# LED Pilot Light Burnouts



## Big John (May 23, 2010)

We've had a rash of LED pilot light failures recently. All the same brand, Schneider ZB4 series.

The blue ones seem to be affected the worst. They're all reasonably new. Installed within the last couple months while we change out a lot of the old incandescent style.

The only thing I've noticed that struck me is these things are specifically marked with a voltage range of 110-120VAC, and some of the control voltages are as high as 130VAC.

Are these things really that susceptible to over-voltage? This has the makings of an expensive mistake; I've already ordered a couple grand worth of these things.

-John


----------



## McClary’s Electrical (Feb 21, 2009)

Big John said:


> We've had a rash of LED pilot light failures recently. All the same brand, Schneider ZB4 series.
> 
> The blue ones seem to be affected the worst. They're all reasonably new. Installed within the last couple months while we change out a lot of the old incandescent style.
> 
> ...


 
Are they powered by control transformers in mcc's?


----------



## Big John (May 23, 2010)

mcclary's electrical said:


> Are they powered by control transformers in mcc's?


 They're all over the place: MCCs, switchboards, dedicated-purpose control panels. 

There's no common environment or voltage source, but they all are in the same plant.

I've already had more than a dozen of them fail. We've got pretty good power quality, so I don't think surges are the issue. The only thing I can really pick out is just that they technically are running at more than 120V. But for $40 per LED, I would hope they can tolerate a little bit of over-run.

-John


----------



## wildleg (Apr 12, 2009)

I'm guessing not.


----------



## micromind (Aug 11, 2007)

I've had pretty bad luck with LED pilot lights in general. It doesn't seem to matter much which brand they are, I'd say the failure rate is about 20 or 30% in 6 months. 

I don't think LED technology is quite there yet. I've seen a lot of traffic signal LEDs fail as well.


----------



## Jlarson (Jun 28, 2009)

I've had pretty good luck with Eaton, Automation Direct stuff and Dialight LEDs. Even on 130 volt, I don't really have any experiance with the Schneider leds though, I'm not real big on Schneider control stuff.


----------



## Big John (May 23, 2010)

Well, that's unfortunate news. This changeover seemed like a good idea at the time, a big part of the push was it was supposed to increase reliability and reduce maintenance. 

I guess we'll just go through a round of replacements until we've weeded out the weak ones, and I'll hold off on any more upgrades until it's clearer exactly what kind of failure rate we're looking at. Thanks.

-John


----------



## LARMGUY (Aug 22, 2010)

Big John said:


> Well, that's unfortunate news. This changeover seemed like a good idea at the time, a big part of the push was it was supposed to increase reliability and reduce maintenance.
> 
> I guess we'll just go through a round of replacements until we've weeded out the weak ones, and I'll hold off on any more upgrades until it's clearer exactly what kind of failure rate we're looking at. Thanks.
> 
> -John


Run your own bench test. Set up a few on plant power and set up a few on a variac.


----------



## Copper88 (Aug 21, 2011)

Do these LEDs have a current-limiting resistor built in? For $40 apiece, I'd hope so. But if not, you probably need to add one. Using Ohm's Law, set the current around 20mA.


----------



## nolabama (Oct 3, 2007)

I have thrown all my led pilots away. I had a bunch burning out and if they failed just right they would trip a control power breaker. Needless to say it was a pita. I think but can't swear to it the lamp holders have to be rated for LEDs


----------



## Big John (May 23, 2010)

Copper88 said:


> Do these LEDs have a current-limiting resistor built in? For $40 apiece, I'd hope so. But if not, you probably need to add one. Using Ohm's Law, set the current around 20mA.


 I'm certain they do, because of the high control power. Honestly, modifying these will probably cost far more in labor than the lights are worth.


nolabama said:


> ....I think but can't swear to it the lamp holders have to be rated for LEDs


 These are complete units, because we're doing a lot of controls upgrades, so this was part of it. 









I think I'm gonna give Square D a call and see if I can talk to one of their engineers. LED pilot lights have been around for almost 2 decades now. I would really like to think they'd have worked out the bugs.

-John


----------



## JRaef (Mar 23, 2009)

Big John said:


> I'm certain they do, because of the high control power. Honestly, modifying these will probably cost far more in labor than the lights are worth. These are complete units, because we're doing a lot of controls upgrades, so this was part of it.
> ...
> 
> I think I'm gonna give Square D a call and see if I can talk to one of their engineers. LED pilot lights have been around for almost 2 decades now. I would really like to think they'd have worked out the bugs.
> ...


Most LEDs operate on 2VDC and have a resistor in the DC circuit as a current limiter, otherwise the LED conducts to destruction. So to get there from a typical US 110-120V supply, you need to rectify and drop the DC votlage. The cheap way to do that is just a PCB mounted diode bridge, a smoothing cap and a dropping resistor. This is what most of the "integral" LED pilot lights are using, especially since they all started going with the newer "High Brightness" LED modules about 4 years ago (which incidently is when Schneider changed from the ZB2 to the XB/ZB4). But in my experience these things are susceptable to voltage issues, especially over voltage, because if the voltage is higher against the same resistance, the current will increase, significantly in this case. If that damages that current limiting resistor, it's toast. By the way, the input voltage tolerance on these is 132V max. But I also think that is a HARD 132V, i.e. not 133V... ever.

Then on top of that, Blue and White (which are really Blue) LEDs need 4VDC to operate, so they need half of the dropping resistance against the same DC supply in order to increase the voltage getting to the LED itself. I think this makes Blue/White LEDs even more vulnerable to over voltage if you think about it, because with less resistance in order to allow more voltage, you also get less of a current limit effect if your voltage goes out of tolerance.

The real solution is to use a little SMPS that can be adjusted to provide the correct voltage regardless of the line input, but that would cost a LOT more to produce and if you don't like spending $40 for the thing, you certainly are not going to like paying $80!

You can get other options on LED pilot lights, i.e. ones that have a built-in transformer that drops the AC down to 6V so the DC circuit is much simpler and more robust.


----------



## Big John (May 23, 2010)

JRaef said:


> ...The real solution is to use a little SMPS that can be adjusted to provide the correct voltage regardless of the line input, but that would cost a LOT more to produce and if you don't like spending $40 for the thing, you certainly are not going to like paying $80...


 The problem is the scale of the project. We're talking hundreds of lights. The idea was to standardize the colors to NFPA 79 and at the same time try to eliminate a lot of the maintenance issues we were having with lamp replacements and a lot of sockets reaching end-of-life.

Unfortunately, I didn't realize these things were that finicky. I think I'm gonna run out the supply I've got, and then see if I can find any specifically rated for 125-130V.

-John


----------



## nolabama (Oct 3, 2007)

Big John said:


> The problem is the scale of the project. We're talking hundreds of lights. The idea was to standardize the colors to NFPA 79 and at the same time try to eliminate a lot of the maintenance issues we were having with lamp replacements and a lot of sockets reaching end-of-life.
> 
> Unfortunately, I didn't realize these things were that finicky. I think I'm gonna run out the supply I've got, and then see if I can find any specifically rated for 125-130V.
> 
> -John


They still gonna blow up. Mine were 130's.


----------



## JRaef (Mar 23, 2009)

Big John said:


> The problem is the scale of the project. We're talking hundreds of lights. The idea was to standardize the colors to NFPA 79 and at the same time try to eliminate a lot of the maintenance issues we were having with lamp replacements and a lot of sockets reaching end-of-life.
> 
> Unfortunately, I didn't realize these things were that finicky. I think I'm gonna run out the supply I've got, and then see if I can find any specifically rated for 125-130V.
> 
> -John


A-B has them for 130V supply that uses that SMPS like I mentioned, so they accept anything from 24V to 130V AC/DC input and optimize the voltage to the LED. I use them all the time, never had any trouble. 

But I don't think they are available in 22mm. Probably just not enough room. Pilot devices are not something I deal with directly but I know the right guy to ask if there is a 22mm version.


----------

