Just wondering if anyone knew exactly what the BC circuit on the miprom 21 unit with ac drive was accomplishing before turning on the BC relay. I know on the DC drives the bc relay comes on with a M contact closure and a RDY closure. On the AC unit I am thinking that the drive applies some current to the motor and then looks to see if the load cell output, which is connected to the disc brake, changes to a certain level which would then allow BC and pick the brake. does this sound about right

Just a guess, is it sensing the full magnetizing of the hoist motor just before it takes off-kinda like lock rotor or DC bus on an AC unit, similar to the full feild sense on a DC unit before it ramps up to accel? Without the DC bus applied to the AC motor being up to snuff the car will not take off.

as I recall the contactor closed and the load balance sequence begins to increase the torque and removes the load from the brake. the cell was adjusted to hold the motor at zero speed until the brake opened . there was a parameter that tripped if the cell was bad or not adjusted correctly and let the motor rotate a little.