variable frequency drive problem

Discussion in 'General Electronics Chat' started by tahir mehmood, Nov 26, 2013.

  1. tahir mehmood

    Thread Starter Member

    Jun 28, 2013
    dear professionals;
    we are having 132 kw VFD for 110 KW motor. the vfd is showing one problem whose code is F085 External Fault, in the manual its cause is written as: external fault triggered via input terminals.the remedy is written as: disable input terminals for fault trigger or eliminate external fault. check if digital input is set ON.
    But unfortunately i dont know how external fault is triggered via input terminals, means there is some fault on motor side? or in VFD. how can we disable the input terminals for fault trigger or eliminate external fault.
    please guide me about this i need quick answers.
  2. Meixner


    Sep 26, 2011
    An external fault is usually something external to the VFD or motor, often a temperature sensor or safety limit switch. The book that came with the VFD should show the terminals used to trigger an external fault.
  3. strantor

    AAC Fanatic!

    Oct 3, 2010
    It's strange you did not provide brand/model information about your drive. How do you expect us to help without that information? Usually, an external fault on a VFD is related to a condition on one of the digital input terminals like Meixner said; perhaps a braking resistor thermal switch or something of that nature. But in some drives (I suspect you are using Siemens MicroMaster 440, and this is one of those drives) you can set up internal logic that writes to bits normally associated with digital inputs. See here for an example, where the user programmed the MM440 to trip on overcurrent via the external fault function. If this is the case, you will need to know how the drive is programmed in order to isolate the cause. Another thing I have seen in the past is when a user changes the default function of an input terminal (default function being external fault) to something else, like multistep speed reference, and then if the drive loses it's program for any reason and the default function is restored, it will cause unexpected faults.