepper motor driver, then choose a good PSU which means as high a voltage as your driver allows.

But if you just want to move the 25kg load very slowly (say under 3 rev/sec or under 30mm/sec) then a 12v supply might do it.

#### tubeguy

Joined Nov 3, 2012
1,157
If that is a 20mm diameter 10mm lead ballscrew then the stepper motor should drive it.

But 12v is way too low for best performance. Ideally if you want good high speed perfromence you buy a good stepper motor driver, then choose a good PSU which means as high a voltage as your driver allows.

But if you just want to move the 25kg load very slowly (say under 3 rev/sec or under 30mm/sec) then a 12v supply might do it.
+1 I have worked on industrial equipment using 6.6 volt rated steppers driven by stepper drivers supplied with 48 VDC. Proper current control is the key.

#### Dritech

Joined Sep 21, 2011
869
But 12v is way too low for best performance. Ideally if you want good high speed perfromence you buy a good stepper motor driver, then choose a good PSU which means as high a voltage as your driver allows.

But if you just want to move the 25kg load very slowly (say under 3 rev/sec or under 30mm/sec) then a 12v supply might do it.
I wish to have at least a speed of 50mm/sec. The reason that I was going to buy 12V power supply is that I will use the same supply to drive a 12V brushed DC motor.
If I choose a 24V power supply instead, is there an efficient way to reduce it to 12V so that I can control both the stepper and the brushed motor with a single supply?

Joined Jul 18, 2013
22,047
The DCV supply for a drive controlled motor should be at least 10% above the motor rated voltage, If using a SCR bridge or a PWM drive for the DC motor, the maximum rpm can be set by the controller, although VX2 will give you a more restricted range (Min to Max rpm).
Max.

#### THE_RB

Joined Feb 11, 2008
5,438
I wish to have at least a speed of 50mm/sec. The reason that I was going to buy 12V power supply is that I will use the same supply to drive a 12V brushed DC motor.
If I choose a 24V power supply instead, is there an efficient way to reduce it to 12V so that I can control both the stepper and the brushed motor with a single supply?
If you want 50mm/sec with a heavy load i would definitely go for a higher voltage supply. If 24v is the max voltage your stepper motor drivers are rated for than go for a 24v supply.

Re getting 12v, you can get 24v->12v SMPS converter modules fairly cheap on ebay. But personally I would just get two supplies.

#### Dritech

Joined Sep 21, 2011
869

Joined Jul 18, 2013
22,047
Personally I am not a fan of SMPS, especially for servo's/steppers, you do not need a regulated supply for these applications, SPMS are difficult to repair and are not so rugged in this application.
If you pick up either a Toroid transformer or toroid based supply that has the required VA then you can wind on a secondary for the 12+ needed for the DC motor, approx 2t/v.
~18 to 20 turns, followed by a bridge and elect. cap.
If you end up with ~14vdc then this will work.
Max.

#### Austin Clark

Joined Dec 28, 2011
412
The current defines the torque, the voltage defines the RPMs. That's pretty much the gist of it.

#### THE_RB

Joined Feb 11, 2008
5,438
...
If I buy the power supply in the link below, will I be able to use the full performance of the stepper motor? or is it way too cheep?

7.4A should be enough to driver a 2.2A per coil stepper motor, right?
...
A 2.2A stepper motor driven with a crude fullstep or halfstep driver will require a maximum motor current of 4.4A (as it has 2 coils).

A 2.2A stepper motor driven from a modern microstepping drive will require a max motor current of 2.2A * 1.414 = 3.2A.

Because you would be using a 48v supply on a 3.96v motor, there will be a LOT of current amplification so the motor consuming 3.2A will only draw maybe 0.5A from the supply, at low RPMs.

The only time the supply current will get near the motor current is during very high acceleration or deceleration.

As an example my CNC machine has a 5A ammeter on the 35v supply, running 3 steppers that have an average motor current of 2.6A*1.414 = 3.7A (times 3 motors = 11.1A. My supply ammeter sits on about 2A most of the time, peaking at a max of 4A or so under high accelerations.

So at low speeds it provides 11.1A of average motor current AND only draws about 2A from the supply.

#### Dritech

Joined Sep 21, 2011
869
Thanks a lot for your detailed replies.

May I ask what driver you use? When buying a driver what should I look for? I was planning to buy 2pcs LMD18245 to drive a single Nema 23 Stepper Motor (23HS22-2804S), but before buying I would like to know if they are efficient enough to let me use the full performance of the motor.

#### THE_RB

Joined Feb 11, 2008
5,438
My machine uses three SLAmStepper microstepping drivers like these;
http://www.piclist.com/techref/io/stepper/SLAm/SLAm_bld.htm

They are good for up to 3A per motor phase and extremely rugged, I have used them in a number of machines with never a fault. However they are Unipolar drivers, and may not be suitable for your motor.