PowerFlex 525 Start Issue

[ncs]

Greetings Fellow Controls Professionals,
I have a weird issue with starting a 2HP PowerFlex 525 VFD. The drive is commanded through Ethernet IP from a Micro800 PLC. I'm controlling three VFD's from this controller. When I set the PFx_2_Cmd_Start but to start the second VFD, it will not start until I alter the speed reference. VFD's 1 and 3 are fine but wired programmed the same. For example, if the speed reference is set to 21Hz and the start command bit is set to start, the VFD will not start until I enter a speed reference to anything other than 21Hz. It happens 100% of the time. Any ideas out there on what to check next? Thanks, M

 

[Jim3846]

this sounds like your start and stop bits for this drive are somehow getting reset or set in the wrong order? Do you use the opposite bit to stop versus start? That way the drive sees a transition of the start and stop bits. Be consistent like the other drive logic for the other 2 that do start and stop consistently in program. Also, check your non default parameters as it relates to the drive that is having the issues and compare this to the other 2 drives that are ok.

 

[Ken Roach]

Because these user-defined function blocks in the Micro family aren't quite the same as cyclic I/O connections (which will be available for 525's with the new 850E and 870E controllers), I can't do much more than guess.

Check your logic carefully and be sure that you aren't just turning off the STOP bit when the START bit goes true. Turn off STOP once the drive feedback shows that the drive stopped.

If the function blocks end up sending both START and STOP true simultaneously, then STOP will override the START, even if STOP falls false shortly afterwards while START stays high.