New Stepper Motor Overheating

I recently purchased a non-captive linear stepper motor (Linear Stepper) to use in a syringe extrusion setup instead of the normal plastic extrusion.

It was working well at first, but I was noticing that it ran very hot (~37 C on the outside of the housing) while in use and now it is making a grinding noise whenever it rotates. I think the problem was that the motor is only rated to 0.4A and I was most likely giving it much more than that, but I am not sure. I chose a 12v motor because I thought that I needed it to be 12v to work properly with the duet board, but after reading some other posts I got the impression that the motor amperage is the most important spec, not voltage. Is that correct?

Also, if I want to keep using this motor (or one with a similar max current rating), is there a way to set the max current for the extruder motor in the firmware?

Yes, using Duet or any other recent 3D printer electronics with constant-current drivers, it is the motor current that matters, not the voltage. It is usually best to choose a motor with a rated current of between 1A and 1.6A and voltage of between 2V and 4V. The motor current is adjusted in RepRapFirmware (for Duet electronics) using the M906 command in your config.g file, see [reprap.org].

Stepper motors do run hot at their rated current. If you want to use that particular motor, I suggest you set the current to 250mA or 300mA, and use a 24V supply. With just a 12V supply, the maximum speed will be lower.

Edited 2 time(s). Last edit at 06/15/2015 02:52PM by dc42.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Ok thanks!

The example has "M906 X300 Y500 Z200 E350" but I don't know what my currents are for the X, Y, and Z motors. Could I send the command "M906 E300" to set the extruder motor current without having to find out the other ones?

Also, I am curious why the 1 - 1.6A and 2 - 4V range is ideal for reprap components when the duet board receives a 5v and 12v input.

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kkozel
The example has "M906 X300 Y500 Z200 E350" but I don't know what my currents are for the X, Y, and Z motors. Could I send the command "M906 E300" to set the extruder motor current without having to find out the other ones?

Yes, you can use M906 E300 to set the extruder motor(s) to 300mA and leave the XYZ motor currents alone. However, if you look in your config.g file, you will find the M906 command in there - otherwise the motors wouldn't move at all.

Quote
kkozel
Also, I am curious why the 1 - 1.6A and 2 - 4V range is ideal for reprap components when the duet board receives a 5v and 12v input.

The maximum current that the Duet can provide to the steppers is in the range 1.2A to around 1.6A (possibly 2A) depending on whether you have a fan cooling it. So you don't want to use a stepper that needs more than that.

The voltage quoted for a stepper motor is only valid when the motor is at rest. As the speed increases, so does the voltage required to maintain the current and to switch the current fast enough as the motor steps. Using a motor rated as between 2V and 4V means that with a 12V power supply, the driver chip has enough headroom to achieve reasonable speeds from the motor.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].