Plc Rack And Power Problems

plcnovel

Member
Join Date
Feb 2006
Location
LHR
Posts
215
Hi To ALL:

I am using the following system:





1769-L31 Compact Logic Processor

1769-IQ16

1769-OB16

1769-IF8

1769-IF8

1769-IF8

1769-IF8

1769-OF8C

MVI69-MCM



History



The whole Assembly is mounted on DIN rail. The power is 220 V AC(50 Hz) which is fed into rectifiers (convert 220 into 24v DC).



We powered up the panel, and after some time the whole PLC system along with I/O cards went down, there was no power in the whole system. But there was a power in the HMI screen and stuff. I metered the power; we are getting the 220 VAC at one side of the rectifiers and 24v DC at the other side of rectifiers. After tracing the power, I check the power in the PLC power supply terminals, and surprisingly there was the power even on the power supply terminal, checked the fuses (on the power supply and in the panels). Everything was OK



Further to my testing, I took out the whole PLC rack along with I/O cards and try to put a separate 24v DC power supply. After supplying this, the following things were observed:



As soon as the power is applied, the processor’s OK LED blinks red for a fraction of a second and again the whole rack went off. Even after excessive tries, it won’t power up.



After this, I took out the processor from the rack, and the let the power supply off (un-screw the terminal) for some time and put the power back on, this time it powers up, but the three Analog input cards were not powered up. So I thought it might be the analog cards creating problems, so I took all three analog input cards from the rack and put the processor back on and power the system up, but this time it did the same thing, processor’s LED blinks red for a fraction of second and then whole system shuts down. At this point even taking the processor out and try powering the system up, will not help, As I have to un-screw the power terminals of the battery and let be stand alone for a few minutes and then screw the terminal again and power cycle it, then it works fine.



I have no idea where the problem is, it might be a processor problem…… It might be the Analog cards…..but what caused it have no idea…..May be the power surge inside the panel, made the the whole system malfunction , or specifically the processor. I would just like to bring this incident up to air so that if any of you guys experienced the same thing, can share his ideas and suggestion, what can be done to prevent it in future….or how can I do more testing to make sure what is being damaged. Any ideas or suggestion on HOW IT HAPPENED< REASONS, AND SOLUTIONS will be appreciated. Thanks in advance.
 
Where is your power supply located?

In Allen-Bradley notes, they are very specific about how far different modules can be away from the power supply. The processor cannot be more than 4 away from the power supply. You may have to rearrange your modules accordingly.
 
I also found this in the user manual:

Use the 1769-CRR1/-CRR3 or 1769-CRL1/-CRL3 expansion cable to
connect banks of I/O modules. You can split a bank right after the
power supply or after any I/O module. Each bank must contain one
power supply. An end cap/terminator must be used on the last I/O
bank opposite of the expansion cable.
The first bank includes the CompactLogix controller in the far left
position. The controller must be located within 4 positions of the
bank.s power supply. Only one controller can be used in a
CompactLogix system.
Each I/O module also has a power supply distance rating (the number
of modules from the power supply). The distance rating is printed on
each module.s label. Each module must be located within its distance
rating.
 
Mark Buskell said:
Where is your power supply located?

In Allen-Bradley notes, they are very specific about how far different modules can be away from the power supply. The processor cannot be more than 4 away from the power supply. You may have to rearrange your modules accordingly.

Well the AB power supply is right next to the processor, here is how they are located pysically:

From Left to right

Processor-->Power supply-->Digital Input-->Digital output-->Analogs--> and then MCM

If you mean transformer , they are also located inside the panel. I already took out the whole rack from the panel and tested it with a clean sperate 24 V Dc source....same problems
 
You should move the powersupply between the first and second IF module. That way, the distance to the CPU is 4 and all modules are less than 8 position away from the CPU. The communication module may need to be placed closer as well.
 
There is a note somewhere about the analogs no more than 4 away too.

I would rearrage the modules:

Processor
IF8
IF8
IF8
Power Supply
IF8
OF8C
MCM
IQ-16
OB-16
 
Mark Buskell said:
There is a note somewhere about the analogs no more than 4 away too.

I would rearrage the modules:

Processor
IF8
IF8
IF8
Power Supply
IF8
OF8C
MCM
IQ-16
OB-16


So if i arrange the modules according to above order, do i have to change my ladder program and I/O Configuration as well. Is there any other combination of modules so that i dont have to alter my program at all. My current module configuration is:

Processor
power supply
IQ-16
OB-16
IF8
IF8
IF8
OF8C
MCM
 

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