Stepper Motor Temperature

[SaraJoy]

I'm currently running a 12V 1.8deg stepper motor, doing a short sequence of about 4 secs duration: one 180deg move, one 90, another 90, with about a second's stopping between each move. There is no load on the shaft.

But!! It is running at about 70deg Centigrade (and still rising), which is about 160F! This is after about 20 mins, and it is sat atop a couple of heatsinks, which are also now very toasty!

Is this normal? Is it going to get hotter when I give it some load?

 

[aolalde]

Most of actual motors are manufactured with insulations rated “class F”. This means capable of operation up to 155 °C (311 F). Under these temperatures the external surface could reach 100 °C depending on the cooling system. Any way check the Voltage applied and current drawn and verify that those are into the rated parameters.

 

[SaraJoy]

Yes I have done so, the voltage is 12V ... However, that voltage is provided via two step-down resistors at 30 Ohms. As the stepper heats up, its own resistance increases from 30 Ohms to about 33, meaning that it gets a higher voltage across it the hotter it gets - bit of a vicious cycle!

The current it pulls is fine, a bit less when it is moving but not by much. It's rated at 0.4A, I assume that's 0.4 per coil, as together they pull 0.8A.

 

[aolalde]

Could you test the motor out of your circuit by feeding it with a 12 V car battery and check the performance?

 

[sreid]

Stepper motors run hot since they are pulling full current even sittig still. Some PWM controlllers reduce the current if move commands have not been received for a while.