# Stepper Motors getting very hot after use

I have a hobby CNC machine running with three cd drive stepper motors in it using a 2amp supply for all of them, it is run by Arduino uno and EasyDrivers. Suddenly I noticed them getting very hot, I am worried it might get damaged, please help I am new to this and cannot seem to find any answer. Also my old pc power supply got damaged which I was using to power the setup with I replaced with a 12 volt 2 amp power adapter, could this change be the reason for the overheat ?

• It is not unusual for stepper motors to get hot. If you want a more detailed answer, you have to provide a lot more details yourself. – Dampmaskin Nov 13 '17 at 18:52
• Welcome to EE.SE, Udit, but the way you have worded the question it would be better on psychics.stackexchange.com - if there is one. You need to provide a schematic. There's a button on the editor toolbar and its easy to use. – Transistor Nov 13 '17 at 18:53
• Okay sure, what details should I provide ? I followed the directions from this site tinkernut.com/portfolio/hack-old-cd-roms-into-a-cnc-machine/… – Udit Sarkar Nov 13 '17 at 18:57
• @UditSarkar - With a simple controller, guaranteed. Get a 5 volt adapter. To a first approximation, the power dissipated in a motor run at low speed (like a stepper) will vary as the square of the applied voltage. Going from 5 to 12 volts will increase the power by a factor of nearly 5. – WhatRoughBeast Nov 13 '17 at 19:06
• i looked at the tinkernut project page that you followed to build this ..... and i say, what were you thinking ???!!! .... the project page uses +5V to power the steppers .... you use +12V and you wonder why the steppers are getting hot ???? – jsotola Nov 13 '17 at 20:00

The motor current is controlled by the driver. You can set the pot on the driver board to set the current as shown in the datasheet:

This is accomplished inside the driver chip by driving the coils with a PWM signal. If the coils were powered continuously from the 12V they would burn out because usually they're only rated for a couple of volts continuous. A 12V rated stepper would be objectionably sluggish.

In some applications the stepper current is automatically reduced when it is "holding" position, which helps keep the motors cooler. I don't know if your setup has that ability. In any case if you keep the surface temperature below 60°C you should be fine. If you intend to operate at higher temperatures you should consult the datasheet for the motor.

The obvious reason for motors to get too hot is that too much current is being run thru them for too long a time.

Several possible fixes follow from the above:

1. Run less current thru the motors.

2. Run the current at a lower duty cycle, with the cycle period small relative to the thermal time constant of the motors.

3. Use bigger motors that can handle the current without overheating.

That said, make sure the motors are really getting too hot, not just simply hot. Some elevated temperature is normal. I'd say anything you can keep your finger on for 10 seconds without getting hurt is not too hot.

How did you decide that it was OK to run 2 A thru these "CD drive stepper motors"? I expect they didn't come with a datasheet. Perhaps they just aren't meant for that much current. The dissipation goes with the square of the current. At 1.4 A, the rise above ambient should be half what it is now.

• I was under the impression, the motors will draw only that much current as required. Correct me if I my wrong, but as I have read in theory even if I provide lot of current the device would draw only that much current as required, it's only if the amount of current needed by the device is more than the rated amps of the power supply does the power supply gets damaged. Also I have tested the system with a PC power supply which could output 16amps on the 12volt rail without heating ! It's only when I short the wires of pc smps by accident and hence destroyed it, I switched to a 12volt 2 amp – Udit Sarkar Nov 13 '17 at 19:19
• 12 volt 2amp supply, because I couldn't afford another smps and 12volt (instead of the 5 volt which I was using from the pc smps) as 12volt adapter is more common and the EasyDriver datasheet said it could take upto 20volt. – Udit Sarkar Nov 13 '17 at 19:21
• I cannot touch the motors for more than a second without hurting myself, just after it's bieng turned off is it normal ? – Udit Sarkar Nov 13 '17 at 19:21
• @UditSarkar The motor doesn't self limit the current like that. The current drawn is a function of the applied voltage, winding resistance and speed (back EMF). If the motor is not moving (as is common in stepper motor systems) the current will be whatever the supply voltage is divided by the winding resistance. Double the voltage and you will quadruple the power dissipated in the windings. It sounds like you need to run it from 5V unless you have a current limiting controller or add some big heatsinks. – Jon Nov 13 '17 at 19:25