Micrologix 1400 1766-L32BWA-"Burnt" Output

[robmx57 0]

Hello, I am trying to flash an indicator light (Banner  K70LBGYRPQ ) every .5 seconds.  The PLC manual says 2.5A per channel.  The light uses roughly 113mA max current @ 24vdc.  I am using output 0 to do this (O:0/0).  I think I may have ruined the output by flashing the indicator light.  Has anyone ever experienced this before?  Is there a minimum pulse time for this PLC?  What do people normally do when wanting to flash an indicator light such as this?  This is not the first time I have seen this happen.   Thanks in advance!

[Joe E. 259]

How long were you flashing the light? That model has relay outputs, which have a relatively limited lifespan compared to solid state outputs. The manual (pages 133 and 135) talks about relay lifespan, which varies according to the voltage/current you're switching. Mechanical life is 20,000,000 cycles, which is about 2800 hours (115 days) if it's cycling continuously every 0.5s. The electrical life is shorter but depends on the voltage/current/inductance/power factor of the switched load (graph on p135).

For something that blinks quickly/a lot, I try to use solid state outputs. The 1766-L32BXB and 1766-L32BXBA have some relay and some DC solid state outputs.

[robmx57 0]

Hey Joe,

Thanks for the response.  Not very long at all.  Maybe 10 minutes maximum.  

[Joe E. 259]

So, when you say the output is "burnt", what exactly do you mean? Can you hear the relay clicking when the output is cycled on and off? If you disconnect the wires and measure the resistance across the relay contacts, what do you get? How long (in terms of months/years) have the PLCs been in service before the outputs fail?

[robmx57 0]

I suppose burnt is not the best way to describe the issue.  I can hear the relay clicking but the light will just stay on, or when its supposed to shut off, it will take an extended amount of time to do so. I have not measured the resistance across the relay contacts (not exactly sure what I should be measuring?)  This machine has been in service since 2016 and has came back for alterations. So far the only output I am having issues with is O:0/0.  Looks like the indicator light has a "flash input control" wire that can be connected.  I have ordered a 5 conductor cable so I can use that instead of the PLC to flash the light.  I am still curious as to why it is acting this way though...

[robmx57 0]

I ended up slowing the flash timers down to 1 second instead of every .25 seconds and moved that wire to output 8 and so far it seems to be ok. 

[pturmel 157]

1 hour ago, robmx57 said:

I am still curious as to why it is acting this way though...

A machine that's been in service for six years?  Blinking twice a second up to ten minutes at a time, how many times per day?  Output 8 will probably last six years, too, and whoever deals with it then will curse you.

[Joe E. 259]

Those are signs of a relay failing. I'm not surprised that it's happening after 6 years in service. For something like that, you're far better off using a solid state output or, like you found, use the indicator light's built in flash function with the relay output staying on steady.