Stepper / Voltage

[ckrantz]

Ok now I'm confused.. I've been reading through posts all evening just doing research on what I want to do. I'm turning a Mini-Mill into a cnc machine. Because I'll be doing a lot of cutting I want to go with the nema 34 4XXoz/in larger motors. I believe I'm sold on the following.

Gecko 202 Drives
24V 10amp Power Supply
Nema 34 434oz/in steppers

Here is why I'm confused. I'm reading some posts with guys saying they are using 5volts to run their motors? Then other posts saying they are running 24 volts. Why would someone be using only 5 volts on a larger stepper motor? I want to get a "fair" amount of speed out of my machine, but still be able to get good cutting capabilities. Any help or explanations would be nice! Thank you!

[DerekZahn]

I doubt anybody is using 5 volts to run their stepper motors. Sometimes people will use 5 volts for the "logic" part of their setup (for example, Geckos need a 5v input). I suppose I could be wrong (got a reference to a specific post?).

Either way, your plan sounds good. You could use higher voltage if you want, and 10 amps is cutting it a bit close but is probably ok.

[ckrantz]

I guess I can see what they were talking about with the 5 volts. So the gecko needs a seperate 5 volts? There is no built in DC-DC convter then..


If I'm running 3 - 2.8amp per phase steppers thats only 8.4 amps that I'd use right? How would I be cutting it close with a 10 amp power supply? Not that I'm doubting what you say, I just want to make sure I'm not missing any needed amperage.

[DerekZahn]

Right, you need a separate 5 volts, which comes from the same place as the step/direction signals. The reason is that the Geckos isolate the motor power circuitry completely from the input logic circuitry.

If the motors are 2.8 amps per phase you should be fine, so never mind what I said before; a lot of Nema 34 motors are higher amperage than that.

[ckrantz]

I'm getting the motors from Automationdirect. Do you know of another source that might have stronger motors? I'm guessing that more amps means more torque?

[DerekZahn]

I'm not the world's foremost authority on stepper motors, though I have used them and like to try to understand things.

Look at the torque curve for those motors in the 10x microstepping mode (which is what Geckos do):

http://web5.automationdirect.com/sta...stepmotors.pdf

By the time they get to 200 rpm or so they aren't any more powerful than their Nema 23 motors and by 300 rpm they are significantly worse. Looking at that curve, unless I'm missing something, they don't look that great to me.

One link for more powerful motors:

http://www.homeshopcnc.com/page3.html

I'm sure there are others, but I'm not in the market for them myself so I don't pay too close of attention. Perhaps others can suggest some, or share their experience with Nema 34 motors.

[ger21]

You'd be better off with 36-48V

[ckrantz]

Thank you for the source, I'm guessing I'll go with the biggest one to accomidate for the large amounts of cutting I'll need to do.

These motors will require a lot of power supply, do you have a source for a power supply to run on the upper scale (36-48) of volts? I've been looking around and it seems I'm going to have to spend almost 400.00 in power supplies alone.

[ger21]

Look at the torque curve for those motors in the 10x microstepping mode (which is what Geckos do):

http://web5.automationdirect.com/sta...stepmotors.pdf

By the time they get to 200 rpm or so they aren't any more powerful than their Nema 23 motors and by 300 rpm they are significantly worse. Looking at that curve, unless I'm missing something, they don't look that great to me.

Those torque curves are using the Automation Direct 30V power supplies. Run them at 60V with Gecko's and you'll get much better performance.

Nema 23 motors will almost always spin faster than 34's, so at a certain rpm 23's will catch up. It should be closer to the 750-1000 rpm range, though for decent motors. But a lot depends on drives and voltages used.

[ckrantz]

so are you saying run the smaller nema 24 motors with just more voltage?

[ger21]

No, I was saying run the bigger motors with more voltage. Ideally, you should find motors which have a torque curve that bests suits your application. Bigger is usually better, unless they won't spin fast enough for the speed you need.