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Author Topic: Hot Stepper motors  (Read 3075 times)

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Hot Stepper motors
« on: April 21, 2016, 05:59:43 PM »
So I own a x carve cnc machine and run it with mach3 and a gecko 540. My motors are 2.8A/phase and I have added the  2.8K 5% 1/4W resistors to the gecko 540. But my motors are still getting hot. They will run for about 30 min. and get hot to the touch. Is this normal? they sound alright. Is there a setting on mach3 that I am missing that might cause this problem? Any help would be appreciated, thanks!

Offline Tweakie.CNC

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Re: Hot Stepper motors
« Reply #1 on: April 22, 2016, 02:01:58 AM »
Steppers are usually run at their rated current and they do get hot.

As a general rule they should not get so hot that you cannot briefly hold your hand on them (maximum case temp. around 65 deg.C).
It could be that the manufacturer of your steppers was over generous with the rating and if you find that they really are getting far too hot then reduce the current (reduce the resistor values to 2k2 or 2k).

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.
Re: Hot Stepper motors
« Reply #2 on: April 22, 2016, 03:24:38 AM »
Thanks for the help. I just ordered some 2k2 resistors, the motors are just getting way to hot. So hot that I can only touch them for a quick second. I hope this helps I don't want my motors to be running that hot all the time it cant be good.
Re: Hot Stepper motors
« Reply #3 on: April 22, 2016, 03:23:22 PM »
I think if you look at the spec sheets for the motors it will list the maximum temperature and the rise above ambient. In both cases I think you'll be shocked by how hot that actually is.

Offline RICH

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Re: Hot Stepper motors
« Reply #4 on: April 23, 2016, 07:10:02 AM »
FWIW,

140 deg F is considered a temperature at which protection against burning should be done. So if you can briefly and lightly hold / touch
the stepper but can't maintain touching it your at or above  140F. Depending on how the stepper is wired can change it's
performance and operating temperature, BUT, again it depends on the particular stepper.  The heating comes from resistance to the
applied current or said differently, no heat not working hard. As long as you stay below the rated temperature of the stepper, and recommend being conservative, you are doing no harm.
The Gecko site provides  a lot of info and worth studying.

RICH

Offline ger21

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Re: Hot Stepper motors
« Reply #5 on: April 23, 2016, 01:01:55 PM »
What voltage are you running at? A lower voltage is probably a better choice, as it won't lower your torque, which changing the resistors will do.
Gerry

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Re: Hot Stepper motors
« Reply #6 on: April 23, 2016, 05:07:28 PM »
Lowering the voltage will reduce the rapids rate at which you begin to lose steps.  Modern step drives control the maximum motor current which means they actually lower the voltage to the motors to keep the current constant.  As speed goes up the back EMF goes up so more voltage is required to produce the same current.  If this weren't true the 67vdc to 80 volt rated drives on my machine would be cooking the motors, they only get get warm.
Re: Hot Stepper motors
« Reply #7 on: April 23, 2016, 05:27:50 PM »
How do you lower the voltage? This part of the cnc I don't know to much about. I just have a 40v power supply. Would reducing that lower the voltage? Cant you just lower the voltage on the power supply?

Offline ger21

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Re: Hot Stepper motors
« Reply #8 on: April 23, 2016, 05:40:34 PM »
Quote
If this weren't true the 67vdc to 80 volt rated drives on my machine would be cooking the motors, they only get get warm.

It's a combination of voltage and current that causes heat, and depends on the specific motors. Some run hotter than others.

How the motors are mounted also makes a difference. If mounted to aluminum plates, which is the recommended method, motors will run much cooler, as the plates are a heatsink.

At 40 volts I wouldn't change the voltage. Most run 48volts, and going to 36 volts would run a little cooler.

Hot steppers are normal, and if you can touch them without being burned, then they are probably not too hot.
Try the lower resistors and see if it helps.
Gerry

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Re: Hot Stepper motors
« Reply #9 on: May 07, 2016, 08:51:20 AM »
The other thing would be to pick up a cheap infrared temp gun at your local hardware store and take an actual temp reading. This way there is no guessing. A properly powered stepper runs shockingly hot. If you have the data from your steppers the max voltage is (sqrt 32 * (the inductance in mh)) . Check the Gecko site to make sure I remembered it correctly. Once you know that you are not overpowering the steppers, you could always add little cooling fans (from all the left over computer parts that you have on the parts shelf) if the temp still bothers you.


 ??? Any mistakes are do to the fact that I am still in the middle of my first cup of coffee.  ???
We never have the time or money to do it right the first time, but we somehow manage to do it twice and then spend the money to get it right.