Allen Bradley VFD Powerflex 700

[Savi 0]

We have a Allen Bradley Powerflex 700 on a crane hoist getting feedback from its own ecoder. From the maintenace standpoint, I was wondering if the encoder, or wiring will go bad in the middle of a pick, how do I bypass it in order to put the load down. On simulation, when I unplug the encoder I get a fault 91 (encoder loss) that will not reset unless I plug it back in. Is there a way to configure an alternate way, where the drive is dumbed down (so to speak) and operate without an encoder? Checking the box "encoderless" would not help. Currently parameter 80 is configured for "encoder" - I tried to change it to "open loop" but did not make any difference. I would appreciate any help. Thank you.

[dmargineau 6]

There are many ways of "rigging" the VFD in order to operate encoderless, however, this should never be attempted after the crane has been fully comissioned and especially when a load is present! There are specifically designed holding brakes or holding brakes built-in provisions for safely lowering the load in case of emergency or electrical malfunctions. Edited 11 Oct 2013 by dmargineau

[Savi 0]

demargineau, thank you for responding. I just wanted to add that in this application the VFD is not counted on, or called on to hold the load on its own in vector control mode, even though it is capable of doing so. The crane hoist has two other brakes - one electrical and one hydraulic controlled by the PLC and a free fall will not happen. PLC has its own encoder (on the same motor) watching for un-commanded movements.