magic smoke: ESC killed motor, or motor ESC ? - RC Groups
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Mar 12, 2012, 05:07 PM
Registered User

magic smoke: ESC killed motor, or motor ESC ?

Maybe some of you can offer some insight:

My EMAX 2805 2850kV gave off magic smoke - and I don't know if it was the Turnigy 12A ESC (which was, admittedly, a bit too small for the 16A or thereabouts whicht the motor draws on 3s using TGS 4,5x4,5) which had died first and shorted one of the phases - OR if it was bad insulation of the motor windings which resulted in a short there.

Last time I was firing up the motor to see if the vibrations are ok (if not i rotate the prop a bit on the shaft until I get good balance) I noticed that the RPM sounded rather low, but not having flown the Microjet for some time I thought, hey I am used to the hight EDF pitch, it might be me.
But after some two minutes of flying, the motor stops rather violently. I glide the plane down and hurry for lunch, I was late anyway. After lunch and coffee, rather carefree, next attempt. Less than a minute in the flight, the motor stops suddenly, very abruptly, again (not in the way it does when the ESC gets too hot or when I reach LVC). I glide down, and before landing I attempt to restart again, and there's a smoke from the motor. Also, there is smell coming from the ESC, but the shrink wrap is ok.

At home I fire the thing up again, ESC giving the usual beeping tones for 3s, and as soon as I apply throttle, a LOT of smoke comes from the windings.

Cutting the shrink wrap off from the ESC reveals a burnt transistor...

Since the motor was running rather cool (at least the bell was always cool to the touch) I was thinking that it must have been the ESC giving up ghost and shorting one phase - but I am not sure, and I have never read that a dying ESC would overload a motor. It could still have been bad insulation on the wires.

What do you think? In the attached picture you also see the heat sink (its backside with the burnt double sided sticky tape)...
Thanks for taking some time to ponder and answer.
Last edited by mopetista; Mar 12, 2012 at 06:04 PM.
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Mar 12, 2012, 06:18 PM
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flydiver's Avatar
I have never heard of an ESC killing a motor. I suppose in some situations it's possible.

Bad motors (shorts and bad connections) create a dead short and will kill and ESC in very short order.

I'm a bit confused. By your own statement it appears the motor was no good. You put a shorted motor on an ESC it will fry

[which had died first and shorted one of the phases - OR if it was bad insulation of the motor windings which resulted in a short there].
Mar 12, 2012, 06:40 PM
Registered User
you are right, I was very stupid to connect the battery again and see what happens AFTER I had seen some smoke, not doing that might have saved the ESC - if, that is, the ESC was not the culprit and had died in the first place.
Well, it wasn't completely dead when I last connected it because it made all the right tones, and supplied juice when I opened the throttle.
All very stupid, a short circuit in my brain.
But still: Anybody out there who has ever seen an ESC dying and killing a motor thereafter by a short circuit or such? I have never heard or read about that either, but some claim that a dead FET might also create a short. Don't know...
Mar 12, 2012, 08:18 PM
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flydiver's Avatar
I wouldn't call it stupid. You didn't know. Most of the stuff we learn in the sport is the hard way.
Now you know.

Do it again....that's stupid.

Rule - if a motor won't run IMMEDIATELY and PROPERLY > STOP!
Figure out what is wrong or pay with fried ESC.
Mar 13, 2012, 04:50 AM
Registered User
Generally, a short in the ESC or in the motor connection wires will kill the ESC, not the motor, because the current will flow through the short instead of through the motor.

Chances are your motor failed -- maybe a bad winding, maybe damage to a winding, or maybe even a bearing failing that caused it to draw more amps than before (happened to me recently).

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