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Old 09-11-2017, 08:55 PM   #1
Douglas Racer
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Default Smoking Motor

I ground ran my Turnigy D2826/10 1400Kv motor with an admittedly slightly large prop (9x6) and smoke came out of it. Thinking it was because I over propped it I installed a 7x5 which according to the specs should be fine. This time it didn't smoke but even at half throttle it became way too hot to touch after a few seconds. I've never encountered a motor getting that hot. Could it something in the ESC settings? I'm running a Mystery 30A ESC with the default settings and a 1500mah 11.1V lipo. Could timing cause this? On the first run the ESC got a bit warm but on the second run the ESC was cool. Thanks for any advice/input.
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Old 09-12-2017, 03:50 AM   #2
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Well the motor is only rated to handle 205 watts, but at a 50 gram weight I would only prop it to 150 watts.

Your 9x6 prop probably put it way over the 205 watts because the motor is only supposed to handle a 9x4.7 at 7.4 volts.

You were WAY over propped at 11.1 volts.
The motor is burned out, that is why it is getting hot with a 7x5, which is still too big at 11.1 volts. You are supposed to use a 7x4.

In all likelihood you now have a paperweight.

Sorry, but once an electric motor smokes weather it is a model motor or an electric lawnmower, it is probably shorted out.

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Old 09-12-2017, 04:41 AM   #3
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  1. Motorcurrent is proportional to pitch¹, voltage squared, Kv³ and diameter⁴
    and
  2. Power is proportional to pitch¹, voltage cubed, Kv³ and diameter⁴.

By going from 2s to 3s motorcurrent wants to increase by factor (3/2)²=2.3. Wants, ignoring a bit of voltage sag due to higher current.

You (also) may have fried your magnets, thus effectively giving the motor a higher Kv.

Even though you propped down the second time around, current was still too high due to increased voltage, possibly increased Kv and still oversized prop,


Losses = copperlosses + ironlosses = heat

  • Copper losses are proportional to current squared (Pcop=I²Rcop).
  • Iron losses = eddy current + hysteresis losses
    • Eddy current losses are proportional to rpm², rpm is proportional to voltage. Therefore eddy current losses are proportional to voltage².
    • Hysteresis losses are proportional to rpm and thus proportional to voltage¹.
(Ignoring aerodynamic, friction & eddy current (in copper) losses, and skin-effect.)

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Old 09-12-2017, 05:00 AM   #4
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Always use an e-flight calculator (e.g. e-Calc, Drive Calculator, Scorpion Calc) to get you in the ball park. And also check a changed/new setup with a watt-meter.
To trust is good, to calculate is better, to measure is a must.
Without a watt-meter you are in the dark, until something starts to glow Your your RC equipment, wallet, ego, battery, controller, motor, house/garage/car will love you for it.

To salvage your motor
Electric Motor Design, Construction and (Re)winding - RCG

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Old 09-12-2017, 05:08 AM   #5
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Originally Posted by Wildflyer View Post
Well the motor is only rated to handle 205 watts, but at a 50 gram weight I would only prop it to 150 watts.

Your 9x6 prop probably put it way over the 205 watts because the motor is only supposed to handle a 9x4.7 at 7.4 volts.

You were WAY over propped at 11.1 volts.
The motor is burned out, that is why it is getting hot with a 7x5, which is still too big at 11.1 volts. You are supposed to use a 7x4.

In all likelihood you now have a paperweight.

Sorry, but once an electric motor smokes weather it is a model motor or an electric lawnmower, it is probably shorted out.

Perhaps, but I don't think I was way overpropped. Reading the comments on this motor there are people running 9 even 10 inch props on this motor with 3 cells without smoke coming out of them. It's only 1400kv. It seems to me it should handle 9 inches without smoke. I'm going try a 6 inch on it and put it on the wattmeter. I think there was something wrong with it to begin with or it's labeled wrong. I was just wondering if the esc timing could cause heat. For $10 I don't care that much if it's a paper weight but I still don't think 9 inches should have caused smoke.
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Old 09-12-2017, 05:21 AM   #6
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Maybe I'm entering something wrong but this prop calculator from one of Ron's links shows only 15.3 amps with a 9x6.

http://rcplanes.000webhostapp.com/calc_motor.htm
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Old 09-12-2017, 02:22 PM   #7
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I run that motor on a glider. 20-30 seconds of power and then off for a few minutes. I run either a 8x4 or a 7x5 prop which is really the limit for this motor on 3s. A 7x4 is a good match. A 9x6 was way too big.

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Old 09-12-2017, 06:32 PM   #8
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Doug pretty simple, you burned up your motor. When you ran the over size prop and let the magic smoke out of the motor, it damaged the motor winding insulation off the wire. The wire used to wind motos has a lacquer or some type of insulation on the wire so when wound does not short out to adjacent winds. You burnt that insulation off and now you are left with shorted windings. You cannot fix it. Well you could fix it if you can open up the motor, take it apart and rewind with new wire.

Take your losses, learn, do not repeat mistake, and move on.
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Old 09-12-2017, 10:39 PM   #9
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I didn't make a mistake other than telling you it was a 9x6 prop. I looked again and it wasn't a 9x6 it was a 9x4.7. Even if it was a 9x6 which it wasn't, I'm still convinced a 3 second run shouldn't have produced smoke. According to this guy's bench test video a 9x4.7 is the ideal prop making exactly the max amps Hobbyking states in the specs. I didn't burn this motor over propping. Perhaps I pushed it to the limit but it should have been able to handle a 9x4.7 with out smoke according to HK's amperage spec, so I actually haven't learned anything. I suspect the motor was faulty to begin with or mislabeled. I wouldn't be surprised if the 2200kv version produced smoke with a 9x4.7. This guy tested a 9x6 and although it was over HobbyKing's stated max it didn't instantly smoke. The results are at 3+40 into the video. My question was actually more about the effects of ESC timing. See video.

https://www.youtube.com/watch?v=GDuo8gmfn9k
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Old 09-12-2017, 11:50 PM   #10
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Ron Van Sommeren would be the best to explain the effects of ESC timing.

Dave R, KI7MTA Proud PGR rider.
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Old 09-12-2017, 11:51 PM   #11
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Originally Posted by Douglas Racer View Post
I didn't make a mistake
My bad. Point I was making is the motor is toast. At this point it matters not if was damaged from testing, or already damaged upon receipt. Unless you used metering during the test is impossible to tell either way. If you had a shorted winding to start with would have instantly showed itself the moment you advanced the throttle. Current would shoot up high with very little throttle applied alerting you to a problem.
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Old 09-13-2017, 01:16 AM   #12
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I just put it on the watt meter with a 5x5E prop and ran it up to only about 2/3 throttle for a few seconds which showed about 215 watts at 20amps. It was but still burning hot. Ron said frying the magnets ups the Kv though so that would explain 215 watts on such a small prop I suppose. For a burnt motor it's still making crazy power though. Maybe I'll put it on a big ESC and see if I can get it to glow.
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Old 09-13-2017, 01:46 AM   #13
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Originally Posted by Douglas Racer View Post
I just put it on the watt meter with a 5x5E prop and ran it up to only about 2/3 throttle for a few seconds which showed about 215 watts at 20amps.
OK but that does not mean it is going into the prop as mechanical energy. A shorted winding will use up a lot of power, but with a shorted winding is not going into mechanical energy, it is burning off heat energy in the form of Watts. If the motor turns a prop, some electrical energy is being converted into mechanical energy with extremely low efficiency. Sure 200 watts input at 20 amps might well be within the Motors operating limits, but if a winding is shorted most of that power is being converted directly to heat. You would have to know RPM's or thrust generated to determine the Motor's Output in Watts, bu tif you did you might see something like 200 watts input, but only 50 watts output orr 25% efficiency. That missing 150 watt is being burned off as waste heat. Should be the other way around with 200 watts input and 150 watts output. Now you are 75% efficient and only burning 50 watts off as waste heat.

The motor did a magic act. It changed itself from a motor to a space heater.
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Old 09-13-2017, 03:00 AM   #14
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You have a point there. The watts are producing a lot of heat. It did seem like it was spinning the prop pretty well though.
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Old 09-13-2017, 04:31 AM   #15
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Originally Posted by Douglas Racer View Post
You have a point there. The watts are producing a lot of heat.
That is the Smoking Gun evidence.

Look at it this way. If you have say a 250 watt continuous power with a max continuous current of 17 amps and you connect a 4S with 20-amp ESC and input 200 watts, assuming the load is not too large like an over sized prop, the motor should never over heat and smoke the wires. It should run all day assuming proper ventilation. Submerge it in oil and can run 600 watts no problem.

If the motor over heats means one of two things. Either the motor is defective like shorted windings or bad bearings/bushings, or too large of a load because there is not enough torque to spin up RPM's proportional to the voltage being applied so the motor is is constantly trying to catch up and cannot do it.

So if your power input and prop size are all within limits and you are over heating the motor means your motor is toast. Smoke tells me burnt wire insulation on the winding causing a short burning more wire insulation. Sooner or later the wire will burn into and you will have an open circuit leaving you with a very cool and quite motor never to be heard from or heated up again.

Anyway, play with it on the bench until you burn it up, because I would not put it in anything I own. He!! I would not put it in your plane either even if you paid me.
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Old 09-13-2017, 04:54 AM   #16
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Take the props off, if the motor still runs hot it is shorted.

I have a nice big power 180 like that. $300.00 motor

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Old 09-13-2017, 05:01 AM   #17
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dereckbc I agree with all you said but I still say running a 9x4.7 for 3 seconds shouldn't have burnt it. If it was any of my other Chinese suppliers other than Hobbyking a replacement would be in the mail already. $10 doesn't really concern me though. I'll just buy a $5 replacement on Ebay that doesn't smoke.
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Old 09-13-2017, 05:03 AM   #18
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Originally Posted by Wildflyer View Post
Take the props off, if the motor still runs hot it is shorted.

I have a nice big power 180 like that. $300.00 motor
I thought running it without a prop was bad? Nothing to lose, I'll try that.
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Old 09-13-2017, 05:07 PM   #19
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magic smoke

Too many hobbies, and not enough time!
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Old 09-13-2017, 05:47 PM   #20
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eCalc shows a 2826 1400 burning up on 9x4.7 with 3S ....

Hobby King specs are actually spot on as I use this motor along with its higher KV versions ...

D2826-10 1400kv Outrunner Motor

Specs:
Rpm/V: 1400kv
Shaft: 3.17mm
Voltage: 2S~3S (7.4v to 11.1v)
Weight: 50g
Watts: 205w
Max Current: 21A
ESC: 40A
Suggested Prop: 7x4(3S) ~ 9x4.7 (2S)
Mounting Hole Bolt Circle: 16mm or 19mm

You do not want to step outside those specs ...

I agree that 3secs is pretty quick to smoke ... but that 9" prop on 3S is a big load on that motor ... she gets hot with 9" on a 2S ....

I understand that you are not happy with replies but honest replies.

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Old 09-13-2017, 07:00 PM   #21
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Originally Posted by Douglas Racer View Post
I thought running it without a prop was bad? Nothing to lose, I'll try that.
It won't cause any damage to a good motor that I have ever noticed or heard about.

If I have a motor of unknown KV, I put a piece of narrow (1/4"-1/2") white tape on the motor casing 180 degrees apart. Shine a LED flashlight on the tape and read RPM with an optical tachometer.
I have the motor connected to my inline wattmeter at the same time.

Now I have RPM and applied voltage so it is easy to figure KV.
I know my method may not satisfy Ron Van S. but it comes close enough for me.

My model room has fluorescent lighting which messes with optical tachs. That is why I use a LED flashlight for a pure steady light. Sunlight is perfect, but I do most of my work in the evenings.

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Old 09-13-2017, 07:36 PM   #22
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Nigel I'm not unhappy with the replies because I now know smoke didn't come from a good motor because of a 9x4.7 Did you look at the video I linked? That guy got exactly 21amps with at 9x4.7 I agree that's pushing it but like I've said it shouldn't have smoked at 21amps. I still wonder if it's a mislabeled 2200kv. When I plugged it into ecalc I came up with 19.54amps which is pretty close to what the guy got in the video got and below the specified max. Have a look and see if I made a mistake. Can you post your ecalc showing results showing it burning up so I can see if I made a mistake?

Wildflyer That's pretty cool. I'm going to try that with a known KV and see how close I come.

Anyway. The motor is smoked and I do not think a 9x4.7 prop smoked it. Thanks for the information from everyone.


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Old 09-13-2017, 08:19 PM   #23
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Hi DR .... I had similar to yours but temp and watts were higher when I used APC ... the Watts were into the red ... that means she's gonna get HOT electrically.

If the windings are deficient in any form, - Toast. We are talking a $10 motor and QC on it will not be as with a Hacker etc.

I use a lot of these motors and similar ... they are not all same and I take care not to go over specs for that reason.

Another example .... 2826 2200kv ... rated for 6x4 ... I use a 6x6 2 blade or a 6x4 3 blade ... it gets warm. Tried a 7x5 2 blade but she was hot and squealed. Pal of mine has same model / same motor etc. - uses same 7x5 and he's ok.

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Old 09-13-2017, 08:48 PM   #24
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I agree I shouldn't have spun a 9x4.7 but I'm the sure the motor was bad to begin with. The guy in the video spun a 9x6 for 33amps without smoking it. I'm with you though. I usually don't push my electrical stuff. I usually under prop and over ESC but this time I didn't. I think the 7 inch prop would have over heated it too though. I'll get over the $10 eventually.
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Old 09-14-2017, 12:48 AM   #25
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Originally Posted by Douglas Racer View Post
... I'm going to try that with a known Kv and see how close I come. ...
Four simple methods for determining Kv
www.bavaria-direct.co.za
→ motor constants

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