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Old Jan 16, 2013, 02:10 AM
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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 3-5 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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Old Jan 16, 2013, 05:40 AM
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There's nothing wrong with the motor or ESC. The problem is the 3-5 minutes of running with no cooling.
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Old Jan 16, 2013, 05:41 AM
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Thats why you should newer run a motor no load for more then a few seconds, its the iron losses that heats up the motor, and at 80C you`ll risking to demagging the magnets.
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Old Jan 16, 2013, 08:21 AM
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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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Old Jan 16, 2013, 09:12 AM
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http://www.aveox.com/DC.aspx

http://www.rcgroups.com/forums/showthread.php?t=1630005
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Old Jan 16, 2013, 09:40 AM
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Thanks Dr Kiwi!

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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Old Jan 16, 2013, 10:13 AM
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However the heat is generated, imagine turning on a 40W bulb for 3-5 minutes, then holding the glass globe in your bare fingers!
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Old Jan 16, 2013, 10:17 AM
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Originally Posted by Dr Kiwi View Post
However the heat is generated, imagine turning on a 40W bulb for 3-5 minutes, then holding the glass globe in your bare fingers!
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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Old Jan 16, 2013, 10:58 AM
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Originally Posted by Nereth View Post
Thanks Dr Kiwi!

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.
The current does matter! The heating is coming from the power supplied by the battery--under no-load, it is basically being turned into heat. In this case it is going into the magnetic heating, both hysteresis and eddy current losses, and perhaps some minor bearing. There is a little resistive heating too, I suspect not much.

Just mutlply that current by the voltage to give you the wattage.
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Old Jan 16, 2013, 11:23 AM
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Originally Posted by Alan Hahn View Post
The current does matter! The heating is coming from the power supplied by the battery--under no-load, it is basically being turned into heat. In this case it is going into the magnetic heating, both hysteresis and eddy current losses, and perhaps some minor bearing. There is a little resistive heating too, I suspect not much.

Just mutlply that current by the voltage to give you the wattage.
I don't know specifically what each one (eddy and hysteresis) is since it's been years since the few minor electrical courses I did, but would I be right in saying one (eddy?) is the currents induced in the laminations by the magnets of the motor moving around them, and the other (hysteresis?) is the magnetism induced and reversed in the same plates as the current in the wires reverses, and the heat generated from this inefficient process?

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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Old Jan 17, 2013, 06:52 AM
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Antony (France)
Joined Sep 2003
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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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