A strange - strange case...

[mikey99]

I'm hoping someone here can provide some insight.

I have had custom made LED potlights + an entire deck powered by multiple groups of LEDs (4 diodes in series) running at 85 mA (with proper selected resistors) while the LED meant for 100mA... so this accounted for me not running a constant current (15V) power supply.

This was fine for months with no problems what so ever!!!

My father decided to install a water-sprinkler system to control our power supplies for the LED's with daily schedules and install a relay which separates the LED groups from the power supply.

This was running for about a week.

After a large thunderstorm last night we noticed that both the outside potlights and the deck has LEDs that are not working (30% stopped working) but they are not burned because the rest of the LEDs that are connected in series with it are working... its just 99% dim. - those that have not been affected are still 100% just as bright.

I cant rule out a few possibilities.

They all stopped working in one day so it couldn't be a gradual shock of the power supply.

The relay separates the power supply from the LEDs so...

Could the wiring act like an antenna for the static...

Could the powersupply deliver a shock after being charged once the relay let it connect with the LEDs through the water sprinkler system.

Power Surge?


I am so clueless, because the LEDs are not burned.

Another group of LEDs which are lighting trees (through a different power supply and not connected to the relay-watersprinkler system) is working 100%. I know its grounded because they directly touch ground but also how come the thunderstorm (if its the case) did not affect those but affected those LEDs connected to the relay. (Probably no powersupply directly connected to ground them?)


I cant rule out any possibilities.

Does anyone has any expert advice on how to protect these sensitive LEDs from environmental/ other types of damages and also what the reason for all these LEDs to stop working all at once?

 

[JohnR66]

Sounds like some were damaged by ESD. Take a dead one out of the circuit and hook it in series with a good LED and 100 Ohm resistor across a 9volt battery.

Does the known good LED light with the bad LED (no light) at forward bias?
Does the good LED light if the bad one is flipped around in reverse bias?

Both will indicate the bad LED has had ESD damage if the good LED lights. Sometimes you can blow the conductive channel open by giving the LED a quick blast of current, Such as the LED in forward bias with a 5 or 10 Ohm resistor with 9V supply. The LED really should be replaced.

ESD can be mitigated by adding a .22uf film capacitor across the LEDs, after any current dropping resistor. Static discharges are typically very short high voltage events that the cap will easily conduct around the LEDs. A high speed diode in reverse bias can help too. Surge protection at the source can help, but in your application, the discharge could be induced on the load side.

 

[mikey99]

Hi,

I will try your suggestions.

What causes ESD.. can the lightning storm be the cause? if the LEDs were not separated from the power supply due to the relay, could the power supply ground / protect the circuits from the damage?

Is there a source i can get drawings / materials for protection of ESD such as something to connect at the power source?

I'm not too educated in this topic so i will do some research but i will really appreciate a reply from a more educated person.

 

[JohnR66]

Electrostatic discharge damage in a white (blue, InGaN) LEDs is caused by a conductive channel that forms in the die. The normal "diode" action may not be in effect as the conduction channel's resistance is too low and there is not enough potential left to operate the rest of the diode junction to make light. This conducting channel will also conduct in reverse bias. I am at a loss to explain the nature of this conducting channel.

Light damage is indicated by a LED that stops emitting light at low current such as 5ma or less. Heavier damage is indicated by a LED that is conducting at rated current, but gives out no light. Of course, a strong surge can vaporize the bond wires or die and blow the LED apart!

I have sacrificed a few LEDs to study ESD damage. Some LEDs have built in protection, but it is limited to light ESD. Some LEDs seem super sensitive.

It is possible for the surge to be introduced into your system through the PSU or to the wires of the LEDs themselves. Lightning is such an extreme high voltage and current it can induce voltages in conductors even if the strike is several hundred feet away.

The ESD protection system depends on how much effort and $$ you want to put forth. It may make sense to put some $$ if the LEDs are hard to replace. The capacitor method would be cost effective.

 

[zipplet]

Thanks for the suggestion with the cap. I have not (yet) had this issue but I'll use that suggestion when wiring fixed power LEDs.

 

[Mark620]

Good information to know.
I am looking at building a cabin - a 12V or 24V system and we plan LED's for lighting.

 

[mikey99]

"Heavier damage is indicated by a LED that is conducting at rated current, but gives out no light."

It seems to be the case. I started replacing the potlight i made using 100 mA (360,000 mc LEDs) and 3 were not emitting light but connected in series in 4 and one LED was emitting light. That means they are conductive but give not light. Sound like a severe ESD.

Ill try the capacitor. Do i just connect it near the power supply for the entire circuit? It there a proper way to connect it?

Also, What if i ground one of the ends of the power supply, will this protect against ESD?

Thanks John!!

 

[zipplet]

The small capacitor is placed *across* the single LED in parallel. I'm not sure the best way for multiple LEDs in series... hopefully someone can chime in.

 

[HarryN]

Hi - is the concept of putting a cap across the leads a useful concept for suppressing voltage spides in auto 12 volt systems also valid? I was wondering about this approach vs. some kind of device which "bleeds off" above a pre-set voltage.

Example - Luxeon K2 size LED being drive at 1.5 amps (or any larger current device). It seems like that would take a larger cap to protect it. I realize that the K2 is already ESD protected, so that might not be a good example, but the general idea of "capacitor capacity" vs "device power level" - I assume is somehow related ?

Thanks

HarryN

 

[JohnR66]

The capacitor idea is a cheap solution for low cost LEDs. I have not tested high power LEDs due to their cost. I can't afford to zap my XR-Es and Luxeons to experiment.

You could always add fast recovery diodes, but the cost escalates.

A capacitor will shunt the rapid spike and should do fine for the OP's problem. Ideally a cap across each LED is needed, but one tied from the first LED anode to the last LED cathode in each series of LEDs should help and be the cheapest solution. The LEDs should be isolated well enough so static can not be introduced on any LED in the series or the surge may pass through the LEDs to get to the shunt cap.

If the deck has metal, such as hand rails, I'd ground them as well as the negative side of the power supply. This could help induced static from jumping over to/from the LED circuit as it seeks ground. You should seek the National Electric Code (NEC) for proper grounding.