Hi all,

Here's a question from me that I needed some help with.
When the stepper motor is driven with 12V, it functions normally, but when the stepper motor is driven with 24V, it gets extremely hot.

What happened here? Is it the increased voltage issue? From what I understand is, if it is driven by 12V, 1A is drawn by the motor, if its driven by 24V, only 0.5A is drawn right? so the power used by the motor should be theoretically the same.

Thanks and Regards,
Nick

 

What is the motors rated working voltage? If the motor is rated for 12 volts and you apply 24 volts you will likely double the current and any motor run on twice its rated voltage will get hot.

Ron

 

What is the motors rated working voltage? If the motor is rated for 12 volts and you apply 24 volts you will likely double the current and any motor run on twice its rated voltage will get hot.

Ron

The motor is rated 24V, 1A per phase.
So it means that, if I increases the voltage, the current drawn by the motor is still 1A?

 

Go down to point 7

http://www.geckodrive.com/support/step-motor-basics.html

 

Go down to point 7

http://www.geckodrive.com/support/step-motor-basics.html

thanks

 

The motor is rated 24V, 1A per phase.
So it means that, if I increases the voltage, the current drawn by the motor is still 1A?

No, it means that at the motor's rated voltage it will draw its rated current. The current draw is a function of the motor's winding resistance.

Class Of Zero, really good link!

Ron

 

If the motor is powered by 12 volts and draws one amp then the motor coil resistance is going to be 12 ohms. 12÷1=12. So if we look at it from the opposite side, 12 ohms passing 1 amp is going to require 12 volts. 12x1=12. Little hard to see the difference so here's another way:

12volts ÷ 1 amp = 12 Ω
12volts ÷ 12 Ω = 1 amp
12Ω x 1 amp = 12 volts

Now, lets substitute the voltage
Since we know the resistance isn't going to change 12 Ω becomes a constant. Therefore, 24volts ÷ 12 Ω = 2 amps (not 1 amp).

Lets look at wattage - that stuff that produces the heat: W(attage) = V(oltage) times A(mperage)
So 12V x 1A = 12 W
And 24V x 2A = 48W

Do you see why your motor got hot under 24 volts and didn't under 12 volts? The coil resistance doesn't change. So when you change the voltage you change the amperage as well. As you can see there's an "Inverse Square Law" at work. Put it this way: A 1 inch square has one square inch. A 2 inch square has four square inches. Four times the area. Doubling the voltage may double the amperage but it multiplies heat production (wattage) by a factor of four. Hence, your motor gets hot.

Since you say your motor is rated for 24 volts at 1 amp then I must conclude that the internal resistance by design is going to be 24 ohms per segment. How do you know at 12 volts you drew one amp? Is that something you just assumed because the motor states it draws an amp? If so, it draws an amp AT 24 volts, not 12 volts. Half the voltage will be four times cooler (less heat) than at 24 volts. And it's not unheard of for a stepper motor to be hot.

A typical motor that just spins freely when power is applied to two leads will draw more current when the motor starts up than when it's free spinning. And if you place a heavy load on it, the slowing down of the motor will produce more heat. If you absolutely stall the motor it will likely get hot enough to burn itself out. Because the motor is relatively free to spin its current draw drops considerably, and I'm not the expert on motors. Since a stepper motor doesn't spin but steps and holds position until commanded to step again, it doesn't run cool just because there's no load. The motor is trying to hold a specific position. That means a particular segment is energized. And warming up. And up. And up until it reaches a temperature based on current and voltage. I don't think I've ever seen a fan on a stepper motor.

So if you're operating at design voltage then the motor is likely designed to survive the temperature it generates. If the motor is bad I suppose it could get hotter. And the hotter it gets the more it goes bad, the faster it goes bad, until total failure.

Your motor was four times hotter because you used twice the voltage. Even if it was rated for that voltage, that's the reason why you noticed a significant difference in operating temperature.

Hope this helps. Long, I know. I'm a "Windy baztard".

 

If the motor is powered by 12 volts and draws one amp then the motor coil resistance is going to be 12 ohms. 12÷1=12. So if we look at it from the opposite side, 12 ohms passing 1 amp is going to require 12 volts. 12x1=12. Little hard to see the difference so here's another way:

12volts ÷ 1 amp = 12 Ω
12volts ÷ 12 Ω = 1 amp
12Ω x 1 amp = 12 volts

Now, lets substitute the voltage
Since we know the resistance isn't going to change 12 Ω becomes a constant. Therefore, 24volts ÷ 12 Ω = 2 amps (not 1 amp).

Lets look at wattage - that stuff that produces the heat: W(attage) = V(oltage) times A(mperage)
So 12V x 1A = 12 W
And 24V x 2A = 48W

Do you see why your motor got hot under 24 volts and didn't under 12 volts? The coil resistance doesn't change. So when you change the voltage you change the amperage as well. As you can see there's an "Inverse Square Law" at work. Put it this way: A 1 inch square has one square inch. A 2 inch square has four square inches. Four times the area. Doubling the voltage may double the amperage but it multiplies heat production (wattage) by a factor of four. Hence, your motor gets hot.

Since you say your motor is rated for 24 volts at 1 amp then I must conclude that the internal resistance by design is going to be 24 ohms per segment. How do you know at 12 volts you drew one amp? Is that something you just assumed because the motor states it draws an amp? If so, it draws an amp AT 24 volts, not 12 volts. Half the voltage will be four times cooler (less heat) than at 24 volts. And it's not unheard of for a stepper motor to be hot.

A typical motor that just spins freely when power is applied to two leads will draw more current when the motor starts up than when it's free spinning. And if you place a heavy load on it, the slowing down of the motor will produce more heat. If you absolutely stall the motor it will likely get hot enough to burn itself out. Because the motor is relatively free to spin its current draw drops considerably, and I'm not the expert on motors. Since a stepper motor doesn't spin but steps and holds position until commanded to step again, it doesn't run cool just because there's no load. The motor is trying to hold a specific position. That means a particular segment is energized. And warming up. And up. And up until it reaches a temperature based on current and voltage. I don't think I've ever seen a fan on a stepper motor.

So if you're operating at design voltage then the motor is likely designed to survive the temperature it generates. If the motor is bad I suppose it could get hotter. And the hotter it gets the more it goes bad, the faster it goes bad, until total failure.

Your motor was four times hotter because you used twice the voltage. Even if it was rated for that voltage, that's the reason why you noticed a significant difference in operating temperature.

Hope this helps. Long, I know. I'm a "Windy baztard".

From the supplied link.

Section 7: Motor Heating and Power Supply Voltage
There are two major causes of motor heating: copper losses and iron losses. Copper losses are the easiest to understand; this is the heat generated by current passing through a resistance, as in the current passing through the motor’s winding resistance. Often this is referred to as “I2R” dissipation.

This cause of motor heating is at a maximum when the motor is stopped and rapidly diminishes as the motor speeds up since the inductive current is inversely proportional to speed.

Eddy current and hysteresis heating are collectively called iron losses. The former induces currents in the iron of the motor while the latter is caused by the re-alignment of the magnetic domains in the iron. You can think of this as “friction heating” as the magnetic dipoles in the iron switch back and forth. Either way, both cause the bulk heating of the motor. Iron losses are a function of AC current and therefore the power supply voltage.

Your motors will get hot, when holding a position, something you can't get away from. If they are rated at 24v/1 amp, they are more than likely going to be ok, yes they will feel warm to hot. The ones on my machine do and even when the outside temp is excess of 35'C I haven't had a problem. Never had a sniff of problem from the Z axis and thats the axis that holds it's position more than any other.

If you really want some great practical advice head over to cnczone, the guys over there are using them in real life applications. They know their (well I'm not going to say it).
Steppers are quite involved in their theory as a lot of things are happening....more than my poor head can get around. I think from memory Mariss from Geckodrive frequents cnczone from time to time.

Another thing, hot is a relative thing and subjective, if you can measure the temps if the data sheet has specs compare them with the specs or if they don't, post a question on cnczone specifying the model number, where you got them, running conditions and temps.

ACC is a good forum and all, but cnczone is The Place to go to get some really really good advice regarding steppers and such. And guys don't take this as a insult.

Anyhow good luck.