steppers getting hot

[macatoms]

I just got my control up and turning motors.I left it setting for a while powered up but not running.I havent tuned the motors in mach 3 yet.There Keling nema 23 570 in/oz.Anyone know what is going on?Thanks Dave

[H500]

Hot is normal.

[macatoms]

Thanks for the info.Dave

[James Newton]

To expand on what H500 said: It's normal for motors that are powered up and not moving to get hotter than they would if they are turning. It's good to have a low power hold in the driver so that Mach 3 can be setup to reduce the power to the motors when they are not actually running during a job.

Motor heat is caused by a number of factors, the primary one being the flow of current through the coil. Low power hold reduces that current flow and greatly reduces motor heat. Counter-intuitively, when the motor is running, slightly less current flows because part of the time the coil is changing direction and the current doesn't have time to reach full flow in any one direction. The faster it turns, the less power it must dissipate, and the less torque it produces.

Another cause of heat in the motor at rest is eddy current loss caused by the AC component of the chopper signal from the driver. The driver you have is a chopper; it turns the power on and off rapidly to control the current sent through the motor. That alternating current induces a current into the metal of the motor, and that current also contributes heat to the motor, in the body, rather than in the coils. This effect does not contribute /as much/ heat as the main current flow, but it /does/ contribute heat. If you use a linear, rather than a chopper, driver, your motors will not heat /as much/ at rest.

Although motor heating is normal, it is NOT desirable. Heat is the enemy of the magnet. The magnets that give your stepper motors their torque, are reduced in strength as they get hot. I can't find the reference at this time, but as I remember, the loss can be significant. I've never seen anyone put heat sink fins on a motor, but it would be an interesting thing to try to get a bit more speed or to solve problems that only show up when the motors are hot.

[JerryBurks]

Mounting on a heat sink plate is recommended by most stepper manufacturers, see Parker Automation FAQ.

It also requires some air flow to get rid of the heat.

[James Newton]

Mounting on a heat sink plate is recommended by most stepper manufacturers, see Parker Automation FAQ.

It also requires some air flow to get rid of the heat.

Exactly, but I've never actually seen that done! LOL... Have you seen any of these hobby CNC machines, or a rep rap or 3d printer or anything with fins and a fan on the stepper motors?

[H500]

Mounting on a steel or aluminum machine is extremely effective. My motors get nearly too hot to touch on a desktop. But on the mill, they barely get warm.

[ger21]

LOL... Have you seen any of these hobby CNC machines, or a rep rap or 3d printer or anything with fins and a fan on the stepper motors?

I've seen one or two with fans.