Motor Cooling Ideas

[digimeat]

I'm working on building a racing go-kart for a competition and am designing a cooling solution. Currently I am planning to have a pump push Dry-Ice cooled 99% isopropyl alcohol for coolant. I am now considering how to most effectively transfer heat out of my DC motor: E30-400. Some of my current thoughts include submerging the entire motor in 99% Isopropyl alcohol as it should act as an insulator and penetrate the casing. Another idea is to pump the fluid through a copper coil surrounding the motor. With the second idea I feel its perfectly safe to use dielectric grease on the coils to transfer heat to the case, but the case is still air-gapped from the windings. Because of this I was also considering adding dielectric grease to the windings directly to bridge the case and the windings. This would bridge the coils to the case and the case to the windings.

Image of copper coil design:

Any suggestions or experience is much appreciated, thanks.

 

[amberwolf]

THere's lots of existing discussion on cooling, heat, etc, in various types of motors.

Some possible searches; not all results will be relevant but you can guess by the title if it might be. There are others that don't show in these searches you can find with other search variations.

https://endless-sphere.com/forums/search.php?keywords=cool*&terms=all&author=&sc=1&sf=titleonly&sk=t&sd=d&sr=topics&st=0&ch=300&t=0&submit=Search

https://endless-sphere.com/forums/search.php?keywords=heat*&terms=all&author=&sc=1&sf=titleonly&sk=t&sd=d&sr=topics&st=0&ch=300&t=0&submit=Search

 

[fechter]

Is that a brushed motor?

The most frequent failure on a brushed motor is the commutator. Forced air is about the only practical way to cool the commutator and brushes. Any kind of oil or grease on the comm will fry it.

Flammable coolant is a bad idea.

You'll go through dry ice really fast if it is efficiently coupled to the motor.

 

[Punx0r]

Water is cheap, safe and boring but is an excellent coolant.

As you've suggested, super cooling of the motor shell is of little use if there is a high thermal resistance from the motor internals (the bits you actually want to cool) and the shell. Oil filling and Ferro-fluid have successfully been used on brushless motors to effectively thermally couple the windings to the shell, but as fetcher says, brushed motors are a different beast.

 

[digimeat]

Thanks for the input! I realize that Isopropyl alcohol is not the ideal coolant and I had actually planned on purchasing Industrial Coolant, however our sponsoring company only gave us a day to create a BOM. Even so, the flash point for this kind of alcohol is 11.7*C which the dry ice should be able to easily maintain, and an auto-ignition temp at 400*C which we won't get even close to. I also wanted to get a brush-less motor, which I think would be easier to cool, but again the very limited time constraint made that very difficult. I am not too concerned about going through dry ice quickly, it is only about $1 per pound where I live and my cooling techniques would be a lot more efficient compared to what the other competitors have done in the past. Traditionally, other teams would simply throw chunks of dry ice onto their motors during pit stops in the race, which I can't image accomplishes much. Forced air is nice in that it is non-conductive and poses little rotational resistance but is a poor conductor of heat. Given that alcohol is also non-conductive would filing the casing with fluid harm anything other than imposing some resistance when accelerating? I worry about using water inside the casing as it can quickly become conductive when exposed to free ions and can quickly cause rust to accumulate.

 

[Ianhill]

The motor you have choose is hard to cool no doubt an inrunner bldc would be the easiest choice with a direct thermal path to the can, The dc motor you choose has very little contact with the can so the heat of the armature travels through the bearing the air gap helps with windage for cooling but the brushes are arcing away introducing more heat at the commutator and themsels are bonded with poor thermal paths so i can almost 200% guarantee that when you overdrive that motor thr commutator is the part that will fail.

 

[Hwy89]

Alcohol + brushed commutator = fire

 

[fechter]

Alcohol + brushed commutator = fire

Right.

With a brushed motor, since the windings are spinning, you can't get a good thermal path to the outside. Forced air is the only thing that really works and I have used it with several motors with good results.

If you get a brushless motor, then cooling becomes a whole lot easier since the windings are stationary.

 

[amberwolf]

Even so, the flash point for this kind of alcohol is 11.7*C which the dry ice should be able to easily maintain, and an auto-ignition temp at 400*C which we won't get even close to.

Brush arcs = plasma. Plasma temperatures are a lot higher than you are expecting. Brush arcs will be continuous the whole time it is in operation, and the higher the load on it, the higher the currents in those arcs, and the hotter the commutator and brushes will be as well. Even if the brushes and comm segments don't get that hot, the arcs themselves will be.

 

[flat tire]

Just mist the whole internals with water. I don't think you'll find a much better short-term cooling solution which is exactly what your dry ice cooled alcohol would be.