Intermittent PLC

We have a slc 5/05 running right now on a 13 slot rack. Power supply is a 1746-P4 (overkill)

For some reason, the plc will "blink" at random times. It will run with no problems for weeks and then out of nowhere it will shut down and immediately reboot.

I have a counter on the first scan and it showed that it did it 3 times this weekend. They have always had this problem and this is the only plc that does it. We have it plugged into a ups battery backup but that doesn't seem to help.

Any ideas?

I had a similar problem once on a machine that would go through mysterious hick-ups. I narrowed it down to an undersized transformer that would get overloaded temporarily when solenoids and motors started up at the same time. I changed the 120 VAC power to a lighting transformer that was nearby and problem went away.
As far as I know the only way the processor would re-boot is if you either go to "Program" and then to "Run" with a key switch or if you de-power the system. Even though you may think that your UPS is OK I would suggest another 120 VAC power source just for the CPU.
Run temporary cord to an outlet that is fed from a different power source. Leave rest of controls as is on the same power source.

kurt.brinker said:

We have a slc 5/05 running right now on a 13 slot rack. Power supply is a 1746-P4 (overkill)

For some reason, the plc will "blink" at random times. It will run with no problems for weeks and then out of nowhere it will shut down and immediately reboot.

I have a counter on the first scan and it showed that it did it 3 times this weekend. They have always had this problem and this is the only plc that does it. We have it plugged into a ups battery backup but that doesn't seem to help.

Any ideas?

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have you tried changing the power supply?

diat150 said:

have you tried changing the power supply?

Click to expand...

not yet. It was installed before i got here and about a month ago when i went to investigate one of its "blinks" i found 2 other power supply's in a box next to the panel. Neither of them work and nobody knows where they came from. (our original elec engineer is no longer with the company)


I will throw a clamp meter on the transformer and see what its rated for and what its pulling. If its anywhere near its limit i will see about getting it replaced.

thanks for the ideas.

Check the input voltage select jumper on the power supply. I once had a system with identical symptoms and the problem was that the jumper was set incorrectly.

will do.

thanks for the tip

I had a Modicon Quantum that did the same thing. It was the previously mentioned voltage selector jumper in the wrong position. I have also seen a pair of older medium voltage drives that put enough trash back on the line when they were ramping up that the UPS and PLC would blink on and off. The UPS wasn't fast enough to keep up. An active UPS cured the problem.

Steve

Don't forget to check that the power supply's securing screws are all-the-way screwed in, to make the connector mate to the chassis.

Also, you know, AB highly recommends grounding the chassis (look at AB's docs), and, mostly I see these out there with no ground on the chassis at all. 'been discussed on this forum many times.

jdbrandt said:

Don't forget to check that the power supply's securing screws are all-the-way screwed in, to make the connector mate to the chassis.

Also, you know, AB highly recommends grounding the chassis (look at AB's docs), and, mostly I see these out there with no ground on the chassis at all. 'been discussed on this forum many times.

Click to expand...

Yes I've fixed a couple of "goofy" problems with an SLC by doing just this. Now I always grind the paint off under the mounting screws on the backplane as well as running a ground wire.