1756-L61 loosing program after changing Battery

[Rob S.]

Good Morning ,

Have a 1756-L61 CPU. Replaced the battery 2 times in the last 4 months. Have a red led on the CPU indicating a bad battery , but no indication on the RS Logix 5000 , while online. Have any of you had this issue ? I believe they are using batteries from another vender.
Have you had any issues with batteries ? Any thoughts want would cause this ? Could it be the CPU ?

Thanks in advance .

 

[Ken Roach]

There was a run of 1756-L6x Series B controllers about five years ago (less than 0.2% of the controllers produced) that would drain their batteries extra-fast. [Link to Knowledgebase article 40779, Access Level Everyone]

I've never heard of the BAT LED coming on without the corresponding status bit in the controller, though.

Is this a new controller ? Series A or Series B ? How often is the main power turned off ?

Has the problem always existed, or did it start occurring after the first aftermarket battery was installed ? Or did you start installing aftermarket batteries because the RA ones were draining fast ?

 

[Rob S.]

If I was going to place a 1784-SD1 Flash Card in the 1756-L61 CPU ,I guess I need to make sure I put the CPU in Prgram mode correct ? I understand how to download it to the card , but how do I make sure it loads from the card , when there is a loss of power ?

Thanks,

 

[Ken Roach]

The ControlLogix User Manual, 1756-UM001, Chapter 3 covers the basics of how to use the Nonvolatile Memory Store and Load functions.

Only the 1756-L7x controllers and new CompactLogix support SD cards; if you have a 1756-L6x controller you need an older CompactFlash card.

 

[Rob S.]

The CPU battery led is on , and the status bit 31 Low Battery is 0 , in the controller tags. I may replace the CPU , I have one on the shelf. I would imagine it would be just install and download, correct ?

 

[Ken Roach]

If the CPU on your shelf has the same firmware revision as the program, it ought to be a simple matter of downloading and going to RUN mode. If the CPU on the shelf has different firmware, you'll need to run the ControlFlash utility first (RSLogix 5000 should walk you through it when you go to download).

I noticed that you referred to the "Status bit 31 Low Battery is 0".

There is no built-in status bit for the Low Battery minor fault in the ControlLogix like there is in a PLC-5 or SLC-500.

Instead, you use a Get System Variable (GSV) instruction to read the Status attribute from the Fault Log object.

The Battery minor error sets Bit 10, not Bit 31.

Check out the logic that is reading that "Low Battery" bit. My guess is that it's not functioning the way you expect.

Go into the Controller Properties, then the Minor Faults tab. You should see a checkmark on the Battery fault, and entries in the Minor Fault log that indicate a battery fault (Type 10 Code 10).

 

[Rob S.]

There is no battery fault in Minor Faults. I am going to get a 1784-CF128 compact card , and see how that works. When you load the CPU and also the compactflash card with the same program , the same firmware should follow to the card , correct ?

 

[Operaghost]

Yes, the firmware will be saved to the CF along with the program.

However, the CF card will not be able to retain current RAM values when power is lost. The CF card can be configured to reload the application following a power cycle which would wipe out all current tag values and reload the values from when the CF card was originally written to.

Likewise, any logic changes made while online would be wiped out following a power cycle. Think of the CF card operation in the same light as downloading from your laptop.

You said the battery LED is on which means you have a bad battery. As Ken says, check the logic relating to the battery. The whole bit #31 sounds possibly like it is expecting to read or write information to an HMI. Look for the GSV instruction.

Can you swap batteries with another CPU to see if a good battery works in this CPU? My first inclination is that you are not using compatible batteries.

OG