Definitive Tests on the Heating and Cooling of Hub Motors
- Thread starter justin_le
- Start date
If FF + Hubsinks isn't enough, the next best option is forced ventilation. You don't have to conduct heat if you simply remove it:
Cooling fans inside Hub motors
Hi all, I've posted about this a few times in other threads, but I think it deserves a thread of it's own as I believe the idea has merit and I plan to try it in the future with my Crystalyte HS4065 once I repair it. If you take a look at Crystalyte Hx series motors (and many other motors)...
endless-sphere.com
Cheers
If you do this, please add a temp sensor on the stator and gather some baseline data. Then it will be a way to see the results. With liquid cooling, while messy, it’s easier, conceptually, to see why it would be very effective at heat transfer. Under load, the stator temp could quickly spike over 100c while the side covers remain barely lukewarm. 50% greater heat transfer sounds impressive until you compare it to how much heat the weakest link, air, can transfer from the stator to the side cover.
@kk64; This page may be useful to you; I found it in a search for something completely different. Haven't read all of it, so don't know the conclusion.
etrike.wordpress.com
Bafang CST – Oil Cooling
I got a ‘like new’, used 20″ Bafang CST geared hub motor from Ebay. The seller stated it only ran 170km. Definitely no exaggeration, since it still turned with noticeably resistan…
etrike.wordpress.com
Justin's Pic:
I like it! IMO it would be better to to remove the heat from the stator and reject it directly to the atmosphere than it would be to conduct it to the shell and then reject it to the atmosphere.
I have been thinking about adding a scoop on one side of my bike to catch the air while riding and direct it towards the motor. I hope to drill holes close to the ID of the side cover on the same side as the stationary scoop and install several small NACA ducts facing the direction of rotation then drill similar holes on the opposite side as close to the OD of the side cover as possible and install the same NACA ducts facing opposite from the direction of rotation...the ducts close to the OD should create a lower pressure region due to the higher velocity when compared to the ducts close to the ID (same principle as lift for a wing) and the ducts close to the ID should intake the higher pressure air delivered by the fixed scoop on the bike.
So basically just an enhanced version of the set up in the pic above.
If anybody has a Leaf motor they have smoked or an extra set of side plates for a Leaf motor, I'd like to buy them...please send me a message via Endless Sphere and we can work out the details
.
Last edited:
Vented and circulating liquid cooling. Currently set to 120A DC/200A phase Peak @60v (BAC2000).
New guy here and decided to jump in at the end before reading a bunch of this thread (it's loooong)
From my understanding of gas powered 2 stroke bicycle engines and considering that most electric hub motors are painted black the convective cooling is going to be degraded by the black paint.
Probably a small issue in the broad picture though.
A number of 2stroke bicycle engines are painted with a fairly thick black high temp paint including on the Cylinder cooling fins. That's bad and really makes them prone to overheating from what I understand.
Yeah probably not a severe problem with electric I'd imagine but thought I'd mention it in case it had been a thing that was overlooked.
From my understanding of gas powered 2 stroke bicycle engines and considering that most electric hub motors are painted black the convective cooling is going to be degraded by the black paint.
Probably a small issue in the broad picture though.
A number of 2stroke bicycle engines are painted with a fairly thick black high temp paint including on the Cylinder cooling fins. That's bad and really makes them prone to overheating from what I understand.
Yeah probably not a severe problem with electric I'd imagine but thought I'd mention it in case it had been a thing that was overlooked.
scrambler
10 kW
Painting hot objects black is actually a good thing as black radiates heat better. It allows them to radiate their internal heat out.
Huh that seems counter intuitive. It's hard to imagine black paint conducting heat better than non oxidized bare aluminum.
The surface oxidation would be the problem for aluminum I think. Perhaps black paint is preferable to an oxidized surface on aluminum.
Apparently plating of silver on aluminum is possible but the silver needs to be polished or have a coating otherwise it oxidises as well?
Beyond my scope of needing to know right now I think!
The surface oxidation would be the problem for aluminum I think. Perhaps black paint is preferable to an oxidized surface on aluminum.
Apparently plating of silver on aluminum is possible but the silver needs to be polished or have a coating otherwise it oxidises as well?
Beyond my scope of needing to know right now I think!
scrambler
10 kW
Interestingly enough, doing some research, it appears painted aluminium does indeed radiates more heat, and therefore cools off more quickly (like 25%)
But the paint color does not make a big difference. Black paint would only radiate 1% more than white paint.
www.bestheating.com
But matt radiates better than shiny
Learning everyday
But the paint color does not make a big difference. Black paint would only radiate 1% more than white paint.
Does the colour of your radiator affect its heat output?
Coloured radiators are all the rage! But do certain coloured radiators perform better than others? We explore...
www.bestheating.com
But matt radiates better than shiny
Learning everyday
Hummina Shadeeba
10 MW
If the aluminum is painted black and outside in daytime isn’t it going to be absorbing a lot of heat from the sun? I see there’s infared-resistant paints available. I just made a battery in natural amarid color (gold) after the last black -tinted one would get hot being in the sun.Interestingly enough, doing some research, it appears painted aluminium does indeed radiates more heat, and therefore cools off more quickly (like 25%)
But the paint color does not make a big difference. Black paint would only radiate 1% more than white paint.
Does the colour of your radiator affect its heat output?
Coloured radiators are all the rage! But do certain coloured radiators perform better than others? We explore...
But matt radiates better than shiny
Learning everyday
How does a layer of paint, which is a thermal insulator, allow heat from inside to get out? The article starts saying the paint has a negligible effect but goes on to say a 25% heat output.
Last edited:
scrambler
10 kW
Black does absorb outside heat, but the premise is about objects that generates a lot more heat than what they receive from the sun so the exchange is in the favor of radiation out rather than absorption in.
As why paint helps radiating heat out, here is one formulation I found on a pgysics forum
"Because radiated heat is heat transferred by light (that is, radiation). The paint is in physical contact with the radiator, so the paint gets heating by conduction, and the paint then cools by radiating heat (as well as a little conduction with the air, and a lot of convection).
Unless the radiator is getting hot enough to glow in optical wavelengths the optical color doesn't matter. If it is hot enough to glow, then black will perform better than white because the ability to emit radiation is the same, from a physics perspective, as the ability to absorb it. If the radiator isn't that hot, then what matters is the "color" in wavelengths you can't see, and shiny metal is good at reflecting light in many wavelengths, so is bad at absorbing/emitting light."
As why paint helps radiating heat out, here is one formulation I found on a pgysics forum
"Because radiated heat is heat transferred by light (that is, radiation). The paint is in physical contact with the radiator, so the paint gets heating by conduction, and the paint then cools by radiating heat (as well as a little conduction with the air, and a lot of convection).
Unless the radiator is getting hot enough to glow in optical wavelengths the optical color doesn't matter. If it is hot enough to glow, then black will perform better than white because the ability to emit radiation is the same, from a physics perspective, as the ability to absorb it. If the radiator isn't that hot, then what matters is the "color" in wavelengths you can't see, and shiny metal is good at reflecting light in many wavelengths, so is bad at absorbing/emitting light."
scrambler
10 kW
All that said an done, this is actually a complicated subject that has to do with what is the predominant cooling mode (conduction or convection/radiation) is being predominant in a given configuration.
An aluminum heat sink with fins and active cooling fan probably loses heat more by conduction than convection and would not gain much being painted.
A flat aluminum surface with no active cooling on the other hand probably loses a significant portion by radiation.
And of course the conductivity of the paint itself matters....
below is an example or Radiation constant
Perfect black body: 5.67
Matted steel: 5.4
Matted zinc: 5.3 (that's why zinc roofs get so hot in the sun!)
Oxidized copper: 3.6
Polished copper: 0.28
Matted aluminum: 0.4 (that's why aluminum roofs are much fresher in summer than zinc ones!)
Polished aluminum: 0.23
Polished silver: 0.17
Reference: Black Body Radiator vs painted surface
An aluminum heat sink with fins and active cooling fan probably loses heat more by conduction than convection and would not gain much being painted.
A flat aluminum surface with no active cooling on the other hand probably loses a significant portion by radiation.
And of course the conductivity of the paint itself matters....
below is an example or Radiation constant
Perfect black body: 5.67
Matted steel: 5.4
Matted zinc: 5.3 (that's why zinc roofs get so hot in the sun!)
Oxidized copper: 3.6
Polished copper: 0.28
Matted aluminum: 0.4 (that's why aluminum roofs are much fresher in summer than zinc ones!)
Polished aluminum: 0.23
Polished silver: 0.17
Reference: Black Body Radiator vs painted surface
Those numbers confirm what I thought. Oxidation does inhibit heat transfer.
I knew silver has very high thermal conductivity from when I was doing flame working (glass blowing on a bench mounted torch). I used .999 silver wire by melting it onto a glass rod and vapor depositing it onto glass to color it. While holding the silver wire even a pretty long length almost immediately when it was exposed directly to the flame I felt it heat up almost instantly.
What gets me about those numbers is the "matted" aluminum. I don't know what matted is but it's kinda surprising that it's more conductive than even silver.
I knew silver has very high thermal conductivity from when I was doing flame working (glass blowing on a bench mounted torch). I used .999 silver wire by melting it onto a glass rod and vapor depositing it onto glass to color it. While holding the silver wire even a pretty long length almost immediately when it was exposed directly to the flame I felt it heat up almost instantly.
What gets me about those numbers is the "matted" aluminum. I don't know what matted is but it's kinda surprising that it's more conductive than even silver.
scrambler
10 kW
Be careful not to confuse radiation which is convection, and Conduction which is by contact.
Hummina Shadeeba
10 MW
I’m sinking a large battery in hard polyurethane foam and wondering if I tint the foam black will that enable the cells to better transfer heat to the foam? Or maybe no radiation/convection is happening and it’s just conduction since in physical contact?
Last edited:
scrambler
10 kW
Polyurethane foam is an insulator, so I would assume it has a very low conductivity and would not transfer much of anything between the battery and the foam.
Hummina Shadeeba
10 MW
Otherwise the battery is in a thin layer of air and I think the foam transfers heat a bit better. Not that there’s anywhere for it to go but at least a bit of a heat sink.
I think could add some filler to the foam like talc or ceramic and could transfer heat better.
I’m really wondering if there’s still radiant transfer of heat if two things are in contact, such as with the cells in black tinted foam vs white
Chalo
100 TW
Air convects; foam cannot. The air layer has to be very very thin before it won't flow around due to temperature gradients.
Battery cooling is definitely a topic I'm interested in learning more about. I've seen battery pack examples insulated with silicone all around and a plastic shell. That didn't seem to me like a great idea.
I understand that protecting the battery from shock and vibration is a little more important than cooling though probably in most cases.
I understand that protecting the battery from shock and vibration is a little more important than cooling though probably in most cases.
Hummina Shadeeba
10 MW
If there’s no airflow and the battery is in a very thermally resistant sealed aramid and plastic box I think the polyurethane will absorb more heat than the air. They’re both bad at getting rid of heat. Is there radiant heating when parts are in contact?
I bet could add stuff to some foam and can still get a strong foam that transfers heat ok.
The purpose of the foam really being building a battery that has no movement from daily road riding or a drop or even a crash.
Attachments
If the battery is properly sized and designed for the usage, it isn't going to generate significant heat and won't need cooling.
If the battery requires significant cooling, it probably needs a redesign with correct cells, interconnects, etc., for the usage it is in.
Sure I think I kinda imagined that.
A question (s) I've been meaning to ask related to batteries and heat (also forgive me for discussion
in a thread on hub motor)
Say a battery pack is properly designed/applied would there be an amount of heat (that isn't desirable) from fast charging (also done in proper way)?
Also wether "fast" or at a usual charging speed is it ok to charge then immediately ride or ride and immediately charge? Is that bad for the pack? Does doing that make the pack too hot (degrade it)?
A question (s) I've been meaning to ask related to batteries and heat (also forgive me for discussion
in a thread on hub motor)
Say a battery pack is properly designed/applied would there be an amount of heat (that isn't desirable) from fast charging (also done in proper way)?
Also wether "fast" or at a usual charging speed is it ok to charge then immediately ride or ride and immediately charge? Is that bad for the pack? Does doing that make the pack too hot (degrade it)?
If any usage or charging circumstances heat the pack up in any significant way, then it can be argued that it isn't properly designed / sized for the application.
If it is PD/S, then you use it in a way that heats it up, you're exceeding what it was designed for....
There are plenty of applications that use cells at or near their max ratings, and so they heat them up. Max ratings are that--max beyond which damage and/or failure is likely to occur. Some things also have recommended ratings, at which they will perform more optimally.
In general, heat shortens the life of components (of whatever kind), and thermal cycling (heating then cooling then repeat) can cause mechanical changes to the structure of components (of whatever kind) that may be detrimental to their designed function.
Heat also generally accelerates chemical reactions and changes, and some of these may be irreversible.
How much heat and/or cycling will cause any particular change depends on the specific characteristics of each cell, device, etc.
Which of those applies to any particular cell or other device you'd have to research and/or test.
Most non-random-chinese cells have some official documentation, or testing by individuals, that shows behavior within some temperature range.
Note that I am not an engineer, just a hack with a small amount of technical training and knowledge and a fair bit of experience over the decades at misusing and breaking things, and helping people fix things they broke.
If it is PD/S, then you use it in a way that heats it up, you're exceeding what it was designed for....
There are plenty of applications that use cells at or near their max ratings, and so they heat them up. Max ratings are that--max beyond which damage and/or failure is likely to occur. Some things also have recommended ratings, at which they will perform more optimally.
In general, heat shortens the life of components (of whatever kind), and thermal cycling (heating then cooling then repeat) can cause mechanical changes to the structure of components (of whatever kind) that may be detrimental to their designed function.
Heat also generally accelerates chemical reactions and changes, and some of these may be irreversible.
How much heat and/or cycling will cause any particular change depends on the specific characteristics of each cell, device, etc.
Which of those applies to any particular cell or other device you'd have to research and/or test.
Most non-random-chinese cells have some official documentation, or testing by individuals, that shows behavior within some temperature range.
Note that I am not an engineer, just a hack with a small amount of technical training and knowledge and a fair bit of experience over the decades at misusing and breaking things, and helping people fix things they broke.
Similar threads
