What happens when a motor wire is disconnected?

[Wheels_78]

Just had a 160A (constant) speed control, from a reputable manufacturer, burn up seconds into it's second use. Application was an RC aircraft and total run time on the system in this configuration was about 7-8 minutes. Maximum load encountered by the control was 150 amps. Post mortem found that one of the three motor wires may have come unconnected before the failure, could this have been the cause of the instant failure? (Motor went from producing impressive power to dead instantly with no unusual noise, I find it very doubtful that this wire was disconnected for more than an instant before failure, if indeed it was disconnected beforehand at all)

Thanks for the input!

 

[amberwolf]

If it disconnects under load, you get sparking across the gap. That means RF and all sorts of electrical noise, potentially including voltage spikes many times the battery voltage, many times the ratings of any of the FETs or any protection devices (if any). Not a lot you can do about that either in controller design or as an end-user, other than do your best to prevent poor connections or retention of them.

If you were electronic, what would you feel like with miniature lightning strikes on one of your outputs?

 

[Lebowski]

I concur with Amberwolf. Putting a large current through an inductor and then disconnecting it, this is how the ignition in your car works !

 

[Wheels_78]

lol, yeah, the car ignition analogy drives it home pretty well.Thanks.

 

[veloman]

I had a phase wire on my 9c come unplugged. It put out 500watts but that was it, and it sounded pretty weird. Controller has been fine since.

 

[amberwolf]

Sometimes nothing bad happens...but I wouldn't count on it.