LED indicator bulbs causing "short circuit"

[jaxun]

Over the past couple of months I have witnessed some of our production lines going down as a result of a “short circuit” condition. This has been traced back to the operator panel LED’s that we have been installing in place of the incandescent light bulbs. Sometimes when an LED faults it actually can act as a short, thus taking the 24VDC to ground essentially. Anyone with a similar experience and remedy, other than reverting back to incandescents?

 

[JRB]

Fuse them, with semiconductor pico fuses.

 

[jraef]

Sounds like a poor design on the LED module, please post the mfr you are using.

But this also exposes a design flaw in your control system. Non-critical circuits that are subject to failures like this should be separated from the overall control system power supply specifically to PREVENT such a cascading failure issue. That's why Electronic Circuit Protectors are made. Each one gives you 4 separated 24VDC circuits with their own protection trips so that a failure or short in one does not take down the others. All of the major players in 24VDC power supplies offer them, here is one as an example.

 

[shooter]

it is not the led but the resistor that is failing.

 

[Bigjimmy]

Switch to a screen-based HMI?! J/k!

1. You could fuse the indicators individually or fuse sections/clusters of indicators. Another option would be electrically-fused output modules (assuming that they are available for your type of controller platform). Another still would be adding wiring interface modules between outputs and panel that feature some type of protection.

2. Are these LED replacement lamps? If so, I would suggest trying to find a model with an integral current-limiting resistor whose wattage could sustain the shorted LED.

As someone else noted, a failure such as this should not bring down the entire process/machine. It would probably be a good idea to add another, separate power supply for panel lighting and/or reconfigure I/O so that the machine can continue to operate when such a failure occurs.

 

[BobB]

I use Izumi (IDEC) LED globes and have never had one fail. Been using them for many years now. Also I never ground the secondary of an isolation transformer or DC supply from a switchmode. No earth then.

 

[Wilso]

Sounds like a poor design on the LED module, please post the mfr you are using.

But this also exposes a design flaw in your control system. Non-critical circuits that are subject to failures like this should be separated from the overall control system power supply specifically to PREVENT such a cascading failure issue. That's why Electronic Circuit Protectors are made. Each one gives you 4 separated 24VDC circuits with their own protection trips so that a failure or short in one does not take down the others. All of the major players in 24VDC power supplies offer them, here is one as an example.

I wish they'd used that logic on my plant. The main line PLC power supplies are on the same CB that feeds a few of the plant fluorescent lights. Couldn't believe it when I saw it.