This bit activates when the drive is required to absorb excessive regenerative energy by the motor and/or load. The drive calculates how much energy it has absorbed. When it has absorbed the maximum amount of energy that it can, the drive will shut down to protect itself.
"Back-driving," also known as "regeneration," means that the motor is being powered to move in one direction, but is moving the opposite direction. Or, the motor is being turned and not under power at all. In these cases, the motor is now a generator rather than a motor.
There are two main scenarios for "back-driving" a motor:
1) A vertical load falling down (i.e. the motor is under-powered or has no power at all).
2) A horizontal move with a large inertial load that is being aggressively decelerated and cannot stop the load as intended. This is rather like a car skidding to a stop.
Issue a RESET command, or cycle power to the drive. As an additional preventative measure, increased internal power dissipation capacity is available through Parker EMN's Custom Products Department. Some Gemini power levels (i.e. -U3/6/12 and -H20) can make use of the external Gemini Power Dissipation Module (GPDM).
The bus voltage can be measured with a volt-meter or oscilloscope on the VBUS+ and - terminals. The VBUS terminals will have a DC voltage on them that is equal to the AC voltage rectified (AC * 1.414 or the Root of 2) plus any voltage caused by the motor regeneration.