EDIT 10/11 9:40am Central: I learned from my partner on this project I got the order of events wrong. I have edited the post accordingly.
I am working on some custom electrical hardware for modifications to a battery powered (24V) vehicle. All of my electronics live inside a painted metal box. Recently, after a laptop was connected via USB to my custom hardware, the laptop was placed onto the metal box and immediately there was a spark, and my laptop screen died without recovery. The laptop was on battery power, and the custom hardware was powered up.
I don't know exactly where the spark occurred. It could have been on the laptop metal case, or at the large data/power docking port on the bottom of the laptop (DELL precision m4800).
About the electronics:
- The custom electronics operate at 24, 12, and 5V, all powered directly from vehicle battery with DC-DC converters.
- All of the custom added electronics share a common ground which is the negative terminal of the 24V main battery.
- I have chosen my 'functional earth' for Ethernet shielding etc to be the box/vehicle frame.
- All of the custom added hardware lives in a metal box that is electrically connected to the frame of the vehicle (my functional earth). There is a 500kOhm resistance between the vehicle frame, and the negative terminal of the battery.
- The vehicle runs on rubber wheels, indoors, on a plastic like painted floor.
I don't understand what caused this spark with enough energy to break my laptop. How could such a damaging potential difference form between the metal box and the laptop case/internals?
Most importantly, how can I safely prevent this from happening again?
Thank you for any help and feedback!