Plc5 red leds then restarts

[Kataeb]

Kindly, when the operator starts a certain function on the machine, its Plc5 has suddenly three red leds, Batt Proc Force, then it quickly restarts again normally. This happens in less than one second.
We tried many things, replacing hardware, ... .

What could be the problem ?
What does it mean to have three red leds at the same time ?
Can we make the plc wait at the red leds ? so we can monitor its alarms .

PLC-5/30 Allen Bradley 1785-L30B

 

[parky]

One thing I can think of is when you run that "Function" what ever it is there could be a short on the power supply, Had this a few times, for example had a solenoid that had a shorted coil, when the coil was energised it dragged down the power for a split second re-booting the PLC. It did not blow the trip on the PSU but either the voltage dropped for a fraction of a second causing the drop out or it spiked the supply enough to cause the PLC to re-boot.
Also, a 24v PSU with a failing smoothing capacitor can also do it, for example under one condition although the voltage has a ripple caused by the failing capacitor it is not enough to trip anything, operating a contactor or solenoid (or a combination of more than one) may cause the current to rise creating a larger ripple on the DC supply.
I have had both these happen although pretty rare.

 

[I_Automation]

Shorting the power supply is my guess too.


Look at that function and see if it uses a card in the rack that nothing else uses. It could be an analog output or specialty card going bad.


Or if it's digital outputs powering older relays or contactors wire a small interposing relay to the output and have it power the larger relay.

 

[JesperMP]

If this happens consistently, you can try to disconnect the I/O.
Start with the I/O modules related directly to the mentioned function.
The I/O is on terminal blocks that swing out when you depress a latch.
If you can get the CPU to run mode, then reconnect the I/O one module at a time to see if that triggers the issue.

In the same way, you can remove I/O modules completely, and if you get the CPU to run mode, reinsert the I/O modules one by one.
Only remove or insert the I/O modules with the power switched completely off.

The openings at the top of the modules are so large that foreign objects can fall in, such as loose strands of wire, and create all kinds of problems. So you could try to remove the I/O modules and look for such foreign objects and clean with air.

 

[JesperMP]

Thinking over it again, I think it is better to focus on only the outputs that change state when the function is activated.
These are probably a few, and rather than removing entire modules it is better to only investigate a few signals.

My suggestion was only pertinent to when the fault appears totally random.

When the 'function' activates, are large coils coils (contactors or solenoids) activated or deactivated ?

 

[parky]

Yes it can be difficult in finding faults like this, the on I had where the solenoid coil was short (well shorted turns) was a difficult one, I noticed an input was coming on just as the fult occured, disconnected it, cured the problem however, it turned out to be a solenoid coil, not the input, it just so happened that the input was off a contact on a solenoid driven system so if the contact was made it drove the solenoid, so no input no energisation of the solenoid, the machine worked the offending solenoid was something to do with correcting registration, it was not noticed as the error was so small but was trying to correct it.

 

[Mickey]

of a second causing the drop out or it spiked the supply enough to cause the PLC to re-boot.

.

Surge protection on inductive load?

 

[Operaghost]

The LEDs on the PLC5 can be easily misread if you aren't looking directly at them from right smack in front of them. One LED can sometimes appear to be another if you are at an off angle.

I mention this only because the FORCE indicator isn't a red indicator. It is yellow. But, if you look at it from an off angle, another red LED (like the battery) might appear to be the FORCE led.

That said, I agree with the comments on investigating shorts on the power supply. Also the surge protection on an inductive load as Mickey mentions. I have seen issues like you describe caused by inductive loads opening, but in our case, it was severe enough that the PLC dumped its program each time it happened.

OG

 

[parky]

Surge suppression is ok, but assuming this system has been in use for some time without problems then it sounds like something has changed, yes it could be some outside interference but if the fault is a component on the system a filter or surge suppression may mask the cause not cure it.