Isolation-Resistance

One Frame Out of 789,272: The Isolation Alarm We Didn't Send

Here’s a number that should have set off every alarm I built.

On June 29, my 2017 Model X’s battery management system reported its high-voltage isolation resistance at 50 kΩ — one tenth of the floor most monitoring treats as the healthy minimum. That’s the kind of reading that, taken at face value, says the insulation between 400 volts and the metal body you touch is failing. On a lot of monitoring setups, that’s a 2 a.m. push notification and a drive to the service center.