Cnc wiring!

[Cobey3289]

Thanks for that jazz.
Stepper drivers and psu's.
I'm going to be running nema 23's 425oz 3amp. What stepper driver should I use? Some are rated up to 3amp and some more and then they are rated voltage wise. Until I decide on steppers I'm assuming I should hold off on psu's.
I see some people use 2 psu's driving two motors each. Can I just use one for the motors and a 5v supply, or is it best to use one for motors, another lower rated for fans etc and a 5v for the board?

Mick

[JAZZCNC]

Thanks for that jazz.
Stepper drivers and psu's.
I'm going to be running nema 23's 425oz 3amp. What stepper driver should I use? Some are rated up to 3amp and some more and then they are rated voltage wise. Until I decide on steppers I'm assuming I should hold off on psu's.
I see some people use 2 psu's driving two motors each. Can I just use one for the motors and a 5v supply, or is it best to use one for motors, another lower rated for fans etc and a 5v for the board?

Mick

Well it's little more complex than just amps.?
Not all steppers are equal and even thou may be rated same size doesn't mean they will perform the same. Inductance rating of the motor is very important to how well stepper will perform with a given voltage.

For instance, motor with high inductance will spin much slower than one with low inductance using the same voltage.
So if the steppers you buy have high inductance it will mean you'll need to run them with much higher voltage to get the same speed as Low inductance motor.

Then you have how the motor phases are wired. Steppers tend to come in two flavors. 4 wire and 8 wire.
4 Wire motors are less flexible because their phases are predefined at the factory. Often their phases will be series wired.
This means they will require much more voltage to achieve high speeds. Parallel wired motors, on the other hand, will reach same speeds with less voltage.
Often you'll find Series wired motors on Mills or machines which require high torque but less speed. This is because they produce higher torque lower down the rpm range but quickly lose torque as RPM's rise.

Parallel wired phases, on the other hand, give less low down torque but carry more torque higher up the rpm range. This is why parallel is preferred for routers.

8 wire motors allow Either series or parallel phases so again are preferred and easier to find than 4 wire parallel wound motors.

Voltage is the key to getting speed from stepper but at same time too much voltage can lead to over heating and resonance issues.
So this brings us back to inductance and why it's important. Lower inductance means higher speeds can be got with less volts and less volts equals less motor heating, less resonance etc.

So to answer your question about Drives and PSU will require knowing more about the motors. Would also help to know more about the machine spec and what you intend to do with it.

However if you want proven setup which works with most small to medium sized routers then the spec below works great.

Nema 23 3.1Nm 4.2Amp 8 wire motor wired parallel. Ideally with Inductance around 3mh or less.
Digital drives with voltage between 70-80V. Leadshine AM882 are great drive.
PSU with 60-68Vdc output depending on drive voltage. Current will depend on #motors and PSU type.

Now the Psu is little more involved because several types but the best solution by far is unregulated Toroidal PSU. It's gets little involved to why best but trust me this is the best setup for stepper motors. If really want to know why I will explain.

The reason you have probably seen people use 2 psu's is because they have bought off the shelf units which have limited current output so not enough to power 4 motors.
However the best solution is to build your own PSU which is very easy to do and doesn't require degree in electronics. We can help you with whats needed and will say if you can't wire this then you can't wire any of the machine it's that simple.
This way you get exactly what you need in terms of voltage and current in one setup and will work out cheaper than buying off the shelf units.

You will need a separate linear PSU for the Control etc and these are best bought off the shelf and cheap enough not bother building.

Hope this helps.

[Desertboy]

Regulated or Unregulated Power Supply
Both regulated and unregulated power supplies can be used to supply the drive. However,
unregulated power supplies are preferred due to their ability to withstand current surge. If regulated
power supplies (such as most switching supplies.) are indeed used, it is important to have large
current output rating to avoid problems like current clamp, for example using 4A supply for 3A
motor-drive operation. On the other hand, if unregulated supply is used, one may use a power supply
of lower current rating than that of motor (typically 50%～70% of motor current). The reason is that
the drive draws current from the power supply capacitor of the unregulated supply only during the
ON duration of the PWM cycle, but not during the OFF duration. Therefore, the average current
withdrawn from power supply is considerably less than motor current. For example, two 3A motors
can be well supplied by one power supply of 4A rating.
Multiple Drives
It is recommended to have multiple drives to share one power supply to reduce cost, if the supply has
enough capacity. To avoid cross interference, DO NOT daisy-chain the power supply input pins of
the drives. Instead, please connect them to power supply separately.

Selecting Supply Voltage
The power MOSFETS inside the AM882 can actually operate within +20 ~ +80VDC, including
power input fluctuation and back EMF voltage generated by motor coils during motor shaft
deceleration. Higher supply voltage can increase motor torque at higher speeds, thus helpful for
avoiding losing steps. However, higher voltage may cause bigger motor vibration at lower speed, and
it may also cause over-voltage protection or even drive damage. Therefore, it is suggested to choose
only sufficiently high supply voltage for intended applications, and it is suggested to use power
supplies with theoretical output voltage of +20 ~ +72VDC, leaving room for power fluctuation and
back-EMF.

http://www.leadshine.com/UploadFile/Down/AM882m.pdf

[Cobey3289]

Thanks guys, the wealth of knowledge on here is great.
My cnc is going to be 100cm x 75cm c beam construction. I intend to cut wood, acrylic and some aluminium with it. At this stage, the aluminium cutting will be to cut bulking blocks for the stickmaking world. Anything else will be ideas that come into my head at a later date.
As stated it will be run by nema 23's 425 oz 3amp motors x4 with8mm threaded rod. I can't say it's going to have a hard life, but that's just my thoughts at the moment. Once built and working, my thoughts and practices may change.
I plan to use a MacBook as my computer for the cnc. This I think will necessitate using a USB breakout board. Are there any particular boards suited to the USB side of things and as I'm heading for USB, was looking at chilli pepper as opposed to Mach 3/4.

Thanks
Mick

[Clive S]

As stated it will be run by nema 23's 425 oz 3amp motors x4 with8mm threaded rod.

Threaded rod and cutting ally don't go together very well

[Cobey3289]

What would you suggest, as that's what come with the mechanical build. I thought at least that's a step up from the belt system!
Mick

[Cobey3289]

Hi Clive,
That's tr8 lead screws not threaded rod, my mistake.
Mick

[Desertboy]

Thanks guys, the wealth of knowledge on here is great.
My cnc is going to be 100cm x 75cm c beam construction. I intend to cut wood, acrylic and some aluminium with it. At this stage, the aluminium cutting will be to cut bulking blocks for the stickmaking world. Anything else will be ideas that come into my head at a later date.
As stated it will be run by nema 23's 425 oz 3amp motors x4 with8mm threaded rod. I can't say it's going to have a hard life, but that's just my thoughts at the moment. Once built and working, my thoughts and practices may change.
I plan to use a MacBook as my computer for the cnc. This I think will necessitate using a USB breakout board. Are there any particular boards suited to the USB side of things and as I'm heading for USB, was looking at chilli pepper as opposed to Mach 3/4.

Thanks
Mick

8mm threaded rod, NO, NO, NO, NO!!!!! My reprap used that for a drive lol this is not reprap territory.

get ballscrews, get a free PC with a parallel port ask on forums and then you can use a £5 breakout board and linuxcnc with the money saved you pay for the ballscrews.

it'll cost ~£250 for 4 ballscrews and fittings for this size.

I think you're better off belt driving than threaded rod, you can do a belt and pinion setup which will be a lot better I'm sure. Just google it there's a few setups out there.