Reliability of LEDs: PF Members' Views and Experience

[jim hardy]

Glad you approve of his technique.

I was also thinking that for some of those things, a battery charged from the 12/24 V could drive a high power appliance for a short while.

yes a big car cranking battery can deliver a kilowatt for a short while. A couple kw generator woouldn't be outrageously expensive if only run during high demand times and one arranged his household activities around the generator. That's easier for a single guy, though.

I must say this TI board looks interesting. 20 real watts is a lot of sound for a living room. Small enough to hide in something else..
https://www.adafruit.com/product/1752

 

[mheslep]

I see two electrical problems.

1, The environmental temperature. ...

This. The latest LED bulbs have a label, something like 'not suitable for enclosed light fixtures', or the reverse.

 

[anorlunda]

I just came across this video. It is instructive the way the guy speculated on failure causes, and how he tracked down the actual failure modes.

 

[Nik_2213]

In my experience, neither CFLs nor LEDs like the heat. Also, the more powerful the bulb, the shorter the life if ventilation is even slightly impaired.Sometimes you can switch designs to a 'skinny' type. Sometimes, you can adapt things. eg Here in UK, we have a zoo of Edison screw and traditional 'bayonet' fittings. ES, SES, BC, SBC etc. Faced with a light fitting that always ran hot and ate bulbs with grim regularity, I bought a BC/ES adaptor, switched to the other type of bulb. With the bulb now two inches further from its too-snug base, it runs sufficiently cooler to last much, much longer. Still, 'Due Care, Please' !

I'm not impressed by 'halogen in bulb' lamps. Although they give a brighter, bluer light, they do not last much longer than a standard incandescent. If you really want a long-lasting bulb, such as for some-where that is hard to access or essential for safety & cold-starts, consider incandescent 'rough service' types. They sacrifice efficiency for endurance...

Sometimes, you can combine different lamp-types in a multiple fitting. We have a tall stair-well where the lights fitting is really hard to reach, but essential for safety. Ordinary Incandescent lamps burned out too quickly, 'rough service' were too dim. CFLs took too long to strike in the cold, would flicker unpleasantly. Powerful LEDs died young. Worse, a family member had photo-sensitive epilepsy; any flicker was unacceptable...

Some lateral thinking produced a solution: I fitted two CFLs and a 'rough service' incandescent. The latter's prompt illumination masked the former's start-up flicker. As LEDs have improved, I've since replaced fading 'rough service' lamps with low-powered LEDs...

FWIW, I've begun replacing our suspended ceilings' 4-foot (1200mm) and 5-foot (1500mm) fluorescent tubes by their LED equivalents. Trial basis as yet, but they are slimmer, much safer to handle and give a nicer light temperature. Just remember to replace the fitting's 'blinky' starter with the 'bridge' device supplied !

I must agree with the comments that power spikes are a lamp-bane. I've fitted several plug-in spike-catchers around the house, the type with a tiny pilot-light warning if protection is active. They seem to help...

 

[anorlunda]

FWIW, I've begun replacing our suspended ceilings' 4-foot (1200mm) and 5-foot (1500mm) fluorescent tubes by their LED equivalents.

I also found the following video an hour ago. It may be helpful to you.



Heat may well be a factor. The interior space of a fluorescent ceiling fixture is very much larger than the interior of a bulb, so hopefully the LEDs will run cooler than in a bulb.

 

[sophiecentaur]

I skimmed through this thread again and I'm struck how, typically of Engineers, the replies were about reasons and possible workarounds. Why aren't you / we all totally disgusted about it and writing rude letters to suppliers? The prices of these devices are only justifiable if they actually last as long as the numbers written in the blurb. The public are being taken for a ride here.

 

[anorlunda]

I skimmed through this thread again and I'm struck how, typically of Engineers, the replies were about reasons and possible workarounds. Why aren't you / we all totally disgusted about it and writing rude letters to suppliers? The prices of these devices are only justifiable if they actually last as long as the numbers written in the blurb. The public are being taken for a ride here.

I did talk about prices and brand in #6. It's worth repeating. If you buy a brand name like Phillips, you're much safer.

You can't expect a company like IKEA to have the same kind of product engineering and testing as a company like Phillips. IKEA needs the flexibility to switch suppliers if necessary, and when switching they can't take a year or more to investigate and qualify a new supplier. They must depend on the statistics of customer complaints and returns to know when a product they sell is faulty.

LED bulbs at very low prices are sold in bulk on alibaba.com . I presume that they are bought by retailers who know next to nothing about the manufacturers.
Here's an example link to an alibaba ad for LED bulbs, €0,21 ($0.25) each in quantities of 60000 per day.. Use your own imagination to think of who buys them, and what names they stamp on them before sale.

 

[jim hardy]

Why aren't you / we all totally disgusted about it and writing rude letters to suppliers? The prices of these devices are only justifiable if they actually last as long as the numbers written in the blurb. The public are being taken for a ride here.

I think it's " the curse of the computer age" .

Windows has conditioned two generations that "workarounds", excuses and patches are the norm. Keyboard anonymity enables surreptitious and underhanded behaviors.
If societal values of excellence and virtue aren't dead they're on the critical list.
We need a Robert Pirsig revival .

[End Rant]

 

[russ_watters]

I skimmed through this thread again and I'm struck how, typically of Engineers, the replies were about reasons and possible workarounds. Why aren't you / we all totally disgusted about it and writing rude letters to suppliers? The prices of these devices are only justifiable if they actually last as long as the numbers written in the blurb. The public are being taken for a ride here.

This is far from the first thread on the subject - I suspect I started some myself. I've expressed disgust in the past, but I've never been a letter-writer. I don't know that it does much.

 

[russ_watters]

I just came across this video. It is instructive the way the guy speculated on failure causes, and how he tracked down the actual failure modes.

One open LED kills the whole string; I guess it is too much to ask that they be wired in parallel?

Heat hasn't seemed to be the issue with the LEDs whereas the CFLs I've lost have looked from the outside like they were overheated(discolored plastic). One thing I've done that seems to help is most totally enclosed fixtures have insulation on the top, inside surface. Ripping it off helps dissipate heat better.

 

[anorlunda]

Might it be that LED bulbs with the circuit at the base might run hotter when hung upside down. I'm thinking heat rises. Heat rising to the base has a harder time escaping than heat rising to the globe.

I can't comment on CFLs. I never owned one.

 

[NTL2009]

One open LED kills the whole string; I guess it is too much to ask that they be wired in parallel? ...

Yes, I think it is too much to ask, at least for consumer grade.

LEDs are current devices. Put them in parallel and you will get current hogging and probably thermal runaway to destruction (or at least uneven light from each LED, which would hurt efficiency). To avoid that, each LED would need its own current supply, and that's just not practical with a lot of LEDs in a cheap lamp.And 12 separate switching supplies may have a higher failure rate than the series string of 12 LEDs shown in the youtube link.

If an LED fails shorted, the string will continue to light, as the current supply will remain the same through the other LEDs. But from what I'm reading open seems to be more common than short. But a short in all parallel LEDs would take out everything.

To protect against opens, a 3.9V Zener can be placed across each of the LEDs in the string (at higher expense of course). The 3.9V Zener would not affect the normally ~ 3.3V LED. But if the LED opened, the Zener would provide a path to the remaining LEDs in the string.

Offhand, I think failures in the driver/switching circuit are more common than actual LED failures. I'll see if I can find a reference for that.

 

[Baluncore]

Many processes and chemical reaction rates, such as the diffusion of material within a semiconductor, double for each 10°C increase in temperature. That can be used to accelerate the lifetime testing of new products. But it appears that the new wave of designers have failed to learn about the Arrhenius equation and accelerated testing.
https://en.wikipedia.org/wiki/Arrhenius_equation

When we operate a device in an environment at a higher temperature than specified, we must expect a reduced MTBF, a shorter life. A device that should operate for 1000 hours at 20°C can be expected to last only 500 hours at 30°C. At 40°C expect 250 hours and at 50°C expect 125 hours. At 60°C expect 62 hours and at 70°C expect 32 hours.

The rate of advance of technology is dependent and reliant on the replacement of the previous product generation. I guess the marketting industry knows you will not need to buy another unit until an existing unit fails. So it is really not surprising that improved cooling is not advertised as an advantageous feature.

Temperature sensitive electrolytic capacitors were the mainstay of consumer electronics repeat sales. Now that things have gone more digital and a few reliable capacitors are available, it is the unreplaceable battery pack that has taken over driving the model replacement economy. When the battery pack does not fail, the manufacturer programs lower performance to increase their sales, while they ignore the social, financial and environmental disaster they are going out of their way to cause at our expense.

 

[jim hardy]

Might it be that LED bulbs with the circuit at the base might run hotter when hung upside down. I'm thinking heat rises. Heat rising to the base has a harder time escaping than heat rising to the globe.

That's a fact .

https://www.edn.com/electronics-blogs/led-insights/4423570/That-60W-equivalent-LED--What-you-don-t-know--and-what-no-one-will-tell-you-

 

[OCR]

...the manufacturer programs lower performance to increase their sales...

Oh, what could possibly make you think that ...? .

 

[sophiecentaur]

Windows has conditioned two generations that "workarounds", excuses and patches are the norm.

Yes. It's all about 'conditioning'. In the not too distant past, we all "knew our place" and didn't question the way society was structured; we accepted our lives from birth to death. Nowadays, we are conditioned slightly differently and to different thingsbut the 'questions' are still not asked loudly enough.

I am struggling for the first time in years with a Windows machine and it is such a business just to get started. Apple, on the other hand, makes the experience warm and comforting - until things go wrong, at which time you realize they don't care just as much as Microsoft don't care. They just do it more prettily.

 

[anorlunda]

I'm really pleased with the direction this thread has turned. IMO, the intersection of engineering and economics is fascinating.

In this case, the topic is not at all new with LEDs. There was a time in history of incandescent light bulbs when consumers could find both "regular" low-cost bulbs and "long-life" bulbs on the store shelves. Long life came at the cost of higher price and lower efficiency. Over the years before the end of incandescent, consumer preferences drove the "regular" bulbs to improve their life, and the "long-life" bulbs to decrease their price. Apparently, the "sweet spot" optimum was somewhere in the middle.

To me, the fascinating thing about that story is that finding the "sweet spot" is an iterative process involving both manufacturers and engineers on one hand and consumer preferences on the other hand. In the case I just described, the optimum was in the middle. But in future cases, the optimum can be at any point, extreme low, extreme high, or middle. Engineering innovations can disrupt the balance as can changes in consumer preferences.

50+ years ago, I worked for General Electric. At that time, light bulbs were the cash cow that made the entire GE giant profitable. Back then, I may have been able to get my hands on GE marketing studies showing the data on consumer behavior. Alas, I didn't get access then and it is probably lost to history today.

But fast forward to this very thread. I can buy LEDs on alibaba.com for €0,21 each. They probably cost €0,20 to make and the manufacturer makes 5% profit. The retail price is €12,00. Somebody in the middle is making lots of profit. Suppose they made an improved long-life model that cost €1,00 to manufacture and sells for €1.,10 on alibaba.com. That increases manufacturer profit to 10%. But how would it influence retail sales prices and profitability? The answer to that question requires much more than engineering.

IMO it is much to simplistic to blame everything on greedy corporations. Consumers have a major say in what they are offered. Consumers can certainly be deceived and cheated in the short-term, but it is wrong to think that they are powerless.

p.s. History buffs should also remind us that this exact problem delayed by several years the "invention" of the light bulb by Thomas Edison (in 188? I forget the date.) There were lots of electric light bulbs around in laboratories for years before that. Edison's lab in Menlo Park NJ tinkered for years until they found a filament that gave a price-performance point that made the bulb an economic success. So in that perspective, this thread merely continues a topic that has been going on for about 135 years. Gotta run now, but I have a link to a free biography of Edison that I'll post when I get a chance.

 

[NTL2009]

I'm not as negative about this planned obsolescence scenario as some here.

Look at our cars - they last far longer than they used to, and require far less maintenance. Instead of regularly changing/adjusting points, timing, spark plugs and oil/filter at 3,000 miles, many cars require no sort of tune up and plug changes are at 50,000 or maybe 100,000 miles. Oil changes are 10,000 miles. It used to be an "event" to turn 100,000 miles on a car (with a xx,xxx.x digit odometer) - now it is routine.

Many of learned the importance of data backups the hard way, from the very unreliable floppy disks of the day. Today, hard drives and flash drives that are thousands of times larger are far more reliable and robust.

Yes, due to modern manufacturing techniques, the old style troubleshoot and component replacement just isn't practical. But it has lowered the cost of these products for us. And who would want a DVD player made with through hole components that a bench tech could replace - it would probably be the size of a bar fridge.

That said, I do wish some products were more modular so we could replace the module instead of the whole thing. I have had to recycle things because of a switch - but it is one of those surface switches that are integrated in with panel electronics, and even getting it apart to clean it was near impossible. But life goes on.

I think LEDs will (and have been I think) improving in durability. Now that the cost has come down, I think people will start looking for quality if it doesn't cost much more. People don't want to have to replace bulbs in hard to get places, and will pay for quality, and some manufacturers will market that.

I may have mentioned this before, but I think physically separating the LEDs from the driver circuit would be a very good thing. With the driver in the lamp fixture base, away from the LEDS, they won't heat each other, and there is more room for heat dissipation around the LEDs, and each will last far longer. And that is modular - replace the driver if it goes bad, replace the LED assembly if it goes bad. We could standardize on a nominal 24 V DC compliant source, with a 3rd pin that would tell the driver how much current to supply the LEDs (like use 1000 Ohm R in the 'bulb' to tell the driver to supply 1 Amp, and scale it up/down with the R value from there (100 Ohm for .1 Amp, etc). That would provide comparability and flexibility.

 

[sophiecentaur]

Look at our cars - they last far longer than they used to, and require far less maintenance.

This is absolutely true. I think you have identified the inconsistency (or perhaps cynicism) of marketing. The huge number of potential car buyers and the high cost of a car (plus competition) has made the manufacturers use reliability as a selling point. Unfortunately, the Light Bulb is a bit like the mouse trap - low cost and not very sexy so people view it in a different light. (Ouch - sorry!)

 

[jim hardy]

It used to be an "event" to turn 100,000 miles on a car (with a xx,xxx.x digit odometer) - now it is routine.

That is so. My last one had 285,000 when i gave it away and I anticipate at least that from my current one(it's at 203k now) .

Cars got so expensive it became necessary to design them so they'll outlast the loan .
What a boon for handymen - i buy $2,000 cars because they last me half as long as $20,000 cars.
With a $40 code reader and reasonably gentle treatment one can likely drive them to 300 thousand miles. Several in my neighborhood are past 400k.

As @sophiecentaur says - first marketer to make an advertisement demonstrating how his company designed his LED lamps to handle heat and prolong lamp life will start a groundswell.
As @anorlunda suggests - an outfit like GE needs brand loyalty . If somebody remembers a positive experience with a simple light bulb it'll affect his decisions on major appliances. I've had bad luck with Frigidaire appliances, probably that's why i notice myself avoiding GM automobiles. Subconscious is funny that way.

old jim

 

[OmCheeto]

Just thought I'd provide some "outlier" data points:

1. None of my LED "bulbs" have failed.

Numerous LED Christmas light strings have failed. Though, from my experiments from yesterday, it appears it was just the fuses that failed. I just looked at where I think the fuses should go, and still can't figure out how to get to them, without hurting myself.​

2. The only new car I ever bought is now 8.5 years old, has 55,000 miles on it, and the only components that have failed so far have been:

1 fuse
1 tail light
2 tires
​

That is all, for now.

 

[Nik_2213]

"One thing I've done that seems to help is most totally enclosed fixtures have insulation on the top, inside surface. Ripping it off helps dissipate heat better."

Please, please be careful: down-lighters etc may use such insulation for fire resistance per 'Building Code'. Not from the light fitting, mind, but from any unrelated room fire. The insulation delays spread through the fittings to the void above and rooms beyond. If a fire investigator discovers you have compromised *any* fire-breaks, then your insurance cover may be voided or significantly diminished...
===
Cars...
I've only had the good fortune to buy a new car thrice in my life. First time, back in the 80s, I had to 'run it in' for several weeks, then get it serviced. In 2003, I was told, "Just take it easy for a few weeks to let the engine settle down." 18 months ago, when I asked about such, the delivery team shook their heads and said, "Go easy for a few days until the 'stubble' wears off the tyres. Then bring it back in two years, 50,000 miles or a system warning, whichever comes first..."

 

[sophiecentaur]

Just thought I'd provide some "outlier" data points:

1. None of my LED "bulbs" have failed.

Numerous LED Christmas light strings have failed. Though, from my experiments from yesterday, it appears it was just the fuses that failed. I just looked at where I think the fuses should go, and still can't figure out how to get to them, without hurting myself.​

2. The only new car I ever bought is now 8.5 years old, has 55,000 miles on it, and the only components that have failed so far have been:

1 fuse
1 tail light
2 tires
​

That is all, for now.

You have just been lucky I think - or else you have always bought top of the range versions. I checked my mains volts today and yesterday and the value in my shed is 232V, fairly steady. I read someone (on their thread I think it was) that the design operating voltage can be 220V. The nominal UK volts can be as high as 240V. There is just a little less headroom to deal with the odd spike of volts. Clearly the life of filament bulbs would be significantly less for nearly 10% higher volts (V^-16 law)

I think it's only a mains voltage problem, though. 12V LEDs on my boat ran and ran.

 

[OmCheeto]

You have just been lucky I think - or else you have always bought top of the range versions. I checked my mains volts today and yesterday and the value in my shed is 232V, fairly steady. I read someone (on their thread I think it was) that the design operating voltage can be 220V. The nominal UK volts can be as high as 240V. There is just a little less headroom to deal with the odd spike of volts. Clearly the life of filament bulbs would be significantly less for nearly 10% higher volts (V^-16 law)

I think it's only a mains voltage problem, though. 12V LEDs on my boat ran and ran.

I currently have 2 experiments in progress, with another completed.

edit: ps. Any idea how to describe diodes "mathematically"? Never mind. I looked it up. It was off topic anyways.

 

[Tom.G]

ps. Any idea how to describe diodes "mathematically"?

Find a graph of diode characteristics you like and make a table of x,y co-ordinates of the curve at pertinent points.

Then visit this page and enter the co-ordinates. The result is a least-squares polynomial fit of the degree you choose; probably about 6-degree for a good diode fit. I've downloaded the page and run it locally.
https://arachnoid.com/polysolve/index.html

 

[OmCheeto]

Find a graph of diode characteristics you like and make a table of x,y co-ordinates of the curve at pertinent points.

Then visit this page and enter the co-ordinates. The result is a least-squares polynomial fit of the degree you choose; probably about 6-degree for a good diode fit. I've downloaded the page and run it locally.
https://arachnoid.com/polysolve/index.html

It doesn't seem to work.
Anyways, it's a bit off topic, so I'll drop the question.

I currently have 2 experiments in progress, with another completed.

Nothing really interesting from my 3 experiments.
1. I chopped up one of my failed old Christmas light strings and found that it was either a blown fuse or a single lamp failure, as the 5 bulbs I tested were ok.
2. I hooked up a string of 4 to my car battery, and although they draw almost exactly the same power, (73 mw AC/lamp vs 79 mw DC/lamp), the DC powered lamps are much brighter. The AC lamps have been on continuously since I bought them, approximately 10 years ago, yielding a lifespan of 88,000 hours. Since the entire string uses only 2.2 watts, I use them as night time navigation lights throughout my house. (There are 3 sets: 1 each for the kitchen, living room, and bathroom) Total annual cost: $7. My guess is that this may have extended the life of my remaining CFL's, as I almost never need to turn them on.
3. I assumed the string of 4 lamps hooked to my battery, being much brighter, were drawing more current, so I was going to leave them on until they failed. Though, I now know that isn't the case, and they will probably outlive me.

You have just been lucky I think - or else you have always bought top of the range versions.

I just checked 2 that are easily accessible and they are both made by "FEIT Electric".
hmmm...
wow.
I think I did get the high end one: $8.21 at Amazon (https://www.amazon.com/dp/B00B7SB0B2/?tag=pfamazon01-20)
vs
a 10 pack for $13 at the local hardware store (https://www.homedepot.com/p/Feit-Electric-60W-Equivalent-Warm-White-A19-LED-Light-Bulb-Maintenance-Pack-10-Pack-A800-830-10KLED-10/206675105)

 

[NTL2009]

Just thought I'd provide some "outlier" data points:

1. None of my LED "bulbs" have failed.

Numerous LED Christmas light strings have failed. Though, from my experiments from yesterday, it appears it was just the fuses that failed. I just looked at where I think the fuses should go, and still can't figure out how to get to them, without hurting myself.​

... .​

​

I only have a few LED bulbs, and not for long so nothing useful to report there (no failures yet though). Although they are finicky with my CFL/LED rated dimmers. I found I need a filament bulb on the circuit to dampen the wave, or provide more load or something, or else they sort of randomly modulate the brightness (not a repetitive 'flicker'). They sell a dummy power resistor (not sure what value it is) to add to fixtures for this purpose, which of course is ironic, as that is hurting efficiency.

As far as Christmas lights, I started buying those about 6 years ago, and have now replaced almost all the old miniature filament lights, and have had ~ 8 strings of 50 in use for at least the past 4 years. Up to ~ 15 strings now. Not a single failure, not a single bad LED, no bad connections - perfect record (and these are cheap $5/50-string from Walgreens. Not quite as warm-white as I'd like ( a little greenish), but pretty good.

With the filament strings, I would replace each bad/bypassed bulb each year to avoid the extra voltage passed through to the rest of the string. I'd try to find the open bulbs, but would give up half the time before I could isolate it (I suspect there were two opens sometimes). So the LEDs have made the holiday season more relaxing - I like them, just wish I could count on buying ones that were consistently the kind of warm like the filament bulbs.

Also, if you are connecting LED strings to a battery, are you using a current limiting resistor? That's important, LEDS are current devices.

 

[OmCheeto]

...
Also, if you are connecting LED strings to a battery, are you using a current limiting resistor? That's important, LEDS are current devices.

Nope. Direct connection.
I just ramped up the voltage to 14.4 volts, and the bulbs survived!
But wow, look at the power difference:

0.072 amps @ 14.4 vdc across 4 bulbs = 1.04 watts =
260 mw DC/lamp
vs
73 mw AC/lamp​

compared to my previous experiment:

0.025 amps @ 12.7 vdc across 4 bulbs = 0.32 watts =
79 mw DC/lamp​

btw, the equation I found on the internets yesterday: I = I0(e^((qV)/(kT))-1)
yielded a current of 9E51 amps for my problem.
Seems a bit high.
As I've said before, I have no idea how diodes work.
Might be about time I figured them out.

 

[NTL2009]

Nope. Direct connection.
I just ramped up the voltage to 14.4 volts, and the bulbs survived!
But wow, look at the power difference:

0.072 amps @ 14.4 vdc across 4 bulbs = 1.04 watts =
260 mw DC/lamp
vs
73 mw AC/lamp​

compared to my previous experiment:

0.025 amps @ 12.7 vdc across 4 bulbs = 0.32 watts =
79 mw DC/lamp​

...

As I've said before, I have no idea how diodes work.
Might be about time I figured them out.

Well, your experiment demonstrates a lot about how diodes work in a circuit. To get your head around it, stop thinking about voltage across them and think about current through them. Their voltage is sort of a secondary "side effect" of the current. We call them "current devices" because that is the primary consideration in a circuit design.

So you see with 14.4 V across 4 LEDs, you were forcing ~ 3.6 V across each one, assuming they were equally matched, but they won't be exactly. At 12.7 V you seem to be close to what you got under their (normal I assume) AC condition, so ~ 3.175 V across each LED.

You observed ~ 1.13x voltage increase resulted in ~ 2.88x current increase. This is why we control current (with a current source - either active, or just a resistor and a higher voltage source) when we drive LEDs, rather than try to control Voltage. Just let the voltage fall where it will.

And this is why we run LEDs in series, not parallel. In series, they all have the same current through them. But two similar LEDs will have slightly different voltages across them at that same current. So if one LED is 3.1V @ 25 mA, and another is 3.2 V @ 25 mA, and you place them i parallel, the lower voltage one will "hog" most of the current. The 3.2 V @ 25 mA LED will draw far less current at 3.1 V (you saw that in your experiment - a slightly higher voltage equates to a much higher current.

Current limiting is the norm for driving LEDs. Some cheap/simple circuits may rely on a voltage source that has high internal resistance (like a small coin cell), so is self limiting. If you pushed that voltage across the 4 LEDS much higher than 14.4 V with a "stiff" power supply, the current would climb and climb, and it would not be much higher before the LEDs were damaged. A spec sheet will tell you the max current, if you can ID the LED.

 

[NTL2009]

Design example:

Say you have an LED like above, that you know will be approximately 3.1V @ 25 mA current, and you want to drive it at that 25 mA point.

Say you have a 5 V supply, and you will use a current limiting resistor in series with the LED to set the current. Take the 5 V minus the 3.1 V across the LED, and you will have 1.9 V across the R. Solve for R = E/I; R = 1.9/.025 = 76 Ohms. So you choose a standard value of 75 Ohms.

If some LEDs are 3.0 V @ 25 mA; and some are 3.2 V @ 25 mA, the current and power won't vary all that much. A close estimation would be 2V/75 Ohms ~ 26.7 mA and 1.8V/75 ~ 24.0 mA. It's slightly more complicated, but that's close enough for any design work I've ever seen (where LEDS are just indicators). The detail comes in as the slightly lower current will also result in a lower voltage across the LED, so you would get a higher drop on the R, so the current would actually drop a bit less - but this is minor, and works in our favor anyhow.

A higher source voltage, along with a higher resistance, makes the source appear as a more ideal current source, and those little effects are reduced even further. IOW, you will get far more LED current/power variation trying to drive an ~ 3.1 V LED with a 3.5V source and lower R, than with a 12 V source and higher R. But that also wastes more power across the R, sometimes not a big concern with indicators, but that is why active switching circuits are often used to drive LEDs with a constant current.

 

[Baluncore]

btw, the equation I found on the internets yesterday: I = I0(e^((qV)/(kT))-1)
yielded a current of 9E51 amps for my problem.
Seems a bit high.

You are wrongly assuming the LED is a forward biassed Si PN junction. The voltage across a diode depends on the doping chemistry and the mode of operation. For example a zener has a reverse breakdown voltage mode, while an LED is a forward biassed diode with a bandgap providing the voltage drop. The wavelength of the light produced by an LED is a function of the chemistry. The bandgap voltage determines the energy in eV, of the photons emitted when an electron falls over the gap. V = 1239.842 / λnm.
A grow light or a household illumination white LED will produce a primary violet light that is then “whitened” by a mixture of fluorescent chemicals. Chlorophyll has florescence sites that convert violet light into lower energy electron transport chains. Shorter wavelength LEDs, with higher energy photons have been harder to discover because the energy is often sufficient to break up the chemical bonds.
A greater LED current results in more electrons crossing the LED bandgap and so more photons being emitted.

 

[Nik_2213]

I've a covert 'spike generator' in our kitchen. I think it is the fridge-freezer, as several adjacent 'spike catcher' adaptors have died, while those opposite have been okay. Used to be you could get 'industrial strength' widgets with a toroid and three replaceable varistors, but the modern 'catchers' just seem to have one (1) non-replaceable varistor, so $ 10 a pop...

I've ordered in a job-lot of clip-on ferrites, 7mm & 9mm, will be loading the 'usual suspects' flex leads in the hope they help...

 

[Baluncore]

I've a covert 'spike generator' in our kitchen.

Old refrigerators and cool-rooms with thermostats controlling inductive loads, had a habit of generating noise when contaminated contacts began to arc. Heat annealed the spring and so mechanical hysteresis was lost from the thermostat. There was a time when the first thing to do when hunting RFI in an unfamiliar suburb, was to find the butchers shop. The community benefited when the butcher's refrigerator worked reliably.

Zinc oxide varistors catch voltage spikes, but the energy of each spike consumes part of the varistor. As an occasional spike catcher they work well, but when they are hit with a continuous train of high energy spikes they die more quickly. Heavier more expensive varistors can accumulate more spike energy and so last longer than cheaper units. Varistor lifetime is predictable. If you can measure the spike energy dissipated in a varistor, and accumulate the total, you can predict the failure of the varistor and so schedule replacement ahead of the failure.

 

[jim hardy]

More than anybody wants to know about "Spike Catchers"
http://www.electronics-tutorials.ws/resistor/varistor.html
http://www.littelfuse.com/~/media/electronics/product_catalogs/littelfuse_varistor_catalog.pdf.pdf

 

[sophiecentaur]

Old refrigerators and cool-rooms with thermostats controlling inductive loads, had a habit of generating noise when contaminated contacts began to arc. Heat annealed the spring and so mechanical hysteresis was lost from the thermostat. There was a time when the first thing to do when hunting RFI in an unfamiliar suburb, was to find the butchers shop. The community benefited when the butcher's refrigerator worked reliably.

Zinc oxide varistors catch voltage spikes, but the energy of each spike consumes part of the varistor. As an occasional spike catcher they work well, but when they are hit with a continuous train of high energy spikes they die more quickly. Heavier more expensive varistors can accumulate more spike energy and so last longer than cheaper units. Varistor lifetime is predictable. If you can measure the spike energy dissipated in a varistor, and accumulate the total, you can predict the failure of the varistor and so schedule replacement ahead of the failure.

This makes me wonder how to record those spikes using very basic equipment. It could be better to know my enemy than just to litter the house with surge suppressors and see if the frequency of casualties goes down. I could use a cheap DMM - set to Pk and give it an external supply but would it catch ms spikes, I wonder?

 

[Nik_2213]

I've now fitted three clip-on ferrites to the fridge / freezer's power lead, ahead of a spike-catcher adaptor coming 'soon'. While prowling with the bag of widgets, I've also fitted one to the clothes-iron lead close to its plug, and one on the lead to the 'mini larder-fridge' by the 'breakfast bar'...

Um, could you monitor the switching spikes non-invasively by wrapping a wire antenna around the power lead feeding a 741 amplifier and bar-graph voltage indicator such as an LM3914 ? Or all by op-amps, such as http://circuitclassics.com/bargraph-voltage-indicator.html

IIRC, powerlines may be monitored by feeding them through a toroid along with a few turns of a 'sensor' winding. Rather than an 'industrial strength' clip-on split toroid, a loose-fit, clip-on ferrite may do as a 'proof of concept'...

{ Sorry, getting hard to type as I now have three of our cats parked on desk in front of keyboard and/or screens... ;- }

 

[sophiecentaur]

@Nik_2213 I have an oscilloscope for just looking at spikes but I want to be able to capture them when they actually happen. It could be any time of the day or night. Also, I don't really want to launch out on a 'Project' to achieve this. Building electronic circuits doesn't appeal enough to make it worth while of I would find a way to do it with a Raspberry Pie or equivalent. I guess I will have to put up with LED failures or become an amateur constructor once more, after several decades.
Enjoy the Cats!

 

[Nik_2213]

You're right, of course !
{ I gave up on electronics after my eyes became 'middle-aged' and solder went 'unleaded'... }

Would this help ? : http://spikehound.sourceforge.net/

 

[jim hardy]

Hmmm. Tying the spikes to some event would be the next step.

Idle speculation here
I wonder, would a MOV "Spike Eater" in series with an old timey photography fashbulb announce a spike.? MOV would absorb the energy and flashbulbs are wrapped in plastic to discourage explosion. . I see flashbulbs occasionally in junk shops with antique cameras ..

I haven't tried it.. You seem practical enough to not make snything dangerous.

old jim

 

[Baluncore]

Turn a new light on-off-on-off-on-off quickly when you first get it, then do it slowly. If it survives that transient then the internal surge protection is probably working. If it fails, return it as faulty.

Clipping a magnetic core onto the power lead will only reduce common mode noise. Differential line noise will remain. To eliminate differential mode noise you must split and oppose the direction of the line pair where it passes through the core, you should also terminate the line on both sides with an RC snubber.

Lightning strikes and the accidental contact of 22kV power lines with one of the three 230V phases below should be eliminated by the electricity authority. They are well insured against damaging your property.

Turning on a resistive device such as a filament lamp or heater that better terminates the line will have an effect on the propagation of RFI and on the amplitude of standing waves. The network is a star of twisted pair lines that radiate outwards from the fusebox throughout the building. Adding an RC snubber to the line can also reduce standing waves and resonance without such a high power consumption.

I built and still use a passive twin-T notch filter to eliminate the power line fundamental and so show the harmonic distortion and the phase of the differential noise on an oscilloscope, synchronised to the phase of the AC line voltage.

I also built a directional coupler into a short extension cord. It was not needed to find RFI sources so much as prove which way the RF energy was travelling, and that the alleged cause was not the problem. Indeed, the device blamed was often better terminating the line at RF and so reducing the RFI.

Instead of blaming spikes you should question the temperature of the semiconductors and the on/off switching transient. After being called on many occasions to hunt the source of “spikes on the supply”, I was always able to identify the real cause of the problem. It was never the mythical magical spikes that were the problem. Blaming spikes for the death of LEDs or MOVs is a bit like witch hunting. Spikes get the blame for much of the vandalism, but they are rarely given a fair trial before being found guilty.

 

[sophiecentaur]

Instead of blaming spikes you should question the temperature of the semiconductors and the on/off switching transient. After being called on many occasions to hunt the source of “spikes on the supply”, I was always able to identify the real cause of the problem. It was never the mythical magical spikes that were the problem. Blaming spikes for the death of LEDs or MOVs is a bit like witch hunting. Spikes get the blame for much of the vandalism, but they are rarely given a fair trial before being found guilty.

The temperature factor may be (probably is) relevant to the short life. But that is no excuse and a half decent 'replacement' LED should survive in the conditions that its ancestors have tolerated for years.
You are right about the 'spike' monster but there are some badly behaved pieces of electrical equipment around in houses - despite modern manufacturing (and import) standards.

You're right, of course !
{ I gave up on electronics after my eyes became 'middle-aged' and solder went 'unleaded'... }

Would this help ? : http://spikehound.sourceforge.net/

Thanks for the idea. Yes, of course, there are dozens of digital oscilloscope modules which can be used with a laptop - I had just not thought along those lines. I might investigate the market. Up until now I have used an ageing analogue 'scope, which is very limiting in some respects.

 

[Nik_2213]

Went to fetch a 'frozen meal' out of *that* fridge-freezer, discovered top tray was seriously iced-up, whole needed defrosting the 'old fashioned' way...

While thaw was in progress, I took the opportunity to swap the 'standard' plug-top for one of the 'spike catchers' recently arrived from A*z*n. To my horror, I found the 'hot' lead's binding terminal's machine-screw was loose enough to wiggle. That can't have helped the noise-level on the power line !

I didn't swap the plug soon enough to determine if binding post had been 'running hot'. There was no obvious discolouration from arcing or scorching on post or hot-lead's 'bootlace' ferrule, but I only peered at them, did not use a hand-lens...

 

[jim hardy]

Yes, of course, there are dozens of digital oscilloscope modules which can be used with a laptop - I had just not thought along those lines.

Hmmm. I'm in the US. If somebody made one that put out NTSC video (analog television) it'd keep a lot of old TV's out of the landfills..
Did UK television go digital too ?

 

[Svein]

Hmmm. I'm in the US. If somebody made one that put out NTSC video (analog television) it'd keep a lot of old TV's out of the landfills..
Did UK television go digital too ?

I doubt you would be satisfied with the quality. NTSC resolution is 640x480 on a 4:3 TV. A cheap laptop has 1366x720...

 

[Guineafowl]

Did UK television go digital too ?

Yes, but you can buy digiboxes (digital -> PAL) and so still use your old CRT TV. We have a little old Trinitron still in service, although the colours are a little ‘off’ at times and it requires a manly thump to get them back again. When I get time, I’ll be looking for some advice on here on how to correct this properly and give the device a service, while there are still CRT people around who remember how to do such things...

 

[Baluncore]

When I get time, I’ll be looking for some advice on here on how to correct this properly and give the device a service, while there are still CRT people around who remember how to do such things...

The adice you will get is to recycle the old CRT, then use an ex-computer LED monitor with a second hand digital STB. You get a huge reduction in power consumption and a huge improvement in resolution.

 

[Guineafowl]

The adice you will get is to recycle the old CRT, then use an ex-computer LED monitor with a second hand digital STB. You get a huge reduction in power consumption and a huge improvement in resolution.

Yes, that sounds like the sensible solution. But I was thinking more in the spirit of keeping an old device alive.

 

[sophiecentaur]

Did UK television go digital too ?

Yes. Years ago. The terrestrial broadcast service was replaced over a fairly short time with FREEVIEW, which is free and replaced pretty much all conventional CTV services.
The switchover was helped a lot by a market flooded with flat screen sets. CRTs died very quickly. (No great loss except for a few lovers of old equipment. )

 

[Guineafowl]

Yes. Years ago. The terrestrial broadcast service was replaced over a fairly short time with FREEVIEW, which is free and replaced pretty much all conventional CTV services.
The switchover was helped a lot by a market flooded with flat screen sets. CRTs died very quickly. (No great loss except for a few lovers of old equipment. )

Er, yes - my love for old equipment is based largely on its repairability and build quality.

Example 1 - my mate’s newish Bosch dishwasher with a PCB fault that renders it uneconomical to repair, despite costing £300-odd. My old Candy unit is 30+ years old, is largely electromechanical, and still has parts available.

Example 2 - the Trinitron has outived a few flatscreens and then some. The chief advantage of the latter being that they take up less space in the skip/dumpster.

Example 3 - My parents have a microwave that is at least 40 years old, and has always been in daily use, in contrast to the crappy units I’ve thrown away after a few years.

 

[jim hardy]

I doubt you would be satisfied with the quality. NTSC resolution is 640x480 on a 4:3 TV. A cheap laptop has 1366x72

Oscilloscope display accuracy is a percent or three , CRT will do fine for that. Precision is in the numbers the computer writes on the screen.

Example 2 - the Trinitron has outived a few flatscreens and then some. The chief advantage of the latter being that they take up less space in the skip/dumpster.

I too have an old Trinitron, a 26 inch that's too heavy for me to move anymore. But it's convenient to the workbench..

Example 4 - the old Trinitron isn't "Smart" so it won't collude with the Russians to build a dossier on me.