Air cooling to good to be true?

[icecube57]

Can air cooling be to good. I reported on my adventures with air cooling before. It works very well but can it work to well.The outside temp was 53 degrees. It was raining. I was 10 miles away from my car. I booked it down the trail doing a solid 30+mph @ 2400w. My meter is saying that my motor is 65F. Im smiling. I finally get to my car it slowly creeps up to 94F . Before my motor always read 10-15 degrees above ambient under load and another 10-15 when at rest after a load. Now its almost a full 40F difference between ambient and motor temp. The cover is luke warm.

Its not even warm yet. Drilling my holes out bigger has affect air cooling the motor in a positive way but its now giving a false sense of security while riding thinking your motor is cool but its actually 40F warmer than I think.

There could be so much air current flowing through the motor that i could be super cooling the probe.The probe is pretty close to the winding. Its embedded into a hole in the stator and its less that half an inch away from the windings. I suppose one of us should use their IR probe on an air cooled motor and check the winding temp through the hole in the cover in comparison to their probe.

 

[gogo]

I think Dogman had a similar issue measuring axle temps. If I recall correctly, he covered the temp sensor with some sort of insulation to get a more meaningful measurement.

*Que Dogman*

But you're right, the bigger holes must be allowing more air circulation.

 

[dogman dan]

Very interesting! Let us know if the same thing happens when it's cold, but dry. I suspect the wet motor, riding in the rain, was getting lots of cooling and like you say, really refrigerated the inner hub, axle, etc. So you got a false low reading. It could happen again in wet, but warmer weather. I suspect that when you stopped, the motor dried out some, and then the temp quickly got warmer. Getting that sensor closer to the windings would be the best solution.

I have also noticed the temp climbing some right after stopping and wind chill goes away when stationary. Never saw it go up 40f though, but I don't have that many opportunities to ride wet here.

I was getting false low readings from wind cooling when putting a sensor externally, like on the axle stub. That far from the windings, I'm really guessing. Good enough for 750 watts though. At 2000 watts, you need to really know actual temps for sure.

 

[Mark_A_W]

Heat Soak.


But 94 degrees F?


That's not even warm...I think. 100 is about 40 proper degrees IIRC.


If it gets above 150C you are in trouble. That's 424.53324 bazzillion silly degrees.

 

[gmouchawar]

Make sure that the air is not cooling the thermistor directly. This can give you low false readings when there is a lot of air going in.
You need to insulate the sensor from the air so it is measuring the core temperature only.

 

[dogman dan]

Yeah, it could have had air cool enough that day to have the same effect as my sensors on the axle, exterior mounted.

 

[John in CR]

For a more accurate reading of your stator temp, I think the place to measure would be in between the metal plates that support the stator on the axle, and use a metalized epoxy to glue it directly to the backing iron of the windings. Then you're measuring out of the cooling air flow with a good direct connection to the metal of the stator. That should give you idea of the core temp of the stator in continuous use. Keep in mind that there will still be a time lag for short term peaks climbing hills.

As Mark said, 94°F isn't even warm, so if that's the temp it drifts to when you stop, then you have nothing to worry about. 10-15° above ambient before ventilating sounds awfully low to worry about exposing the motor to the elements with ventilation. I've only just started worrying about cooling due to higher power I'm running, but that's because my motors started getting too hot to keep my hand on more than a 2-3 seconds after a hill.

John

 

[dogman dan]

At 53 F and raining, I'm suprised he saw 94F. But I bet pulling 2400 watts on a nice 90f summer afternoon, he's gonna have to watch the temps.

At lame 1000 watts, I don't even monitor temps untill it gets above 80F. Unless I'm climbing pikes peak or something.

 

[amberwolf]

Or just glue the sensor directly between two sets of windings.