Definitive Tests on the Heating and Cooling of Hub Motors

[jansevr]

The problem with running a no load test is that the power consumption is very low. 100-200w at most depending on the voltage. Even if you run the motor for extended periods of time to let the motor's heat saturate you still don't get a good idea of real world usage where power is 10-20x if not more than the no load test. I have some ferrofluid ready in a 35mm motor just need some free time to devise a controlled system of loading the motor. I'll try to shoot for 1000w first and 20-30 minute test. Two identical motors except one with ferro and one without. Hopefully I'll have some free time in the next week or two and be able to get good data that I can share here. Looking forward to seeing other people's results as well. And thanks again to Justin for all the great work and advancement in e bike technology

 

[Cowardlyduck]

I do have a stand and some clean cardboard so might try that to see if any oil leaks initially. Good idea Macribs.

Both motors have 2 sets of different types of temp probes, so I will definitely be able get some accurate results.

The no load testing has it's limit's as pointed out, but in my case I already have 2 sets of data on the performance of the fans under consistent load and conditions.
https://endless-sphere.com/forums/viewtopic.php?f=30&t=56965&start=25#p946731
https://endless-sphere.com/forums/viewtopic.php?f=30&t=56965&start=375#p1123565

I might revisit these hills and re-test under similar conditions to compare.

Cheers

 

[Offroader]

cowardlyduck, try to test also with the motor sealed, even if it is a temporary single run with just tape over the holes.

I honestly can't see how you can use the statoraide and have all those open holes at the same time.

 

[johnrobholmes]

The problem with running a no load test is that the power consumption is very low. 100-200w at most depending on the voltage. Even if you run the motor for extended periods of time to let the motor's heat saturate you still don't get a good idea of real world usage where power is 10-20x if not more than the no load test. I have some ferrofluid ready in a 35mm motor just need some free time to devise a controlled system of loading the motor. I'll try to shoot for 1000w first and 20-30 minute test. Two identical motors except one with ferro and one without. Hopefully I'll have some free time in the next week or two and be able to get good data that I can share here. Looking forward to seeing other people's results as well. And thanks again to Justin for all the great work and advancement in e bike technology

Using a FOC controller like Justin offers lets you dump an exact amount of waste heat into the motor with field weakening mode, and without a load. Get heat shedding similar to 1000watts input by adding about 10 amps waste.

 

[DanGT86]

cowardlyduck, try to test also with the motor sealed, even if it is a temporary single run with just tape over the holes.

I honestly can't see how you can use the statoraide and have all those open holes at the same time.

I thought the statoraide leaking out was just the extra and the magnets held the functional amount. I was under the impression that the "trick" so far has been finding just the right amount to use.

This may have been covered here already but is there any way to get this stuff out of the motor if you change your mind later? Sounds like a 1 way trip since it creeps in between the magnets so uniformly. I noticed Ebikes.ca offering a motor now with it added as a regular item so I guess they have enough confidence in it. That is very reassuring to see.

 

[johnrobholmes]

it wipes out easy with a paper towel, no big deal.

 

[jansevr]

Using a FOC controller like Justin offers lets you dump an exact amount of waste heat into the motor with field weakening mode, and without a load. Get heat shedding similar to 1000watts input by adding about 10 amps waste

Has Justin or anyone else done a test at 1000w? I might have missed it.

 

[MrDude_1]

This may have been covered here already but is there any way to get this stuff out of the motor if you change your mind later? Sounds like a 1 way trip since it creeps in between the magnets so uniformly.

Dont worry about missing it... after a couple months of talking about it, I asked about how to clean it out afterward.. apparently I was the only one to ask.
From the top of page 46 by my count:

I have a side question...
if you get FF on permanent magnets, how DO you get it off? will it dissolve in brake cleaner or acetone? what washes it off or breaks it down?

Oh that's a great question that I totally forgot to address. The stuff we've been using comes off super easily with an absorbent paper towel. I've now filled and cleansed out close to a dozen different motors with the Statorade during the course of the wind tunnel testing and cleaning has never posed any challenges. The capillary forces pulling the fluid into cloth fibers are much stronger than the magnetic forces holding it back. There's no need for any solvent dilution or anything like that unless you wanted to get it squeeky clean.

What's also nice is that unlike oil fill, there's no mess in disassembling the hub with the small amount of FF. You take it apart and 95% of the fluid is right on the magnet junctions. Wipe it off with a cloth/towel, then wipe the bit that's left on stator, and the hub is pretty clean again. Removing actual iron/magnetic particles from a motor is a real bitch, this is nothing like that.

 

[Cowardlyduck]

That was fast! My statorade arrived today...less than a week after ordering. I guess that's what $41 in shipping gets...and that was the cheapest option.

I didn't mention I would do it previously, but I am also trying some FF in my Recumbent's '1000W' Golden motor. It doesn't really need it for cooling as the hottest this motor ever gets (rarely, in the middle of summer only) is about 70C on the magnet ring which is about 90-100C in the stator based on measurements from my other motors. Being a commuter however, the recumbent is all about efficiency, so keeping the motor cooler should increase range a bit which would be nice.
The motor is vented only on one side like this:

The stator and magnet ring are also painted with electrical insulating varnish:

It will be interesting to see if the FF reacts with this varnish in any way.

I added the Ester based FF to it at the recommended 5ml and spun it up to 60kph off the ground without any coming out through the holes. So far so good.
I didn't bother sealing the side covers as I really can't be bothered pulling this motor apart again right now. It will be interesting to see if it does seep through the gap.

The addition of FF did however add a someone puzzling scraping sound and a small amount of drag to the motor. I think it's fine, but the motor definitely spins down from free-wheeling off the ground faster now than before, so I'm not sure how negligible the added drag from the FF really is in this case. Maybe it will 'break in' This motor has been used almost daily in vented form for over 4 months, so there might be a bit of accumulated dirt in there that's also contributing to the scraping sound.

I don't have any temp sensors mounted on this motor, but do have temp sensing/colour changing stickers on the magnet ring (which is how I know the outside of the hub gets to 60C). I imagine the outer ring will now get hotter faster, but hopefully not go much above 60C...time will tell.

Cheers

 

[Cowardlyduck]

After a month of daily riding with minimal air holes (4 x 1" holes on each side) I opened up the motor to take a look at the fluid and it doesn't look contaminated at all.



I think FF and air holes is a winning combination.

Sure, it will probably eventually get contaminated, the more and larger air holes you have the quicker this will happen. If it gets contaminated just clean it out and add more. I regularly pull 6kW on my 9C with it staying below 100C no problem.

I put FF in my fan cooled HS4080 last night.
Riding stop/go WOT round the backyard didn't feel any different, and the temp seemed to rise just as fast. Switching on the fans cooled things off nice and fast like before.
Time will tell if it's a problem running large/lots of vents with fans combined with FF.

Cheers

 

[Cowardlyduck]

Went for an off-road ride today with the HS4080. The ambient temp was around 32C with very hot sun beating down.
TBH I didn't notice a huge difference with the FF added, vs no FF. There is a discernible difference from straight venting without FF...but at a guess I would say it's only 5-10C cooling improvement within a 35-65C winding temp range for the slower, steep kind of off-road riding I do. Maybe that's because the speeds, and therefore air flow is slower?
I ran my fans a few times when temps approached 60C+ and the cool off period seemed approximately the same as prior to adding FF...maybe a touch quicker.

The one thing that's puzzling me though is the noise my motor seems to make as the FF heats up. I noticed the noise on my other (Golden motor) motor also, but not as loud, although it doesn't get as hot. Today I noticed that it gets louder as it heats up, so I went nuts on my bike around the back yard to heat the motor up to about 75C and took this video:
[youtube]ZSqksGeMpVU[/youtube]
Does anyone have any idea what is making the noise and why it gets louder as it gets hotter?

I should also mention that this motor is twice recovered from near death, on it's second axle, 3rd set of phase/hall/temp wires. Admittedly it's done some weird things a few times, like shorted phases for no apparent reason and a wobble that self corrected. It's been running fine for a little while now though, and the fact that the noise mentioned above also occurs in one of my other motor's tells me it's not anything to do with this motor's 'uniqueness'.

Cheers

 

[hillzofvalp]

Sounds like the seal by the bearing doing something weird... Maybe the interference fit gets worse when the metal expands..?

 

[Cowardlyduck]

Sounds like the seal by the bearing doing something weird... Maybe the interference fit gets worse when the metal expands..?

I guess that's possible since adding FF causes the heat transferred to the side-plates and therefore the bearings to be far greater. I'm using shielded bearings though not sealed, so it is unlikely to be that I think.

I can hear the sound coming from the magnet ring area on both my motors, so I'm pretty sure it's the Ferro Fluid causing it.

Cheers

 

[Hummina Shadeeba]

The shielded bearings would allow the ff in verse if they were fully sealed.

Maybe the internal clearance in the bearing isn't enough and you could get bearings that account for that with a higher "c"rating. since you only hit 70c that's not too much for a properly fitted bearing and maybe it's the expanding bearing housing and shaft. I've had bearings seize from heat in a shorted motor that probably wasn't too hot for a standard bearing (230f) but the shaft and bearing housing expansion caused it to be squeezed.

I've stumbled on a need for thermal epoxy as my stators spinning on its seat and need to be glued down. I think the dense aluminum seat expanded and became deformed as its been restricted by the less expanding steel. I heard a slight ticking when accelerating and braking and luckily realized before it was too late that the motor leads had been holding the stator from completely spinning and ripping the wires


Coincidentally there's a thick aluminum wall within 5mm of the stators windings and would make a great heat sink as well as a start to the further aluminum of the skate hanger.
I can't decide what would be best:
1.pot this whole stator and use a vacuum with a very thin resin to get all the air out
2.Pot it all using resin with thickening filler that will transfer heat better but trap bubbles that will be an insulator on a winding somewhere inside
3. pot 1/4 of the stator where it is close to the wall with best thermal conductor I can get that will stick


You can see there's not much airflow from the small holes



How are electronics (esc or charger) encased in a hard resin able to expand even when they're painted with a soft silicone...there's nowhere for the soft silicone to push to and it won't compress?

 

[jansevr]

The insulating varnish on the stator and magnets combined with the ferrofluid could be producing these effects. It might be possible that there is not enough space between the stator and magnets. 2 thin layers of varnish and the way the ferrofluid sits in the air gap could be making more friction than a motor that is not varnished. The heat in the motor might have something part in this as well if it effects the ferrofluid and creates less space/more drag

 

[Cowardlyduck]

Hummina Shadeeba, I think a lot of what your saying is only applicable to skate board hub motor's...not E-Bike hub motors as is the case for me and most others in this thread. I'm sure FF might have some applications for skateboard hub motor's, but this thread and all testing so far has been focused on E-Bike hub motor's, so not sure how much of the lessons learned would convert across.

The insulating varnish on the stator and magnets combined with the ferrofluid could be producing these effects. It might be possible that there is not enough space between the stator and magnets. 2 thin layers of varnish and the way the ferrofluid sits in the air gap could be making more friction than a motor that is not varnished. The heat in the motor might have something part in this as well if it effects the ferrofluid and creates less space/more drag

I was thinking something like this might be the case. I've got 2 layers of varnish on both the stator and magnet ring so it would add up.
How could I verify if this is the case though?

Any other thoughts?

Cheers

 

[jansevr]

If the motor was running before you added the ferrofluid it's most likely the problem. However considering people have run the ferrofluid in unvarnished motors without any troubles this seems like part of the issue as well. If this is the case that would make running ferrofluid in an air cooled motor difficult considering the motor can't be properly protected from water.

 

[Cowardlyduck]

If the motor was running before you added the ferrofluid it's most likely the problem. However considering people have run the ferrofluid in unvarnished motors without any troubles this seems like part of the issue as well. If this is the case that would make running ferrofluid in an air cooled motor difficult considering the motor can't be properly protected from water.

You could be onto something...I have painted all my motor's with varnish, and so far my only other motor with FF added also makes a similar sound.

The confirmation will be when I get my Leaf motor back up and running. It's also varnished to about the same level as my HS4080. The only difference will be I will add the synthetic based FF vs the Ester based stuff in the other motors.

Another thought that occurred to me was, could the Ferro Fluid be foaming up at all? I just wonder if the heat/friction combo could be causing some kind of foaming to occur?

Cheers

 

[macribs]

I wonder if different motors will have different sweet spot for the amount of FF needed?
Joostj got a QS v3 with 5 ml FF, and still reaches 130 C. Seems high with FF. Could it be that 5 ml is too little? Wider stator etc.
Even if the QS v3 is in a 19" wheel temp seems high.

I am about to fill FF too, and luckily I have not yet gotten the varnish. I'll think I will hold back for now on the varnish and try FF first.

 

[Cowardlyduck]

I wonder if different motors will have different sweet spot for the amount of FF needed?

Joostj got a QS v3 with FF, and still reaches 130 C. Seems high with FF. Could it be that 5 ml is too little? Wider stator etc.

I was thinking the same thing when I added the same 5ml to my 28mm wide Golden Motor as I did to my 40mm wide HS4080.

We need to keep in mind that the function of the FF is to thermally link the stator to the shell. So if the FF bunches up on the ends of the magnets where the magnetic field is, it should not matter how wide the stator is...just how many and how large the magnets are.

Maybe we should be adding an extra ml of FF for every extra 5mm of stator width over 30mm?
So a 35mm stator gets 6ml, a 40mm wide 7ml and a 45mm wide 8ml. I'm just guessing.

Cheers

 

[macribs]

Wonder if Justin came to any conclusions about the amount of FF in various width motors? When he concluded 5 ml what motor was he testing then?

 

[Cowardlyduck]

Wonder if Justin came to any conclusions about the amount of FF in various width motors? When he concluded 5 ml what motor was he testing then?

If you really want to know you can trawl back through this thread...from memory I think it was mainly 30 and 35mm stator widths he tested with.
That being said, many are now using it in the MXUS 3000 with good results. I don't know what amount was used though.

Cheers

 

[macribs]

Yeah I was kind of hoping to avoid that, that someone would magically pull it from memory, this thread has grown so large it is hard to find back to all important posts. I might do a search during the weekend if weather is still shitty

 

[Hummina Shadeeba]

Why not add as much thermally conductive resin as possible to fit anywhere and everywhere other than the airgap instead of just coating the windings with a thin coat. Radiant heat transfer is effective the less air between parts so I'd think the whole stator and rotor should be potted leaving just a sliver of an air-gap.

I'll be potting my skate hubmotors and vacuuming to see how they perform.

There is a lot of variation in price and ability of the many products available and there's a bunch of up-and-coming materials using advanced fillers like carbon with much better ability...and likely crazy high prices. I read you can simply add up to 90% powdered Quartz as a thermally conductive filler.

Anyone ever try just pouring carbon powder in a sealed motor?

Maybe people aren't thinking of their frames as heatsinks. With a connection between the motor shaft and the bike being more designed for heat transfer I bet it'd be better than air. And using air to cool almost always means wind drag

 

[Cowardlyduck]

I finished repairing the fans and putting my Leaf motor back together tonight.

As mentioned I added thermal paste on the side panels and added the synthetic Ferro Fluid.

I wanted to see how it formed on the magnets so added <1ml before re-assembling the motor.

Before I added the rest of the Ferro Fluid I tested for any noise generated when turning the motor:
[youtube]fieeFvoaGC8[/youtube]
As you can see/hear, there is almost no noise.

After adding around 5ml, I tried again:
[youtube]Xb_SaO2dgxY[/youtube]

So I would say that's pretty conclusive evidence Ferro Fluid does make noise in a hub motor.
Granted, it's not much noise, and for those with sealed motor's you'll likely never hear it.
I would say it might just get louder as it gets hotter also...just not sure why/what exactly causes it yet.

Cheers