Cooling fans inside Hub motors

[Offroader]

I think I solved how to add heat sinks to the interior of the stator. I had this idea but finally got around to working on it. Problem with adding heatsinks to the interior is that you can't buy any that can fit the circle.

Simply milling down a regular heat sink to about .2mm thickness makes it flexible and it will bend around the circle. It also saves weight because I'm not looking for thermal mass.

This is a test heat sink I tried to see if milling it will make it bendable. The actual heat sink I will use will have about 32 mm fins for lots of surface area.

I'll have to make something to hold the heatsink in place until the thermal epoxy cures, but this shouldn't be too difficult.

Now the hard part how to pass air through these heatsinks in my EDF cooling setup. I have some ideas on this but will need to do some experimentation to get it right. I want my single 30mm EDF to ciruclate some air through the heat sinks before exiting the hubmotor. This should really help cool down the stator a lot if done correctly. I'm adding a lot more surface area to the stator, in the order of 10x-30x depending on how many of these sinks I use.


Left heatsink is thickness before milling. Right is with it milled down to ~.2mm.


Before pushing it in place.


Heatsink bends around the interior of the tape roll.

 

[Cowardlyduck]

Hi guy's,

I posted this in a few other threads also, but here I want to talk about how great these fans are going for me.

https://vimeo.com/157341682
[youtube]PfNklMqsXKY[/youtube]

To make the video requires lots of doubling back, up/down steep hills, which generates a lot of heat. My controller has a problem currently where it limits power if the motor temp exceeds about 65C which I am still working on solving, so the fans cooling effect was essential to enabling me to make this ride/video work.
It also seems the addition of the 7th fan in series was a good move as they don't sound in any way overdriven now. So hopefully they last a long time now.

Also, so far the addition of Ferro Fluid doesn't seem to be causing any drawbacks, however it also doesn't seem to be helping a huge amount, although it's really hard to know how effective it could be given the issue I currently have with my setup. I'm seeing maybe 5-10C lower average temps if I had to guess, but it doesn't seem to speed up cool down times by any noticeable amount.

Cheers

 

[Offroader]

Cowardlyduck, starting using my new build without my EDF cooling and riding really sucks without it. I didn't realize just how good I had it with the EDF cooling.

Temps quickly get to 120C and at that point controller starts to limit power. At the point the motor heats up anything I climb will quickly heat my motor to 120C.

It has gotten to the point I avoid climbing anything steep even at the beginning of my ride to not overheat the motor

It isn't even all that hot here yet and it gets much worse in the summer heat.

Before with the EDF, I would just turn it on when needed and could drive as hard as I want for as long as I want and it would never get to 120C unless I climbed the steepest hill at full throttle after just climbing a steep hill. Nothing will stop the overheating if you climb long enough at full throttle.

It makes sense because the EDF pushes out such hot air when it is on that it will burn your hand after a few seconds.

Lucky for me, I simply just need to hook up my electronics, two buck converters and speed controller to get everything working again.

 

[Cowardlyduck]

Wow! Yeah, you often don't know how good you've got it till it's gone.

I think your EDF solution is more effective than mine as I don't see such a dramatic difference when not running my fans. There is definately still an appreciable difference though, and I still think it was worth doing.

Offroader, have you considered adding any Ferro Fluid to your setup also?

Cheers

 

[Offroader]

To be honest, I can't see how Ferro Fluid can come close to my cooling setup so I don't think I am going to use it.

I haven't even modified my cooling setup to flow air more direct through the windings. I also got a better speed controller to run my fan even higher. I may even direct the outside air flow to not recirculate the hot air. So my setup should even get better.

The amount of heat that comes out of my motor when the fans are running is extreme. All the holes on the outer edge of my motor are pushing out air hot enough to burn you. There is no way you can get that amount of cooling through the motor case.

So to be honest, I'm not even going to try it. I kind of know I will be disappointed compared to what I am using now.

 

[Cowardlyduck]

As a direct comparison having just Ferro Fluid or just fans, I couldn't agree with you more Offroader, but that's not what I meant.

I've added Ferro Fluid to my motors as well as running fans. i.e. Vents + Fans + Ferro Fluid, all combined.
It's sound like you really don't need the added boost though, so probably not worth the hassle for you TBH.

I've found it helps slice a good 5C off temps at low speeds and more at higher speeds. For me my fans aren't quite up to the task of rejecting the heat 4KW+ continuous makes, so adding the Ferro Fluid definitely gives it that edge.

Cheers

 

[madin88]

I think your EDF solution is more effective than mine as I don't see such a dramatic difference when not running my fans. There is definately still an appreciable difference though, and I still think it was worth doing.

offoraders setup is definitely better.
your fans only blowing air from one side to the other and not over the windings / endturns or over the stator teeth.
when climbing slowly steep hills and such tings, the fans should outperform FF.

IMO it makes no sense to use FF togehter with Fans or a vented motor generally. because when riding on dusty grounds, the FF will turn into a grinding compound.

 

[Cowardlyduck]

offoraders setup is definitely better.
your fans only blowing air from one side to the other and not over the windings / endturns or over the stator teeth.
when climbing slowly steep hills and such tings, the fans should outperform FF.

IMO it makes no sense to use FF togehter with Fans or a vented motor generally. because when riding on dusty grounds, the FF will turn into a grinding compound.

I don't dissagree that offroader's setup is more effective at cooling, but I don't think that it means it's 'better'. I think it's just different. It's certainly has the added complexity of using an ESC, where as mine has the complexity of multiple points of failure in each fan...so just different. I think both approaches are entirely valid and work well for different setups. In my case I required no modification at all of the stator supports as the fan size matches the existing holes perfectly.

I disagree with your statement about the air not flowing over the windings / endturns. The way I've made it, this is exactly what it does do. Perhaps you need to be reminded of my vent locations:

HS4080

35mm Leaf motor
The air must flow right past the winding endturns in order to move in and through the motor. This is precisely what happens as you can see from my testing results. I'm also able to place a finger directly onto the windings when stopped without it burning or even feeling warm because the air flow cools it so quickly.

Yeah, the fears of the FF turning into a grinding paste from the dust/dirt are valid, and I had/have the same fears. However nobody else has done it yet, so it is still unknown how quickly this will occur or if it will be as bit a deal as it seems, so I'm being the guinea pig and trying it out for myself. If we all just assumed our predictions were correct and never tried things, we would never learn anything.

Cheers

 

[Offroader]

I believe mine has the benefit of flowing through the stator - magnet gap. I wonder how much heat that actually removes there vs going through the windings.

Forgot to add that my cooling may push air through the windings inside the stator. However, I don't know how much air if any can be forced through this area. It would be huge if air did get through.

 

[Cowardlyduck]

I believe mine has the benefit of flowing through the stator - magnet gap. I wonder how much heat that actually removes there vs going through the windings.

Forgot to add that my cooling may push air through the windings inside the stator. However, I don't know how much air if any can be forced through this area. It would be huge if air did get through.

Yeah, that makes sense. Removing the heat directly from the source is always going to be the better option.

In my case, because of the fans pulling air through the stator support, although it is going past the windings, it was not going through the magnet gap anyway. This is one reason I added the Ferro Fluid as there is not much air movement in that area anyway.

Cheers

 

[Offroader]

I'm going to purchase the new MXUS 4T motor with curved magnets.

I'll be modifying this one for EDF cooling. This MXUS motor cooling is a must because it doesn't have the thermal mass of the cromotor.

I'm going to put in a larger 35mm EDF fan into this one, and try to do all the improvements for better air flow internally and externally.

This will be the ultimate cooled hub motor.

 

[Allex]

Perhaps you should at least try out the ferrofluid/oil cooling before drilling and modding with fans? While the fluid may be less effective, this could be that it's just what you need to not exceed the critical temperature.
Emmet use this with great success and I believe that his riding style is a lot like yours:
"I've never come close to overheating my H4065 motor since cooling the stator with 110ml of castor oil and sealing the hub. Before that it, overheating ended every ride!"
https://endless-sphere.com/forums/viewtopic.php?f=6&t=23996&p=1169246&hilit=castor#p1169246

 

[Cowardlyduck]

Allex, I don't doubt that oil cooling like that might be effective but to just not exceed the critical temperature is also allowing far lower efficiency for the rest of the riding time.
What I mean to say is, the effect of the cooling fans is not just about keeping the stator from melting down. It also greatly improves the overall efficiency of the motor while riding giving greater range even though it uses some small amount of power to do it.
It also means that if you've just climbed a steep hill you don't have a large mass of hot oil to worry about, and you also don't have the added unsprung mass of oil to deal with. not to mention the mess (even if it can be minimised, it can't be eliminated).

I think Ferro Fluid definitely has it's place, which is why I've added it to all my E-bike hub motor's now.
I'm even running a combo of Ferro Fluid + oil in an old geared '250W' hub motor I'm pushing at 750W.
https://endless-sphere.com/forums/viewtopic.php?f=3&t=53322&start=25#p1168020
So far it's held up ok:

So yeah, oil cooling has it's place...I think it's in geared, and low power hubbies where you don't need much oil and don't care about unsprung weight much.

Ferro Fluid seems to me to be applicable to almost any hub, but doesn't give high end cooling performance like fans do IMO.

Cheers

 

[Offroader]

Perhaps you should at least try out the ferrofluid/oil cooling before drilling and modding with fans? While the fluid may be less effective, this could be that it's just what you need to not exceed the critical temperature.
Emmet use this with great success and I believe that his riding style is a lot like yours:
"I've never come close to overheating my H4065 motor since cooling the stator with 110ml of castor oil and sealing the hub. Before that it, overheating ended every ride!"
https://endless-sphere.com/forums/viewtopic.php?f=6&t=23996&p=1169246&hilit=castor#p1169246

I considered oil and researched it on the forum. While it did seem to work well, I decided not to use oil because of leaks. There seemed to be nobody who who was able to control the leaking. It is something I didn't want to deal with and still don't.

Ferro Fluid is supposedly much better with leaks but doesn't work as well as filling the motor with oil. I don't believe Ferro fluid can work as effectively as what I have.

I have a lot of fun just climbing really steep hills, driving slowly for 10-15 seconds and then climb another steep portion of the hill. During these 10-15 seconds I have my motor cooling with the fans. Ferro Fluid wouldn't do anything for me in these cases.


I also can't see how Ferro Fluid can come close to cooling to what I have. I don't know how it would compare, and would be a little mad if it was as effective because it is much easier to use than EDF cooling. But I seriously have my doubts it can cool as effectively. I don't want to dirty up my motor with it to try it out also.

What I have simply works, I can drive as hard as I want in the hottest days of the summer without overheating.

 

[Cowardlyduck]

I decided to add some extra thermal heat shedding capability to my Leaf Motor and since I added Ferro Fluid, it makes more sense to do now.

So I bough 50 of these 25x25mm black heat-sinks for this and other projects:

And a bunch of cheap 1.5mm thick thermal padding
I cut up the thermal padding to match the heat-sinks:

Then stuck them all around the magnet ring and tied them down with some thick string:

It was pretty fiddly/tricky to get all the heat-sinks to stay in place while I tied it all down as the thermal padding doesn't really provide much sticking force and it was a game of catch up for a while until they all stopped falling off.

However the end result was worth it, looks great and feels pretty solid:

I also added some glue in the only gaps left to lock in the threads and prevent movement:

Given the hottest I was regularly seeing the magnet ring get before was about 75C, I don't expect a huge improvement from just these alone, but combined with the Ferro Fluid, side cover vents and 7 x cooling fans I'm running with, I think only the most extreme use cases will cause me heat problems now.

Cheers

 

[John Bozi]

class act with the cab merlot

What does

Thermal Conductivity: 2.88 K/WK

mean?

I am interested in how much of the heat is directly passed through those pads from a non flat to flat surface. Wonder if those heat sinks could be beaten into shape for more contact.

Because if there is any air gap or those pads don't pass the heat on then they be more insulating heat.

Looks bloody awesome though!

 

[fechter]

Bending them slightly would allow better contact but would be pretty challenging. I could imagine something like curved plastic blocks in the jaws of a vise.

Silicone glue has pretty good thermal conductivity. I'd use it instead of the pads.

 

[Cowardlyduck]

class act with the cab merlot

What does

Thermal Conductivity: 2.88 K/WK

mean?

I am interested in how much of the heat is directly passed through those pads from a non flat to flat surface. Wonder if those heat sinks could be beaten into shape for more contact.

Because if there is any air gap or those pads don't pass the heat on then they be more insulating heat.

Looks bloody awesome though!

Thanks! I'm also glad with how it turned out appearance wise. I think it strikes the right balance between function and discreetness.
The tiny air gap is taken care of by the 1.5mm thick padding. Not ideal for heat transfer, I know, but better than nothing. Bending them is too much of a pain IMO.

Silicone glue has pretty good thermal conductivity. I'd use it instead of the pads.

That's a good idea. I do have some thermal epoxy, but not enough for this job, and it's too pricey to get enough to do it properly, but silicone would work well.
If they come off for any reason, I might do it again with silicone.

Cheers

 

[Cowardlyduck]

I finally got around to opening up my HS4080 to see how it had faired with Ferro Fluid (Statorade) together with venting and fan cooling.

Well, the pictures speak for themselves.
Before cleaning:

The dirt build-up isn't as bad as I was expecting TBH. I am a little surprised at how little of the Ferro Fluid was left however. I had hoped more of it would stick around, and I'm honestly not sure how it left the motor given how aggressively it sticks to the magnets.

After cleaning:

The surprising thing for me was that when I went to clean it up (with wet wipes), the red varnish wiped off also, but only on the steel surfaces. It did not wipe off the copper windings. Interesting!
I can't recall weather I used type A or B (Synthetic or Ester based) on this motor as I had one of each and used them both on different motors....I may have made mention of it earlier in this thread if that matters to anyone. I think, from memory I used about 5-6ml...maybe that wasn't enough?

Many people are probably thinking it was obvious that this would happen, however I needed to try it to be sure myself. I knew this would happen to some degree, but how fast, how much and what kind of impact were the real unanswered questions.
I used the motor for about 4 months and probably put about 800km on it, mostly off-road, a few times in the rain.
It did not get hotter than about 85C during this time as the motor has another strange problem where power drops off over this temperature. I think it could be the heat-shrink softening in the section through the axle and the phases may be shorting...really not sure TBH.

It will be interesting to see the results from my other 2 motor's in similar situations.
I have my Leaf motor also with Fans and Ferro Fluid, however I used slightly more Ferro Fluid, and the vent holes are smaller.
The other motor is a 28mm generic Golden motor (9C clone) that is only vented on one side with no fans, however is ridden almost daily on the road on my Recumbent commuter.

I won't be doing this again as the increased cooling performance seen was not that great in comparison to the fan cooling. Perhaps that was because the Ferro Fluid didn't stick around, however I did arbitrarily test it straight after adding the Ferro Fluid and only saw 5-10C decrease in temps while running my fans vs no Ferro Fluid.

All in all, it was a good little experiment and I'm glad I was able to easily undo it with no permanent damage to my motor.

Cheers

 

[amberwolf]

The surprising thing for me was that when I went to clean it up (with wet wipes), the red varnish wiped off also, but only on the steel surfaces. It did not wipe off the copper windings. Interesting!

I suspect grit in the dust that gets in the motor via the air holes mixed with the FF, and swirled around in the air gap might've begun scrubbing the paint off.

If the FF suspension fluid is also a solvent for that paint, then it could make it worse, but it might not have to be in order for grit to do it.

If there was no problem with this happening before using the FF, it might simply be the FF suspends the grit on the magnet surface better than water (or air) did.

 

[madin88]

looks like the FF turned into dust and there is nothing left from the oil basis.
when painting my motor black i found out that the paint did not hold well on magnets. i could chafe it off with my fingers.
so painting magnets makes necessary to use a primer, but IMO it makes no sense if you use FF. you better leave the surfaces unpainted.

 

[Alex07]

How much power do the fans use ? Also since it runs lower temps you would offset some of that efficienct loss with cooler lower reistance windings. Not sure how to work out the Cost/benefit in watts etc of the fans usage vs resistance of windings,

 

[Cowardlyduck]

looks like the FF turned into dust and there is nothing left from the oil basis.
when painting my motor black i found out that the paint did not hold well on magnets. i could chafe it off with my fingers.
so painting magnets makes necessary to use a primer, but IMO it makes no sense if you use FF. you better leave the surfaces unpainted.

Yeah, I agree with that. I will be interested to see how much FF is left on a well sealed hub after long term regular use.

How much power do the fans use ? Also since it runs lower temps you would offset some of that efficienct loss with cooler lower reistance windings. Not sure how to work out the Cost/benefit in watts etc of the fans usage vs resistance of windings,

On paper the 7 fans I currently run draw a max of around 17W, however I've measured it at about 35W in the past.
I think the long wire run contributes to a lot of losses, but that's ok as 35W is still pretty good IMO.
The nice thing is, because I've wired them in series, when I got WOT and the voltage sags the fans speed drops meaning they need and draw less power. This means that at the time I need the most power, I'm getting it. Then when I let off the throttle the fans ramp up again as the voltage rises.

I don't really know how to measure the efficiency benefits either, but given these motors often waste hundreds of watts in heat under high load conditions I think the ~35W consumed would in-fact save more than that in efficiency benefits when the motor is really hot.
It makes less sense however when the motor is not so hot, and for this reason I usually turn the fans off when the temp drops below about 50C.

Cheers

 

[Cowardlyduck]

My HS4080 is back in operation now. I removed all the Ferro Fluid as above, and cleaned it up.
I fixed up my broken temp sensor by splicing it into one of the wires of my other temp sensor in the hope that it wouldn't mess things up. Unfortunately it did and now both my LED display sensor and Adaptto KTY83 sensor are both out of whack, but it's not so bad as to make me want to open everything back up again to change it. At the moment from what I can tell, the temp is roughly half way in-between them, with my LED display being too low and the Adaptto being too high.

While I was at it, I attached some heat-sinks to the magnet ring with thermal epoxy:

The irony of doing this now without Ferro Fluid is not lost on me, but I already had all the stuff to do it, and it will still make some difference so who cares.
There are 8 total, roughly evenly spaced. To attach them, since the thermal epoxy takes a couple of hours to start setting, I had to do them one at a time spaced out over a long period. That wasn't a problem as I just quickly did one at a time in-between other tasks over the course of a week. I also just shoved a small piece of cloth around each heat-sink when it was in place to prevent it moving while it set.
I used far less epoxy than I thought I would with only 3/4 of one set of 7g tubes being enough for all 8. I'm going to do my Leaf motor next, and will probably use 12 or more heat-sinks on it.

Cheers

 

[Offroader]

OK, so I will revive this thread about my ultimate cooling forced air modification. I'll call this version 2.0.

The older 1.0 version worked extremely well but was very inefficient in many ways.

My new 2.0 version will be used in a MXUS turbo motor. I've learned a lot from my 1.0 version, and know exactly how to make it a lot better.

It will have a larger EDF fan, which should double the air flow rate, and more than triple it on max.
It will also have better internal ducting to allow the air to flow through the windings better, instead of blowing right over the top of them.
It will also have outside the motor a large duct to keep the intake and exhaust air separated so that hot exhaus air isn't being sucked back into the motor.

I predict this should greatly improve the cooling rate of the windings.

My goal is to blow away any other cooling methods on the market, especially FF + hubsinks. This will be the ultimate air cooling mod to a hub motor.

I plan on making some of the ducts out of 3d printed plastic, I'll design the ducts on my computer and have them printed locally.

My goal is to have so much airflow through the windings that I can keep the temps below 110C even on the steepest hill climb.

Here is a modified drawing of my design.