SLC keeps losing programs upon outages

our SLC5/01 (1747-L511) keeps losing program whenever there is power outage. There is no battery LED warning light. There is no EEPROM. Don't these PLC CPUs keep programs in the CPU internal memory as long as the battery is good?

Yes, an SLC-5/0x controller should keep the user memory in RAM for as long as the battery is good. The modular controllers like SLC-5/01,02,03,04,05 also have a capacitor that can hold the RAM memory for days or weeks.

If your controller is clearing its memory at each power cycle, and no EEPROM is loading an empty program, then both the battery and capacitor have failed and the CPU needs to be replaced.

Any program that runs in a 5/01 will run in a 5/02 or 5/03 as well because they have the same (or larger) instruction set and memory, and a DH485 network port.

Ken Roach said:

... then both the battery and capacitor have failed and the CPU needs to be replaced.

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As long as we don't power cycle, the CPU retains the program. I will try a new battery. Thank you Ken.

I have seen the root cause of this symptom in a SLC end up being a bad rack power supply.

OkiePC said:

I have seen the root cause of this symptom in a SLC end up being a bad rack power supply.

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I had experience with bad power supply in two instances. In 1 case I swapped with remote rack power supply for quick fix.

Normally, yes.
we had 2 slc 500 plc's that the electronics for the memory capacitors and battery backup components failed due to age or a power spike.
if that happens, the plc will loose the program every time. we sent them to a vendor for repair.
james