What happens when the battery is completely drained?

[AMP3R]

Let's imagine the situation. We are driving along the highway and the battery runs out. As I understand it, both contactors will open? But this is not possible because there is nowhere for the energy from regen to go. Please explain the physics of the process.

[arber333]

Let's imagine the situation. We are driving along the highway and the battery runs out. As I understand it, both contactors will open? But this is not possible because there is nowhere for the energy from regen to go. Please explain the physics of the process.

Lets not talk like that here...
The idea of BMS is that it should stop the car BEFORE battery gets depleted. Some will reduce torque output and some just cut the torque altogether. There should be no connection to the DC contactors. Of course different story if 12V battery would get depleted. But then something would be wrong with DCDC converter...

If what you said would happen, then your cells (or some of them) internal resistance would go up up up and they will heat up to the point of ignition.
You would have a burning wreck.

[AMP3R]

Everything is clear with the battery. I'm interested in the inverter protection mechanism when the battery runs out. Do the contactors remain closed until the car stops?

[P.S.Mangelsdorf]

As someone who has done this (long story): As long as there is 12V power to the inverter, its not going to randomly open the contactors. It will continue attempting to draw power out of the battery, and the car won't go anywhere. The only way that fully depleting the HV would cause contactors to open is if you are only using a DC-DC and have no 12V battery (I'm not even sure how you'd do that anyways).

Arber is correct, you should have the inverter programmed with a minimum voltage so that you never run the HV truly flat. What happens when you hit that is the inverter begins to severely limit power, i.e. hit "limp mode." If you are an idiot like me and insist on continuing to push the car to stone-cold dead, it will not open the contacts, it will just continue to slow down until it stops completely. Limp mode is noticeable. Continuing to try to drive in limp mode makes you a traffic hazard. But, limp mode will let you get to the nearest highway exit.

Just to reiterate: Doing this is a bad idea. Doing this on a public road is an unsafe idea. But, doing this should not cause contactors to open.