SLC 500 Memory - Volatile or not?

Hello All.

We've got a machine that's been unplugged from power for 1-2 years. I'm wondering what are the chances that the PLC program and HMI screens are still in there. At the moment I cannot easily power it up to find out. We're sending it to somebody who's going to expect to turn it on and find it functional.

What do you think - are they likely to be disappointed?

My guesss would be the PLC has lost it's program.
HMI might be okay, depends on model and features.

Without a battery installed, the SLC can hold its program for hours and maybe days with the main power off.

With a battery installed, the SLC can hold its program for months and maybe years with the main power off.

With an EEPROM installed, the SLC will hold its program indefinitely with the main power off.

I'd give you one chance in four that after 2 years the battery is still holding the program, if there's no EEPROM installed. If that's not good enough, send your guy with a way to load the program.

I have personally witnessed SLC's hold memory for 1 year or more, but that's with a fresh battery.

The environment also affects the battery; if this thing has been in a field cabinet in Bakersfield for two years, it's toast. If it's been chilling in a nice air-conditioned room, you have a better chance.

Try powering up just the PLC without powering up the whole machine.

I took a spare computer power cord, lopped of the female receptacle end, stripped the jacket back, and put a couple of ferrules on the conductors for times when I need to check things like this.

Try powering up just the PLC without powering up the whole machine.

Click to expand...

Excellant idea!