help sellect power supply please?

I am buying 3 of these motors. I am going to be building a 3 axis cnc machine. I'm not sure what power supply to select cause the motor data sheet sais 2A at 3v per phase. But the power supplies are 12v? And I want to to half stepping as well which I understand draws double the current cause 2 coils are on at once?

Please help me select a power supply from the site as it's basically the only place I can buy from

Let me give you guys more information. I think I might have jumped in to deep. I plan to build my own driver for the motors, I was planning to just use power mosfet to supply the power to the coils. But now I see or I think (I don't know) that I need to regulate the voltage to the motor? For example if the motor is rated at 3v and I have a 12v power supply do I need to add some type of regulator to regulate the voltage down to 3volts?

I see a driver as a simple thing? Like u just use transistors or mosfet to supply power to the motor. As simple as that. Is this wrong? I was under the impression that I do not need to buy an expensive motor driver and I can get away with building my own cheap driver just using mosfet? Am I wrong?

see a driver as a simple thing? Like u just use transistors or mosfet to supply power to the motor. As simple as that. Is this wrong? I was under the impression that I do not need to buy an expensive motor driver and I can get away with building my own cheap driver just using mosfet? Am I wrong?

Basically yes.

The motor will not move as fast if you give it only 3V. But at 12V you will give the motor too much current. So you have to have a chopping regulator. This turns on the coil and monitors the current, once it reaches the set current, for you this will be 2A it turns off the coil for the rest of the step. This is not a simple thing to do and normally you get an IC drive to do this rather than cobbling up your own system.

Seriously consider 24V, 36V or 48V supply for a CNC machine - leadscrews are
very slow otherwise. Speed is proportional to supply voltage.

see a driver as a simple thing? Like u just use transistors or mosfet to supply power to the motor. As simple as that. Is this wrong?

Chopper drives are an absolute requirement for a 1.5 ohm motor driving a
serious load, otherwise you’ll have a system only capable of 2mm/s rapids! Yes
you can build your own, but you’ll need to know what your doing and it takes
8 MOSFETs, 2 comparators, 2DACs, a microcontroller and two current-sensing
circuits… None of the single chip solutions cope well above 1A due to the limitations
of DMOS MOSFETs integrated onto a chip, for 2A a circuit with separate MOSFETs
is best.

You will need microstepping to get control over resonance too of course. Start with
1/8 or 1/16 microstepping and experiment to see what works best on your rig.

I read somewhere to allow about 1/2 or 2/3 of the motor current per motor for the supply
(chopper drives are effectively buck converters), so 3 2A motors might only need
3 to 4A supply or so. The supply only draws significant current on the rapids.

There are many CNC forums which will have much more information about sizing
motors, choosing mechanical components and so forth.

Ok thanx guys, I think I will have to pass on this project then cause I cannot afford to buy expensive drivers. I struggle to understand this because I have a small stepper motor that I drove with 2 H bridges and a 12v battery. The motor worked like a charm, I could drive it back and forth no problem. So why is it that the little motor never drew too much current when I started it? Is it maybe because the motor was rated at 12v? Which I highly doubt it was being so small.

I think part of my problem is I just want to drive everything with transistors:( and plainly put I can't.

With a driver, do I just connect my arduino to the driver, the driver to the motors and any powersupply to the driver and away I go?

Why does this have to be so difficult:(

What do you guys mean with the word "rapids"?

I cannot afford to buy expensive drivers.

Have a look at this project of mine, the drivers are not expensive.
http://www.thebox.myzen.co.uk/Hardware/CNC_Conversion.html

I struggle to understand this because I have a small stepper motor that I drove with 2 H bridges and a 12v battery.

That motor was not under very much load and wasn't going very fast. A CNC is a lot more demanding.

Grumpy_Mike:

I cannot afford to buy expensive drivers.

Have a look at this project of mine, the drivers are not expensive.
Proxxon MF70 Miller CNC CONVERSION

I struggle to understand this because I have a small stepper motor that I drove with 2 H bridges and a 12v battery.

That motor was not under very much load and wasn't going very fast. A CNC is a lot more demanding.

Holy crap!!!! That thing is amazing!!! I tried clicking on the link for the stepper drivers but looks like it has been removed or something. I think building a cnc machine is way over my head now. It looks too complicated. Especially the software side of things as well. It's so frustrating though. I read up on stuff every night but none of it makes sense, and there is just so much I forget what I have read.

I don't want the fastest moving cnc. I just wanted to make something that maybe even moves 1mm/second or something.

Maybe this is a dumb question but I don't understand how a stepper motor is driven, with voltage or current? Does it draw current according to the voltage u give it and the coil resistance? Or does the back emf of the motor effect the voltage u supply to it? Can a constant current source not work? Maybe if the motor is rated at 2A can't you just use a 24volt power supply and feed it 2A all the time?

This whole thing confuses me. If you feed a motor 2A what are u exactly doing? Say for example you are stepping slowly so the motor doesnt require alot of current. So now u feed it with a constant current source, so will the power supply increase its voltage until the current into the motors coil is 2A? What will happen to the motor? Will it get hot or what? Will it even accept the 2A?

https://www.robotics.org.za/index.php?route=product/category&path=18_95

Which stepper driver on this page would work to drive the 3 motors I have mentioned above? Excuse this retarded question but how do these drivers work? Do I connect my arduino signal pins to them and then the motor to the driver and the powersupply to the driver? Or is there more involved to it?

Say for example you are stepping slowly so the motor doesnt require alot of current.

No the slower you step a motor the more current it takes. A stopped motor takes the maximum amount of current.

? Does it draw current according to the voltage u give it and the coil resistance?

Yes the maximum current is simply ohms law, that applies for a stopped motor. When you try and run it faster the coil takes time to build up in the coil. So if you supply the voltage to get the current limit when it is stopped then there is insufficient time to get much current into the motor when it is moving. So to get the current into the motor faster you up the voltage. This means that when the motor is stopped there is too much current.

Can a constant current source not work?

In theory it could but the response would have to be a lot faster than most constant current supplies are or need to be.

This driver is similar to the ones I used in the CNC
https://www.robotics.org.za/index.php?route=product/product&path=18_95&product_id=531

This was the one I used in my latest big project
https://www.robotics.org.za/index.php?route=product/product&path=18_95&product_id=69

Attached a photo of the project. For an example of the scale those are people at the bottom of the picture:-

Oh wow that is HUGE!!!!!! WTF dude who are u? Did u study robotic engineering or something haha? That's really awesome hey! Well done! By the way what are those huge gears? Just a display or what?

The smaller driver https://www.robotics.org.za/index.php?route=product/product&path=18_95&product_id=531 as u showed in this link. I see it only supplies maximum 2A? So just to understand. Will I only require maximum current at stand still?

If the speed of the motor increases does the current requirements decrease?

Will I need to buy 3 of these to drive 3 motors?

Do these drivers do the stepping for me? Or must I still switch between coils and polarity with my arduino to actually drive the motors?

Oh yes I almost forgot. Do current requirements increase when you do microstepping? When 2 coils are on at the same time?

The big gears are just for show, it is driven by a belt drive, behind two of the irises is a TV screen, in the bottom unit a sculpture is revealed, one of three that can be rotated into view. It is in a new arts block at my old university. I did do it with a team of others. No never taken a robotics class, they did not have such a thing when I was young. Who am I? Just this guy you know. But been making stuff for 40 years or so. See the biog on my web site if you want to Know more. :slight_smile:

One of those drivers will drive one motor, you can set the current with a small pot. If you run it at 2A you will need a heat sink on the chip. There is no need to run the current at the maximum just run it as hard as you need for the job.

Yes the current will drop the faster you go but the idea it to try and keep it up as close as you can the the set current. Yes the drivers do the stepping patterns for you just give it a step pulse and direction level. Micro stepping do not increase the current requirements as there is less current in certain parts of the cycle.