Hi All,

We have a hydraulic press that is being controlled by Siemens S5-95U PLC . Lately the S5-95U has been randomly stopping during operation thus causing the hydraulic press to stop running. However the S5-95U instantly returns to RUN status after stopping. This is the first time it has happened after a decade of service.

Prior to the random stops issue, around January 2021 the S5-95U completely stopped and the program in the RAM was erased so we had to replace the PLC battery and restore the program with our backup. Strangely, the PLC battery we replaced still had 3.4VDC upon checking. What's even more baffling is that even after we replaced the PLC battery with a new one,  Battery LED is still yellow although the program is still retained in the RAM.

In summary, we have two concerns:

1. S5-95U randomly stops and resumes during operation ever since we were forced to replace the PLC battery and restore the program.

2. PLC battery has been replaced but the Battery LED is still yellow but the program is still retained in the RAM.

I have a suspicion that the two concerns I mentioned above are somehow connected but I lack the technical expertise to diagnose. I'm hoping someone can help me figure out our issue. Worst case, I think our S5-95U needs to be replaced.

Thanks,

Why is a battery fault signaled when you insert a back-up battery, even though the battery is new?

Hi,

I am also baffled as to why the Battery Failure LED is on even if we did replace the battery. We also checked the battery voltage on the multimeter and it is full.

Thanks,

Have you read this?
This means the depassivation of the lithium battery.
If lithium batteries are stored for a long time, they can become passive.

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Since the storage time of the lithium battery is usually not known, we recommend the following procedure:

• Insert the backup battery(ies) in the battery compartment.
• Acknowledge any battery failure message from the power supply unit with the FMR button.
• If you cannot acknowledge the battery failure, wait a few minutes and try again.
  
  
• If you still cannot acknowledge the battery failure, remove the battery(ies) and short-circuit them for 1 to a maximum of 3 seconds.
  
  
• Replace the battery(ies) and try once again to acknowledge with the FMR button.
• When the display of the battery failure message goes off, the battery(ies) is (are) ready to operate.
• If the display of the battery failure message does not go off, the battery(ies) is (are) empty.

Hello,

On your picture i see an EEprom, PLC should load the program from EEprom in case of battery failure.

Regards,

Marcjan

Hello jm_agro

You mentioned that the 95U randomly stops and resumes operation again?. Usually if the a 95U stops, it requires intervention to restart. Either by toggling the Run/Stop Switch or cycling Power to the unit. 

Do you have the means of going online with Step 5 and checking the Diagnostic (ISTACK/BSTACK)

Also as Marcjan mentioned you have a EEPROM, not RAM in your 95U. If the problem is not battery or input power to the PLC related, It cold be that a programming change was done and not saved on the EEPROM. When the battery failed, the program was reloaded from the EEPROM but may be now missing these changes.

Regards / m.f.g