Power Supply and motor requirements

[tizdall]

Hi all,

I am designing a cnc machine and am trying to figure out what my motor and power supply requirements would be for the following applications:

Routing (usually a 1/4" dual spiral upchuck carbide bit):

Plywood
Composites
wood
mdf
plastic
foam
soft aluminum

Running at a feedrate of about 100-150 IPM.

The motor/power supply package I am looking at is as follows:

(4) 3.15V, 3.5A Nema 23 Stepper motors
(1) 48V, 12.5A Power Supply
(1) G540 Driver/controller

My questions are:

Is this too much power for the application?
Could I use a 24-36V 8.8A system instead and get similar results?


Regards,

tiz

[Hyrum R]

I'd stick with the 48v personally. You'd get better performance out of the motors. And don't use anything besides the G540 unless it's some G201x's or 203v's. (But there would be no point unless you were using bigger motors.) What you have listed there sounds really decent. Depending on your drive mechanism, you should easily get the speeds you're wanting. If you go to rack & pinion, I wouldn't be surprised if you could get over 600 ipm with that setup.

One more note: The power supply doesn't have to be 12.5 amps for those motors. But I'd still try to stick with 48v.

[Pplug]

The G540 has an internal 7 amp fuse. If you use a power supply rated higher, it is a waist of money. The g540 cannot make use of this extra power.

I don't know why resellers have kits with 12 amp power supplies, they are worthless over 7 amps.

[tizdall]

That is interesting that resellers offer the 12.5A in their kits if it doesn't actually help:

CNCRouterParts

What should I go with for the value of the current if not 12.5?

Will it still function smoothly with a 48V 7.3A power supply?

[Pplug]

I have a G540 3axis kit from Keling that has 3.5 amp motors and the 7.3 amp 48volt power supply, it is incredible! Go with the 7.3 amp power supply for $49

Page Title

My machine runs as smooth as silk.

[tizdall]

How does operating a single motor on the x axis affect the performance? I was thinking about making the machinable area 2' x 6'.. do you think a system composed of:

(3) 380 oz-in Nema 23 motors
(1) 48V 7.3A Power supply
(1) G540 controller/driver

would be able to cut through plywood and other composites at 150 IPM + with only 1 motor powering the x axis...?

[hemsworthlad]

Go with the larger power supply, you have 4 axis available and if you use 4 x 3.5A motors then you'll be slightly under powered with 7.5A psu.
If you work as a rough estimate the PSU Amps should be 68% of the total number motors amp's 4 x 3.5= 14 / 68%=9.5.
Thats why they offer the larger supply it also allows some extra over head for other things you may pull off it.

I think the 7A internal fuse will be more to protect the BOB side of the gecko's not the drive. . . . 7A is low for a 4 x 3.5A axis drives so cant see it being for the drives.?

More amp's wont hurt anything it just cost's more. Me personally i'd rather be over than under powered and have drives tripping out on me when pushing the machine hard.

[Hyrum R]

I burned up two of those Keling power supplies already. I think the biggest problem though was sawdust getting in and ruining the fans. Another thing to keep in mind is that when your motors rapidly decelerate, it can feed power back into the drives and power supply. I'd personally just spend the extra money on an unregulated power supply, since it can handle a lot more abuse.

[Pplug]

As far as I know, you go over 7 amps and the fuse blows!

I have just finished retrofitting my small router. It has 10mm pitched ball screws and I can rip through wood at over 300ipm! The first time I did it, I was blown away by the speed and power of the 380oz/in motors and ballscrew combination. I have one ballscrew on each of my axis though.

This is quite a step up from the leadscrew, xylotex, 217oz/in motor at 24 volt combo I started out with a few years ago!

I bet youll have no problems with your setup.

[tizdall]

If you calculate the cost of going with (4) motors instead of (3) and pair that with the 48V and 12.5A power supply, there is an additional cost of $132 to add the extra motor into the system. (ie cost of the motor + cost of upgrading the power supply to 12.5A)

I am not necessarily convinced that I need the extra motor for my given 'range' of applications.

How can I go about figuring out whether I need the extra motor in the system or not?

Ideally, I would like to see 2 versions of the same machine, one using the enhanced 4 motor system and the other using 3 and a lower power supply and seeing whether the difference is noticeable and/or worth it when cutting plywood, wood etc on a 2' x 6' bed at around 150 IPM

Also, I am currently using a threaded rod and anti-backlash nut for my drive mechanism. Would my power requirements go down if I switched to a ball and screw system? Or a Rack and pinion?

[hemsworthlad]

It's not today you need to think about it's tomorrow.? Your needs may change and with the G540 you will have the capacity but not the means to use it with a under sized PSU.

Hyrum had the right idea with building your own PSU, for larger supplies it often works out cheaper and being unregulated it suits the drives better.
It's very easy to do with only 3 components needed, toroidal transformer, capacitor and Bridge rectifier.
With the right size transformer It can be sized exactly to suit your motors voltage needs giving ultimate performance. Those supply's at 48v will still probably be leaving your motors underperforming slightly, say probably because I dont know the full specs.
Voltage is the key to speed performance with steppers the amps handle the torque, with a purpose built supply you can have the best of both matched to your system. The bought linear supplies are always a compromise somewhere often being under powered on the voltage side.

Ballscrews are typicly 90-95% efficeint threaded rod will probably be 20-30% at best. The differance between the two is night and day so a machine with ballscrews will easily use smaller motors than one using threaded rod.
Threaded rod really is not very accurate and the pitch often varies along it's length, ballscrews are precision made and even the cheapist made are still light years in front of threaded rod.

R&P is probably 50-60% efficient but does suit longer axis machines better than typicly mounted ballscrews.
For a machine 6` or over just cutting wood then I would go with R&P and drive the long axis from both sides with the largest Nema23 motors the G540 can handle, matched to a suitable power supply this will give a great combo for cutting wood.

Belt drive is also a very good and efficeint system typicly 80-90% or better and can be done quite cheaply. At 6` it's certainly worth considering and will easliy handle your needs.

Hope this helps.