Batteries are typically used to store variables that need to be non-volatile. This can be values entered via HMIs it can also be parameters that are entered 'at the factory' that characterize a particular system but they don't want to immortalize them into flash or whatever the code is stored in. Lastly, batteries are required if any realtime calculations are needed. The battery keeps a clock running.

Keith Cress
kcress - http://www.flaminsystems.com

Hi thanks for the reply. That is interesting because I have seen some YouTube videos demonstrating the complete loss of application program when the battery is removed and main power is off. In my case I have a 1756-L55 processor, FW version 8.21 that has been without power for a few years now. I plan to turn it back on and re-commission the system it is connected to but I am not in possession of the original RSLogix5000 project. The concern is that without non-volatile storage and without a working battery the PLC will be without a program to run. I've had a look at the data plate inside the processor and there is no suggestion of memory expansion.

1756-L55 is only the logic board. It appears to have no non-volitile memory on the board.

A non-volatile memory board was available, but since you don't mention it you may not have one.

The battery is required to maintain the program on the logic board memory.

If there's no non-volitile memory board in place, your PLC will not be able to run and since you don't have the original project, adding the non-volatile memory won't make it run.

You probably won't be able to retrieve a version 8 project unless you have Logix5000 running on a WindowsXP machine. When Windows7 was introduced, older versions of Logix5000 were abandoned, but I don't remember the cut off but I believe it was around version 12 or so. Also, a 5555 processor probably won't support the later versions of firmware either. If so you'll be forced to abandon the controller entirely. I've encountered this in the past but don't remember the hardware and firmware compatability but you can look that up on the Rockwell website. FYI, the latest Rockwell ControlLogix firmware versions are somewhere north of version 32 now.
Another thing, if you want to use flash memory to store your project, you may configure your controller to load the program from there on power-up or if the processor faults. I never use flash memory because my PLCs are networked and all current programs are archived for quick retrieval. Also, if you make a program change you have to remember to store it to the flash card or else the controller will load the old program when it is configured to do so.

Brad Waybright

It's all okay as long as it's okay.

b7031719; What kind of machine or process is your PLC running?

Keith Cress
kcress - http://www.flaminsystems.com

Yes, the battery is for memory retention, the standard memory for that processor is SRAM so it needed a battery. Depending on the vintage, you may have been able to add an additional long term battery to the rack, but if you didn't mention it, it's not likely there. Also depending on which version you have, there is/was a non-volatile memory module that could have been added. There are 7 versions of the 5555, 4 of them (M12, 13, 14, 16) could NOT accept the non-volatile memory card, 3 of them (M22, 23, 24) could.

If you have powered it up and the Batt light is red, then it's likely toast. Maximum life AFTER the warning light comes on is 26 weeks (1/2 year) but can be as short as 8 weeks depending on the size of the program and ambient temperature it was kept at. If the Batt light is not on, you may be OK, life expectancy is up to 3 years (again de-pending on program size and ambient temperature).

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