Safe max temperature for a geared motor ?

[Jil]

I haven’t found a specific topic about this.
What is the maximum continuous inner temperature that a geared motor (GMAC, Bafang G310, Shengyi…) can handle with no impact on its lifetime ?
80, 100, 120°C… ?

 

[TorontoBuilder]

The typical low end of the scale is class A insulation.

It's rated for 105C max continuous temperature for 20K hour life. But there is a class O which is only rated to 90C... I'm unsure of what the windings in the typical mid-drive ebike motors are rated for because I have never seen this published.

The manufacturer's usually state only ambient temperature: -20 to + 55℃ and max power ex. 48v 1000w

Based on the above though I suspect they use wire with an E class insulation rated 120C

That said motors with hall effect sensors commonly use lower operating temperature rating of 85C (some are rated 150C) IIRC... so in practical terms if you dont know what you have I'd not want to exceed 85C

 

[Jil]

Noted, thanks.
I had in mind to set a thermal rollback at around 90°C.
The motor will probably be a Shengyi SX2.
At what temperature can the plastic gears be damaged, because less prone to sustain torque as they become softer ? I would guess 90°C is a safe limit ?

 

[hias9]

Unfortunately it's very hard to get technical details from Bafang, but I would guess the G310 uses 150 degrees Celsius rated wire.
I regularly run it up around 110 degrees Celsius at the stator and the wire looks like new after a few thousand miles.
Only the cords became a bit darker.
However after about 200 miles I had gear failure at only 90 degrees Celsius and motor case was not even warm. I reduced max torque from about 44Nm to about 36Nm and used high quality grease rated for 150 degrees Celsius after that.
Regarding the hall sensors, I don't know the rating of those used in gear hubs, but I guess it's way higher than 85 degrees Celsius.
On large DD hubs usually 150 degrees Celsius rated hall sensors are used.

 

[Jil]

and used high quality grease rated for 150 degrees Celsius after that.

What grease is it please ?

 

[hias9]

Molykote EM-30L. I used a bit more than half of the 50 milliliters tube for the G310.

 

[Jil]

Thanks ! :thumb:

 

[Comrade]

I reduced max torque from about 44Nm to about 36Nm and used high quality grease rated for 150 degrees Celsius after that.

How did the grease contribute to the failure?

 

[hias9]

I dont know if it contributed.
Below is a picture of how it looked.
The main reason is probably due to the 43-44Nm maximum torque which is still within what Grin for example recommends as maximum, but way higher than the 30Nm it is officially rated for by Bafang.
When I changed gears after that I also replaced the grease and reduced maximum torque to about 36Nm.
I was using a temp sensor on the stator which showed only 90 degrees Celsius when it happened and the case was not even warmer than body temperature.

 

[spinningmagnets]

China is famous for presenting a high-quality prototype. And then, after production starts, they slowly begin introducing cheaper internal materials.

The Hall sensors become low-grade generics that didn't pass A-grade inspection...if there even was a QA inspection.

Same with the soldering jobs and the quality of wire insulation. Assume the worst.

Past efforts have shown that staying below 90C might be good.

If you are running hotter that this (which is fine if thats what you want to do), then you are converting a LOT of battery watts into waste heat.

Hot wire has more resistance than warm wire, so running hot adds another layer of inefficiency.

 

[hias9]

It’s not really a lot more watts. Resistance simply increases linearly with temperature, so efficiency will be lower at a higher temperature. If I simulate my G310 in the grin simulator and compare 90 Celsius to 110 Celsius, we are talking about a decrease in efficiency of 0.3 points (high speed) to 1.3 points (low speed).
If ambient temperature is 30 Celsius, 110 degrees is 33% higher than ambient than 90 is, so the motor can dissipate more heat.
So if you allow your motor to run hotter, it can take more watts continuously (while sacrificing some efficiency).
But I can only say for the G310 that 110 max works fine on it and the winding wire looked like new after a few thousand miles. Other motors might use cheaper components (especially the winding wire insulation) which are rated for a lower temperature.