Thermal Dynamics, stepper motors

[joel0407]

So I've done some searching and found that my motors probably aren't getting too hot to worry about but before I reached that stage, I had some questions.

I thought they were getting to hot so I was looking at ways to cool them. Some of the things I considered were, just heat sinks, just fans or both.

I already know from turbo engine intercoolers, the big chunk of aluminium is not always there to dissipate heat all the time. It's dissipating heat all the time but it's also a mass to absorb heat at extreme times and then off load that heat in the low times. Now since the steppers tend to run at full current all the time, I figure a heat sink with mass isn't the best option but a heat sink with extra surface area might be. Then rather than have a huge finned heat sink, I could use a fan. Even PC Processor heat sinks aren't there so much as to cool but keep to add mass to keep the temp from fluctuating. Since there has to be mass, might as well put it in a finned design to create more surface area and assist with cooling. Some water cooled engines, the water cooling is just to spread the heat and prevent hot spots. With a stepper, it's like I have a constant known heat source that I need to cool. I don't need to add mass to even out the temp, Adding a heat sink to one side will probably do less for evening out the heat.

Then I had the question. Why don't I just direct the fan directly at the motor. Can a piece of aluminium stuck up against the motor pull more heat from the motor than a flow of cool air over the same place? That's pretty much where my question lies. Will something cool faster with lets say a 25 degree C flow of air or will it cool faster being in contact with a 25 degree C piece of aluminium? Let make it a little simple and say the aluminium will be not be allowed to heat up, it's water cooled to a huge radiator or something like that. Just go with contact versus cool air.

Happy Days.

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[joel0407]

So I've read that any material (including gas) cant heat up or cool down fast than another. All good. The rate of heating or cooling is dictated by the temp difference of each material. The greater the difference the faster the temp transfer. Conductivity of the matter effects the ability of the material to move the temp away from the connecting surfaces and thus keeping the temp difference greater.

Gases don't conduct temperature well at all however I'm interested to know if the air that is in contact with the material we are heating or cooling is kept moving, can we effectively move more heat away than that same material being in contact with a solid such as aluminium?

Interesting the conductivity of water vs aluminium here: Thermal Conductivity of common Materials and Gases.

Aluminium 205 vs Water 0.58.

Water is 1/400th as conductive of heat than water however a steady flow of room temperature water over a material will cool it much faster than simply putting a block of aluminium against it. So doe the same go for a steady flow of air, although less conductive than aluminium, will it cool better?

Happy Days

[ger21]

If they aren't running too hot, then there's no reason to cool them. If they are running too hot, then you are either running them at too high of voltage, or with too much current. Either is likely to damage the motors, whether you try to cool them or not.

[joel0407]

Nah. Not getting too hot mate. Just thought they were and started to wonder about a few things. That's why I've posted in "off topic"