Hub motor cooling ideas

[tostino]

I have been trying to think of the best way to increase my hub cooling.

I have a Bafang, so even if I were to make my side cover swiss cheese, the whole side is covered by my freewheel anyways. I don't think there is any benefit of cutting holes. I know on the 9C and X5, there is room for them, and it seems like they make a huge difference.

So my second train of thought went to computer cooling methods. My video card memory has little heat sinks on them to keep cool.
I am thinking that lining the outside of the hub with these little heat sinks using thermal glue like this. I would use enough heat sinks so most of the top of the hub is completely covered, and even possibly some on the side covers.

In addition to this, I also think using thermal paste to help the flow of heat from windings to stator/axle. I would put thermal paste in the black area of this picture but on every one:.

The reason I am wanting to do this in the first place is I am pushing the little Bafang to 35mph. Where I am is completely flat so heat buildup from hills isn't an issue, however, I am worried I will eventually fry it if going full throttle against a headwind, or even just riding a long time. The temp here just hit 99 today (it's really not much cooler until we get into late december).

Do you guys think this is a worth-while effort, or am I wasting my time?

Thanks for what ever insight you guys may provide!

 

[dogman dan]

Worth a try, and report back to us how it works. I haven't temp sensored my fusin gearmotor yet, but I find the heat is located at the axle using infared thermometer.

No suprise, that is the part directly connected to the windings, so it will heat sink towards the axle first. When I had sensors on my heinzmann, which did the same thing, I found that the temp on the rim of the hub would be still pretty cool when the 170F temp sensor inside the motor shut it down. The temp sensor I had on the axle end would be at about 150-160 f then. It got me wondering about heatsinks on the axle ends, but on than motor, I had no axle left to put another nut on. I was thinking heatsinks welded to a nut or something.

 

[fechter]

I'd guess the outside of the motor doesn't get too hot as is (at least not compared to the windings), since it has outside wind blowing on it. Adding fins to the outside will only help a little (but it might look cool). You need to move the heat from the windings to the outside somehow. A long metal path is just about as bad as a short air gap. If the motor can circulate the air inside faster, you can increase the heat transfer from the windings to the outside case. If the magnet rotor has some holes in it, you might be able to make some fins or blades that act like a blower fan when the motor runs. I'm thinking like some strips of real thin plastic glued to the rotor somewhere and bent into a blade next to the hole.

The axle is made of steel and has a very long path, so I don't think you can get much total heat through it.

Swiss cheezing the side(s) and blowing air through the motor is really the most effective way of getting heat out of the windings in a motor like that. You could do just one side and blow in and out of the same side. Of course this approach is not so good in the rain, dirt, etc, but if the intake to the blower is protected, the positive air pressure will tend to keep crap from getting in.

Regardless of cooling, it would be a really good idea to have some kind of temperature sensor on the windings and prevent them from going over 150C or whatever the rating of the hall sensors is. You can give it tons of power as long as you don't exceed the max allowable temp. Ideally, the temp sensor should be tied into the current limiter circuit to gradually back off on the current as you approach max temp. This would make things fairly idiot resistant.

 

[tostino]

The problem with swiss cheesing one side is that the side that has access to the windings is completely covered by the freewheel. The other side goes to the gears. The rotor has NO holes whatsoever between the magnets and the air gap is so small I don't think I could cut the plastic strips with enough accuracy for them to fit in the air gap.

Oh, maybe I miss-understood what you were trying to say. I just thought that I could put fins protruding out from the rotor that are just short enough to not hit the side cover. I have enough space to do it on both sides it seems.

 

[tostino]

I am trying to think of a way to use a TEC to cool a hub motor, but I am not even sure if it's possible.
Anyone have any ideas? maybe putting them on the axles with heat sinks hanging off?

 

[Drunkskunk]

Link was onto a pretty cool Water cooling Idea.

 

[jag]

Contrary to some of the other replies, I think putting little chipset heatsinks on the surface of the hub motor will help. Likewise any other means of increasing the surface area of the motor will help. It is more difficult to figure out how much it will help. If you were able to measure both inside (windings) temp and outside cover temp you could calculate it. For instance suppose the windings temp was 100C, air temp 20C and surface temp 40C w/o heatsinks, and you managed to lower surface temp to 25C, then the heat energy transfer would increase (100-25)/(100-40) = 1.25 or 25%

 

[tostino]

Contrary to some of the other replies, I think putting little chipset heatsinks on the surface of the hub motor will help. Likewise any other means of increasing the surface area of the motor will help. It is more difficult to figure out how much it will help. If you were able to measure both inside (windings) temp and outside cover temp you could calculate it. For instance suppose the windings temp was 100C, surface temp 40C and air temp 20C w/o heatsinks, and you managed to lower surface temp to 25C, then the heat energy transfer would increase (100-25)/(100-40) = 1.25 or 25%

Awesome math. I just made a little excel spreadsheet to make it nice and easy to do those calculations.

Glad to see the possible potential of little heat sinks! I guess i'll see what I can do with about $30 worth of them as soon as my motor is working again!

 

[GTA1]

Is there a way to direct cool air into the innards of the motor without introducing dirt, moisture, etc.?

 

[tostino]

Is there a way to direct cool air into the innards of the motor without introducing dirt, moisture, etc.?

Possibly drilling a hole through the other side of the axle? Other than that I don't see a way. I already spent 4 hours trying to get all 6 phase wires and the halls down the other side of my axle, so nothing more is fitting in there!

But if was to drill a hole down it, I worry how much I would weaken it.

 

[TylerDurden]

Bunt-pan:
http://endless-sphere.com/forums/viewtopic.php?f=2&t=9791&p=165152&#p165152

 

[GTA1]

Drill holes, and install little scoops that introduce air into it.

And don't ride in the wet... at all.

Or try to fashion a filter / air cleaner with a scoop that utilize centrifugal forces to separate out the water before the air goes into the motor.

 

[TPA]

slots in the surface between the spokes, with internal fins if there is room, and a hole through the other axle.

then it behaves much like a pump, with air flowing one direction, put a filter over the axle hole. 8)

 

[cycleops612]

Heat is an important problem, but isn't the answer, at least partially, readily at hand?

The spokes!

Maximise heat transfer from the hub to the spokes and its then quickly dissipated, certainly by the spinning wheel of a normal commuter.

Conductivity could be considered in spoke choice

thermal paste on spoke/hub connectors may help

the spokes themselves could have further heat sinks - a spoke would fit snugly between the fins of many types.

too much heat getting to the rim could be a problem, but i think the basic reasoning is sound. It could shed a lot of heat & its simple

I imagine one simply loosens each spoke (or maybe just compresses the wheel to loosen spokes temporarily) , cleans the contacts & injects some thermal paste & re-tightens with a torque spoke wrench or to the same pitch..

also, perhaps a thread exists on the stator that could have an unshielded thick copper wire () to transfer heat to the frame.

Maybe ebikes will be unpainted alloy in future. Look like crap but great radiators.

Having a smoke with the wheel in a puddle should be effective & harmless.

I have no problem whatever on my 350w 36v 22kg 21 gear alloy mid drive MTB. The motor housing is integrated in the frame. Fantastic bike. Never a heat problem.. Would handle 450 watts easy, & so light. Far better than 700 watt & heavy for most. (if you wish, google TDE1202Z - pretty much what I have)