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Freeing the motor to avoid overheating
« on: February 26, 2010, 08:49:39 AM »
Hello all,

Can anyone tell me how to include code to make sure the motor stops being energized when standing idle or at the end of a job to avoid overheating the motors. How is it actually done hardwarewise. I mean what pin should be connected to the "free motor" screw terminal on the driver and where in the configuration can this pin be assigned.

Thank you
Bluebird

Offline RICH

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Re: Freeing the motor to avoid overheating
« Reply #1 on: February 26, 2010, 09:03:00 AM »
Manny drives provide for auto current reduction. And there have been problems posted where the setting of outocurrrent reduction, say after 10 seconds / via some kind of timer setting on the drive created all kinds of problems when running a file. Then also maybe you have excessive current to the drives to begin with as i have left mine on by mistake, yes they get rather warm, but never enough to cause damage.
RICH
Re: Freeing the motor to avoid overheating
« Reply #2 on: February 26, 2010, 02:17:49 PM »
Hi RICH
Thanks for your help. I asked this as a precaution really. I have never dared to leave the drivers idle for long. Although the driver does cut the current down by 50% after only a tenth of a second, I still think it is a good idea to be able to include this feature in the Gcode to make sure the motors are freed at the end of a run.

Cheers
Bluebird

Offline Sam

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Re: Freeing the motor to avoid overheating
« Reply #3 on: February 26, 2010, 04:54:02 PM »
If the motors were free, they would loose position. This may or may not be of importance in your situation, however it's generally not desirable for most. As Rich stated, motor heating is not a problem if everything is set up correctly. Most of the time more heat is generated from cutting a 3d code, rather than just sitting idle with a auto current reduction drive.
"CONFIDENCE: it's the feeling you experience before you fully understand the situation."

Offline bowber

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Re: Freeing the motor to avoid overheating
« Reply #4 on: February 27, 2010, 07:10:36 AM »
I've not yet had a problem with the steppers getting hot when stood.
If I'm not doing anything for an hour or more then I just turn off the drivers and have an input into mach to let it know that an emergency stop has been triggered so no code will run.

Steve
Re: Freeing the motor to avoid overheating
« Reply #5 on: February 27, 2010, 02:42:56 PM »
hey bluebird,
 to turn stepper drive on en/nopower pin I inverted the signal to low to turn power off because high is on and low is off.  (or nopwr) so my step drives are always off, used a Ic to send a low signal to controller, then a high signal from mach to turn back on.( tried a resistor to pull high, and low but my controler did NOT like that. It wants HIGH OR LOW nothing in between, thats whyi used a switching IC
anyways I used the m7 m8 coolant command to  turn my x-y on and m9 to turn off at the end of cycle. you may want to pause a few seconds after power on just to make sure it is fully energized before running program. the only problem with doing this is that you have to run a separate m7 m8 command to do a axis home or jog.
  The motors really shouldn't get that hot, they run almost as good at a lower power setting, I have small motors so I run them at max amerage, then turn them off.

just a thought??
Steve
Re: Freeing the motor to avoid overheating
« Reply #6 on: February 28, 2010, 08:17:33 AM »
Hi,
Thanks to all. Your help is appreciated very much. I have been fiddling around with Mach3 configuration options and have just found an option under the heading"general Config...", then under the section titled "Prgm end, M30 or rewind" under which you can tick "Turn off all outputs". Has anybody else tried this? Does it actually do what it says. I used it in Gcode and after some idle standing, one of the motors was as cool as a cucumber but the other one was warm to the touch. (I only have 2 motors). So I cannot tell weather this was due to this option or is unrelated. If anybody has had any similar experience with this pls. let everyone benefit from the information.

Cheers Bluebird
Re: Freeing the motor to avoid overheating
« Reply #7 on: March 01, 2010, 08:46:04 AM »
Hi, It's not desirable to disconnect power from steppers at any time, position will be lost even just a small bit each time they are shut off eventually leading to
large errors.

Some drivers have an internal current limiting circuit to reduce power when not in motion so if you have one of these drivers, no worries.

If your driver doesn't have this circuit then you should set the current through the stepper to the steppers specs.

Current rule of thumb is if you wrap your hand round the stepper and then count 30secs before pain begins to set in. Then thats fine.

Saying that, A while back when cnc was new to me I built my own stepper drivers to power 3 Nema34 size steppers current at 4amps/phase to retrofit an old mill.
When the steppers arrived I found 8 wires "oh, 4 phases" I thought and then built the drivers to supply 4amps to the 4 phases. Little did I know that the steppers were 2 phase so my current calcs were way off.
So when I do the hold the stepper trick I can only count to 3, Strangely enough though, Until recently the mill had been used nearly every day for my business for nearly 10 years, Its only gathering dust now as I bought another mill and have converted to servo drive.

Cheers
John