PLC Battery Replacement

There are a lot of variables, the main one being how much time does it spend in the PLC with the PLC powered down?

According to the PLC-5 Enhanced and Ethernet User Manual:

@60 degrees C, powered off 100% of the time: 256 days
@60 degrees C, powered off 50%: 1.4 years
@25 degrees, powered off 100%: 2 years

There are more details in the manual:
Publication 1785-UM012D-EN-P
Appendix A-4

I have heard that multi-billion dollar operations, i.e. GM, Toyota, etc.., change their batteries once a year.

We keep our machines powered on 24/7. We also get brown outs one a month or so and don't have any battery problems.

We never change batteries. Probably not the best idea, but it has worked so far.

But, we also run our machines into the ground pretty fast. Most machines here are under 12 years old.

After 30 - 40 million parts, they get replaced with a newer model.

The only battery I have had to replace lately was on a new L32 CompactLogix that would dump it's memory when power was cycled.

Actually turned out not to be the battery, it was an inductive spike from a 480v to 120v transformer. A line filter cleaned it up.

So from what I see, if you leave your machines on all the time, batteries aren't that much of an issue.

The only problem with leaving you machines on all the time and never changing the batteries is when you DO have one of those power blips.

I've recently been through another round of batteries in PLC 5 BASIC modules in one of our plants. They remember to change the PLC batteries, at least occasionally, but they never change the BASIC module batteries. Then the PLC runs, but they wonder why the scales/reports/etc aren't working.

I recommend changing the batteries annually. Or EEPROM.