Beware of FerroFluid!

[rg12]

A friend with a QS205 motor with ferrofluid in it just called that his ASI controller (highest end controller on the freaking planet) shut power to the motor saying that there is a short between the phase and the body.
Opened the motor and found out that one of the phases that is covered by a white heat resistant fabric has soaked up some ferrofluid and started conducting between the phase and the body that it was leaning against.
A dumber controller would have just let full power blast through a shorted area and create mayhem out of copper.

 

[pullin-gs]

....

 

[spinningmagnets]

Some people have made up their own recipe of "ferro fluid". I am very interested in where this FF was acquired from?

If this is true FF, then this is useful information. If this is a home-brew FF, that is also very important to verify...

 

[amberwolf]

ASI controller (highest end controller on the freaking planet)

I don't know that that is true, though it is fairly advanced.

Opened the motor and found out that one of the phases that is covered by a white heat resistant fabric has soaked up some ferrofluid and started conducting between the phase and the body that it was leaning against.

The ferrofluid wouldn't be able to cause a short unless the insulation was already damaged (probably during the winding process in manufacturing).

The insulation on windings is rather difficult to remove; nothing in ferrofluid shoudl be able to remove it. Ferrofluid is used (was designed for, AFAICR) inside speakers between the magnet coils and the magnet, so it would be very bad if it were capable of doing that.

So the ferrofluid actually helped find a problem, not cause it.

 

[cheeko]

Iv never thought of using it, it will keep little bits of metal in it it which can't escape the fluid. There must be shelf live to it.

 

[rg12]

ASI controller (highest end controller on the freaking planet)

I don't know that that is true, though it is fairly advanced.

Opened the motor and found out that one of the phases that is covered by a white heat resistant fabric has soaked up some ferrofluid and started conducting between the phase and the body that it was leaning against.

The ferrofluid wouldn't be able to cause a short unless the insulation was already damaged (probably during the winding process in manufacturing).

The insulation on windings is rather difficult to remove; nothing in ferrofluid shoudl be able to remove it. Ferrofluid is used (was designed for, AFAICR) inside speakers between the magnet coils and the magnet, so it would be very bad if it were capable of doing that.

So the ferrofluid actually helped find a problem, not cause it.

I would be happy to hear if there is a better controller than ASI on this planet although I highly doubt it (have much experience with it).

About the issue, when phases are twisted together and covered then they are soldered together, so solder conducts pretty well to create a short between the body with the ferrofluid soaked in the heat resistant fabric insulation.

About where the ferrofluid is from, it's the "original" statoraid which I don't believe is any different than the one you can buy in pounds from alibaba as the manufacturing process of ff is super complex and I highly doubt that statoraid is more than just a brand sticker and not a high tech chemicals lab.

 

[danielrlee]

ASI controller (highest end controller on the freaking planet)

I don't know that that is true, though it is fairly advanced.

Opened the motor and found out that one of the phases that is covered by a white heat resistant fabric has soaked up some ferrofluid and started conducting between the phase and the body that it was leaning against.

The ferrofluid wouldn't be able to cause a short unless the insulation was already damaged (probably during the winding process in manufacturing).

The insulation on windings is rather difficult to remove; nothing in ferrofluid shoudl be able to remove it. Ferrofluid is used (was designed for, AFAICR) inside speakers between the magnet coils and the magnet, so it would be very bad if it were capable of doing that.

So the ferrofluid actually helped find a problem, not cause it.

I would be happy to hear if there is a better controller than ASI on this planet although I highly doubt it (have much experience with it).

About the issue, when phases are twisted together and covered then they are soldered together, so solder conducts pretty well to create a short between the body with the ferrofluid soaked in the heat resistant fabric insulation.

About where the ferrofluid is from, it's the "original" statoraid which I don't believe is any different than the one you can buy in pounds from alibaba as the manufacturing process of ff is super complex and I highly doubt that statoraid is more than just a brand sticker and not a high tech chemicals lab.

'Statoraid' is a very specific grade of ferrofluid, FerroTec APG 1110:
https://ferrofluid.ferrotec.com/products/ferrofluid-audio/apg-1100-series/apg-1110/

Are you sure this is what was used? Your statement suggests that you believe it is interchangeable with any old low-grade formulation.

 

[rg12]

I just confirmed that with the guy, so yeah he bought the "original" statoraid from their website.
Though it doesn't matter, any ferrofluid which is a liquid can apparently get soaked into fabric doesn't matter what quality or characteristics it has.

 

[fechter]

So it would seem that the ferrofluid is conductive. This could be easily tested. The oil base should be a good insulator but the iron oxide particles may be conductive.

The ASI may be very sensitive to this conductivity.

If "just enough" ferrofluid is added to the motor, it should all stay in the gap between the rotor and stator. My guess is the conductivity would not be enough to generate heat or damage anything. I could imagine it causing issue with hall sensors if enough of it got on the signal wires and bridged to something else.

 

[rg12]

So it would seem that the ferrofluid is conductive. This could be easily tested. The oil base should be a good insulator but the iron oxide particles may be conductive.

The ASI may be very sensitive to this conductivity.

If "just enough" ferrofluid is added to the motor, it should all stay in the gap between the rotor and stator. My guess is the conductivity would not be enough to generate heat or damage anything. I could imagine it causing issue with hall sensors if enough of it got on the signal wires and bridged to something else.

That's what I thought too, the guy called me that the motor is dead, then I told him to check continuation between the motor axle and one of the phase wires and spin it by hand and it didn't beep.
Also with a regular chinese Green Time controller it worked no problem but the ASI controller didn't let the motor run and thought it's a short.

 

[metri]

I've had success with Statoraid and my QS205 motor. I run a KLS controller and in well over a year, haven't had any issues. It keeps the temp lower on my motor than without it. I have some left over, I can measure the conductivity, though it shouldn't be getting away from the magnets. I used to use oil cooling in my previous motor and that was just messy, though effective. It's hard to generalize about FF from a few anecdotal accounts. I do know GRIN did a lot of testing with many people before putting it out there. The tests results were all published and done scientifically. I have no association with Grin, but thought I'd add my experience as it's with the same motor and I ride daily.

This isn't to say FF isn't conductive and didn't cause an issue with your friends motor. That I don't know. It's simply curious how a magnetic fluid got away from the magnets. My understanding, is that the particles in FF are coated in a surficant that prevents clumping and particle settling. Another interesting statement is how the phase wire was leaning on the body. The body might have some cast ridges in it, and not be completely smooth. Regardless, the phase wires should be well away from the case. If they were touching, there would be rubbing, which could itself cause an issue. Maybe the body you mean is the cast part of the stator. If multiple phase wires were conducting to the stator, that would be a problem.

Good luck with the repair, I'd suggest giving statoraid another chance.

 

[markz]

A few things about Ferro Fluid, Alibaba is rife with counterfeit, home brew, scammers you name it!
Its the Chinese way of life! The Chinese have no regard to copy right laws, they openly counterfeit everything and authorities hardly ever do anything unless there is pressure.

There might be another angle to the story, and I wonder if the amount of Ferro Fluid you add to a motor is a factor.

 

[liveforphysics]

Has anyone tested if it can absorb enough water over time to gain electrolyte-esque behavior? Maybe humidity can make the micro particles clump into macro particles that aren't insulated from eachother?

The base oils are the same oil bases used by Nissan and GM and Tesla inside motors for cooling and lubrication purposes, and exposed to electricity.

My hunch would be it's chaffing related and the fluid wasn't a direct factor, but if someone has some fluid to test, might as well blend in water or salty water and let it sit in a warm place for weeks, then absorb off the excess water and test the fluid for changes in dielectric strength. It should change some amount as it absorbs water, whether that's meaningful or not is something easy enough to test.

 

[metri]

I tested the fluid on its own today and it isn't conductive. I also looked at the inside of a side cover of a QS205 and it has lots of ridges in it. This sounds to me a lot less like a problem with ferro fluid and more a problem with motor wiring. I even soaked some up in a paper towel and that was still not conductive. I don't think it likely that water would mix in with the ferror fluid (oil?), and as I mentioned, the particles are coated in a surficant to prevent clumping. The sample I tested is well over a year old, was still uniform and magnetic.

I suspect the insulation was stained by ferro fluid but that it didn't itself contribute to the short. The phase wires touching the case and rubbing would be a far more likely candidate. Without pictures, video or other documentation, I would write this one off to wrong diagnosis. This is a second hand story about a failure with no documentation. If statoraid really had a design flaw and caused shorts, don't you think hundreds of people would have had the same or similar issues?

I will add the caveat to my reply that I'm no chemist, didn't see the failed motor and only have my ferro fluid to test. I only have my personal experience with Statoraid to draw from. I could be wrong and present my opinion in case it is useful.