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What is 'too hot' for motor temps?

What is 'too hot' for motor temps?

Old 06-15-2015, 07:45 AM
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Default What is 'too hot' for motor temps?

I know motors may vary in their tolerance for high temps but I ran a Hacker 21.5 without a fan yesterday for the first time (broke a fan blade recently) and it temped at 231 when I finished my practice run. There was a faint motor smell after the run but it still worked, it was just slow, even as I started my run.

The motor is about 15 months old and was showing signs of weakening already so it may have been weakened by a combination of our desert heat and racing it in those conditions.

What motor brand has a history of running cooler than their competition? And what fan is going to push more air? Looking to buy into a comfort zone when I make my next purchases. Current consideration are the R1 Wurks 21.5 as well as the Trinity 21.5 high torque motor but I don't know what else is comparable in speed that will run cooler than the rest.

My recent history is running a thin Muchmore Ultra High Speed fan on my 21.5 motor mounted to a clamp-on motor heat sink, and the temps were still around 170-180.
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Old 06-15-2015, 08:03 AM
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I wouldn't say there's an exact figure, but I thought anything over 160 was pushing it.
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Old 06-15-2015, 08:07 AM
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Heat of brushless motor the end of motor. Not cuz of electronics but heat demagnetize the permanent magnet, the rotor. Rethink you gear ratio. To high will cause it, mostly your pinion. I forget 21.5 is considered a stock or intermediate motor. Your pinion too high. You must bash a lot lookin for speed only. Find out the spec on ESC for lowest KV motor it'll take for speed. Same thing racing a coarse. pinion decisions.
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Old 06-15-2015, 08:28 AM
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I always considered 190 the cut off zone
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Old 06-15-2015, 08:52 AM
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I like the motor to be 160 at the most. The "fast" guys will typically have the timing jacked up more and run around 185. This shortens the life of the motor and 200+ is alot easier to reach if your running 190 vs 160.

At 230 you at least damaged the magnet/rotor. Check the stator for any signs of heat damaged wires or melted epoxy. If the stator is fine you might be able to get away with just buying a new rotor.
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Old 06-15-2015, 09:03 AM
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Originally Posted by Geezatec View Post
You must bash a lot lookin for speed only.
WOW! Really? That was an ignorant assumption! How could assume that so casually? Did it ever occur to you that just maybe I only need the speed? Don't be misled by my low post count, I don't live here.

...NEXT!
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Old 06-15-2015, 09:09 AM
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Depends where you temp. I have the MT4S/Sanwa Vertox Zero combo in my TC. I have had telemetry read out on my Radio at 190, when temped on the outside of the can it says 150. So what really is safe? Internal temps or external? My d4 1s still pulls strong after a whole season.
I want to try the Scorpion power systems motors. They are supposed to be built like their airplane motors, the magents are rated to 200 degrees C the wire to 180c, so I hope the car motors are as well built.
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Old 06-15-2015, 09:13 AM
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Originally Posted by 2uzferunner03 View Post
I like the motor to be 160 at the most. The "fast" guys will typically have the timing jacked up more and run around 185. This shortens the life of the motor and 200+ is alot easier to reach if your running 190 vs 160.

At 230 you at least damaged the magnet/rotor. Check the stator for any signs of heat damaged wires or melted epoxy. If the stator is fine you might be able to get away with just buying a new rotor.
Thank you for the tips!!

160 will be nearly impossible to maintain since our summertime track temps are around 120-140, air temps are around 100-115, and to keep up I have to max out the timing in my 21.5 GT car... as all the fast guys do.

Many of my fellow expert 17.5 racers also max out their timing, so in order to compete I must follow suit or be content being a back marker....and I don't know anyone that is content in that spot....after all this is racing.
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Old 06-15-2015, 09:15 AM
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I've had the solder melt at around 212, so I wouldn't go over 200, I always try to stay between 160 and 180. The epoxy in the stator could warp when it gets over 210, and it's hard to tell if it is warped other than the fact that your motor will be slower. I've melted a number of motors in the past racing 2 cell 21.5 oval when the pavement was over 140 degrees
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Old 06-15-2015, 09:20 AM
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let me say that 230 degrees is way too hot. ...you'll surely ruin your motor running that hot.

I would suggest checking your gearing, -lowering the size of your pinion should help greatly reduce the strain on your motor and thus the high temp's your seeing. Also, get a heat sink and fan on that motor ...this should drop temps by about 10-25 degrees. ....last, you mentioned you run in really dusty conditions? I suggest using an air compressor to blow away any debris from your motor and then oiling at the ends where the shaft is visible at each bearing.

That should get your temps to a much lower rate.

I get nervous whenever my temps get above 170 ...not to mention a hot motor will not run as fast and strong as a cooler motor.
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Old 06-15-2015, 09:43 AM
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Originally Posted by OttoKrosse View Post
Thank you for the tips!!

160 will be nearly impossible to maintain since our summertime track temps are around 120-140, air temps are around 100-115, and to keep up I have to max out the timing in my 21.5 GT car... as all the fast guys do.

Many of my fellow expert 17.5 racers also max out their timing, so in order to compete I must follow suit or be content being a back marker....and I don't know anyone that is content in that spot....after all this is racing.
I live in a valley area where air temp can be as high as 105F and track temp up to 140F. When I ran 21.5T, I've never had to run a fan on the motor with 2.8-3FDR. This applies to speed passion and Kill shot motors. 17.5T is different story. Not sure if it's your motor that is going bad or others. I'd check all the drive trains for bindings, esp. bearings first. Then move on to FDR. for 21.5T, it can go pretty low to 2.8. If track's small, use higher, even above 3.5. Try what everybody runs first and work your way up/down. If you hit lots of brakes, it raises electronics' temp for sure. W/ 21.5T, you rarely need brakes. If you do brake a lot, and as long as the other above all checked out, and if the temp is still hot, it may be your driving style. easy on throttle, let it roll before you make turns. If you cannot make proper turns w/o using brakes, except very tight hairpins, then your car isn't set up right. Even hairpin turns don't require lots of brakes with 21.5T. Make appropriate changes mechanically on your car so it turns better.
Make sure you don't have drag brakes. You don't need it at 21.5T. That raises temp as well.
Good luck.
Oh BTW, I would buy a new motor anyway as the other gents rec'd. Once motor hits over 200F, its performance won't be there anymore even if it still runs. High motor temp raises battery's and ESC's temps as well. Take it into consideration.

Last edited by snuvet75; 06-15-2015 at 10:31 AM.
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Old 06-15-2015, 10:31 AM
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Get a 30mm fan that can handle 2s lipo like the superior hobbies f5 fan
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Old 06-15-2015, 10:59 AM
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On an engineering standpoint, increasing your motor temp from 50C to 80C, or from 122 to 176, the resistance of your motor has increased 12% just from heating, that's at least 12% power loss, and as you had to burn more of your battery to get that temperature that's even more loss.

Last lap counts as much as the first!
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Old 06-15-2015, 12:06 PM
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Maxing out timing does not automatically equate to faster speeds by default. Reducing timing and adding pinion can have the same or better effect, it all depends on your motor. The only thing increasing timing does guarentee is a higher temp.
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Old 06-15-2015, 12:11 PM
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Originally Posted by DesertRat View Post
On an engineering standpoint, increasing your motor temp from 50C to 80C, or from 122 to 176, the resistance of your motor has increased 12% just from heating, that's at least 12% power loss, and as you had to burn more of your battery to get that temperature that's even more loss.

Last lap counts as much as the first!
Think your confusing power with efficiency. Brushless motors don't start fading in power until they're overheating, 190+
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