Jan 16, 2013, 01:10 AM  
Joined Jun 2012
811 Posts

Discussion
Motor heating up to 80+ deg C during no load tests
This is a 174 gram motor (http://www.hobbyking.com/hobbyking/s...ner_Motor.html) doing a no load current test on 4s, my OSD reads 2.8 amps, could be innacurate (will check with wattmeter later), and after about 35 minutes of this, it gets to 80 degrees C (measured with temp probe).
That seems like it shouldn't happen unless it is either going through massive winding resistance (which I find unlikely, will test tonight as well) or something like the ESC motor brake being partially on and dumping energy straight into the motor. The ESC is a 60a plush from several years ago. Can anyone tell me what could be going on? 
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Jan 16, 2013, 07:21 AM  
Joined Jun 2012
811 Posts

What causes the iron losses? I.e. what are they proportional to? Current? Rotational speed? Voltage? Load? Switching speed?
Because it seems like a fair amount of heat generation to have to deal with in the air  the cooling on that motor is pretty bad even though I have cut huge holes in the foam around it to promote airflow, almost no air is able to run through the core of the motor, only some hits its left and right sides while it runs. 
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Jan 16, 2013, 08:40 AM  
Joined Jun 2012
811 Posts

Quote:
So looking at that thread, most of them are saying that, in the same motor, it is chiefly proportional to RPM, or values that change in lockstep with RPM (commutations), although someone mentioned current (not sure whether to conclude current matters or not...). If that is the case, and current doesn't matter, then indeed these losses will not increase, and may infact decrease, when a prop is added and max speed decreases slightly? Not to mention potentially added cooling. 

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Jan 16, 2013, 09:17 AM  
Joined Jun 2012
811 Posts

I assumed, before this thread, that most of that current was used splashing air around inside and around the motor, so I didn't think the heat was dissipated internally =D

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Jan 16, 2013, 10:23 AM  
Joined Jun 2012
811 Posts

Quote:
The losses from the former would be independent of current, the losses in the second would be linearly related to it as far as I can reason, as long as the waveform in the windings is the same? Is one of them negligible compared to the other? 

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Jan 17, 2013, 05:52 AM  

Hi
No load losses are mainly a) Magnetic hysteresis losses b) Eddy current losses c) friction losses (BB + noise) d) ESC losses (probably small, not easy to estimate) e) copper no load losses are very small generally An order 3 polynomial W versus rpm is generally a good fit see graph for 3 Dualsky XM6360 different windings http://www.rcgroups.com/forums/showp...77&postcount=2 Heat is developped both in the stator lams and in the rotor Louis 
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