# What do each of the 4 stepper motor wires do?

I'm relatively new to electronics- I have a question about the power given to a stepper motor. Is the power a constant flow, or does it need to be modulated? I would think it needs only constant power from the two positive and negative wires and the other two wires to send control signals.

I've looked all over for an answer, but everywhere it just says "the stepper driver will take care of powering it!" How do they work?

2 pair of wires. Therefore 4 wires. One pair of wire are terminals of a wire coil. The other pair of wire are terminals of a different wire coil.

When you drive a current through the coil, a magnetic field is produced in the coil. The rotating thing (rotor) inside the stepper has magnets added at various spots. When the coil is generating a magnetic field, it can make at least 1 of those magnets become attracted to the coil's field. Pulling the magnet means also making the rotor move - that's because the magnet is attached to the rotor. But, once the magnet reaches the strongest attraction point....it can't go anywhere anymore....stuck there. So, the trick is to then turn off this coil's magnetic field (by removing the current).....and then put current into the other coil. This other coil is located at a different spot/location. The magnetic field from this coil can then pull one or some magnets along....to make the rotor move (step) again.

This is the simplest case. There are other configurations. But it's basically the clever usage of magnetic fields and clever placement of magnets on a rotating structure .... to push or pull the magnets around in some sort of sequence. It's like 'follow the leader' sort of thing. A magnetic field is the leader, and the magnets on the rotor follow it around (get drawn to it) like sheep.

Circuitry is needed to drive a constant current into a coil. Obviously, to put a current into a coil, you have to apply a voltage across the coil's pair of terminals..... but the circuitry will control the amount of current to keep that current fairly constant.

Wow- thank you for the detailed answer! So that means the positive and negative power wires have nothing to do with the spinning, because they are just getting switched by signals of the other two? (They can just constantly feed power?)

Stingray63Vette:
Wow- thank you for the detailed answer! So that means the positive and negative power wires have nothing to do with the spinning, because they are just getting switched by signals of the other two? (They can just constantly feed power?)

You are right about that. The current will provide the magnetic field and get good torque (force) produced..... so the stepper's shaft can get pretty nice force on it. The faster you switch the current between the coil pairs.... the faster the stepper will step. But there will be a mechanical/physical limit to the speed, because flipping too fast between the coils doesn't get enough energy into the coil..... to get good torque. It's kind of like..... you got a whole line of empty buckets on the ground...in a row. And you have a watering container. If you move the water container slowly over each bucket ...as you walk from one bucket to another.... you can get a fair bit of water (energy) into the system. But if you walk too quick..... each bucket will only get a light sprinkling (not much energy) into them. And if you sprint past the buckets...... probably get nothing into the buckets at all.

Thank you for the help I appreciate it!

Might I bother you with another question? No one answered on it when I asked yesterday, and it has fallen down into the solved and forgotten topics...

I have 14 NEMA 17 motors that need 4 volts, 1 amp each. Can I simply hook them up to a solderable plastic breadboard connected to a power supply like one of these without damaging the motors, transformer, or burning up the little board?? What power would I need to get? (5V, 12V, 24V, and 1a, 2a, 5a, 15a, 20a, 25a, 30a, etc?)

(I have a means of controlling them, it's just my stepper driver is not able to supply enough power)

Thank you for any advice you can give!

"solderable plastic breadboard" ??? plastic melts if you try to solder it!

1A isn't too tricky to deal with.

You haven't mentioned your stepper motor drivers - you'll probably want 14 DRV8825 modules...

When I said solderable breadboard, I just meant the green part. I believe that is a plastic with fibers mixed in .

I am using SD8825 modules to drive the motors now, which I have moved to NEMA 23 size because the order was canceled. I will use 4 drivers to control 5 motors, eliminating the need for a second power supply. (23’s are much more powerful) I will run two Z axis motors in series because they don’t need to move too fast.

As for creating a new thread, I thought I should rephrase the question I was asking. I didn’t really understand what I should do, as the answers only made me more confused! When I attempted to clear my confusion, no one responded. So I started this thread, a more basic question. I guess changing to NEMA 23’s voids the whole topic, but the info I got was helpful!

Thank you! I believe this topic is solved!

I guess changing to NEMA 23's voids the whole topic,

No.
A lot of beginners miss this point but a NEMA xx just specifies the physical size of the motor, it has nothing to do with the current / speed or anything else about the motor.

Hi,

Tom...

@GrumpyMike- I mean having a smaller # of bigger motors instead of more smaller ones to feed. It will be easier to set up with my X3.

TomGeorge- I'm actually subscribed to Learn Engineering! Cool video-thanks!

I appreciate the help!

If it is important that the steppers remain in sync it is better to use one larger stepper (and pulleys where the other steppers would go) than several smaller ones

For the z axis you should use one larger stepper and pulleys as the drives.

Yes, that is the basic design concept I am going for. Hopefully it will minimize skipping.

It appears that the NEMA 23 motors need 3.78V at 4.2A. The SD8825 driver can only handle 2.5A, which means I will have to power the motors separately from the drivers again. This time, however, there are fewer motors.

My calculations are:
3.784.2 = 15.876 watts per motor
15.876
5 = 79.38 watts in total (5 motors)

This means I need 80 watts, preferably at 12V. This means that I need around 6.667 amps, correct? I don't know where to find a LED light strip power supply with that amperage...

When I get the correct power supply, I will solder the DC ends to the rail of a breadboard. I can then connect all of the motors in parallel, and in theory, run the CNC mill smoothly.

Anyone's thoughts on this? Is there a better way to do it?

This means I need 80 watts, preferably at 12V.

No it doesn't. You are mixing up power with current and voltage.

Your calculations show you need 80W but at 3.78 V. That is 3.78 V @ 21 A.

A power of 80W at 12V would be a power supply of 12V @ 6.6A, which would not be able to power your motors.

It appears that the NEMA 23 motors need 3.78V at 4.2A.

Did you understand what I said about calling it a NEMA 23 motor?

The SD8825 driver can only handle 2.5A, which means I will have to power the motors separately from the drivers again.

No you can not power a stepping motor separately from a driver. If you try and power a motor with 3.78V then the performance will be rubbish. It is much better to use a higher voltage and then the driver chops the voltage ( turns it of and on ) to limit the current to 4.2A ( or less ). This allows the current to get into the inductors faster and hence allow you to use a faster stepping rate.

Yes, I understand what you mean. I just don't know how to make it work with the CNC stepper driver board I have...

Does that simply mean I cannot use this board and its drivers with NEMA 23's?

I just don't know how to make it work with the CNC stepper driver board I have

You adjust your stepping motor driver to deliver it's maximum current, the fact that is is slightly less than your motor can take is just tough, it will still work only at very slightly reduced torque.

and its drivers with NEMA 23's?

Stop it. This is three times I have told you about calling the motor this. Are you not paying attention? Do it again and I will stop speaking to you because it means you are incapable of learning anything and I will just be wasting my time.

NEMA 23 specifies ONLY the motor's mounting dimensions, nothing about it's overall size, power, voltage, AC or DC , stepper or shaded pole or squirrel cage. ONLY the mounting dimensions.
Even if you went from a "smaller" NEMA 17 to a "more powerful" NEMA 23 you may have a LESS powerful motor than the 17. It's TORQUE that makes the difference.
As NASCAR'S Curtis Turner (I believe) said "Horsepower sells cars, TORQUE wins races".

Stingray63Vette:
I have 14 NEMA 17 motors that need 4 volts, 1 amp each. Can I simply hook them up to a solderable plastic breadboard connected to a power supply like one of these without damaging the motors, transformer, or burning up the little board?? What power would I need to get? (5V, 12V, 24V, and 1a, 2a, 5a, 15a, 20a, 25a, 30a, etc?)

If you have as many as 14 motors........ each requiring 1 Amp..... you mainly have to focus on the current through the coil..... like 1 Amp current.

To get 1 Amp into 1 coil ..... you have options. One option is to know the coil's operating rating.... eg. 4V DC, 1 Amp. This means.... if you deliberately apply 4V across the coil terminals (and leave that applied voltage there for a long enough amount of time .... then this particular coil will likely get 1 Amp flowing into it. In this case.... you would need to have a voltage source that is able to at least supply 1 Amp when producing 4 Volt DC. Now..... that's for 1 coil. But these particular stepper motors have 2 coils. So what happens if both coils happen to be active at the same time? And what happens if we use the same voltage supply? That could mean the supply might need 2 Amp. 1 Amp for each coil. There are 2 coils all together.

In this case, we would need a supply that handles at least 2 Amp while producing 4 Volt DC. That would mean.... this 4 Volt supply needs to be able to be able to deliver at least 8 Watt of power. Another way of looking at power handling of the supply is..... if you got 14 steppers... and assuming all steppers are active at the same time.... then the 4 Volt supply would need to handle a whopping 14 x 2 Amp = 28 Amp. Anyway, in this sort of system...the assumption is constant voltage supply at the required (rated) voltage, to produce the required operating current through the coil.

The other option .... is a current limited DRIVER supply. This will be a power source of some sort having a control feature that prevents the current from going above 1 Amp. This driver supply is usually powered by a main parent DC power supply. The driver supply (eg.... DRV8825) will apply whatever automatically-controlled voltage it needs to apply to get the required 1 Amp current. There is usually a metallic dial that you can twiddle with a screw-driver (on DRV8825 drivers) for setting the current limit..... which is the current limit to each coil. I assume that the particular current limit setting is applied to both coils. So if you set a current limit of 1 Amp..... then the maximum amount current that will be able to flow in EACH coil is 1 Amp. For this setup...... it will be a case of 1 driver for 1 stepper motor. And.... in the end.... it all depends on how much current the main power supply is able to deliver.... (which will depend on the voltage of the main power supply, and the rated power of the main power supply).

And..... regarding the bread-board ..... as long as the circuit tracks of the bread-board can handle whatever amount of current is going to be running through them..... then ok. So you need to know how much current the internal bread-board tracks can handle ---- possibly 0.5 Amp...maybe. Depends on the kind of board you have.

Stingray63Vette:
It appears that the NEMA 23 motors need 3.78V at 4.2A

Alas there is no single-chip solution for that current level, you need a stepper driver with discrete
mosfets (much less on-resistance compared to single-chip DMOS devices). Typically such drivers are
industrial stepper drivers (expensive, but some budget brands are out there). Such a driver
will have on-resistance well below 0.1 ohm, which is what you want when driving a <1 ohm winding.
[ because you want the waste heat mainly in the motor, not the driver! ]

FORGET THE VOLTAGE RATING. Steppers have a current rating and a winding resistance
and winding inductance (which usually dominates the impedance in normal operation).

Lower resistance and inductance of windings means better performance from a given
supply voltage. Normal supply voltages are 24, 36, 48, 60, 80V (and even higher!). The voltage
is about overcoming the inductive impedance and rotational back-EMF, basically more
volts = faster motor top speed. The 3.78V you quote above is basically meaningless for a working
motor.

For CNC with leadscrews you ideally want lots of speed, ie low impedance windings, high supply voltage…

Point me to a Nema 34 motor that had less torque than a nema 11 motor.

There's a reason for motors being larger and it's correlated to the current they require (and torque the deliver)

While you are technically right to say it refers to size only it's bit harsh to punish someone for referring to nema 23 as a higher current motor when the correlation does exist.