Allen-Bradley 1771-ACNR15 sometimes going to IDLE and returns to RUN

Hello to all,

We have a system where old PLC I/O modules are being used with control logix processor with the help of controlnet adapter module 1771-ACNR15 located in old I/O rack and 1756-CNBR module located in control logix processor rack. The distance between the two racks is very less.

The problem: Sometimes 1771-ACNR15 is going into idle mode resulting stoppage of drives. It is comming back to run mode automatically.

We have used GSV instruction to obtain fault code and it was found to be 516.
After observing for several inputs we have found that for a particular DI transition this is happening (our physical observation only).

My doubt is can any DI transition cause this kind of behavior that too sometimes? We are unable to find exact reason for this occurrence.

Any help is welcome.

http://www.plctalk.net/qanda/showthread.php?t=40012

The above thread also talks about this error. It may help you out or give you additional ideas on next steps.

Regards,

Hello,

Problem was solved. It was because of faulty battery, which was used for UPS supply to PLC panel.

System Description: Actually problem appears sometimes, not frequently. This can be explained as follows: The raw supply for the UPS is taken from MCC bus and when all the two drives of the MCC run then for a start of third drive is causing voltage dip. Because of faulty battery UPS isn't able to give constant output for that moment, hence PLC ACNR15 gets power interruption.

After changing battery we aren't facing this problem.

In my opinion, you still have a problem.

if a 3rd drive starting up is causing the voltage to sag, then your transformer is undersized and will eventually fail.
for the current requirements, take the largest motor current X 1.25, then add the other 2 motor currents, add any other devices, add 50-100 amps for things you forgot.
then find a transformer that meets your needs.
you must then derate for the ambient temperature (maybe 1 or 2 other derate factors) - I cannot remember.
find the new transformer size and I would even go up 1 size, someone always wants to add things later.

then look at the wire terminal rating and size the wire according to therminal ratings.

If I an incorrect on what I have stated, someone please correct me.



james