eBike Motors - How hot is too hot?


Local time
3:01 AM
Aug 17, 2020
After riding home 19mph into a headwind, 110 degree heat, High 280 percent assist my Yamaha PW-SE motor’s case was almost too hot to touch; 3 seconds to fingertip pain so probably around 140 degree case temperature. I don’t think this was at peak power; probably averaging 300 watts.

This much heat is mildly concerning to me; bearings are probably OK up to 180 degrees and nylon gears are heat-resistant, but the motor controller board is inside the case and probably cooking.

Yesterday I backed off a bit; very similar hot weather but I dropped a gear so 15mph, slighly higher cadence and Standard 190 percent assist. My personal comfort in the heat was about the same, but the motor temperature after the ride improved; there wasn’t a noticeable difference between the motor case and the bike’s frame.

To preserve motor longevity, I’ll be backing off a bit and gearing down in the summer heat; IIR losses in the motor means that fifty percent more torque is double the resistive heating. Spin more and slow down to avoid overheating.

I’m hoping to commute on the eBike throughout the summer; before the eBike I would avoid heat index condition of over 105; usually in Phoenix heat index is much below measured temperature.
All the ebike motor systems I've used have thermal protection built-in. When they get too hot, they will shut down or go on Eco or safe mode.

Sooo assuming Yamaha did a decent job with that motor, It'll have heat protection and I wouldn't worry.

One thing to do is go "all-in" and try to get it to protection mode. Also can email the manufacturer what their numbers are.

The old Levo used to to do it in cases you stated. The new Levo... I hear will almost never shut down.
My concern isn’t the single-incident catastrophic motor meltdown; it’s more about repeated high-temperature thermal cycling and its effect on reliability. After a while of this, at a microscopic level the aluminum contact areas on those power transistors begin to look less like new-fallen snow and more like a lava field. Riding in the Phoenix area I feel like I’m probably pushing the boundaries a bit; that’s why automotive companies test out here but I haven’t heard of the Specialized or Haibike Arizona test facility. The exception might be Pivot, located a couple of miles from my house and not far from South Mountain Park.
One thing I like about the thermal protection on the Levo is that it basically doubles the ebike riding distance. Whilst old timey mountain bikers are waiting for cool evening air on a blazing hot summer day, I can head out on my favorite trial during the hottest time of day when no one is around. The Levo quickly gets hot and cuts the voltage back. That is the same thing as going to eco mode. I noticed that one of the de-rates limits top assisted speed to 10 mph. So not only does it limit voltage to the motor it also watches the road speed so that means it has a double limiter. I've pushed it even farther on the heat scale and was limited to 3-4 mph. That was one of the best long distance climbs I've ever done on one charge.
OK, now I see what fc really meant; the Levo watches out for the motor so you don’t have to. I like that concept of graceful degradation of performance.
Do the motors generate enough heat to potentially start a fire if the bike is laid down in weeds?