beatle
Active Member
Correct, the 12v systems remain online even after the loop is cut, but in order for the DC-DC converter to have any input on the HV side, the HV contacts need to be closed, and for that to happen, the contacts need voltage from the 12v. If the fireman's loop is disconnected, the 12v cannot close the contacts which isolates the HV battery. I don't think the DC-DC can operate independently to power the 12v systems function even if the 12v battery is taken out of service while the car is on.
From that doc:
When cut, the First Responder Loop disables 12V power going to the airbag circuit. Cutting of the First Responder Loop also removes 12V power going to the high voltage contactors inside the HV battery pack. Cutting the first responder loop does not disable the 12V battery system. The 12V battery negative cable must be cut in order to disable the 12V battery system.
...
When necessary, the negative battery cable should be double cut to open the 12V battery circuit. Care should always be taken to not make contact with the positive and negative battery terminals when double cutting the negative battery cable. In addition to the high voltage system, Model X has a low voltage electrical system. Its 12Vbattery operates the SRS, airbags, windows, door locks, touchscreen, and interior and exterior lights. The DC-DC converter in the high voltage system charges the 12V battery, and the 12V battery supplies power to the high voltage contactors, allowing high voltage current to flow into and out of the high voltage battery.
From that doc:
When cut, the First Responder Loop disables 12V power going to the airbag circuit. Cutting of the First Responder Loop also removes 12V power going to the high voltage contactors inside the HV battery pack. Cutting the first responder loop does not disable the 12V battery system. The 12V battery negative cable must be cut in order to disable the 12V battery system.
...
When necessary, the negative battery cable should be double cut to open the 12V battery circuit. Care should always be taken to not make contact with the positive and negative battery terminals when double cutting the negative battery cable. In addition to the high voltage system, Model X has a low voltage electrical system. Its 12Vbattery operates the SRS, airbags, windows, door locks, touchscreen, and interior and exterior lights. The DC-DC converter in the high voltage system charges the 12V battery, and the 12V battery supplies power to the high voltage contactors, allowing high voltage current to flow into and out of the high voltage battery.