Definitive Tests on the Heating and Cooling of Hub Motors

[Punx0r]

You might claim ATF is not conductive, but how many people here have tried the many different formulas of ATF in their hub motor? There are so many brews of ATF. Conductivity seems to be a "don't care" property in [edit: some] ATF spec sheets.

I'm normally happy to categorise ATF as dextron 2, dextron 3 etc.

A quick google and this was the first thing that jumped out for ATF conductivity: http://www.mvfri.org/Contracts/Final%20Reports/Chilworth_final.pdf

Dextron 3 is 7000 pico-siemens per metre. You can also get a feel for the conductivity of different mineral oil products.

Conductivity being the reciprocal of resistance, you could work out current leak if you assumed, say 100V phase-to-phase potential and spacing between the uninsulated ends of the phases of 1cm.

It's very long use in hydraulic systems and automatic transmissions suggests to that it is safe in contact with various gaskets and seals, long-lived and stable, and has decent viscosity and thermal conductivity.

Use whatever you feel best suits your individual requirements

 

[liveforphysics]

It does matter which ATF gets used, but not for conductivity reasons.

It's because the detergents lead to foaming in high speed operation, which leads it to building pressure and forcing out the bearings or wherever it can, along with the foam not doing as good of job as oil for cooling.

Thinest non-detergent ATF if your winner. I know this one doesn't foam even with 7,000rpm rotors spinning in it:

http://www.redlineoil.com/product.aspx?pid=137&pcid=9

 

[Emmett]

Why risk ruining the motor and have your ebike drip oil like a gasser if you don't significantly increase the power at which it can continuously run? The missing part of the oil cooling strategy that I've seen no one run is to increase the exterior surface area of the motor. Double the surface area doubles the heat it can transfer to the environment at the same temperature.

That's easy for me to answer. I cannot air vent my H4065 hub because I always ride on dirt, with many small creek/gully crossings, and often muddy sections, even in dry weather, there is dust plus water crossings. Trying to clean the bike and motor after a ride would be a time consuming nightmare. I'm typically up and down with the throttle all the time. Full power bursts of up to 1 minute up a hill section, then I back off. Mostly on/off power all the time. When I back off the throttle or coast down some hill section, I want my stator to be cooling. Because as it currently is, my thermal sensor cuts in when I still have 50% battery left. I try to give it moments to cool, but once the stator temp is up, my fun session is over.

I will try an different motor, but any heavier and it ruins the offroad handling of the bike. So a H4040 or mini-cro seems like the go for my next hub, also a MX rim and more tire. Heavier rubber, but I really need more tire for traction and rim/wheel protection. Off topic sorry... with a H4040 or mini-cro, my same cooling issue will happen, just later in the ride. For sure I'll increase hub external surface area. Great advice that is.

I dont see why there has to be a leaking mess - if the axle is a very firm fit into the bearing inner races (which mine is), and the hub is only 1/4 full. Sealing the side covers is trivial. Sealing the cable exit would be easy too. As is putting some high temp silicone inside the sheathing containing the bundle of wires exiting via the axle grove. A 1.5mm breather hole near the side cover centre might weep a tiny bit of oil at times, and that's one reason why I asked about using a biodegradable oil. My other concern with ATF is the different types. ATF ain't ATF. I would certainly try some only if it states the dielectric value in the specs. But will it eat my plastic components? Seems like using ATF requires some luck.

Edit: thanks Punx0r, that report shows that particular Dexon-III ATF is "medium conductive". So many ATF concoctions out there. I might try castor oil, or else some transformer oil. I still don't see any advantage in ATF. Just some risk.

 

[fellow]

Actually, has anyone on ES used any type of ATF in a hub yet, or just speculated?

I'm using ATF on my overvolted and overamped Q100H hub motor. So far no problems (300Km and counting). I'm using ATF in my ZF 4HP20 automatic car transmission too. Lots of wires layed directly in ATF there powering solenoids at 14.4V and all kinds of sensors at 5V-14.4V. No problems there . This is inside oil sump of ZF 5HP18, pictured (by someone else, not me) upside down, the wires are in direct contact with in ATF:

My second Q100H build is also ATF cooled. Its at 0,9kW peak (55V, 16A). Not bad for a motor originally rated at 350W continuous at 36V.

 

[Cowardlyduck]

Emmett, you may want to reconsider forced air cooling.
I used to live in Sydney, now live in Canberra and ride mostly off-road here. I can tell you the dirt/dust/mud (and snow) is far worse here than it was for me in Sydney. Water crossings as well...
[youtube]iMIEGfayg30[/youtube]
This was with 25mm PC cooling fans running at full tilt. No issues.
Check my thread about it here for more info:http://endless-sphere.com/forums/viewtopic.php?f=30&t=56965
Results here: http://endless-sphere.com/forums/viewtopic.php?f=30&t=56965&start=25#p946731
For our type of off-road riding forced air cooling is THE most effective solution. Yes the dirt/dust build up is a concern, but not unmanageable, and certainly not something you have to worry about after every ride. When you get sick of the mess from oil cooling, at least you can still clean up the motor and do forced air cooling then.

So a H4040 or mini-cro seems like the go for my next hub, also a MX rim and more tire. Heavier rubber, but I really need more more. Off topic sorry... with a H4040 or mini-cro, my same cooling issue will happen, just later in the ride.

No such thing as a HS4040...I got confused about this originally as well. Crystalyte only make 2 versions of the 40mm wide motors...a 3 turn (HS4080) and a 4 turn (HS4060). The 80/60 stands for the speed at full throttle on 72V...some resellers instead listed the speed on 48V, so the HS4060 becomes the HS4040...but it's the same motor.
Also, if you plan on getting another motor for your Fighter, be aware of the non-standard axle/drop out width. A stock standard HS40xx motor from Crystalyte will not fit your Fighter out of the box.

Cheers

 

[John in CR]

Emmett,

Oil is going to come out no matter what you do, because as the motor heats up positive pressure is created. Look at the oil cooling thread for some of the novel ways guys use to minimize it. It's not much leakage in any event. Add lot's of surface area and I'm sure you'll be happy with the results. Personally, I think that for anything more than light trail use a hubmotor is a poor solution, though I'm building a 2wd for trail use. For a serious offroader I'm definitely going with a mid-drive though, with the motor shielded from the elements but extreme on the ventilation for 15-20kw peak input geared for a 40-45mph top end, so it will have the torque of 30-40kw geared for 80-90mph. While you guys struggle with underpowered rigs with too much weight in the wheel, I'll be tearing it up like a featherweight motorcycle with no heat concerns, no noise, and no shifting. It won't be submersible, but damn close.

 

[Emmett]

Thanks guys. I shall give oil cooling a go, and report back with results. I'm clear on hub motor types and being able to revert to air venting later if I want to.

John, I loath the weight in the rear wheel and thought about it a lot before buying a Stealth Fighter. I wanted to get out on the trails now, in 2014, looking like a push bike to casual observers, and it's working great. Except for this stator heat build up issue...

 

[izeman]

there is no going back from air cooling to oil cooling and vice versa, more or less. if you drill holes you can't fill it with oil. that's obvious. but if you fill it with oil and drill holes afterwards you can't paint it with anti rust or something like that because you won't be able to get the oil completely out of the windings.
so trying air cooling first and then oil cooling is doable as you just need to buy new side covers to revert it.

 

[Punx0r]

Even if you can't get the windings clean (immersion in degreaser should achieve this) it doesn't matter because they don't need to be painted - only the magnets and stator iron do.

 

[izeman]

Even if you can't get the windings clean (immersion in degreaser should achieve this) it doesn't matter because they don't need to be painted - only the magnets and stator iron do.

so? windings are easier to clean, but will never get everything out that has been sucked into the stator. and it will come out again. paint won't stick to it for very long. believe it or not.

 

[amberwolf]

Double the surface area doubles the heat it can transfer to the environment at the same temperature.

I cannot air vent my H4065 hub because I always ride on dirt, with many small creek/gully crossings, and often muddy sections, even in dry weather, there is dust plus water crossings.

FWIW, if you don't want to air cool it but do wnat to increase surface area, you could either make new side covers (best) that have as tall a ribs as you can get sticking out fo the sides, for greater surface area, like typical heatsinks for electronics, or add such fins to them in a number of ways.

Then add similar fins to the rotor between the spoke flanges--this is easier than doing it ot the sidecovers without making new ones, as you could use a large hose clamp to secure two or more semicircular fin sections to it, or various other methods including pins or bolts thru holes added to the flanges.

 

[Punx0r]

Even if you can't get the windings clean (immersion in degreaser should achieve this) it doesn't matter because they don't need to be painted - only the magnets and stator iron do.

so? windings are easier to clean, but will never get everything out that has been sucked into the stator. and it will come out again. paint won't stick to it for very long. believe it or not.

You said you can't use air cooling on a motor that's previously been oil-cooled because you can't get the inside clean of oil to paint it. I'm suggesting you can.

 

[izeman]

Even if you can't get the windings clean (immersion in degreaser should achieve this) it doesn't matter because they don't need to be painted - only the magnets and stator iron do.

so? windings are easier to clean, but will never get everything out that has been sucked into the stator. and it will come out again. paint won't stick to it for very long. believe it or not.

You said you can't use air cooling on a motor that's previously been oil-cooled because you can't get the inside clean of oil to paint it. I'm suggesting you can.

did you do it? i tried. atf is sucked inside the stator plates. you won't get it out with detergent. and you can't paint surfaces that aren't oil-free. sure you can. but you will have paint flakes coming off sooner or later. that's just my findings your's may differ. if you never did it yourself you may think about it before you fill your motor with oil and decide against it afterwards. it's less mess if you just buy a new motor and start from the very beginning with a clean motor. just my 2c.

 

[Emmett]

I use INOX MX3 in my Crystalyte H4080. It is very low viscosity and hasn't eaten anything. I've used it for about a year and do some very extended hill climbs up forestry roads...temp usually sits around 60degC but can climb to my cutoff point of 85-90degC on one steep-extended section. You only need about 100ml - 120ml, so the lower quarter of motor has the windings covered. It will greatly improve cooling. You need a small breather hole: I drilled a small breather hole (2mm) on the freewheel side-cover near the axel. Also a fill hole on the other side (about 8mm) which you can thread and plug with a bolt. I use a syringe to fill. That's it... sure beats drilling heaps of large holes in your side covers to let dirt and water in.

Well thank you! Today was one of my most successful days on two wheels. A tiny $5 mod with huge benefits ...

I can now ride my Stealth Fighter until my battery switches off! That might sound like a case of "so what" to most people. My problem was the stator temp limit always kicked in well before I'd run out of battery power. The solution was to put 100ml of castor oil inside my hub. Just 100ml (all my local chemist had), and I sealed the hub and drilled a 1.5mm breather near the sprocket. I didn't care about the oil viscosity. Was happy that it's a good dielectric liquid and it's totally non-toxic.

I started out taking it easy, ended up going real hard. My usual on/off power usage on dirt trails. Jumping things, some whips, scrubs and some nice power wheelies, making a corner berm out of everything in sight, throwing it into flat sweeper corners with full power, look backs to marvel at my roost, blitzing up 100m segments of rough terrain trying to maintain 25+ km/h, cringing when I smash over large rocks hoping I don't pinch flat (again), or snap the forks. All up I rode for 95 mins. Air temp in the shade was probably around 29C while I was out there. I was physically stuffed, the rear shock was cooked, but my H4065 castor oil cooled hub motor wanted more. Heaps of animals out in the bush because it was 35C earlier in the day. The lizards always seem to pause and admire my army grey Stealth fighter. It felt like a dream.

The DC-1 displayed motor temp only got up to 1/3rd of full. Normally it's up at full temp (whatever deg that is I don't know) after about 30 mins, then soon the alarm would sound and power limiter cut in, and it took hours to cool naturally. Today my controller temp was very low, but that is normal for my bike. I was thinking all this cannot be happening. Waiting for something to cut out. I'd pull over, take off a glove and touch the hub and controller just to be certain. Yes the hub was hot. Too hot to touch for more than a few secs, but the stator must have been shedding more heat. The motor was pulling as strong as usual. As quiet or perhaps quieter than air filled.

Only the tiniest weep of castor oil came out the breather. I would have drilled a 1.0mm hole if I had the size bit.

In my world, with my kind of bike usage, this test was a definitive as it gets.

 

[itchynackers]

Welcome to liquid cooling! Now all you have to do is defend yourself against the "holes are better" gang. If they would only just try it...

 

[Emmett]

Thanks. No oil mess yet. Perhaps I should give credit to Stealth for the nice fit of their axles. As madmaxNZ and you have said, just try it.

I had a second ride with it today. No hub temp limit reached. Not even close. Sure it's only two test rides, and today was much cooler with about 22C air temps, but it's looking positive. With my power usage pattern, I expected oil inside a sealed hub might help a little, but I'm surprised it works as good as it does.

Knowing how bad my stator temp problem was previously, no matter how much better the heat transfer is from stator to the hub casing, I assumed my average stator heat output rate would eventually be too much for the hub's exterior surface to keep up and dissipate. But somehow it helps greatly. The stator temp sensor rises then holds at a safe value. I'm not pushing the motor real hard. That is my uphill segments are not steady full power, and these uphills are complete in less than 5 minutes. Plus I'm focusing hard to keep the H4065 motor in it's happier RPM range of 20 to 40 km/h, which is tough for me on tight trails. But the point is I'm riding at least as hard as I was previously without oil cooling, and now the stator is certainly not getting super hot. Also the hub exterior does not feel any hotter to touch. It might even be cooler, but I don't understand how that could be true.

With a possible net increase in stator generated heat, ES users Allex and John in CR have warned me about the risk of permanent heat damage to the rotor magnets. Until I do something to increase in external hub surface area, I'm not sure what I else can do about that, beside keeping the hub clean, and taking it easy, which means only using full power in short bursts while I monitor the situation.

 

[John Bozi]

Surely there are two es members living in the same area where one has air the other oil cooling and can do a motor challenging ride with gopro footage, to put all these air oil comparisons on camera and lay the differences to rest.

 

[itchynackers]

There would still be too many differences for any one camp to claim victory. The only way I see (which members would agree on) is to have Justin compare the two methods in his lab setting, so as to minimize variables. Otherwise, it doesn't matter if you climb Pikes Peak, speculation persists.

 

[izeman]

as i've tried oilcooling i can say that it's a GREAT way to remove heat from the windings. i was able to ride my hs3540 with more power for longer. but it came for the cost of oil leakage. and a reason to go electric for me was to have NO oil patches in my garage
so yes: it works great. can't compare it to air cooling with holes in the covers though.

 

[itchynackers]

Yes, you are right. You CANT compare it to air cooling, since oil cooling works so much better. If you are getting an oil "patch" in your garage, you obviously need to improve the system, not abandon the concept. If we didn't improve the technology on things, we'd still be using sharp sticks to hunt.

 

[GCinDC]

Thanks. No oil mess yet.

hey emmett, glad to see you just went and did it! did you take any pics of the how you sealed it, particularly the wire slot? i always ended up w/ leaks.

so do let us know if it leaks.

not sure if you saw this thread, fyi: Oil cooling your hub- NOT snake oil!

 

[izeman]

Yes, you are right. You CANT compare it to air cooling, since oil cooling works so much better. If you are getting an oil "patch" in your garage, you obviously need to improve the system, not abandon the concept.

if you watch my posts about this you will notice that i, and several others experienced the same problems. it heavenly depends on the motor make you have. those with a wire slot are hard to make leak proof. if you go the hard route, make a new axle and new bearings in a modded side cover you will have a great motor in the end. and i guess this is the way it should be done if you want it to be bulletproof and durable. my motor was not leaking for some time, but after some days the oil found it's way out ...

If we didn't improve the technology on things, we'd still be using sharp sticks to hunt.

real man out run the dear to death, or catch it and strangle it to death. at least this i how we do it here in good ol' europe

 

[Emmett]

Thanks. No oil mess yet.

hey emmett, glad to see you just went and did it! did you take any pics of the how you sealed it, particularly the wire slot? i always ended up w/ leaks.

so do let us know if it leaks.

not sure if you saw this thread, fyi: Oil cooling your hub- NOT snake oil!

Hi GC, No I hadn't seen that thread. So thanks.

Mine leaks. Very slowly on the left side, between the axle and inner bearing race. Just have to give it a rag wipe before and after each ride day. One day I'll open the hub up, clean off the castor oil and try seal it. But I'm not too worried about it at all. Very slow leak. No leak out the wire slot.

This 100ml (or maybe 90ml now) of castor oil has completely transformed my riding experience. The net cooling effect of the hub motor is so much better. I can ride until may battery is empty. Every ride, without a doubt. When I do get the stator temp up a bit high, I just ride lightly and it cools down quickly to a safe level. Skeptics can say anything they like about the theory. I can say that if you are on/off the throttle on dirt trails, BMX tracks or the like, then sealed oil means the hub sheds much more heat.

A smidge of oil also comes out my 1.5mm vent hole. Using castor oil means clean up is easy.

Maybe I'm dreaming, but my H4065 motor also feels smoother, quieter and maybe more powerful. Maybe the cooler stator flows more amps. Don't know. But the thing works. Without oil it did not.

I've got 1L of castor oil coming next week. So it'll be interesting to see what the old oil looks like. If dark and burned after 10 rides, that's no problem, since it's quick and easy to drain and refill.

 

[bowlofsalad]

Mine leaks. Very slowly on the left side, between the axle and inner bearing race.

Well, this feels a bit like providence, I was just writing a question in a thread about this very subject. Your post, more or less, proves a theory to be accurate.

The stemming of this thought goes back to a video I saw of Justin discussing the various routes for water ingress. I wasn't sure if he explored this very route water ingress from the bearing races (and for others, oil escape). The reason I am making this post is because the solution is pretty simple (well, probably not as much if you've already oiled the hub), a little sealant around the inner and outer races should solve this issue very quickly. The idea of implementing this concept sounds less than ideal, but oil leaking sounds a bit worse to me, and lots of water getting in sounds even worse.

I wouldn't know which sealant would be ideal for this, http://simplybearings.co.uk/shop/Engineers+Adhesives-All+Engineers+Adhesives/c4460_4540/index.html?dd_data={%2239%22%3A%220%22%2C%2262%22%3A%220%22%2C%2267%22%3A%220%22}&_=1415498402138&page=1 but this place has an excellent list of sealants, one of them may be the ideal sealant for this application.

Sorry if this is common knowledge or already discussed, it's news to me.

 

[Emmett]

Yes, I agree. It will be fairly easy to seal it. Removing the castor oil will be easy with some acetone or brake cleaner fluid. To seal I'd use some suitable sikaflex sealant. The trick will be ensuring I don't bond the bearing race too permanently to the axle. A bead of sika on the outside, on both sides might do it. Then I can cut it away before pulling the hub apart in the future. I'll work something out.

Don't know what you mean about "lots of water getting in".