Dear sir,
we have a jumbo roll production machine which is controlled by Ge fanuc PLC series 90 - 30. In that plc, the battery low LED is always glowing(ON). I replaced the new battery. But, after 15 days ,the battery low LED is again ON. What is the problem in this PLC? Can anybody solve my problem?
Thank You.
nijam

 

The normal backplane voltage is supposed to be a little higher than the battery voltage, and there are supposed to be diodes to block current flow from the backplane to the battery when the PLC is powered up. I'm not sure whether those diodes are physically located on the power supply module or on the backplane. All this is to ensure that there is no current flow from the battery while the PLC is powered up normally.

If you have a second I/O rack in your system, try swapping power supplies between the CPU rack and the expansion rack. Just be sure to install the battery in the power supply on the CPU rack. If that doesn't work, the problem may be in the CPU rack.

It's either that or the mixture of modules in the CPU rack is drawing near maximum current, enough to drop the backplane voltage level to below the battery voltage level, allowing current to flow from the battery. Double check your module's current draw. If it's close to the limit (15 watts), consider using a high capacity power supply or moving some of the modules that use higher current to a different rack.

 

This could be a firmware problem. Strongly suggest you check with GE-Fanuc before chasing too many red herrings.

 

The life of the battery also depends on the ambient temperature ( the place it was stored and used)and the shell life.
If the shell life of the battery is near, then you might experience this problem. This can be verified by buying a new battery from another source.

regards,
Sekar