Kodin said:
ID assume ATF would dilute the fluid.
Hello Kooldin,
Perhaps, but more likely the oil will simply leak out unless the motor is sealed, recall some of the ferrofluid leaking from a stock unsealed motor in Justin's insanely fascinating recent experiment, this is radically more likely to occur with plain oil.
Magnetism keeps the ferrofluid in place, it's a magnetic fluid. Ferrous means an alloy primarily made of or containing iron, ferrous alloys (You could say iron alloy and be saying basically the same thing) are often described this way to describe their magnetism. Put a magnet up to a piece of non ferrous alloy (aluminum alloys, for example) and observe that the magnet does nothing, then do the same with a ferrous alloy.
I still personally have a crushing amount of interest and reading to do on ferrofluids, whos interest was recently spiked by Justin. An important question, though this isn't a nail in the coffin sort of idea for certain, that I have is at what temperature does a ferrofluid begin to demagnetize. Much like the permanent magnets within all of our electric motors, certain temperatures begin to permanently demagnetize permanent magnets, something like 120c for many magnets if I recall correctly. Naturally, if the ferrofluid demagnetizes, it will move like an ordinary fluid.
https://www.youtube.com/watch?v=kL8R8SfuXp8
Kodin said:
The whole point of ferrofluid is the nanoparticles make the fluid stay by something similar to capillary action. Keeps the suspension fluid in one place.
Capillary action is actually a source of a fluid 'leaking' or moving to areas where it is unwanted in many applications involving electric bicycles and electronics in general. Think of putting just an edge of a vertical piece of paper towel into water and watching the water slowly 'move' up the paper towel. To illustrate what I am referring to, this capillary action is especially problematic involving stranded wires (like the kind we use for electric motors, stranded wire carries similar ampacity but becomes significantly more flexible), due to the massively increased surface area of stranded wires, the oil travels through the wires relatively quickly rapidly. Many have wondered how to inhibit this issue with capillary wires, one of the answers is a solid connector(think anderson power pole) that is not being submerged or it's opposing wires exposed to the oil. This capillary action is one of the reasons why oil inside of a motor is so problematic and why ferrofluid may stand a much greater chance of not escaping from the motor, magnetism, hopefully, will literally inhibit most of the capillary action while still enabling effective thermal transfer and maybe some degree of corrosion prevention.
https://www.youtube.com/watch?v=w_tc8tlEoBs
Learning is fun!
There are still some issues with the ferrofluid idea that I imagine, namely one that has been an issue for electric bicycle motors for some time. As the motor temperature increases and decreases the pressure inside the motor will continually increase and decrease with it. As this happens atmosphere and moisture will be continually drawn in and out of the motor, what ends up occurring is some moisture condenses or stays within the motor, perhaps some of it evaporates or leaks out, but evidently often not at a rate quickly enough in many scenarios. Justin has done an amazing job of illustrating this in the past talking about and illustrating how he has opened motors and cups of water spilled out, this problem is likely to become exasperated by any degree or attempt to seal. What is likely to happen is water will accumulate within the motor to a point which I imagine unwanted effects may occur. Some issues that are likely to happen is either the ferrofuid emulsifies with the water and you end up with still yet a ruined motor, the water trapped within the motor freezes (for us nutty cold weather folk) within the motor and seizes it at least temporarily, or maybe something as simple as the hall sensors either get shorted out or destroyed by the excess fluid and so on.
If you wish to understand this breathing or pressure idea a bit better get a typical thin walled 500ml plastic water bottle and tighten the cap on it well. Place the bottle under a hot water tap with the cap on tight for a minute or so, squeeze the warm bottle to feel how the walls of the bottle seem to be under some level of increased pressure. Then, while listening closely, open the lid of the bottle. After you listen, quickly close the bottle lid tightly once more and observe what happens to the walls of the water bottle. This is an issue with basically all electronic devices (and plenty of motors) and one of the reasons why potting electronics (like ebike controllers) may be an ideal way to treat them where mild to heavy degrees of exposure are likely to happen (like riding an electric bicycle outside on a very humid or even mildly rainy day). I could go on in insanely far too much detail, but an alternative to potting electronics that still enables relatively easy access to the boards components is conformal coating, many variables within this train of thought but it's great to have keywords for the interested reader handy with a search engine.
