UV light + electric current = boom?

[DarioC]

As others have suggested, have a experienced electrical person carefully pull the wall plate and first and foremost check for exactly where the arc took place. That will be your best clue as to what happened. If there was sparking there should be some visible marks. The physical characteristics of the controllers are the next best source of information. Hope you get to feeling better and let us know what you find out eventually.
DC

 

[OmCheeto]

I'm not much of a electronics person, but might there be UV responsive circuits in the variable speed controller ?

I suppose we could contact the manufacturer. Anyone try that yet?

 

[OmCheeto]

Also, the slider switches are different. The fan one mechanically clicks at four separate stops, the light one does not.

Which narrows down our choices to either Lutron model S2-LFSQ or S2-LFSQH.
"single pole, 3-speed fan/light dual control. Max ratings are 1.5A fan/300W incandescent/halogen light"
[ref: Lutron Support Center]

Nothing in their FAQ or Troubleshooting sections about "UV light" mishaps.

 

[Asymptotic]

Nothing in their FAQ or Troubleshooting sections about "UV light" mishaps.

This got me to thinking about welding. Arc welding generates massive UV (enough that after only a few minutes exposure welding-induced 'sunburn' occurs), but I've never heard of it doing anything odd to nearby electrical gear. Electronics damaged due to stray electrical currents are another matter.

 

[OmCheeto]

This got me to thinking about welding. Arc welding generates massive UV (enough that after only a few minutes exposure welding-induced 'sunburn' occurs), but I've never heard of it doing anything odd to nearby electrical gear. Electronics damaged due to stray electrical currents are another matter.

I did something similar. I tried to figure out the natural UV levels from the sun. Wiki says that it's 10% of total, so that would be around 100 watts/m^2.
These "secret agent" toy UV penlights all put out about 5 milliwatts, but there's little information on beam spread. Fortunately, a group of people analyzed the geometry and output after a child damaged his eye after staring at one for about 40 seconds.

1. The LED emission angle was 50 degrees. The beam diameter at the 1 cm exposure distance (LED to cornea) was 9 mm. About 1.4 mW entered the boy’s pupil which had a diameter of 3.4 mm. [ref]

The OP's description sounds almost identical as far as distances go, so:

1.4 mW through a hole 3.4 mm in diameter yields: 154 watts/m^2 (toy output)
which is about 50% more than the sun.

Though close enough I think, that natural sunlight entering this model of fan controller would do the same thing.

I would do the experiment myself, but the unit costs $27, and I have no use for such a device, nor the "secret agent" pen.

 

[DarioC]

Good investigating OmCheeto, and calculating. I see the unit is an enclosed box, so much for just checking behind the panel. I'm just now thinking about how we could get the manufacturer to donate a unit or supply some detailed design information.

 

[OmCheeto]

Good investigating OmCheeto, and calculating. I see the unit is an enclosed box, so much for just checking behind the panel. I'm just now thinking about how we could get the manufacturer to donate a unit or supply some detailed design information.

I would recommend what several other people have already recommended: Have someone who knows how to wire an outlet look at it and see if there's a problem. Shouldn't take more than 5 minutes.

 

[DarioC]

Ah yes, but the circuit is in an enclosed "box", that will be a problem I think.

Meanwhile, I found some LEDs in a parts drawer that are rated almost identically to the ratings of the spy pens. That is 405 nm and 5 mW, so I'm going to set up an experiment with AC line voltage and multiple materials and adjustable air gaps. I already have a variable gap setup from when I was overhauling the magnetos for my airplane.

I'm having thoughts about some connection with photo emission experiments that I did some time ago.
I hope the moderators will keep this open so I will be able to report any results or lack thereof.
DC

 

[Rive]

Which narrows down our choices to either Lutron model S2-LFSQ or S2-LFSQH.
"single pole, 3-speed fan/light dual control. Max ratings are 1.5A fan/300W incandescent/halogen light"
[ref: Lutron Support Center

According to google results this dimmer has a fairly closed chasing, so whatever it was, it was within. Unfortunately, I could not find any picture about the inside of this unit.

Based on the usual circuitry of such dimmers, any mishap within the Si part of the circuitry would result just a full speed operation.
Therefore, my bet lies on the cheap foil cap of the filter circuitry. This cap (and an 1-2W resistor in series, which is a good source for dramatic sparks) usually bridging the triac.
And cheap foil caps are transparent...

 

[DarioC]

Negative results yesterday on the minimum gap UV experiment. I have had an interesting experience with very light soot in a computer tripping ground fault outlets so I am considering that combination and similar situations.

A question for he OP: Did the controller fail, or is it still functional?

 

[OmCheeto]

According to google results this dimmer has a fairly closed chasing, so whatever it was, it was within. Unfortunately, I could not find any picture about the inside of this unit.

Based on the usual circuitry of such dimmers, any mishap within the Si part of the circuitry would result just a full speed operation.
Therefore, my bet lies on the cheap foil cap of the filter circuitry. This cap (and an 1-2W resistor in series, which is a good source for dramatic sparks) usually bridging the triac.
And cheap foil caps are transparent...

I've sent a request to Lutron for an internal diagram of the controller. Crossing my fingers.

But as a couple of people have pointed out, young scientists aren't always forthcoming with exactly how they arrived at their results.
I know my usual response at that age when attempting science but somehow nearly burned the house down was; "I don't know."

 

[jim hardy]

How old is that dimmer / speed controller ? Might it be a three wire style ?

interesting articles on them here..

http://www.ledsmagazine.com/article...-issues-to-ensure-compatibility-magazine.html

https://www.digikey.com/en/articles/techzone/2014/jul/ics-answer-the-challenge-of-dimming-led-lamps-in-triac-driven-circuits

 

[OmCheeto]

How old is that dimmer / speed controller ? Might it be a three wire style ?

interesting articles on them here..

http://www.ledsmagazine.com/article...-issues-to-ensure-compatibility-magazine.html

https://www.digikey.com/en/articles/techzone/2014/jul/ics-answer-the-challenge-of-dimming-led-lamps-in-triac-driven-circuits

Does this help?

Q; "What is the minimum load?"
Lutron; "The minimum load for this dimmer is 40W."​

ps. It may be a few days before I get a response from the company:

Lutronbot; "Thank you for contacting Lutron email support. Your email has been received, and one of our Technical Support Representatives should contact you within 1-2 business days."

Though, it is the holidays, so...

 

[OmCheeto]

Ouch!

Hello [Om],

Thank you for contacting Lutron Support! We would be unable to provide any circuit diagram as this is confidential information. As far as the possibility of this happening, I would need to collect more information:
-What model dimmer was affected?
-Do you know where exactly the UV light was shined?
-Is the dimmer now completely dead or does a part of it no longer work?
If you have any further questions, please feel free to contact Lutron Technical Support, anytime, 24/7.
Thank you,​

bolding mine

edit: Never mind what I said earlier about actually buying one. Not sure what I was thinking. I'll wait for the spring garage sales, and see if I can pick one up for 50¢.

 

[jim hardy]

'll wait for the spring garage sales, and see if I can pick one up for 50¢.

I too love "beating the system" .

And you keep it out of the landfill. Or at least postpone its arrival there by some years.

Anyhow - this thread is interesting. Hopefully somebody will experiment with such a device and a UV. source on the bench

If you want to assure something will positively happen all you have to do is publicly proclaim it impossible.
So, 'Color me skeptical but ready to learn . '

old jim

 

[bc1235]

I like Charles Link's ion theory. An interesting way to test this is to set up a controlled circuit that isn't going to blow circuit breakers. What I would do is create a circut like this: You will need a long piece of wire with a plug on one end (maybe cut off the receptical end of an extention cord leaving the plug and wire, a plastic electical outlet box, a 120 v electical outlet, an outlet cover plate and a lamp.
Now this part is a little tricky; you need to wire the outlet so each of the two are independent, then wire them in series with each other so that the current flows from the plug to one side of one outlet, out the other side of that outlet into one of the terminals of the second outlet then back to the return end of the wire. So now you have two outlets in series. Plug a lamp into one of the outlets. I'd start by putting a 100 watt lightbulb in the lamp (want to keep from blowing circuit breakers). Now time to test. Aim the laser at the unused outlet and see what happens. If nothing happens try a higher watt blub in the lamp. A 100 W blub is about 150 ohms. A 500 watt bulb is about 30 ohms. I'm not sure the amprage will have much effect but it could be a factor.

I don't know if that will answer any questions but it would be an interesting test.

 

[bc1235]

I like Charles Link's ion theory. It might be interesting to set up an experiment and test it out. I suggest getting a plastic outlet box, a 120v outlet and a cover plate from your local hardware/building supply. Cut the outlet end off an extension cord so you have the plug and a long piece of wire. Electrical outlets are designed to be in parrell so there are metal strips connecting the two in series. Remove one of them and leave the other in the circuit. Now attach one end of the wire to open end of one of the outlets and the other wire to the open end of the other outet. So what you should now have is a complete curcit with the two outlets in series. Plug in a lamp into one socket and aim the laser into the other and see what happens. If the light blinks it could be a positive result, Repeat the test with different light bulb wattages. A 100 watt bulb is about 150 ohms, a 300 watt is about 50 so if the circuit current is a factor it could work with 300 W where it might not with 100. Keep your fingers out of the live contacts and never work on a live circuit. I accept no responsibility for any harm to person or property (got to get the leagle crap out of the way)

 

[OmCheeto]

It would appear that the OP has until tomorrow to respond to the only unanswered question; "Has the device failed?"

An email I received from the manufacturer timestamped Dec 28, 2017 @ 1:33 PM:

Hello,
Our records indicate we have not received an update on the current status of this issue. We will close this case in 5 business days unless we receive a response from you indicating the issue is unresolved. If you are still experiencing this issue or need additional assistance after the case has been closed, please feel free to reply to this e-mail to re-open the case automatically at any time.
If you have any further questions, please feel free to contact Lutron Technical Support, anytime, 24/7.
Thank you,

Lutron Technical Support​

bolding mine

@SW Dad , time is running out.

 

[Steeve Leaf]

I think your sun signature is all over the wire nut ( with inadvisable ink :)

Reference https://www.physicsforums.com/threads/uv-light-electric-current-boom.934703/

 

[Steeve Leaf]

Maybe Inadvisable ink spray on the panel ?

 

[darkwood]

I would suggest that we are all getting a little exited with the theories here when we haven't ruled out the most probable answer, even though the son says he was doing nothing more than shining the UV led into the switch the odds are because it went bang and the son realized he was in big trouble that he covered his rear end and lied about the chain of events, given this is probably a mechanical switch housed in a insulating enclosure then the led can only shine into the switching chamber, there will only be a feed and switch line running through at that point which will not go boom as that is the nature of the switch to close these together, also it is likely mounted on a metal box and there would be a big gap between ground and any live wires...
2 possibilities here IMHO -
-A trapped wire or poor termination blew itself clear and was shorted because he was physically messing with it externally.
-He was prodding something into the slot that may have created a short.

I find it highly unlikely that shinning a child safe low mW led pen into the switch slot is going to cause any kind of problem at all, we use higher powered UV equipment to zap bugs and things hanging in shops often next to switchgear.
The OP want to kick his sons butt and ring out the truth here

 

[sophiecentaur]

I was lucky I wasn't punished by my parents for my stupidity.

Ye gods. Parents can be so booooring, cannot they?
Now you are grown up (?) you can do the experiment under safe and controlled conditions.
I favour the photoelectricity explanation but the conditions are not easy to obtain.

Also, the son could be lying. As if . . . .

 

[The Electrician]

I decided to perform an experiment. I cut off a line cord from an old expired appliance and connected to a porcelain light bulb socket. I cut the line cord near the light bulb and exposed half an inch of the stranded conductor on either side of the cut. I splayed out the strands of copper and taped down the cord ends with the splayed ends very close together. The ends of the strands have somewhat sharp ends from the cutting process and the copper strands are clean. Here's a photo (a little blurry unfortunately) showing the setup:

Following is a video of the experimental procedure. I have an ultraviolet flashlight that produces a beam of 365 nm UV with a total radiant power of 750 mW. The line cord is plugged into a wall outlet so that the gap shown in the photo above is in series with the bulb and the 120 VAC from the outlet (through a 1:1 isolation transformer for safety). I momentarily short across the gap to show the incandescent bulb lighting up. I then play the UV beam across the gap from an inch or two away. This is much more intense and shorter wavelength UV than that available from the pen light shown in post #1. A difference in my setup is that if the UV causes an effect in the gap in my setup it won't cause a bang and short tripping the circuit breaker, but rather should just light up the bulb.

If my 750 mW, 365 nm UV beam can't initiate an arc across the gap, then it wouldn't be likely that the 5 or 10 mW, 405 nm pen light could. I made the gap in my line cord as small as possible with clean copper strands.

It's up to each reader to draw their own conclusions from this experiment.

https://emailhosting.wistia.com/medias/h0i05oulyq

 

[Rive]

I decided to perform an experiment.

Since you have a decent UV source, could you please check out some (transparent/partially transparent) foil capacitors?

 

[The Electrician]

Since you have a decent UV source, could you please check out some (transparent/partially transparent) foil capacitors?

Sure, if you'll tell me just what you want me to do, and with respect to what particular capacitors?

 

[Rive]

My idea about this case was that the filter circuit (cap and resistor in parallel with the dimmer) caused the sparks: especially the resistor (most likely some 1-2W cement type) which blown up after the cap started to conduct due the UV.

Prerequisite is that the cap should be some transparent, foil type and has reaction to UV.

I don't really know what kind of equipment do you have at hand. What I'm curious about is the behavior of (transparent) foil caps under UV light and high voltage (stay safe, please).

Ps.: a failure in the filter circuit would be also consistent with the fact that the stuff is still working.

 

[The Electrician]

My idea about this case was that the filter circuit (cap and resistor in parallel with the dimmer) caused the sparks: especially the resistor (most likely some 1-2W cement type) which blown up after the cap started to conduct due the UV.

Prerequisite is that the cap should be some transparent, foil type and has reaction to UV.

I don't really know what kind of equipment do you have at hand. What I'm curious about is the behavior of (transparent) foil caps under UV light and high voltage (stay safe, please).

Ps.: a failure in the filter circuit would be also consistent with the fact that the stuff is still working.

By "high voltage" do you mean anything other than the 120 VAC from the wall outlet?

 

[Rive]

By "high voltage" do you mean anything other than the 120 VAC from the wall outlet?

The best would be with 120VAC, but that's also the most dangerous, so no way I'll ask for that directly you know...

 

[The Electrician]

The best would be with 120VAC, but that's also the most dangerous, so no way I'll ask for that directly you know...

My EE degree plus decades of experience qualify me to do this test. I didn't bother saying it earlier because it didn't occur to me that anyone else would be likely to bother repeating the experiment, but I used a 1:1 isolation transformer for my own safety, and I don't recommend that anyone else do this.

Here is the stash of miscellaneous film capacitors that I've accumulated over the years. There aren't many transparent/translucent capacitors in there:

If there were an R/C series pair connected across the triac, I would suppose that a good designer would use an "X" capacitor for that purpose. I found a typical X capacitor which is also transparent:

You can see all the agency approvals on this capacitor (made by RIFA), but I have no way of knowing if the encapsulant is transparent to UV. I'm not going to create another video, so I will only report my results. I connected this capacitor across the gap in the line cord shown in the earlier video and played the UV from the flashlight on the capacitor from every angle. I got so close that the capacitor was touching the window in the end of the flashlight. There was no sign of any action from the light bulb.

I found two other transparent capacitors, a polystyrene cap and a polycarbonate cap:

I repeated the experiment with each of those, with the same negative result.

Later today I will try measuring the insulation resistance of these three capacitors with DC using my Fluke meter on conductance range. This can measure insulation resistance up to the gigaohm range, but with only a few volts applied. I will also apply about 50 VDC from a power supply and measure leakage current. Both these measurements will be performed with and without exposure to the UV.

 

[Rive]

I repeated the experiment with each of those, with the same negative result.

Thank you very much, that more or less settles it: it was also a dead end then.

 

[jim hardy]

If i could like a post multiple times i would like Electrician's 199X .

"One experiment is worth a thousand expert opinions"

I'm back to 'Open the fixture and look for smoke residue' .

old jim

 

[The Electrician]

If i could like a post multiple times i would like Electrician's 199X .

I'm back to 'Open the fixture and look for smoke residue' .

old jim

It's hard to imagine how very much UV could penetrate the box anyway, especially if there's only 5 mW from the pen to start with.

You're right on; a look inside is what's needed.

 

[darkwood]

So I guess we go back to the lying little lad scenario which with 30yrs experience in this trade was my first thought and most likely scenario; with a gullible father to boot

 

[The Electrician]

I followed up with a measurement of the 3 transparent/translucent capacitors' leakage as a measurement of insulation resistance, and as an indicator of internal photoelectric effects. With 50 volts DC applied to a given capacitor and with a DVM set to the microampere range in series, I shined the UV flashlight at very close range on the capacitor under test.

WIth the polystyrene and polycarbonate capacitors in circuit the leakage current without UV illumination was less than 10 nanoamperes. With UV illumination from the 750 milliwatt flashllight there was no detectable increase in leakage.

The RIFA X capacitor exhibited a leakage of about 270 nanoamperes without UV illumination, and showed no detectable increase with UV illumination.

I was hoping that there would be some detectable effect from the UV illumination, but no joy.

 

[Rive]

I was hoping that there would be some detectable effect from the UV illumination, but no joy.

Sigh... A single good experiment can massacre any amount of ideas
Thank you for following this up.

I know that some old potentiometers can produce fine graphite (or something like graphite) dust. Maybe that, on a surface? That equipment seemed to be quite old...
But it's just some afterthought. I agree with Jim Hardy that it's already hopeless without dissecting that box.