Motor and ESC caught fire... help!

[Philbruh]

So was just about to fly a build when I had the great idea to test out the motors (with no props) on the bench to see that everything was working before I took it to the park. I may have gotten a little too throttle happy because the front left motor started to smoke, then caught on fire... then the ESC also caught on fire...

Please see deceased motor and ESC attached

Any ideas on what went wrong:
- Is it a shotty soldering job or was it me pushing the throttle without props? The PDB has ESC outputs at 25 amps but the ESC's run at 12amps which could be reason
- Faulty ESC or motor? It is an Emax MT1806 2280KV, not sure what the ESC is as it came from a DIY kit
- Did I cable tie the ESC too tight to the frame? The cable tie was rubbing the burnt out section of the ESC before it lit up

Not sure what to do from here either... I removed the part, tested the three other motors and they are working fine (for now), along with the receiver and flight controller. Is it safe to say that this was isolated to these two components? I'm thinking of just replacing these two only and keeping the rest

Current build is the following:
- EMAX MT1806 2280kv motors
- ESC (unknown), 12A (ESC that caught fire was the one that's attached to the flight controller)
- CC3D flight controller
- Matek mini power hub (ESC outputs on this are rated at 20amps, 25amps burst current)
- 3S, 2200mAh battery
- X8R receiver (powered through the 5v BEC output on the PDB)

 

[GJH105775]

You shouldn't test without props. Between the PID loops going wild and the lack of resistance to spin it is easy to damage the motors. The coil shorting due to either the higher RPMs or the heat is probably what caused the ESC to catch on fire.

What props are you going to be running on these? Your motors should pull less that 12 amps, but going over that by much for long would also be able to cause a fire.

 

[RGJameson]

Also a good idea to make sure your motor mounting bolts aren't too long and scraping the windings.

 

[Philbruh]

Also a good idea to make sure your motor mounting bolts aren't too long and scraping the windings.

First thing I checked, I was using really short screws that barely caught to the initial set of threads in the motor

You shouldn't test without props. Between the PID loops going wild and the lack of resistance to spin it is easy to damage the motors. The coil shorting due to either the higher RPMs or the heat is probably what caused the ESC to catch on fire.

What props are you going to be running on these? Your motors should pull less that 12 amps, but going over that by much for long would also be able to cause a fire.

I'll be using 5 x 4.5 x 3 props (dalprop cyclones). The models thrust sheet indicates these draw 10.6 so i'm assuming that will be safe?

 

[Philbruh]

Another thing I would like to know is if the PDB's "ESC output" current has any negative effect on the ESC's? The PDB sheet states 20amp continuous and 25amp burst.... does that mean its constantly feeding 20 amp to the ESC's? (Mine were only rated at 12 amp). If so I wasn't aware that there was a relationship between the PDB and the ESC's and can't seem to find a related thread on this. Does this output rating matter?

 

[dragger201]

Phil...........just so you know.........your PDB doesn't "feed" your ESCs. They draw as needed from you PDB. If your ESCs are drawing only 10a then that is all that is being feed thru your PDB. Also, I don't like gainsaying other members, but EVERY program that is used to program FCs that I've used will tell you that initial arming and testing is to be done without the props. I would not recomment running at full throttle without props, but all initial testing of arming and running I've done has been without props.

The problem as you described it would appear to me to be a connection that was not complete for conduction. A bad connection will act like a transformer........converting amps into volts in order to bridge that bad connection. If this occurred in the motor then a quick heat build up could have burnt an insulation that lead to a direct short which in turn could have done in your ESC. I don't understand enough about ESCs to be sure if a motor short would do that. I would check the ESC to Motor connections to see if one of them is burnt or more burnt then the others. Then disassemble the motor and see if you can find the burnt spot. Just for understanding what can happen, 30amps at 120volts can be converted to 55amps with enough voltage to jump a 1/4" gap and weld steel.

 

[Philbruh]

Gotcha, thanks for the clarification of current draw on the ESC's, glad to know its safe to use my power board and I don't need to fish out too many new parts

I just uploaded the image of the ESC. You can see that one of the black thingy's is clearly burnt out and 4 of the coils in the motor are black as well. I'll disassemble the motor tonight for a clearer analysis. Due to the sequence of the fire (motor first --> ESC second), I think its safe to say this was something to do with the motor?

 

[dragger201]

You can see that one of the black thingy's is clearly burnt out

Hey Phil.........that maybe where it all started. If that connection was bad, you'd get a voltage spike and with 12amps behind it that could translate to way to much voltage, which would then burn the motor creating more voltage spike and that would do the ESC............oh, the black thingy..........is that one between the ESC and the motor???(I shouldn't assume).............

 

[Philbruh]

Thanks, I think that's what happened.

Just to clear my mind it wouldn't be the fact that I am powering my FC from the ESC via the Black/red/ yellow signal wire? I find it coincidental that this esc that went up in flames was the only of the four that was powering the the FC. Ive seen this as common practice in many videos though

And by black thingy a I mean the small black squares on the esc, I attached an image of the burnt esc in the first post

 

[dragger201]

And by black thingy a I mean the small black squares on the esc, I attached an image of the burnt esc in the first post

Yeah, Phil, that looks like where it all started. Other then a short caused by bad solder job, I think if the power for the FC was the problem then there would have been damage to your FC itself.............

 

[GJH105775]

Thanks, I think that's what happened.

Just to clear my mind it wouldn't be the fact that I am powering my FC from the ESC via the Black/red/ yellow signal wire? I find it coincidental that this esc that went up in flames was the only of the four that was powering the the FC. Ive seen this as common practice in many videos though

And by black thingy a I mean the small black squares on the esc, I attached an image of the burnt esc in the first post

If the ESCs were being over-worked then the ESC that is also acting as BEC could very well be the first to go up. The black thing is a FET, they handle switching the DC to make it into the 3 Phase AC that the motors use. Once one started to fail the heat would cause it to draw even more current exponentially. I agree with dragger201 on testing without props. Low RPM required to see if the motors are turning the right way and to test the arm and disarm won't hurt the motors. With the props it could flip and damage the model, as well as go full throttle into your face as you plug the battery in. So you really don't want to test with props on.

If you were to have a short between two phases in the coil (a screw could do this) you would certainly be able to get a fire. There a voltage potential between any of the two phases of 3 phase AC while powered. Take a look at this animation to get a better idea. The ESCs are taking that DC from the batteries and making as it is on the chart using the transistors.

I like to spin my motors by hand after getting them soldered and mounted to test for a short across the phases. When you spin it by hand you produce a tiny amount of electricity (the motor acts like a generator), this power will resist motion and act like active breaking. You can test this by spinning the motor without the wires touching and it should spin freely (unless you just had the ESCs powered up in that case you get FET drag). If you touch any two of the wires together and try to spin it it should resist you unless you have a broken coil or wire.

A short usually will damage more than one FET, but so will pulling too much current. The heat produced could have burned some enamel off the coils in your motor. Might try spinning it a bit and seeing if you meet any resistance or using a multimeter if you have one.