Comparing Motor Case Temp to Internal Temp

[m52 power!]

Is there any general temperature range to compare the outside case of the motor and what the internal should approximately be?

Reason being is I am seeing higher temps reported on my CA than I was expecting. I am running a crystalyte 4065 on 72V LiFe and max 50A. Continuous watts at speed is around 2300. After 10 minutes CA is reporting 100C. After 20 minutes CA is reporting 115C. I have my CA set to start limiting at 100C and off at 120C.

I took some measurements at the end of my ride. The max temp on the case was 62C, while CA reported 110C. Does this sound like a normal temperature differential?

Is there any other way to confirm it is reporting the correct temperature?

 

[Drunkskunk]

Unfortunatly, no. I think it was Dogman who did some testing on that about 5 years ago. The internal temp can spike quickly, while the external temp can remain cool. there isn't a good path for the heat to move from the windings to the wall of the case in stock form. That's why many put cooling holes in the case, or use oil cooling on their motors.

One of the things you can do, however, is verify the calibration of your temp probe. Boiling water is always 100c. Naturaly half melted icecubes in a glass is always 0c. if the probe is close on both of those, you're good.

 

[z50king]

Water can be above 100C when heat is added in a pot. If the surface of the water is just giving off visible steam, it is close to 100C. If there are bubbles coming from the sides of the pot, the water is above 100C.

There will be a large temperature difference between inside the motor and outside. If inside and outside surfaces are the same temperature, no heat is traveling from the inside to the outside. The amount of heat transfer from hot area to cold area based on the temperature difference is not linear. Bigger difference gives much more heat transfer. Smaller difference gives much less transfer

 

[dogman dan]

That sounds like a big difference to me too. But weather and type of motor play a part. And wattage too.

Calibrating the sensor with hot water should work. You could just compare the sensor with another thermometer you know is true using water of any warm temp.

1 Your wattage is enough to really heat a motor fast, so the difference is still quite plausible if you load is heavy enough. Dirt riding up some really steep hills? 15% grade on up can heat up hubbies nice and fast. I've melted a motor that had cool covers. That was not normal, but it can happen, even on a warm day.

Anyway, my point is you might find the difference smaller 10 min later, when the heat transfer to the cover catches up. And I find it quite plausible that you reach 110c. Even on the flat, plausible after a run of 10 miles. Cutting off at 120c should result in never browning the windings. Bump to 130c?

2 Weather. The 50-60 F difference I was measuring was found at 70-100F weather. Full summertime. In colder weather you'd expect the cover to remain cool much longer in cool weather. I was looking for motor overheating in normal 500-1000w use in my climate in summer. I knew I was fine in winter, and never collected the data for winter. In summer, a heat spike inside took about 5 min to show on the cover thermometer. This showed why the feel the cover test could fail you. I found the axle heated sooner, and more consistently agreed with inside than the cover.

3 A gearmotor will transfer the heat to the cover slower. I have no data on the heat difference for gearmotors. I had a temp sensor both inside and outside of a dd motor similar to a crystalyte 407.

 

[z50king]

Why does no one vent the geared motors? Especially if they are not viscous oiled?

 

[dogman dan]

Dirt will get in and clog up the grease on the gears. Grease plus dirt equals lapping compound.

 

[mvly]

If you regen hard and accelerate often in stop and go traffic, the winding can get hot much faster than the casing. You need to slow down so the head can transfer to the case to cool it off.

I find that if I ride in stop and go a lot and stop for a long red light, the temperature drops faster than if I did a long ride and stop for the same amount of time with similar ambient temperature. Point is, slow down or stop for a while to let the winding heat transfer to the case. Otherwise, cut holes in the motor casing so you can cool the winding faster. Or like what other here recommend: put oil and seal everything assuming your bearings are water proof/resistance. It should keep your temperature quite low if you use oil for your scenario.

 

[John in CR]

Water can be above 100C when heat is added in a pot. If the surface of the water is just giving off visible steam, it is close to 100C. If there are bubbles coming from the sides of the pot, the water is above 100C.

Not any plain water I've heard of without adding a pressure sealed lid like with a pressure cooker.

 

[John in CR]

I took some measurements at the end of my ride. The max temp on the case was 62C, while CA reported 110C. Does this sound like a normal temperature differential?

It could be, but it really depends on a lot of factors that affect the heat transfer from the outer shell or impact the amount of heat being made. This would be comprised of the ambient temperature and the coefficient of convective heat transfer, which would be affected by your speed, wind velocity and direction, the airflow over your bike near the motor, the rpm of the motor, etc. On the heat generation side, your load, road grade, wind, phase/battery current limit ratio, or even the air pressure in your tires would be factors.

Lets not forget about the measurements too. Where the temp sensor in the motor is located on the stator and where on the shell you measure the exterior temps would have a big impact in the differential.

If you simply want to know if the CA temp is correct, compare the 2 temps before your first ride in the morning. As long as the sun hasn't been shining on the motor, the 2 should be virtually identical.