I suddenly lost power about 25 minutes into my flight the other day. This happened while using only 5.6kW at cruise control for about 4 minutes. In the air I decided to try and power cycle the BMS, but when I reached back I discovered one of the wires had come unsoldered from my connector. Furthermore the connector was melted together so there was no getting it apart.
My flight was conservative, only using full power for less than 15 seconds for take off, and one more short burst of power to climb out of a field for 15 seconds. My ESC logs never showed anything above 70°C and nothing else in the logs looked out of the ordinary.
My theory of what happened was the wire slowly unsoldered itself little by little over the past 10 flights. I haven’t abused the throttle enough for something like this to happen, so there must’ve been a bad solder joint. I don’t hold this against Paul, because I’ve learned first hand that these qs8 connectors are not easy to solder. I did discover a large sludge of flux on the wire that could’ve been inhibiting the connection. I’m sure as the solder bridge gets smaller and smaller, it takes less and less power to heat up.
So I went on to replace the qs8 connector. I removed the two power wires for the ESC to make soldering easier. But when I went to put the wires back onto the ESC studs, one of the studs effortlessly torqued off. So warning, these aluminum studs can only be torqued once! Luckily APD can fix this. The stud is soldered and press fit to the PCB. They have the proper tools to replace this stud for me.