Author Topic: motor set up  (Read 2992 times)

0 Members and 1 Guest are viewing this topic.

Offline martin

  • Active Member
  • Posts: 10
    • View Profile
motor set up
« on: October 15, 2014, 03:26:16 PM »
Question for the machine building experts if you don't mind please.
I've got an old Gerber system 48 which has been updated with new steppers & runs under mach3, It runs via a parallel port bob using Leadshine Am882 drivers & 3.1Nm stepper motors that are wired in Parallel configuration.

The AM882 set up instructions are pretty good & I had no problem setting the machine up & getting it running properly, recently I had to go back to the set up guide & while reading about seting up motors in different configurations I started to think that maybe I would be better with the motors wired is series rather than parallel.

The guide briefly describes each set up & what caught my eye was the part that said that with series low speed torque was better but when operating at high speed torque was reduced & with parallel high speed torque was good but low speed torque wasn't so good.

So the question is what would be classed as high speed & what would be classed as low speed ? The machine is quite old & is belt driven so I don't tend to run it that fast, well I don't think I do but not being sure what is classed as fast & slow speed I;m not really sure, just wondering if I would be better with the motors set up to run series rather than parallel

Offline ger21

  • Global Moderator
  • *
  • Posts: 6,127
    • View Profile
    • The CNC Woodworker
Re: motor set up
« Reply #1 on: October 15, 2014, 05:34:49 PM »
I think that they neglect to tell you that this only applies if the same voltage and current is used with both wiring methods.

Stepper motors are rated for holding torque, when the motor is not spinning. Whether wired series or parallel, the motor will have the same holding torque.
Now, as rpm's increase, the torque begins to drop off

If parallel has more torque at higher speeds (which it does), and both start with the same amount of torque, then a series wired motor will never produce more torque than a parallel wired motor, unless the parallel wired motor is supplied less current. Remember that a parallel wired motor has twice the current rating of a series wired motor.

What exactly is high speed and low speed would tend to depend on the specific motors you're using. You'd need to see a torque curve to see where the torque falls off for the motor when wired bipolar series. Every motor is different, and the voltage you're using plays a role here too.

Generally, I would say that you can get away with bipolar series on smaller Nema 23 motors if you don't need much more than 600-800 rpm. If you need rpm's higher than that, then parallel is usually a much better choice.
Motors wired bipolar series may run cooler, due to the lower current.

The bottom line, though, is that switching to bipolar series will not give you any more torque than you have now.
Gerry

2010 Screenset
http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html

Offline martin

  • Active Member
  • Posts: 10
    • View Profile
Re: motor set up
« Reply #2 on: October 16, 2014, 03:47:47 AM »
Thanks for the reply Gerry, I was actually assuming that this was using the correct current settings for the selected wiring configuration, they show wiring configurations for 4, 6 & 8 wire motors & give examples of voltage & current settings for some leadshine motors.
It was the mention of low & high speed movements that had me wondering, my machine runs really slowly compared with some that I have seen. That is possibly me being way to cautious with it, it runs that slowly that I have fitted a zimmer frame lol.
Motor temperature was actually something that had me checking the set up initially, the motors don't seem to run very warm at all & should be running much warmer than they are.