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Old 12-14-2012, 06:58 AM   #1
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Default Use of thermal paste with heatsink?

Has anyone tried using thermal paste between the motor and heatsink?

This type of paste was mentioned yesterday in my university on Thermodynamics class, to improve heat conduction between two objects or media. I soon serched it and found it's cheap and easily obtainable in any PC shop. The contact (at least mine) between the heatsink and motor is sloppy, which results in movement of the heatsink. This means that there is air between them, and air is a poor heat conductor which finally means that the heatsink it considerably cooler than the motor which is not what we want. Obviously the heatsink is not taking as much heat as it could (and should). Hay anyone tried this and found any noticeable difference in temperatures? I run in a class where with a heatsink and 2 fans motor temperature is still a major issue, so even a few degrees down is progress.
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Old 12-14-2012, 07:22 AM   #2
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I use some between the stator and the motor casing, and then some more between the casing and the heatsink.
It does make quite a difference to the temp, but remember, if your motor is on the edge already when you use the compound, you can't just up the timing etc to reach the temps you had before.

I use a cutdown version of the old brushed LRP heatsink, which is a very snug fit, but using the paste makes it better.

Make sure you are VERY carefull if you use graphite paste as this can conduct more easily than the silicone based stuff.

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Old 12-14-2012, 07:31 AM   #3
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Generally I'd say it is a good idea, but you have to be careful about the layerthickness of the thermal paste, as the thermal conductivity decreases heavily with increasing thickness(which might be the case here as the heatsink is sloppy as you said).
You might want to consider simply buying a heatsink with a tight fit as thermalpaste kinda always ends in a mess(at least for me lol).
What works best for me to cool my motor is a nice capable 5V 40x40mm fan mounted behind the motor and connected directly to my battery or receiver.
It's much lighter as well
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Old 12-14-2012, 08:29 AM   #4
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as with computer microchip uses, thermalpaste exists to fill the tiny pits and voids between two otherwise flat objects. it also provides an interfacing material "Thermal Interfacing material" for heat to transfer better between different metals ect.

never thought to use it between the stator and can, but its a good idea to use it whenever possible to help improve the efficiency of your heatsink. of course, very difficult to put a heatsink over the motor without completely displacing the thermal paste, but the point is to have a minimal layer left after its been spread anyway. to fill any valleys ect that you cant see.

an example of way too much paste is the tekin redline motors with the groved can. that would suffer from too much TIM, but probably still better than nothing. probably wouldnt even run a heatsink on the finned can motors.
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Old 12-14-2012, 08:49 AM   #5
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Two types Grease and Silicone. Grease dries up like Elmer's Glue. Cleaning it up maybe messy. Silicone, taken off with water. Used many times with heatsinks, Computers and microchips, power Transistors.
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Old 12-14-2012, 08:51 AM   #6
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I would recommend thermal pads instead of paste, as the paste makes a big mess everywhere. You can get them in various sizes and thicknesses, as well as different conductivity ratings. Generally, the more it costs, the better it conducts.
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Old 12-14-2012, 10:07 AM   #7
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Since you are in thermo class ask your professor if the colored anodizing hurts the thermal transfer much. Possibly the paste it's a messy move if the anodized motor can and heatsink can't conduct heat well on their own. Just a thought.
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Old 12-14-2012, 11:01 AM   #8
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Quote:
Originally Posted by SS LS1 View Post
Since you are in thermo class ask your professor if the colored anodizing hurts the thermal transfer much. Possibly the paste it's a messy move if the anodized motor can and heatsink can't conduct heat well on their own. Just a thought.
Actually, Aluminum oxide is more thermally conductive than just plain aluminum, so it will help
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Old 12-14-2012, 12:31 PM   #9
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One of the biggest mistakes I see at the track is people mounting their fan right next to their motor impeding air flow output. This drastically reduces the cfm output minimizing the effectiveness of a fan. It is much better to space the fan away from the motor 5/16" - 1/2" if at all possible and is often a design flaw of many fan mounted heatsink designs IMO. One of the reasons I do not use a heatsink.

Usually you can hear this phenomenon if you wire up your fan and listen as you move it closer and farther away from the motor can. The pitch of the sound will change when you start getting the fan too close to the motor. This pitch change is letting you know the minimum distance you need to achieve maximum airflow from your fan.
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Old 12-14-2012, 12:57 PM   #10
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Quote:
Originally Posted by SS LS1 View Post
One of the biggest mistakes I see at the track is people mounting their fan right next to their motor impeding air flow output. This drastically reduces the cfm output minimizing the effectiveness of a fan. It is much better to space the fan away from the motor 5/16" - 1/2" if at all possible and is often a design flaw of many fan mounted heatsink designs IMO. One of the reasons I do not use a heatsink.

Usually you can hear this phenomenon if you wire up your fan and listen as you move it closer and farther away from the motor can. The pitch of the sound will change when you start getting the fan too close to the motor. This pitch change is letting you know the minimum distance you need to achieve maximum airflow from your fan.
If you have to run a fan and a heat sink, your loading the motor too much in my opinion. I do agree with your statement about the fan placement, however.
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Old 12-14-2012, 02:13 PM   #11
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Now you have me thinking if a thin dab of tim between the motor
Mount would be beneficial.
Also. Use arctic silver ceramique. It stays in paste form long after application. Arctic silver 5 or similar hardnens. It does a better job of transfering heat but a crash will break it
Loose.
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Old 12-14-2012, 10:07 PM   #12
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Quote:
Originally Posted by The Captain View Post
If you have to run a fan and a heat sink, your loading the motor too much in my opinion. I do agree with your statement about the fan placement, however.
I agree, that'd why I don't see the need for a heatsink (or even own one) if you fan is placed properly.
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Old 12-15-2012, 04:03 AM   #13
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The main problem I see with a fan on it's own, is that it is only trying to cool one phase properly, the heatsink at least helps even out the cooling process.

The advantage of keeping the motor cooler than normal is better efficiency during a run.
LRP motors etc never get their fastest laps in the last third of a race as they get so hot.

It is a pain to clean off, but how often do you have to take it all apart.

When I do take the heatsink off, there is always a thin uneven layer across some of the heatsink and some of the motor, despite that fact that the LRP style heatsinks are so difficult to get on and off, so the paste is still filling in those tiny voids.
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Old 12-15-2012, 06:27 AM   #14
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Heat sink paste are a good thing to help with heat transfer.
If you have a poorly designed heat sink that leave a big gap to the motor, it will still help a lot as it is much much better than air.

You even have the gap filler pads that are very good. We use this on pcb's and thick film hybrids to transfer heat even from the substrate to the mechanic assembly.
Here we are using thicnesses up to 1 cm.

But of course. The smaller gap to fill, the better.

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Old 12-15-2012, 10:06 AM   #15
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Raw alum will conduct heat much faster than anodized alum. Anodizing is an insulator and protective finish for alum. Racers simply won't buy raw alum heat sinks.

The heat is generated from the windings which is transferred to the magnets and motor case. The best way to cool a motor, is to have a fan blow cool air into a "ventilated" case.

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