QS273 temperatures

[gabry]

In the past years i've seen a lot of people talking about this motor, most of them giving 25/30kW no proble, and over 500 phase amps, but my experience was completely different...

SPECS:

• Motor QS273 40H 3.5T
• Controller: Mine, VESC based, 150A battery 350Aphase (400A peak)
• Battery: 20S LiIon 72V 90Ah nominal (84V max)
• Motor temperature limited to 110°C (120°C absolute max)
• Frame custom build stealth bomber like frame, steel/aluminium
• Weigth total around 160kg, rider/gear included

Last week i did some off-road riding in Italian Alps and i noticed that the motor doesn't dissipate heat at all, in up-hill riding at low speeds (5 to 25km/h) at phase currents between 200 and 350A i had to stop every couple minute. During the road driving temperature are much better due to higher speeds and lower phase amps, basically anytime phase amps exceed 150A motor starts to get very hot.
The thing i found weird is that outside rotor temperature was between 35 to 45°C when internal temperature was over 100°C, on the same roads with an escooter and same specs i get max 80°C internal and 50/60°C external, the ΔT between external and internal temperature of this motor is huge in my case, up to 80°C.
I opened the motor the first day i got it, didn't put ferrofluid or oil but i checked bearings, seals and added two waterproof pressure relief vales.

Motor runs fine, and torque is pretty good, but i didn't expect it to heat up so much and takes even longer to cooldown.


Now, is just my experience or is it always like that?
i'm thinking about doing one of those:

- adding synthetic or mineral oil inside the motore to improve heat exchange (messy)​

- adding ferrofluid (messy)​

- add internal fans (somewhat simple, works?)​

- find a way to liquid cool the stator running two thin copper pipes via the axle (most efficient, most complex)​

What do you think is the best solution, as in the future i'm going to upgrade the controller to hopefully give this motor 250A battery 700A phase.

Internal temperature measured via KTY83/122 already inside the QS273, external temperature taken via infrared thermometer.

I've already used mineral 10W40 engine oil (car) into brushless motors and they works fine after years, but was always messy as oil leaks even through wire strands

​

 

[E-HP]

Ferrofluid isn’t messy. Without ferrofluid or other cooling, the symptoms sound normal for riding those speeds. Why are you riding so slowly?

 

[gabry]

Ferrofluid isn’t messy.

From my point of view is messy as it will leave an oil film. For sure less massy than oil bath.

Without ferrofluid or other cooling, the symptoms sound normal for riding those speeds.

I was used to 50/55H 11" 1500W rated escooter motors that at similar conditions had way lower ΔT between external and internal, i was expecting better performances from this bigger motor but didn't consider those smaller motor make much more revolutions so may cool faster.

Why are you riding so slowly?

Speed it's related to terrain conditions mainly, doing enduro on wet rocks, the first piece it's at a 15% to 30% grade on wet rocky terrain with bends, anyway the problem is present even at higher speeds when accelerating over 150A phase.
Only was to keep motor under 80°C was keeping phase under 150A and power under 4kW, that's why i felt weird about people pushing it at 1000/1500A.

PS i'm driving this thing in Italian Alps, what would be the best cooling method suggested of the one listed?
has some of you tried one of those?

 

[E-HP]

When you stop to let the motor cool, how many degrees per second does the temp decrease?

 

[gabry]

When you stop to let the motor cool, how many degrees per second does the temp decrease?

About 250s average from 110°C to 85°C or about 0.1°C/s
From 85°C to 65°C about 0.03°C/s
From 65°C to 30°C an ethernity.
From 100 to 110°C in about 30s or about 0.3°C/s, basically is cooling down 3 times slower than is heating up at just 300A phase.

 

[scianiac]

Doesn't really sound like ideal conditions for a hub motor, most of the wattage claims are from people riding them on the road at high speeds where the motor is much more efficient so less heat of course, it's not really about the higher speeds cooling the motor with more air, it's about how efficiently the motor is running. Hub motors in anything other than tiny wheels suffer very high resistive losses at low speeds. Ferrofluid or oil will help a lot. If going with FF then heavily varnishing the motor to conduct the heat down through the coils and into the stator will also help a little bit. Smaller wheel would also help but there are of course many issues with that solution. Slow, steep, rough terrain is really the ideal territory of mid drives.

 

[E-HP]

Fans would be the only non “messy” option. Out of the others, ferrofluid is by far the least messy, and you wouldn’t need to seal the hub. You may not care if you don’t have rear disc brakes.
I’ve found that cool down time is the best measure for comparisons since there are too many variables on the heating side.
Your cool down times are pretty slow, so you need something. I recently replenished my statorade. The motor looked new inside and the old statorade was right where I put it, with a little less carrier fluid. Afterwards my cooldown times were back to normal. Heating time was similarly extended. The downside of drilling and fans is the opportunity for crap to get into the hub, which I would be concerned about when riding dirt and mud.

 

[gabry]

Doesn't really sound like ideal conditions for a hub motor, most of the wattage claims are from people riding them on the road at high speeds where the motor is much more efficient so less heat of course. Slow, steep, rough terrain is really the ideal territory of mid drives.

You are 100% correct, from testing and simulation {0:10}km/h < 60%, {10,30}km/h < 80%, and so on, the best i measured was cruising at 80km/h. Didn't measure the efficiency on the 11" motor i'm using but they run at more than double the rpm, so could be in a more efficient range.

Slow, steep, rough terrain is really the ideal territory of mid drives.

Unfortunately i was forced to use hub motor as i needed a silent motor and capability to have pedals for legal reasons. Also most of the roads are good enough to drive at a decent speed, just some piece are very challenging, like 1km every 20km.

ferrofluid is by far the least messy, and you wouldn’t need to seal the hub.

I need to have a sealed hub, that's why i added the vents, as i ride in mud/water.

You may not care if you don’t have rear disc brakes.

I do have rear disc, but the motor has pretty god oil seals on the shaft.

The downside of drilling and fans is the opportunity for crap to get into the hub, which I would be concerned about when riding dirt and mud.

OH wait, i meant to put fan inside the motor but keeping the motor sealed, just to improve the thermal exanche with the hub motor case.

I think i will try to find some ferrofluid here locally, one option that was intriguing me a lot was the water cooling, but haven't found anyone doing something like that and sharing their results on those motors.

 

[gabry]

Main thing is that the outer case is basically cold, meaning there is very minimal heat exanchage, probabily caused by the fact the the ring where the magnets are mounted is made of steel and not aluminium like in a lot of other hub motors, and steel is a pretty bad heat conductor

 

[dominik h]

Some motors use curved magnets, then you have a smaller air gap and a better thermal conduction to the outer shell.

Sotion offers a water cooled hub motor, but it is to heavy for bycicles.

 

[E-HP]

I think i will try to find some ferrofluid here locally, one option that was intriguing me a lot was the water cooling, but haven't found anyone doing something like that and sharing their results on those motors.

There’s a member here that used that method. I recall he adds something to it to make it more effective. Plus I think coolent that raises the boiling point would be necessary anyway.

 

[E-HP]

I’m adding diy low profile heat sinks next. I’ve collected enough info now, using certain routes over the last couple of years to tell for sure if they improve anything.

 

[gabry]

There’s a member here that used that method. I recall he adds something to it to make it more effective. Plus I think coolent that raises the boiling point would be necessary anyway.

Yeah by water cooling i meant water + additives in a closed loop (not flooding the motor).

I’m adding diy low profile heat sinks next.

I could try that, i've access to a CNC, but didn't want something too big as i ride in mud/grass/rocks, hubsinks seems big for a 273, there isn't much space from the 19" rim

 

[E-HP]

Yeah by water cooling i meant water + additives in a closed loop (not flooding the motor).

I could try that, i've access to a CNC, but didn't want something too big as i ride in mud/grass/rocks, hubsinks seems big for a 273, there isn't much space from the 19" rim

Mine will be even with the flanges. I need to keep a low profile, so it doesn't attract attention. I was riding today and luckily saw a cop at the stop sign and had to slow down quickly and move my legs around while I passed by.

 

[gabry]

Mine will be even with the flanges. I need to keep a low profile, so it doesn't attract attention. I was riding today and luckily saw a cop at the stop sign and had to slow down quickly and move my legs around while I passed by.

That also, but with a qs273 motor and 6kWh battery it's already weird compared to italian ebike ("250W" motors and 0.3/0.5kWh batteries).
I could do something like that, 25mm high, or 20mm high if i want it a little more concealed, to be invisible it needs to be high 10/12mm

 

[E-HP]

That also, but with a qs273 motor and 6kWh battery it's already weird compared to italian ebike ("250W" motors and 0.3/0.5kWh batteries).
I could do something like that, 25mm high, or 20mm high if i want it a little more concealed, to be invisible it needs to be high 10/12mm
View attachment 355823View attachment 355824

I think they'll be fine on your bike without needing to be invisible, as long as you don't paint them florescent yellow and put flashing LEDs in between the slots. You need all the help you can get with those slow climbs.

 

[gabry]

I think they'll be fine on your bike without needing to be invisible, as long as you don't paint them florescent yellow and put flashing LEDs in between the slots. You need all the help you can get with those slow climbs.

I made them like the drawing but they did touch the spokes anyway (width 24mm height 25mm) si i had to trim them, I think the only way to put them in my case is to glue them with epoxy or high temperature silicone

 

[n00b]

About 250s average from 110°C to 85°C or about 0.1°C/s
From 85°C to 65°C about 0.03°C/s
From 65°C to 30°C an ethernity.
From 100 to 110°C in about 30s or about 0.3°C/s, basically is cooling down 3 times slower than is heating up at just 300A phase.
View attachment 355814

And no ferrofluid or heat sinks?

 

[gabry]

And no ferrofluid or heat sinks?

Yes, that's why I was a bit flabbergasted, I expected better heat dissipation from a "8kW" motor. Need to improve cooling a lot before going over 5/600A phase.

 

[E-HP]

I made them like the drawing but they did touch the spokes anyway (width 24mm height 25mm) si i had to trim them, I think the only way to put them in my case is to glue them with epoxy or high temperature silicone

I’m using thermal epoxy that I believe can still be popped off with a little persuasian, in case I break a spoke. I’m going to do a loop of safety wire around the center in case.

 

[Gruesome]

It's a bummer that there probably isn't any extra room between the inside of the side covers and the stator. (If there was spare room, the manufacturer would have made the motor slimmer, or the stator wider.) Putting taller ridges or 'paddles'/fan blades on the inside of the rotating side covers would be the easiest way to build a fan inside the motor. Although, looking more closely at the pics in this post, maybe there is a bit of room to make the existing radial ridges taller without touching the rotor? You could measure by closing the lid with some putty inside where you want to measure the distance between stator and side cover. If there is room, even if in only some of the radial space (like, further inwards, away from the coils), I would try that first.


Next best, since there are openings in the stator, might be to mount a fan in one of these section cutouts, blowing air inside the motor from one side cover against the other, thus making air circulate through the stator openings, and improve heat transfer from the stator to the side covers. Maybe a small 120V AC fan connected in parallel with one of the phases would work?

 

[E-HP]

Air is a very poor conductor of thermal energy, so blowing it around instead of out, won't do much.

With vented sidecovers, they can be effective for blowing the heat out.

Leaf / leafmotor / leafbike high efficiency 1500w motor

Here's "System A" with half the current and twice the current. But with double the current, the max torque is still the same at 300 N-M That's interesting. It makes sense when you consider that a higher voltage increases the rpm with which the motor can produce a given torque output...

endless-sphere.com

 

[Gruesome]

Air is a very poor conductor of thermal energy, so blowing it around instead of out, won't do much.

You are not conducting the heat through the air, you are using convection to transport the heat. The heat transfer coefficient to air is a strong function of air speed. Still, admitted, even doubling or tripling it might not be enough. It doesn't help that the OP's motor is probably only making one rotation per second when his problems occur (2m circumference wheel => 2m/s = 7.2 km/h). So the extra blades attached to the side covers might just move too slow. Still, that's the easiest thing to try. Note the paddles don't have to be metal, I would try something non conductive and kind of pliable, in case one of them rips loose...

The guy in the post quoted by E-HP did mount fans inside the stator, in addition to drilling holes. If you can get rid of the air, you only suffer the heat transfer coefficient to air once, instead of twice, once from the stator to air, and then from the air to the case/side cover.

 

[gabry]

Next best, since there are openings in the stator, might be to mount a fan in one of these section cutouts, blowing air inside the motor from one side cover against the other, thus making air circulate through the stator openings, and improve heat transfer from the stator to the side covers. Maybe a small 120V AC fan connected in parallel with one of the phases would work?

That was one of the idea proposed, but connected to the 5v used for hall sensors. Blades mounted to the cover won't work at those low speed, I could try oil bath, that will work for dure but it's quite messy if I need to clean it or if a leak appears

 

[gabry]

At the end i made them 70mm length, 21mm height, 23mm width. If you don't look too much closer they are barely noticeable, once used and dirty I don't think they will be visible. I made a through hole so I can pass a safety cord if needed, like you said @E-HP