Micro stepping confusion

[ger21]

What is the pitch of your screws, and are the motors wired bipolar parallel or bipolar series?
It sounds to me like a very poorly matched system of screws and motors.

You probably have 3 times more motor than you need. A G540 package with 380 oz motors is capable of much higher performance than you're looking for with the right leadscrews.

[rrc1962]

IMy question is why with the lower amp setting is it working?  I thought that the more amps I push to the motor the more power I would have, but I must have been off in my thinking.

Probably because the power supply can't supply the rated current to the motors.  All you did is reduce the current going to the motors, which reduces power, but the power supply can now keep up.  In your case, the motors are so oversized that the reduction in power is not staling them. 

I agree with the comment above.  A G540 and some 380oz/in motors are more than enough for your setup.

[kencor1]

The max that my drivers are rated for is 80v. Would it make that much difference to go from 72V to 80V ?

Tom

[rrc1962]

Your problem is not voltage, it's current.  What's the current rating (amps) of your power supply?  What is the current rating of all of your motors? 

[kencor1]

Here are the specs for my power supply.  Unregulated Power Supply 1440W, 72VDC/20A ,120VAC or
230VAC, here is a link to my motor specs  http://www.kelinginc.net/KL34H2120-60-4A.pdf

Thanks for the Help on this.

Tom

[ger21]

I'll ask again:
What is the pitch of your screws, and are the motors wired bipolar parallel or bipolar series?

[Tweakie.CNC]

Gerry,

Looks like the motors just have the one set of bipolar windings at  6 Amps per phase.

Tweakie.

[kencor1]

My screws are 16mm 5 lead import ball screws, at least that's what I think I remember they are.
I guess my thinking may have been wrong. I wanted alot of power so I thought that the bigger motors would be better. If I want to get a bigger power supply does anyone have a suggestion on what size and where I could buy one?.   I really don't want to have to buy all new motors.
 So what application would warrent the larger 1200oz nema 34 motors?

Thanks, for all of the advice, I am a woodworker by trade and the electronics stuff is really not my strong suit.

Tom

[ger21]

The bigger the motors, the slower their maximum speed tends to be. You're screws are basically 5 turns/inch, so you need 500 rpm to go 100 ipm.

Depending on inductance, most steppers have a maximum usable rpm of about 1000. Although smaller, low inductance motors can be good for up to 1500rpm, or even higher.

I've seen torque curves of similar size motors that only have 150-200 oz-in of torque over 300rpm.

You'd be a lot better off with screws with a 10mm lead, or even 25mm lead. Those would give you 2 or 5 times more speed, while keeping the steppers moving slower where they have more torque.
Your 5mm lead gives you a large mechanical advantage at the expense of speed. At very slow speeds, you're probably getting several hundred pounds of force. But at high speeds, you have none.

Going from 72V to 80V probably wouldn't make a noticeable difference. And likewise, while changing motors would give you better performance, those screws are still hampering your performance.

To answer your question, big motors and 5mm pitch screws are best used on big, heavy machines that need lots of force, but not higher speeds.

[kencor1]

Thank you Gerry for explaining for me. I think I will look into getting the bigger pitch screws sometime in the future, for now I at least have a better idea of what is happening.  Do you know of somewhere that I can start looking for the screws, that wont cost an arm and a leg.

Again I would like to thank everyone that has replied to me, this forum is truly a wonderful font of information.

Tom