Definitive Tests on the Heating and Cooling of Hub Motors

[macribs]

Serious increase in motor robustness with just a few drops of substance.

Just like most of the famous athletes does with their magic needles

 

[Offroader]

I think what someone needs to do is mount a wireless thermistor to the outside of the motor case to see how hot it is getting while moving.

I know that my cromotor case gets super hot to the touch if I stop driving, but as soon as I start moving even a small amount at low speeds the hub motor is shockingly cool to the touch.

You can easily test this by letting the motor get really hot to the touch by letting it sit, then drive for just 10 or 15 seconds and touch it again and you will be shocked just how quickly it cools off.

This tells me that adding fins will do very little for cooling while driving, but possibly a bigger impact when the motor is sitting. But how much of an impact will it have while sitting with little airflow with fins should be tested.

 

[markz]

Serious increase in motor robustness with just a few drops of substance.

Just like most of the famous athletes does with their magic needles

What you talking about, athletes arent juiced, Right Lance Armstrong!
Remember "Oral Use Only"

 

[speedmd]

adding fins will do very little for cooling while driving, but possibly a bigger impact when the motor is sitting. But how much of an impact will it have while sitting with little airflow with fins should be tested.

Agree. They would however take much heat away even if stopped with the vertical columns of convective air quickly forming and rushing up and around the hot motor through them. May be significant depending on the fin sizing qty and shape. May be just enough to stop some melt downs.

 

[MrDude_1]

I think what someone needs to do is mount a wireless thermistor to the outside of the motor case to see how hot it is getting while moving.

I know that my cromotor case gets super hot to the touch if I stop driving, but as soon as I start moving even a small amount at low speeds the hub motor is shockingly cool to the touch.

You can easily test this by letting the motor get really hot to the touch by letting it sit, then drive for just 10 or 15 seconds and touch it again and you will be shocked just how quickly it cools off.

This tells me that adding fins will do very little for cooling while driving, but possibly a bigger impact when the motor is sitting. But how much of an impact will it have while sitting with little airflow with fins should be tested.

and IR temp sensor makes more sense than rotating the sensor with the wheel... but yes, I agree.

Since 90% of my electric bike/scooter usage is to and from work, It would be easy for me to log everything for a few weeks (including air temp) then repeat with the fluid in it.

 

[amberwolf]

As a speculative note, for those that ride in the rain a lot but still get hot motors, finned outer surfaces of the motor (sides/between flanges) would probably increase heat dissipation, by what percentage I don't know how to calculate--could it be significant?

Not that I would worry about that here in Phoenix...even our "rainy season" we're in now means we get some sprinkles and occasional short downpours, even hail, every few days. :lol:

I'd have to provide my own "rain" via some sort of external misting system to do anything significant in the way of cooling.

Or an external fan mounted on the frame/fork that pulls air (via duct?) over the (finned?) surfaces, preferably controlled by a temperature sensor in the windings, with a manual switch for always-off or always-on and/or speed control.

 

[justin_le]

Back on the topic of test results, I'm finally working on the thing that has me most excited, which is testing out the ferrofluid effects on one of the prototype Grin motors. For those who don't remember, this one has a 2.5mm gap space between all the magnets, and so the behavior of the FF could be quite a bit different than when the magnets are butted up against each other.

https://endless-sphere.com/forums/viewtopic.php?p=1106731#p1106731

I finished all the tunnel tests yesterday with no FF, and am now running it with 1mL incremental additions.
View attachment 1
In this case, rather than doing it just at 200rpm, I'm testing the stator->core conductivities at both 200 and 400 rpm in case the higher motor speed causes centripetal forces push the FF away from magnets and air gap and flat against the back iron instead. With the Crysatlyte H motor, remember that at 200rpm there was no leakage at all from the side cover, but when I increased this to the 400-500rpm part of the testing then I had fluid escape from the inadequate seal on one of the side plates:
https://endless-sphere.com/forums/viewtopic.php?p=1113357#p1113357

As well, we've just finished potting the MXUS stator which had been modified with a plurality of thermistors separately located on the copper windings and in the stator backing.

This is a silver potting compound because it has metallic aluminum filler as the thermal conductive element. Recall from the earlier tests on this hub that we had about a 6.5 degree temperature difference between the copper and the steel/aluminum when using the FF.
https://endless-sphere.com/forums/viewtopic.php?p=1112018#p1112018
Now we'll be able to directly assess how well the potted core keeps the copper and steel temperatures uniform. Although the steady state improvements might not be too substantial, 5 degrees or whatever, the transient benefits at really high power inputs could be more significant, since then the copper heat generation can be more directly and immediately absorbed by all the steel.

If all goes well the Grin motor results will be done by end of today, and the potted core experiments will take place over the weekend.

 

[spinningmagnets]

If anyone new to ebikes is reading this (admittedly technical) thread...I am again amazed and impressed by Justin and his obsessive drive to follow where-ever the evidence leads him on the quest to improve the publicly-available knowledge-base to bring electric bikes to the masses in the coming paradigm-shift...

Justin tested and published the tech data to definitively establish what was needed for torque-arms
https://endless-sphere.com/forums/viewtopic.php?f=2&t=14195

The Cycle-Analyst ebike computer was selling just fine, but...he decided to add the temp sensor "amps roll-back" feature in the V3

He develops and "makes available to everyone for free" a spoke length calculator that is the shining example that nobody else can compare to...(http://www.ebikes.ca/tools/spoke-calc.html)

He develops and "makes available to everyone for free" a motor simulator that is the most accurate...even for motors that his business doesn't even sell (http://www.ebikes.ca/tools/simulator.html)...and then...

He starts this thread, builds a test chamber (like the Wright brothers)...and publishes the data in real time, for free...

Justin...kudos bro, you are the man.

 

[fechter]

Can you see anything when the stator is in place? Seems like the FF would be attracted to the stator iron more than the gap between magnets. It will tend to get flung back out at speed though. Filling the gap between magnets would help, but be a lot of work. I guess just fill it with FF.

Now we just need high-speed photography of the gap while the motor is running...

Just kidding. How it looks would be interesting but not likely to change how you do anything.

I did a little more FF research and the ester based oil should be better at elevated temperatures. It's like the oil they use in air conditioning compressors.

I was also trying to get some formulas for heat dissipation vs. surface area, but this does not look very straightforward. A lot has to do with fin geometry and air speed. Obviously more surface area is better but it's not a linear relationship.
Most references also mention that bare aluminum is quite poor at radiating due to low emissivity. Anodizing or other coatings help a lot. With zero air flow, radiation may be as much as 25% of the total heat dissipation.

 

[spinningmagnets]

Ester is the base material for aircraft hydraulic fluid...low smoke...low flammability...thin fluidity.

 

[Nathan]

What you'll find is that the addition of Statorade won't have much of an effect at all on the wh/km efficiency unless you're in situations where the motor core was getting up in the 100-150oC regions, and then it can start to be a player. For instance here is a trip with 3 big hills (~13% grade) and a fairly with stock H3540 Crysatlyte motor. Core gets to 180oC by the end of the trip, motor is running at 67.5% efficiency at the cursor location, and the winding resistance is at 0.24 ohms, and the journey burned through 98.6 wh/km (would be way better if the "regen enabled" was checked, but motor would also totally overheat)
And the exact same scenario with the only difference being ferrofluid in the core. Now we end the trip at 115oC, with motor running 71.4% efficiency, 0.20 ohms phase resistance, and using 93 wh/km for the run, compared to 98.6 wh/km previously.

So in the situation of high loads where we see the same motor have a ~115c - 180c= 65 c winding temp difference to the ferro fluid we can expect a 71.4% - 67.5% i.e 4% gain in efficiency which is pretty good !

I wounder would this winding cooling effect be more or less pronounced if the winding resistance was higher or lower on motor ? i.e what would happen in the case of high resistance 60 ohm windings or low resistance 4 ohms ? would the temperature resistance change due to ferro fluid be more less pronounced ?

 

[auraslip]

Hhere is my contention with this idea that I haven't seen anyone address.

Is it abrasive? Will it rub the magnets or stator down? Because if anything magnetic gets in the FF, it's staying in there and that would be bad news.

Does it break down over time into something abrasive? What does this stuff look like after 10k hard miles?

 

[markz]

Hhere is my contention with this idea that I haven't seen anyone address.

Is it abrasive? Will it rub the magnets or stator down? Because if anything magnetic gets in the FF, it's staying in there and that would be bad news.

Does it break down over time into something abrasive? What does this stuff look like after 10k hard miles?

Rust as well.

 

[macribs]

Hhere is my contention with this idea that I haven't seen anyone address.

Is it abrasive? Will it rub the magnets or stator down? Because if anything magnetic gets in the FF, it's staying in there and that would be bad news.

Does it break down over time into something abrasive? What does this stuff look like after 10k hard miles?

No as it seems now from testing done by Justin Ferro fluid is not abrasive. Nano particles will stay suspended in the fluid and will not be able to "polish" the surface.

Some members has already done years of riding with Ferrofluid without problems. If you look at the sale thread for FF syringes Justin are looking for people who would like to test ferrofluid so that we the community can gather enough data to make valid claims about life expectancy, how FF works over time and discover all potential down sides from using FF in hubmotors.

If you feel the risk is too high, steer clear. And go on with your life. If you on the other hand is curious about how Ferrofluid might impact your motor, e-biking experience and everyday life order that syringe and inject into motor and start taking notes. Absolutely worst case scenario you would kill your hub due to FerroFluid. If you can live with that give it a go. If not drill your hubs covers, fill it with ATF, or do absolutely nothing to improve cooling and come close to de-magnetization heat point just by riding - as you see whatever choice you make to cool down/not cool down your hub might impact motor lifespan.

Vented side cover might cause corrosion, ATF might frock up adhesive and will most likely cause oil dripping whatever you do and doing nothing at all might also shorten the motors lifespan because you will be more likely to over heat your motor on one of your rides.

If you see ferrofluid in this context I would say of all known ways of cooling a hub motor, Ferrofluid is probably the least likely method of cooling to shorten motor lifespan.

Rust as well.

Regarding rust/corrosion it seems vented side covers will be more likely to cause corrosion then ferro fluid inside hub. The oil coating of the motors internal should prevent corrosion? Keep in mind that moisture from the air can seep into the motor even if you do nothing to modify your motor. Water can travel via cables or get sucked into motor and can start to corrode even if you never have opened your motor.

Best bet to avoid corrosion would be to spray paint the internals with inti corrosion, look at what Doctorbass have done. While your at it, give it a coat of flatt black to aid the cooling by radiation. Inject your hub with FF and seal and close the motor. You should be able to inject and forget and ride without any worry for a long time. And by the time your motor is "worn out" there are likely newer, more efficient and better motors on the market anyway

 

[MrDude_1]

Best bet to avoid corrosion would be to spray paint the internals with inti corrosion, look at what Doctorbass have done. While your at it, give it a coat of flatt black to aid the cooling by radiation. Inject your hub with FF and seal and close the motor. You should be able to inject and forget and ride without any worry for a long time. And by the time your motor is "worn out" there are likely newer, more efficient and better motors on the market anyway

you could also epoxy pot the whole thing like he did above.. that thing is never going to rust. lol.

 

[auraslip]

There is nothing wrong with skepticism. Lets talk about my concerns rather than side tracking the discussion.

Regarding rust/corrosion it seems vented side covers will be more likely to cause corrosion then ferro fluid inside hub. The oil coating of the motors internal should prevent corrosion? Keep in mind that moisture from the air can seep into the motor even if you do nothing to modify your motor. Water can travel via cables or get sucked into motor and can start to corrode even if you never have opened your motor.

IIRC Justin has been recommending to his customers that have corrosion problem to drill the side covers to let the moisture out when it heats. Any moisture in a hot motor will be gone after a ride. You have a sealed motor, then moisture will be sucked in when it cools.

 

[fechter]

I'm not too worried about abrasion, but certainly something to consider. The FF particles are around 10um in size and always coated with oil. The gap between the magnets and stator is generally well over 1mm, so no way the particles could bridge the gap. Over long periods of operation, I could imagine sort of a polishing effect on the surfaces. If the plating on the magnets wore through, it could allow them to corrode. If the surface of the stator iron was polished bare, I don't think it would hurt anything. I suspect the way the particles are suspended in the oil will prevent them from pushing with enough force against the surfaces to create any wear. There will tend to be a boundary layer that doesn't really move so particles in contact with the surfaces have nearly zero velocity.

Time will tell. I want to see the 20,000 km pictures of the motor insides.

 

[macribs]

There is nothing wrong with skepticism. Lets talk about my concerns rather than side tracking the discussion.

Regarding rust/corrosion it seems vented side covers will be more likely to cause corrosion then ferro fluid inside hub. The oil coating of the motors internal should prevent corrosion? Keep in mind that moisture from the air can seep into the motor even if you do nothing to modify your motor. Water can travel via cables or get sucked into motor and can start to corrode even if you never have opened your motor.

IIRC Justin has been recommending to his customers that have corrosion problem to drill the side covers to let the moisture out when it heats. Any moisture in a hot motor will be gone after a ride. You have a sealed motor, then moisture will be sucked in when it cools.

There are skepticism then there are skepticism By this I mean and what I was trying to get across earlier, as of today we do not have enough raw data to conclude how ferro fluid will affect a hub motor, longterm. Or even different hub motors. We will not know before real world testing is done by several members here. Because we don't know each component of a hub motor, and that makes it hard or even impossible to know how things will interact together over time. Could it be that motors from one manufacturer works great with Ferro fluid but others might see less success? Possible, we don't know - yet. And that is why ferro fluid now is part of a larger scale real world community experiment - to test ferro fluid inside various hub motors. With different usage, power and efficiencies.

And because large scale testing is not completed yet we can't say for sure. That means if you fill your hub with FF you are becoming part of an experiment. That experiment could improve your e-bike life, or it could cause problems or even premature wear on your motor. Premature wear is not likely I think, and from Justin's testing we have not seen problems yet. Testing so far shows us FF is easiest, and cheapest way of cooling hubs. Indications by all testing are good that ff will just work. For various riding styles, various climbs, and various setups. For most of us.

Look a few pages back in this thread and you will see one member has been using FF for a while. Maybe he can tell you more about what motor and conditions he has been using FF?

About venting/not venting, for me personally vented side covers is not an option because we put salt on roads 4-6 months of the year to prevent icy conditions. For us vented covers is a bad thing, as salt water would cause corrosion. And that salty slush will penetrate anything possible. So yes you are right, for most people vented covers will actually help to avoid corrosion.

 

[liveforphysics]

Can't speak for anything long term, but can tell you my last ride was harder than Ive ever pushed this motor and its not smelling foul afterwards like it used to with only half the amount of average power. It seems almost impossible 4.5cc of any material could do this, yet it works.

 

[MrDude_1]

Can't speak for anything long term, but can tell you my last ride was harder than Ive ever pushed this motor and its not smelling foul afterwards like it used to with only half the amount of average power. It seems almost impossible 4.5cc of any material could do this, yet it works.

well, to be fair, the 4.5cc of material is not doing the cooling... the sides and air are. Its just the last piece of "thermal wire" to move it to the covers.

Then again. I didnt look at the username before I started writing this reply.. so not only am I telling you something you already know, but you're probably laughing at me about it. lol
While I have your attention, can I ride the deathbike?

 

[speedmd]

my last ride was harder than Ive ever pushed and not smelling foul afterwards.... It seems almost impossible 4.5cc of any material could do this

"Armstrong" brand "Statoraid". :lol:

 

[Offroader]

I don't think abrasion is anything to worry about. When my cromotor magnets became unglued I heard scratching and rubbing inside the motor and motor was hard to turn. I drove like this for a while also. The magnets must have been pulled off the motor case and into the stator. When I opened the motor there was lots of dust and the blue paint on the stator was worn off completely and the magnets protective coating on the top was mostly rubbed off. There was lots of abrasion but I don't see any noticeable difference in motor performance compared to my other cromotor once fixed.

The cromotor rates the KV RPM of the motor and it is actually around the same as my other cromotor if that is any kind of valid test.

 

[justin_le]

Ester is the base material for aircraft hydraulic fluid...low smoke...low flammability...thin fluidity.

It also smells a bit funny, wheras the synthetic oil base has no odor at all. But otherwise in all performance and behavior tests I can't really tell the difference, though I should clarify most of my recent experiments were with the synthetic base since that was the bottle the I had had opened and received first.

 

[MrDude_1]

Ester is the base material for aircraft hydraulic fluid...low smoke...low flammability...thin fluidity.

It also smells a bit funny, wheras the synthetic oil base has no odor at all. But otherwise in all performance and behavior tests I can't really tell the difference, though I should clarify most of my recent experiments were with the synthetic base since that was the bottle the I had had opened and received first.

Working with engines, I notice a diff between ester base and synthetic varnishing... but this is at at higher temperatures... something these hub motors will never see.
Did you ever do any oven testing?

 

[justin_le]

I don't think abrasion is anything to worry about.

Exactly. Nevermind whether particles <10 nanometers in size can really be construed as abrasive (that's like 100 times smaller than the wavelength of light), they are also suspended in oil surrounded by surfactant so would wouldn't be touching the material surface. Plus the fact that the magnetite fill in this material (according to MSDS) is in the single digit percentages, so even if you were to boil of all the liquid from your 5mL injection you'd be left with just a few hundred milligrams of solid dust residue. By comparison I've taken apart old hub rusted hub motors that had literally tablespoons of rush powder, paint debris, etc. to clean out, and the motors survive that just fine.

The question about material compatibility with magnet adhesives is no different than with other liquid fill attempts. Anything bonded with epoxy I wouldn't worry about at all. But, in a worst case where magnets do come loose and slip, it's really not that difficult at all to slide the magnets out of the motor shell, scrub things nice and clean, and then glue them back with an appropriate adhesive.

What does this stuff look like after 10k hard miles?

That is an great question which only 10,000 miles of testing will tell us, which is why I'm hoping that people will experiment on a broader scale and use the stuff so we can all find out, I'll be doing my 2 bits for sure but with most things you don't really learn all the ramifications until there is a large user base. There's a good chance that over a certain amount of time there will be seepage or lossage and an occasional fluid top-op could be required, we will see. Adventuresome types will try to figure out answers, and those who aren't and just want to wait and see can simply wait and see.