How to cool down a stepper motor?

[gimpo]

Hello everybody,

my little Nema11 stepper motor gets quite hot (this is normal since it absorb around 1.3 A). I would like to add some kind of heat protection by adding a sort of heatsink.
My idea is to use the long mounting alu-bracket as heatsink too. In this way I will avoid a big and bulky construction.

It would be possible to insert some thermal paste between the bracket and  motor surface in order to maximize the heat transfer?
Also: I googled around and I've got no definitive answer about what thermal paste are electrically conductive and what are not. Any suggestion? 

P.S.
This stepper should be used outdoor.

[Siwastaja]

Stepper motors are designed and rated to be used as-is. First make sure you are staying within datasheet ratings + some margin (say, derate current by some 20%). If you still feel uncomfortable with the temperature, reduce current further, if possible, or pick a larger motor.

Gluing heatsinks on is a commonly used trick but really just an ugly hack. I doubt mounting a fairly small heatsink, as typically seen, does much difference. With a fan moving air around the motor, you have better chances to have a real cooling effect, compared to a small passive heatsink which maybe adds some 5-10% of surface area of the motor and does that through additional thermal interface which likely halves the gain.

If the motor has large even surfaces then of course you can mount heatsinks. Use standard heatsink compound. It works given the gap is very small (say less than some 0.1-0.2mm), requiring even surfaces. For passive heatsinking to be effective, I would be looking at heatsink surface area many times (5-10x) more than the motor surface area, coupled through as much motor area as possible.

[SparkyFX]

Check if you can change how it is driven. If you can change the system mechanically to hold position/angle without being driven you can skip all considerations for heat dissipation.

[gimpo]

Hello Siwastaja,

thanks for the info.

Unfortunately I cannot install a bigger motor because of space problems. So I have to run this small one at full power.
Roughly, the "L" shaped bracket will have two times the surface of the motor, and much better ventilation. So I think it should add some benefits. Even lowering the temperature of 15-20% take me on the safe side and will provide a "safety" margin.

The bracket should be something like this:



I would put some thermal past along all of the lower motor surface.

Since this motor will be used outdoor, it is not clear to me if common thermal paste will get dry and will crack under the sun of an hot summer day, or if it will freeze and crack in winter (-5/-10 celsius degrees).
I was thinking about a little fan too, but I have no idea how to provide a minimal waterproof characteristics in such case... 

[gimpo]

Check if you can change how it is driven. If you can change the system mechanically to hold position/angle without being driven you can skip all considerations for heat dissipation.

It would be really nice if I could do that. I saw some nice examples of steppers with embedded geared-boxes on the market (for example on www.servocity.com).
Unfortunately I have to be able to manually turn the motor shaft in some (rares) emergency situations. This is a "must-have" requirement of my project... 

[james_s]

Can you change it to a servomotor? Those can behave like a stepper motor when driven appropriately, but they can be much more powerful and more efficient. I don't think steppers are used much anymore due to the electronics required to drive servomotors becoming so cheap.

[langwadt]

Can you change it to a servomotor? Those can behave like a stepper motor when driven appropriately, but they can be much more powerful and more efficient. I don't think steppers are used much anymore due to the electronics required to drive servomotors becoming so cheap.

steppers have much more torque than servos of the same size and the drive with modern ICs is dirt cheap

[fourtytwo42]

Hello everybody,

my little Nema11 stepper motor gets quite hot (this is normal since it absorb around 1.3 A). I would like to add some kind of heat protection by adding a sort of heatsink.

There is another possible solution and that is add intelligence to the driver, in some applications it is not required to develop the full torque 100% of the time, for example when stationary or not accelerating/decelerating, by controlling the current according to torque needs power dissipation is reduced.

[gimpo]

Hello everybody,

my little Nema11 stepper motor gets quite hot (this is normal since it absorb around 1.3 A). I would like to add some kind of heat protection by adding a sort of heatsink.

There is another possible solution and that is add intelligence to the driver, in some applications it is not required to develop the full torque 100% of the time, for example when stationary or not accelerating/decelerating, by controlling the current according to torque needs power dissipation is reduced.

Anyway, I have ordered a small device on Aliexpress equipped with the AS5600 magnetic encoder to monitor tiny shaft movements. I'm not trying to build a closed-loop system, I want simply de-enerigize the windings when a small rotation of the shaft is detected.

As I know, servos are good at high rpms. That is not my case.
I need just good torque for small rotations (max 90-100°) of the shaft at low rpm (100? 200 rpm?)

[fourtytwo42]

Maybe just maybe it might help if you described the application a little bit ?
It's not normal to de-energise a stepper when an unexpected rotation is detected as that implies the holding torque is insufficient.
A rotation measurement device is not normally required as the degree of rotation is known by the number of steps stepped UNLESS there is insufficient torque and slippage is occurring.

[gimpo]

There is another possible solution and that is add intelligence to the driver, in some applications it is not required to develop the full torque 100% of the time, for example when stationary or not accelerating/decelerating, by controlling the current according to torque needs power dissipation is reduced.

That is a very clever observation! 
Actually, when I measured the max load required by my application, I noticed that the force necessary to keep the load stationary is less than the one necessary to move it. Why I forgot this detail???

But... I'm scraping my head now... I use the "Big Easy Driver" to drive my stepper. With that I have only two options:

1. turn on or off the motor with a digital command (i.e. energize or de.energize the windings)
2. manually adjust the current of the windings by tuning a little potentiometer on the board.

So there is no way to increase/decrease the current by using a microntroller (in my case an Arduino Pro Mini).... 
Any idea?

[fourtytwo42]

Yes, you modulate it with a PWM drive, so the on/off signal instead of being static is a square wave of variable duty cycle.
The frequency you choose is somewhat dependant on the motor and driver characteristics plus your hearing!
As the driver is DMOS it should manage 10Khz or even 20Khz without trouble

EDIT Ghaaa I see this A4983 thing is already intelligent, two intelligences may end up fighting each other!

[gimpo]

Maybe just maybe it might help if you described the application a little bit ?
It's not normal to de-energise a stepper when an unexpected rotation is detected as that implies the holding torque is insufficient.
A rotation measurement device is not normally required as the degree of rotation is known by the number of steps stepped UNLESS there is insufficient torque and slippage is occurring.

AH! So you want to know the details of my invention that will change the world??? 

I'm just wasting my time and money to build an "intelligent" throttle-lock for my motorcycle.
When the driver must suddenly shutdown the gas because of unexpected traffic conditions, then the micro-controller should detect the initial force applied on the throttle and immediately turn off the current. This will make make the rotation of the throttle itself more easy and with (almost) zero effort for the right hand.

[gimpo]

EDIT Ghaaa I see this A4983 thing is already intelligent, two intelligences may end up fighting each other!

Wait a minute! Stop the world, please.
Are you telling me that the A4983 can electronically modulate the current? 

[fourtytwo42]

Maybe just maybe it might help if you described the application a little bit ?
It's not normal to de-energise a stepper when an unexpected rotation is detected as that implies the holding torque is insufficient.
A rotation measurement device is not normally required as the degree of rotation is known by the number of steps stepped UNLESS there is insufficient torque and slippage is occurring.

AH! So you want to know the details of my invention that will change the world??? 

I'm just wasting my time and money to build an "intelligent" throttle-lock for my motorcycle.
When the driver must suddenly shutdown the gas because of unexpected traffic conditions, then the micro-controller should detect the initial force applied on the throttle and immediately turn off the current. This will make make the rotation of the throttle itself more easy and with (almost) zero effort for the right hand.

Ohh gosh I am very sorry, I can assure you I am not one of those dasterdly industrial spies we hear about trying to steal others ideas 

Looking at that driver chip it just controls the current within a step, there is no variation according to the mode, for example when stationary, by the sounds of it in your app it could spend a fair amount of time stationary, in that case you could modulate the ENABLE input to reduce the power dissipation, for example 50% duty cycle would halve the power. I guess the frequency probably has to be low enough not to confuse its (A4983) intelligence so a few hundred hertz might be worth a shot but you need to avoid any mechanical resonance, of course it might end up comforting the drivers hand too 

[fourtytwo42]

EDIT Ghaaa I see this A4983 thing is already intelligent, two intelligences may end up fighting each other!

Wait a minute! Stop the world, please.
Are you telling me that the A4983 can electronically modulate the current? 

It does but in a kind of dumbo way because it doesn't know about the wider world 
All it does is use the modulation to generate a constant stator current rather than one controlled by V/R in the static case.

[gimpo]

Ah!
So I cannot use it from the external world...

[fourtytwo42]

Ah!
So I cannot use it from the external world...

I think you can, it seems to run at 25-30Khz, so if you SUPER MODULATE it via the ENABLE pin at a much lower frequency it has no option but to obey 

[gimpo]

Looking at that driver chip it just controls the current within a step, there is no variation according to the mode, for example when stationary, by the sounds of it in your app it could spend a fair amount of time stationary, in that case you could modulate the ENABLE input to reduce the power dissipation, for example 50% duty cycle would halve the power. I guess the frequency probably has to be low enough not to confuse its (A4983) intelligence so a few hundred hertz might be worth a shot but you need to avoid any mechanical resonance, of course it might end up comforting the drivers hand too 

This sounds crazy, but could work. In this way I could decrease a little the current when full torque is not necessary.
As I wrote above, I'm just searching for a little margin in motor temperature to take me on the safe side. I think that even a 20% lower current should lower the temperature more or less of the same amount.

Anyway, now both Pololu and Sparkfun have migrated their products to the A4988 chip. As I see from the datasheet, the mechanism used to control the current is the same (PWM).

[tszaboo]

What's even the point of cooling it down? There isn't anything heat sensitive in it. There isn't any electronics in it, just some wires and some metal and oil. Unless it is like 90 degrees hot, I dont see a reason why you want it cooled.
In fact, maybe it doesn't even get proper lubrication or the bushings in it don't work properly if it is not at design temperature.

[gimpo]

Ah!
So I cannot use it from the external world...

I think you can, it seems to run at 25-30Khz, so if you SUPER MODULATE it via the ENABLE pin at a much lower frequency it has no option but to obey 

I try it in the one or two days. No doubts. 
I just have to find where my wife hidden the key of my little lab. She say that in Christmas time I have to stay with the family, not playing with electronics.
Wife = 

[fourtytwo42]

Ah!
So I cannot use it from the external world...

I think you can, it seems to run at 25-30Khz, so if you SUPER MODULATE it via the ENABLE pin at a much lower frequency it has no option but to obey 

I try it in the one or two days. No doubts. 
I just have to find where my wife hidden the key of my little lab. She say that in Christmas time I have to stay with the family, not playing with electronics.
Wife = 

FANTASTIC, mine too, asking what I am typing away at instead of making her evening Cocoa, seasons greetings and good luck

[langwadt]

There is another possible solution and that is add intelligence to the driver, in some applications it is not required to develop the full torque 100% of the time, for example when stationary or not accelerating/decelerating, by controlling the current according to torque needs power dissipation is reduced.

That is a very clever observation! 
Actually, when I measured the max load required by my application, I noticed that the force necessary to keep the load stationary is less than the one necessary to move it. Why I forgot this detail???

But... I'm scraping my head now... I use the "Big Easy Driver" to drive my stepper. With that I have only two options:

1. turn on or off the motor with a digital command (i.e. energize or de.energize the windings)
2. manually adjust the current of the windings by tuning a little potentiometer on the board.

So there is no way to increase/decrease the current by using a microntroller (in my case an Arduino Pro Mini).... 
Any idea?

use a gpio (and resistor) connected to Vref to pull the reference voltage down a bit, reducing the current

[gimpo]

What's even the point of cooling it down? There isn't anything heat sensitive in it. There isn't any electronics in it, just some wires and some metal and oil. Unless it is like 90 degrees hot, I dont see a reason why you want it cooled.
In fact, maybe it doesn't even get proper lubrication or the bushings in it don't work properly if it is not at design temperature.

I would agree with you. Furthermore, 99,9% of commercial stepper have a Class-B insulation. If I remember correctly, this means an heat resistance up to 110 °C.
Nevertheless, I wrote at two manufacturers and both have answered with the same karma: "max environment temperature MUST be max 50 °C". So, if you close your stepper in a box, that must be the max temperature inside your box.

In a hot summer day of August I think that you're going to crash that limit very easily. So any temperature grade saved is like gold for my outdoor application.
(I also plan to add some opening in my enclosing box somehow, to guarantee a minimal ventilation added to an external heatsink.)

[gimpo]

FANTASTIC, mine too, asking what I am typing away at instead of making her evening Cocoa, seasons greetings and good luck