Definitive Tests on the Heating and Cooling of Hub Motors

[minde28383]

To reach your goal you would need to design most effective air blades to scoop as much air as possible; blades being from the very rim to to the very hub ring, long as possible. The smaller the wheel the faster you need to spin it to reach the same travel speed on the road, but the smaller the wheel the shorter the blades becomes. Therefore it will be not enough air flow with short blades and low rpm. Wheel rpm might be ~700 max, but you won't spin it always that fast, sometimes you move very slow and generate heat and need motor to cool down and small blades are generating almost nothing at low rpm. So you theoretical cooling approach would work only for fast running ebike and possible small wheel, but again, smaller the wheel spins faster but has less space for air blades.

To test it in real life try supplying low voltage (or just slow it down by pressing it to make it spin slower) to reach low RPM to you house air FAN which is used in hot summer days to cool things down, and you will see that low RPM generates very low air flow. If you need big air flow from low rpm you need big vents which you can't install inside wheel because there is no enough space.

Let imagine that there was unlimited space to install air blades. These very light, strong, always dirty, blades would generate air flow only to outer hub ring, but hub side covers would get no air flow. To solve this you would need to make fan blades wider which would be wider than hub or make some air flow channels, wings to direct air flow to hub covers. After laying you bike on the ground you would brake those off or bent if soft metal. I have to admit it would look futuristic.

Artificially blowing air to your hub is secondary. Preferably first thing you you need to do is to remove air gap between rotor and stator ie between spinning thing inside motor and outer hub ring (magnets). And cheapest fastest solution to that is using already widely available Ferrofluid (Fero fluid), and if FF does not solve the heat problems than adding radiators which are available for 205 hubs like mxus205 and qs205, maybe it works in narrower 205s.
Another option is more technical, and requires hub modification - liquid cooling imlementaion. In that case you would require, small pump, houses, radiator, modifying axle. You can acquire hubs of 9kg, modified mxus with liquid cooling implemented, but these are twice the price and therefore not so much popular.

There are implemented cooling solutions where air is pushed with high rpm fan directly to copper to windings (not to outer hub ring). This solution did not appeal to masses and is almost solo approach due requiring quite big modifications from not readily available parts to be acquired. To reach that cooling solution you need hub motor which has static (not spinning) hub cover (like it is implemented in geared hubs); make a holes in both side covers; blow air to one side hole and suck from another hub cover hole. That possible and workable solution, but you will have more sophisticated ebike with more parts possible to brake. These geared hubs are prone to brake under high loads anyways and makes noise under high load because of gears, reduction.

But no matter above, most inventions are made by fail trial methods so think of another solution. Another brake through would be to design motor with higher efficiency so that there would be no need to cool it down. Maybe you need bigger motor?

 

[John in CR]

Hello, will such a thing work:
the wings stretched between the spokes ,
directly near the hub , directed along the wheel ,deflecting air flow to the hub ?
only the game with the size, name and file editing helped

No, such blades (wings you're calling them) will through air away from the motor like any centrifugal fan. It might cause very slightly more flow at the motor shell itself as the air is sucked away from center.

You can direct more air flow toward the hub shell with air scoops that direct air from the bike moving toward the motor that would otherwise bypass it completely. I've done that with some success, but the trick is making it look like part of the bike. Here's what I did:
View attachment 1

While these worked to some extend due do my car type speeds, I didn't achieve great cooling until I vented the motor with intake slots on one side and exhaust slots at the perimeter of the other side with centrifugal blades outside of the exhaust slots that create great air flow through the motor.

 

[Cowardlyduck]

This...
View attachment 1

It still going strong over 3 years on...still works great.

Cheers

 

[andrei-8]

Thanks for answers!

 

[DasDouble]

Hello, will such a thing work:
the wings stretched between the spokes ,
directly near the hub , directed along the wheel ,deflecting air flow to the hub ?
only the game with the size, name and file editing helped

No, such blades (wings you're calling them) will through air away from the motor like any centrifugal fan. It might cause very slightly more flow at the motor shell itself as the air is sucked away from center.

You can direct more air flow toward the hub shell with air scoops that direct air from the bike moving toward the motor that would otherwise bypass it completely. I've done that with some success, but the trick is making it look like part of the bike. Here's what I did:
SuperV air scoops side.JPG
SuperV air scoops rear.JPG
While these worked to some extend due do my car type speeds, I didn't achieve great cooling until I vented the motor with intake slots on one side and exhaust slots at the perimeter of the other side with centrifugal blades outside of the exhaust slots that create great air flow through the motor.

have you made some serious tests on that or is it just a feeling that it became better?

 

[John in CR]

Hello, will such a thing work:
the wings stretched between the spokes ,
directly near the hub , directed along the wheel ,deflecting air flow to the hub ?
only the game with the size, name and file editing helped

No, such blades (wings you're calling them) will through air away from the motor like any centrifugal fan. It might cause very slightly more flow at the motor shell itself as the air is sucked away from center.

You can direct more air flow toward the hub shell with air scoops that direct air from the bike moving toward the motor that would otherwise bypass it completely. I've done that with some success, but the trick is making it look like part of the bike. Here's what I did:
SuperV air scoops side.JPG
SuperV air scoops rear.JPG
While these worked to some extend due do my car type speeds, I didn't achieve great cooling until I vented the motor with intake slots on one side and exhaust slots at the perimeter of the other side with centrifugal blades outside of the exhaust slots that create great air flow through the motor.

have you made some serious tests on that or is it just a feeling that it became better?

Almost 6 years of running higher power into a hubmotor than anyone else, and the motors run cooler than any running more than minimal power levels is serious enough testing for me. While I don't have the tools or patience to do the kind of work Justin does, that doesn't mean it doesn't work. The benefits at low rpm are more limited, but I did run a smoke test and starting at around 10mph the motor started drawing air through.

 

[ltu]

its migth interest some test using the m3 liquid solution usuality used for cooling server.
have better heat transfer compare to AFT

 

[DasDouble]

Hello, will such a thing work:
the wings stretched between the spokes ,
directly near the hub , directed along the wheel ,deflecting air flow to the hub ?
only the game with the size, name and file editing helped

No, such blades (wings you're calling them) will through air away from the motor like any centrifugal fan. It might cause very slightly more flow at the motor shell itself as the air is sucked away from center.

You can direct more air flow toward the hub shell with air scoops that direct air from the bike moving toward the motor that would otherwise bypass it completely. I've done that with some success, but the trick is making it look like part of the bike. Here's what I did:
SuperV air scoops side.JPG
SuperV air scoops rear.JPG
While these worked to some extend due do my car type speeds, I didn't achieve great cooling until I vented the motor with intake slots on one side and exhaust slots at the perimeter of the other side with centrifugal blades outside of the exhaust slots that create great air flow through the motor.

I will design this and print it with my 3D printer for Vector frame in a week

 

[andrei-8]

Hello ! Changed the configuration of my bike, 36V MXSYS direct drive front wheel, set 72 v controller instead of 36 v, dynamics significantly increased, speed from 35 to 55 km h, flies up the hill, but also became more heated - to a maximum of 55-60 degrees on the covers after stopping after 10 minutes. Can anyone say approximately how much it will be on the winding of the motor, how far is the critical temperature? I do not want to engage in unnecessary activities in vain: to drill the lid, put the fan ...

 

[wturber]

Hello ! Changed the configuration of my bike, 36V MXSYS direct drive front wheel, set 72 v controller instead of 36 v, dynamics significantly increased, speed from 35 to 55 km h, flies up the hill, but also became more heated - to a maximum of 55-60 degrees on the covers after stopping after 10 minutes. Can anyone say approximately how much it will be on the winding of the motor, how far is the critical temperature? I do not want to engage in unnecessary activities in vain: to drill the lid, put the fan ...

You may be able to extrapolate/guess from some of the information and test results provided here:
https://www.ebikes.ca/product-info/statorade.html

I think Statorade is a good, perhaps necessary, step in keeping a DD motor's core at a reasonable temperature.

 

[justin_le]

to a maximum of 55-60 degrees on the covers after stopping after 10 minutes. Can anyone say approximately how much it will be on the winding of the motor, how far is the critical temperature?

If you know the elevatation profile that you were riding around then you can use the nearest hub motor that I have thermally modeled on our trip simulator here to get a good idea of what the motor core temperature is like for a given shell temp when the bike is underway.
https://www.ebikes.ca/tools/trip-simulator.html

Underway with most DD hub motors a shell temp of 55-60oC would means a very hot motor core, ex:


Once you stop riding the bike, then the motor shell temperature will increase quite rapidly even as the core temperature decreases since there is no longer any air flow on the motor shell. It will peak in 5-10 minutes, then it will decrease again, as you can see here from actual test data on a MXUS DD motor in our wind tunnel thermal characterization. It was running at 400 rpm / 40kph and then stopped where you see the power (red line) drop to zero.



Your best bet for sure is to install an actual temperature sensor inside the motor stator itself to really know what is going on with the core temperature.

 

[DasDouble]

Sorry for kidnapping the post, but does anyone remember where you could get these 3D printed files from? I remember having seen it on endless sphere, originally I guess from the russian forum but 1. don´t speak russian 2. can´t remember from where exactly.

I have a 3D printer now and want to test it out. Thanks a lot for help!

 

[Rix]

Sorry for kidnapping the post, but does anyone remember where you could get these 3D printed files from? I remember having seen it on endless sphere, originally I guess from the russian forum but 1. don´t speak russian 2. can´t remember from where exactly.

I have a 3D printer now and want to test it out. Thanks a lot for help!

This unit was developed in Russia, as you alluded too, and the one I had seen was on a Mac 10 hub motor running 6kw reliably.

 

[Hummina Shadeeba]

Sorry for kidnapping the post, but does anyone remember where you could get these 3D printed files from? I remember having seen it on endless sphere, originally I guess from the russian forum but 1. don´t speak russian 2. can´t remember from where exactly.

I have a 3D printer now and want to test it out. Thanks a lot for help!

does this spin? wouldnt a scoop need to be stationary? if its spinning it's going to be throwing air out through centrifugal force in the same direction its trying to scoop it in

 

[wturber]

Sorry for kidnapping the post, but does anyone remember where you could get these 3D printed files from? I remember having seen it on endless sphere, originally I guess from the russian forum but 1. don´t speak russian 2. can´t remember from where exactly.

I have a 3D printer now and want to test it out. Thanks a lot for help!

does this spin? wouldnt a scoop need to be stationary? if its spinning it's going to be throwing air out through centrifugal force in the same direction its trying to scoop it in

As I recall, it is stationary.

 

[Hummina Shadeeba]

how much of the heat from the motor could be removed as radiant with black magnet plating and painted motor case. but there's no black just a dark grey at least.

 

[Cowardlyduck]

how much of the heat from the motor could be removed as radiant with black magnet plating and painted motor case. but there's no black just a dark grey at least.

I painted the inside of a hub black years ago for this same reason. No idea how effective it's been, but at the time I thought why not...4+ years and 15000km later that motor is still going strong on my daily commuter with no signs of overheating, mind you I only run it at 25% over spec.

Cheers

 

[Hummina Shadeeba]

What would be the breakdown of heat leaving the coils from a sealed motor?

Conductive transfer- the stator thermal conductivity sucks being electrical steel which is likely as bad thermally as electrically conductive as typical, with layers of epoxy as well.


Convective transfer- I've seen fans in a motor but forget was it sealed? If sealed and heating the air and then the air transferring the heat to the motor case, if that were effective it would seem a passive method with integrated blades in the motor rotor sides would be worth doing and maybe could set up a circular path for the air to be forced through at high speed,no?

Radiant heat transfer, I guess since no visible light would be infrared and maybe ultaviolet? NASA made some new carbon nanotube black paint to catch like 99% of radiation- nano-velvet. What electromagnetic radiation is catchable w just black and what would be emitted by the coils? Maybe the highly reflective magnets and rotor are bouncing and trapping it?

 

[Cowardlyduck]

Convective transfer- I've seen fans in a motor but forget was it sealed?

Yeah that was me and a few others:
https://endless-sphere.com/forums/viewtopic.php?f=30&t=56965&start=400#p1198704

Unfortunately a lot of the images were hosted on a site that went under...but here's a few I still have showing how I mounted the fans (12 of them) and cooling holes in the hub:




I did this to several motor's (Leaf motor and HS4080) as well as adding ferro fluid. They are both still going strong to this day.

Cheers

 

[John in CR]

What would be the breakdown of heat leaving the coils from a sealed motor?

Conductive transfer- the stator thermal conductivity sucks being electrical steel which is likely as bad thermally as electrically conductive as typical, with layers of epoxy as well.


Convective transfer- I've seen fans in a motor but forget was it sealed? If sealed and heating the air and then the air transferring the heat to the motor case, if that were effective it would seem a passive method with integrated blades in the motor rotor sides would be worth doing and maybe could set up a circular path for the air to be forced through at high speed,no?

Radiant heat transfer, I guess since no visible light would be infrared and maybe ultaviolet? NASA made some new carbon nanotube black paint to catch like 99% of radiation- nano-velvet. What electromagnetic radiation is catchable w just black and what would be emitted by the coils? Maybe the highly reflective magnets and rotor are bouncing and trapping it?

Some heat conducts from the stator out of the motor via the axle, but that's a pretty small amount due to the small outside surface area of the axle. Radiation is also pretty small due to the low temps involved. The lion's share of heat transfer is first convection to the inside surfaces, conduction through the magnets and metal to the outer surfaces, and then convection to the outside world.

I run extreme power, up to 31kw peak input, into some of my high efficiency hubmotors. On bikes I have with more than 17kw peak input, I ventilate them for the bulk of heat transfer by convection directly from the stator to the outside world. I tried a number of passive ventilation strategies with modest results until I tried taking air in on one side of the motor through small holes all over the side cover on the intake side, and larger holes or slots at the extreme perimeter of the cover on the exhaust side. The exhaust vents have radial blades in front of them to turn the motor itself into a centrifugal fan. A smoke test demonstrated that blades create flow into the intake side starts at about 10mph and gets so strong a high speeds that smoke was even drawn across the shell on the outside as well as through the motor.

This system works so well that I rarely see stator temps above 70°C, and with hard riding on mountain climbs the highest I've seen is 103°C, and that was up a continuous 20% grade accelerating hard up to 80kph after every switchback of the road. Without pushing them to failure, not even hubbies weighing almost 3X as much have exceeded the performance of my modded motors, and due to the relatively low internal temps I doubt even a liquid cooled system could fare better.

Here's a shot of the exhaust side of one:

 

[Cowardlyduck]

Yeah, certainly Johns method works also...if you ride like him. aka high speeds, on road where the centrifugal forces can actually do something.

In my case I ride predominantly below 50kph and lots of 20-30kph off-road up large/long hills. Not ideal for a hub motor I know, but to make it work without resorting to a giant anchor, the fans work for me.

I will also add, that for 90%+ of people simply adding Ferro Fluid + HubSinks is sufficient, and what I would recommend for most now. In my and Johns case we did all this before Ferro Fluid and Hubsinks were a thing.

Cheers

 

[John in CR]

Yeah, certainly Johns method works also...if you ride like him. aka high speeds, on road where the centrifugal forces can actually do something.

In my case I ride predominantly below 50kph and lots of 20-30kph off-road up large/long hills. Not ideal for a hub motor I know, but to make it work without resorting to a giant anchor, the fans work for me.

I will also add, that for 90%+ of people simply adding Ferro Fluid + HubSinks is sufficient, and what I would recommend for most now. In my and Johns case we did all this before Ferro Fluid and Hubsinks were a thing.

Cheers

I only go fast on the highway. Most is in town, lot's of stop and go with speeds generally 20-30 and some 40's on bigger roads, and that really heats up motors. My motors flow air above 10mph. Cars go slower here than stateside. Most highway limits are 80kph (50mph) with some empty stretches 100kph (62 mph). That is with smaller wheels 19" up to a biggest on my enduro of 21.5", so higher rpm at same speed. If my blade thing wouldn't have worked so well I would have gone actively blown, but thank goodness I don't have to listen to fans or change them when broken. My motors don't have any space for fans...very little internal air compared to common DD hubbies. That makes them transfer heat when sealed, and I can get away with sealed on my commuter rocket getting 17kw peak geared with the 16" OD wheel for a top end of only 65mph or so. On the 20km commute in to the shop, I use to douse it with water upon arrival when I rode it hard on the highway with hard launches at it's 3 lights. The way in was a net climb of 40mm with wind in my face so it used 30-50% more energy on the way in depending how I rode each way.

 

[Hummina Shadeeba]

An open motor has a great ability to be cooled with a passive or active fan as you guys did. And a motor case with little air shows to transfer heat better to the case. How much heat could be transferred to the case through radiant heating if an ideal black lining were on the magnets and all in the case? And how much heat could be transferred to the case through a sealed motor with internal blades by transferring the heat from windings to the air and then the case?
An open motor seems great for passive cooling potential but an open skateboard motor will be picking up dust and want to keep it sealed.

Does anyone do a passive fan inside a sealed motor with blades on either side circulating air through the airgap and then back through gaps within the windings? That paired with the all black inside seems worth a shot.

Looking above in the thread at the large difference temp between the motor case and actual windings, and with the deterioration of winding enamel with heat and just increased resistance with increasing heat..what's ur actual winding temps and what are u considering acceptable and anything concrete worth looking towards as a guide? In practice I'll cook bearing grease if not the thick heat resistant stuff but otherwise not obvious. I plan to put temp sensors in.

Just talked to Epic Resins that do winding epoxy n don't even know if their thin unfilled stuff will increase the dialectic strength and winding longevity. Anyone had good experience w thermally conductive epoxy coating or potting?

 

[justin_le]

An open motor has a great ability to be cooled with a passive or active fan as you guys did. And a motor case with little air shows to transfer heat better to the case. How much heat could be transferred to the case through radiant heating if an ideal black lining were on the magnets and all in the case?

You can see my test results here on a large DD hub motor with vent holes:
https://endless-sphere.com/forums/viewtopic.php?f=2&t=48753&p=1095507#p1095507

Have a read of that.

The thermal improvement by having the motor insides fully painted in black was slight, going from 0.154 oC/watt to 0.147 oC/watt, so only about 2% better. If we started with a hub that didn't have open vent holes on it in the first place then I suspect the percentage improvement would be higher as there wouldn't be as much convective cooling from outside air so the effect of radiant exchange would be higher as a percentage. Probably like 5-6% if I was to hazard a guess. It's not nearly as much as actual convective transfer from a fluid in the gap, but I suppose even a small improvement is better than nothing!

 

[Bullfrog]

Heat transfer....

In theory....you can transfer a lot more heat with Radiant heat transfer than any other means, followed by Convection, and last but not least Conduction BUT in reality the answer is "It Depends".

Radiant heat transfer is proportional to the temperature difference between two surfaces to the fourth power regardless of the distance between them (for the most part)...best example is the sun heating the earth. But with a motor you have to transfer the heat from the motor windings to the housing first and then to the atmosphere/surroundings so anything along the way can really slow down the heat transfer. A small air gap is a terrific insulator and conduction through an aluminum housing is relatively slow...although aluminum is a really good conductor as far as Conductive heat transfer.

The ducting that "DasDouble" posted would be an awesome way to increase the convective heat transfer if you used a fan to increase the air flow. It is the best option I have seen for using convection to cool a hub motor and if you added a filter to the inlet you could keep from pumping dust/dirt into the motor but you'd also cut down on the air flow so once again "It Depends".

Below is a pic of what I ran long a long time ago when I was trying to get the gearing as low as possible...only way to change the gearing for Direct Drive or Internally Geared Hub Motors is to use a smaller diameter wheel. It was a 20" rim that was 57mm internal width and a 4" wide tire. With the 14s battery, the speed was about 20 mph on level ground with my 12T MAC. We called it the "Clown Bike" because it looked like it should be in the circus with three or four clowns on it instead of on the trails with me on it.

Biggest problem was the steering...it steered really slow with the increased rake angle. Oh yea, the ground clearance wasn't that great either but I wanted to take it to an extreme to see how much difference it would make and it helped but not as much as I had hoped...and then I started playing with Automatic Transmission Fluid, Distilled Water/Mocool, Ferrofluid, and any other means to thermally connect a motor to the surrounding housing.

Somebody mentioned spinning a MAC too fast...I never had any problems or issues with my 12T MAC in a 20" rim and a 14s battery and I ran it on pavement for many miles with a narrower 20" rim/2.00" wide tire for many miles before going to the set up with the 4" tire. Not saying you won't have problems...I just didn't experience any.



I passed on the ducting and forced air because it was a little more complicated in the long run than liquid cooling like ATF and Ferrofluid plus the ducting would require a fan, filter IMO, and a power source to run the fan which could easily be the same battery that powers the bike but it would decrease the energy available for riding.

Next experiments I have planned are to lace a 12T MAC in a 24" rim and run a 3" wide tire. Add four ounces of distilled water and Motul Mocool to the motor and ride off road. Why a 3" tire...I run it at relatively low pressures to give me some cushion as a pseudo suspension on the rear of my hardtail and off road, the lower pressure isn't a concern. If you ride high mileage on pavement...keep your tires properly inflated or you can overheat them and have a catastrophic failure.

Two things I plan to take to an extreme....
A. Amperage...increase it until I think I have enough torque or something breaks. Installing an 18 FET controller is the first step.
and
B. Increase the voltage with a 20s (72v nominal) battery until I go too fast or something breaks.
and
C. Some combination of A. and B.

Parting comments...I am just a 12 year old trapped in an old man's body :lol:.