ACOPOS Warning 38008: Bleeder: No current flow when having DC bus connection to other drives

There have been some support cases in which possible causes of the ACOPOS warning 38008: " Bleeder: No current flow" got identified when powering on axes , mostly in connection with ACOPOS P3.

Basically, when the controller of an axis is switched on, the chopper is switched on with 100% DutyCycle for 20ms. For one sixth of the mains period (20ms/6 @ fn = 50Hz), the DC bus voltage is lowered with the maximum braking power of the braking resistor.

Possible causes

  1. If the DC bus voltage is lowered by at least 2% , then it is implied that a braking resistor is wired. This condition is normally sufficient for individual modules without a DC bus connection to other P3 drives.
    In an support case it was observed, that in a DC bus connection of several ACOPOS P3 drives, however, the check might cannot detect a reduction of 2% of the DC bus voltage. The specific cause in that case was that the DC bus capacity increases when having a DC bus connection to other drives, which consequently lowers the reduction. The workaround in this case was to write bit6 (0x40) in MOTOR_TEST_MODE. This should work.

  2. In another support case it was the case that during the switch-on of an ACOPOS P3, which was connected to other ACOPOS P3 drives via a DC bus connection, regenerative energy was returned to the DC bus by another axis at the same moment. During the internal test with regard to warning 38008 this will also influence the reduction of the DC bus voltage and the test can be falsified. If this is the case, the warning can also be deactivated via bit6 (0x40) in MOTOR_TEST_MODE.

Suggestion is to first verify what the hardware structure looks like in the used machine and whether there is a DC bus connection between several drives.
If this is the case, the next step is to verify whether one of the above points could be present. In this case, the warning could be explained and it can be deactivate via bit6 (0x40) in MOTOR_TEST_MODE.

A trace recording of the DC bus voltage in the event of an error on the affected module would also provide information about how far the DC bus is actually reduced when the controller is switched on (2% reduction would be necessary according to the test condition with regard to warning 38008).