SLC Battery Light is on... Why program isn't lost after weekend (turned off)

AutomationTechBrian

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I was at a customer's today and 2 of 3 SLC 5/03s had the Battery Light on. I showed it to the maintenance guy and asked him when the last time the panel was powered down for an extended period of time. He said last weekend! I don't understand why they don't loose the program. The PLC power is off when the panel is powered down. Does a SLC 5/03 have EEPROM, non-volatile memory that I don't know about? I thought it was all volatile memory. What am I missing? I see municipal water and waste water plants with the same situation. They said the BATT light was not relevant to their setup.
 
Your SLC5/03 can have an EEPROM (its an option) see PDF

Also... The battery lite on just means its low, it can still hold the program. Depends on how low.

IMPORTANT The SLC 5/03, 5/04, and 5/05 processors have a capacitor that provides at least
30 minutes of battery back-up while the battery is disconnected. Data in RAM
is not lost if the battery is replaced within 30 minutes.
 
Last edited:
I have seen the capacitor hold the program for a full day.

Also, the battery light coming on means the battery has crossed a threshold. it doesn't mean it is fully depleted. It could still be functioning just at less than optimal capacity.

I used to tell people when that light comes on you may have up to two weeks before the battery fully dies.

So, EEPROM, capacitor, battery not dead yet. Three possibilities.

OG
 
the slc500 series has 2 methods of maintaining the program.

the primary method is the battery.

the secondary method is the internal capacitors on the plc card itself.
these are meant to hold the program long enough for you to turn the power off to the plc, remove the plc card, and replace the battery so you won't have to reload the program. I have known the caps to hold a test program for months.

please remember, this is not a guarantee they will work, so have the program backed up before killing the power or replacing the battery.

I had to have a 5/04 that lost its program everytime the power was lost.
the plc board went bad and the battery never saw the plc memory.
I had it repaired by teamsesco, its now on our stock room as a spare.

james
 
I had a site do similar recently all the battery lights were on - was a mixture of ab and Siemens. They weren’t concerned as wasn’t causing them a problem. Went back to the site a few weeks later and they said they seemed to have lost some mods a previous employee had done on one of the plcs. I had a quick look and compared online prog with a back up I had taken on a previous visit and found online had the mods missing. It was an s7-300 with an eprom however the mods had only been saved to the volatile memory and not the emotion so they lost them. I had to copy over my backup. All the other plcs had the versions on the cards which were correct. Moral of the story - don’t rely on the EPROMs unless site it has the correct programs!
 

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