Re:Ford’s recall of Mustang Mach-Es in 2022 is under investi...
by londons_explore on Tuesday August 22, 2023 @01:37AM
(#37219068)
The contactor likely wasn't too small - that is a basic engineering thing that ford wouldn't have overlooked.
Instead they probably screwed up something in the precharge or disconnection process.
The contactors should only open or close when zero current is flowing. However that's often hard to achieve. Specifically, things either side of the contactors often have smoothing capacitors in, and all those smoothing capacitors need to be charged to the exact same voltage as the battery to ensure there is no sudden large current as the contactors close. If that happened, even once or twice, the surface of the metal contacts becomes non-flat, and then the contactor will have a higher resistance and overheat.
There is the same problem when opening the contactors. No current must be flowing, but sometimes that's hard to achieve when there are lots of things connected to the high voltage bus, and any one of them might be drawing or supplying current. It isn't helped by the fact that opening the contactors will probably be done in most fault conditions - and fault conditions could easily have large currents flowing.
Instead they probably screwed up something in the precharge or disconnection process.
The contactors should only open or close when zero current is flowing. However that's often hard to achieve. Specifically, things either side of the contactors often have smoothing capacitors in, and all those smoothing capacitors need to be charged to the exact same voltage as the battery to ensure there is no sudden large current as the contactors close. If that happened, even once or twice, the surface of the metal contacts becomes non-flat, and then the contactor will have a higher resistance and overheat.
There is the same problem when opening the contactors. No current must be flowing, but sometimes that's hard to achieve when there are lots of things connected to the high voltage bus, and any one of them might be drawing or supplying current. It isn't helped by the fact that opening the contactors will probably be done in most fault conditions - and fault conditions could easily have large currents flowing.