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Author Topic: Static Initiated Fail?  (Read 4592 times)

Mike Sokol

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Static Initiated Fail?
« on: October 28, 2014, 12:04:21 am »

One of my NSZ readers sent me a picture of a 12-volt LED overhead lighting fixture that was factory installed in his brand new RV. He claimed that he got up off of his couch, walked across the floor and touched the exterior of the light fixture. He felt a shock and  the bulb in the fixture dimmed, got really bright, then started smoking and burned up internally. He didn't understand how he was shocked by 12 volts DC, or how he burned up the fixture as you can see below.

I suspect that what he felt was a static shock like you might feel walking across the carpet and touching a doorknob. But in this case, by touching the outside of the plastic fixture he made a tiny spark jump from his hand to the electronics inside. That spark could have punched through a P-N junction in the LED current limiting circuitry, dumping a LOT of current from the 12-volt supply into the LED's. There is no individual fuse on these fixtures, just a 20-amp fuse on the battery feed wire. So that's a lot of amperage potential if the circuitry looses its current limiting.   

Doing a little more digging, another RV installer told me there's been a lot of these new imported LED lighting fixtures burning up for unknown reasons. So I wonder if perhaps they're being zapped by a static jolt from someone on carpet, which shorts out their current limiting circuitry, and allowing full battery current to flow through the LEDs, causing a burn-up.

Thoughts?
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Mike Sokol
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Stephen Swaffer

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Re: Static Initiated Fail?
« Reply #1 on: October 28, 2014, 08:07:07 am »

Typically what I have seen for current limiting is just a resistor-the LED is a steady known load-I would think in fact it could be designed to run without any current limiting and for efficiency in lighting less is more.  But others may be smarter on that side.  A static shock should just go to ground though, so I am not sure how it could have affected internal components?

I do know there is tremendous pricing pressure in LED lighting-have heard that some manufacturers sell their reject chips and they wind up in cheaper lighting fixtures.  My supplier carries 2 identical looking, same lumen output/wattage rating from a supplier-price is about 40% higher for one-but it has better color rendering, etc-they were forced to start offering the cheaper version to compete with big box pricing.  My guess is everyone in the supply chain for that light is getting beat up on price-and even the end user has no idea how to compare lighting so who cares-cheapest wins-and if we have to do a few warranty repairs oh well.  Price is more important than quality and the result is what you see.
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John Roberts {JR}

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Re: Static Initiated Fail?
« Reply #2 on: October 28, 2014, 09:16:42 am »

+1 Static caused a fault in the drive electronics.

Is there UL or similar safety agency rating on those fixtures?

JR
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Jonathan Johnson

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Re: Static Initiated Fail?
« Reply #3 on: October 28, 2014, 10:55:26 am »

Is there UL or similar safety agency rating on those fixtures?

Because vehicles typically aren't subject to building codes, including legally-enforceable electrical inspection, I doubt that they'd go to the effort and expense of having low-voltage devices tested and listed by a safety agency. Many of the 120V devices are UL listed, only because those same devices are supplied to installations that will be inspected.

The RVIA does have safety standards and does perform inspections of member manufacturers. Of course, a manufacturer that is not a member of the RVIA would not be subject to those programs. Whether or not they test individual components, I don't know.
« Last Edit: October 28, 2014, 10:57:49 am by Jonathan Johnson »
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John Roberts {JR}

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Re: Static Initiated Fail?
« Reply #4 on: October 28, 2014, 12:10:32 pm »

Because vehicles typically aren't subject to building codes, including legally-enforceable electrical inspection, I doubt that they'd go to the effort and expense of having low-voltage devices tested and listed by a safety agency. Many of the 120V devices are UL listed, only because those same devices are supplied to installations that will be inspected.

The RVIA does have safety standards and does perform inspections of member manufacturers. Of course, a manufacturer that is not a member of the RVIA would not be subject to those programs. Whether or not they test individual components, I don't know.
I ask because UL performs a rigorous analysis of how products fail and how individual components fail. So this seems to fall in that wheel house.

The automotive industry generally uses modest sized fuses, perhaps 20A@12V is not excessive for incandescent lighting it seems a lot for modern high efficiency LEDs.

If it burned up internally but did not cause a larger fire, or danger from excessive smoke, that might be considered an acceptable failure mode. UL mainly dislikes starting house fires or killing people, but products self destructing is a market concern not human safety issue..

JR
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Mike Sokol

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Re: Static Initiated Fail?
« Reply #5 on: October 28, 2014, 04:02:07 pm »

Is there UL or similar safety agency rating on those fixtures?

I don't think so, but I've forwarded the fail pictures and email info to the US importer/distributor of these LED fixtures. I'll see what he says...
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Mike Sokol
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Mike Sokol

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Re: Static Initiated Fail?
« Reply #6 on: October 29, 2014, 11:36:25 pm »

I heard back for the "manufacturer" of this LED module, and their engineer came up with what I consider to be a nonsense failure mechanism for it burning out. He proposed that the RV's 12-volt converter (essentially a 120-volt AC to 12-volt DC power supply that charges the 12-volt lead-acid batteries) must have had a momentary diode failure that dumped 120-volts AC into the battery system and burned out the LED module in addition to shocking the RV owner. The failed power supply diode then fixed itself before damaging any other electronics or the main storage battery. And, of course, this occurred at the exact second the RV owner touched the light bezel.

Yeah, and Martians ate my homework... :o So I'm calling BS on his proposed failure mechanism. After making my doubts known to the president of the company, he agreed to send me several LED fixtures to see if I can blow them up with a static discharge.

Should be fun...  ;D
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Mike Sokol
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Stephen Swaffer

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Re: Static Initiated Fail?
« Reply #7 on: October 29, 2014, 11:57:55 pm »

I heard back for the "manufacturer" of this LED module, and their engineer came up with what I consider to be a nonsense failure mechanism for it burning out. He proposed that the RV's 12-volt converter (essentially a 120-volt AC to 12-volt DC power supply that charges the 12-volt lead-acid batteries) must have had a momentary diode failure that dumped 120-volts AC into the battery system and burned out the LED module in addition to shocking the RV owner. The failed power supply diode then fixed itself before damaging any other electronics or the main storage battery. And, of course, this occurred at the exact second the RV owner touched the light bezel.

Yeah, and Martians ate my homework... :o So I'm calling BS on his proposed failure mechanism. After making my doubts known to the president of the company, he agreed to send me several LED fixtures to see if I can blow them up with a static discharge.

Should be fun...  ;D

Not to spoil your fun-but the answer is yes you can!

I am guessing that dumping 120 VAC to a 12 V battery circuit would blow up more than an LED-though you might want to use care proving that theory.
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Steve Swaffer

Mike Sokol

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Re: Static Initiated Fail?
« Reply #8 on: October 30, 2014, 12:15:50 am »

I am guessing that dumping 120 VAC to a 12 V battery circuit would blow up more than an LED-though you might want to use care proving that theory.

I'm not going to try to prove HIS theory... I'm going to try to prove mine. So if he wants to rig up a test to dump 120-volts AC into a 12-volt battery, he's going to make a battery/bomb I think.

I'm going to hook up one of his LED fixtures to a 12-volt car battery with a 15-amp fuse and 14-gauge wire, establish a ground-plane for the negative line, then flash the fixture with a piezo barbeque lighter held to the outside of the plastic bezel.   
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Mike Sokol
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John Roberts {JR}

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Re: Static Initiated Fail?
« Reply #9 on: October 30, 2014, 09:35:17 am »

Yup that definitely sounds like a BS answer. No real engineer with half a clue would claim that.

JR
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Re: Static Initiated Fail?
« Reply #9 on: October 30, 2014, 09:35:17 am »


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