Can you not find green/yellow, or something else without red? Purple stripes perhaps?
I don't think you'll like this, but it just might be worth a mention. Incandescents work for many years when heavily dimmed.
NT
Wrong post. Try this one.
You can order parts from these guys. Here is the link again.
Rick C.
That points to: That 3mm LED has 3 leads with a common anode. How am I suppose to wire that for for back to back diode operation that will light up with either polarity? There were plenty of 3mm green-green 3mm LED's with either common anode or common cathode available such as: I couldn't figure out how to wire them, so I ignored those. I couldn't find any that had 2 LED's in series which could easily be wired back to back.
Anyway, thanks for the suggestion.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
No. I've found red-green and red-blue but nothing else. I couldn't use it anyway because the convention that green means things are working, and red means problems. There are 2pin 3mm RGB LED's in red-green-blue that look interesting, but I don't think anyone would appreciate watching a color cycling light show.
Yep. One of these perhaps: The price is a bit high, but tolerable. At 24v my guess(tm) is that the 36v light will dissipate about 1 watt, which isn't horrible but might be high in an unvented plastic cover. By comparison, the solenoid uses 83mw. I'll need to make some temp measurements, but I think it might work without melting.
If the red-green LED is unacceptable, I would probably go with gluing two SMD 0805 green LED's together, wiring them back to back, and living happily ever after.
I'll take back my previously having thanked you for NOT suggesting an incandescent lamp.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
lol
1w is in the typical ballpark for a relay, so is fine in your average relay sized box. How much that surrounding bit of plastic impedes airflow is another question.Lol.
How you might make a back to back 3 leg green work: Wires to the outer legs. An smd diode across each half, sandwiched between its legs. If you solder the inner lead to the smds first the outers should not be hard to do. That just might be a solution.
NT
Good idea. I'll try it later tonite if I can find some green SMD LEDs. I may need to scrap some boards for parts.
The center to center lead spacing on a 3mm LED is 2.54mm. The wire spacing on a 0805 SMD LED is 2.0mm, so I think I can make it fit and work. It would be nice if I could get the light emitting "top" of the SMD LED directly against the bottom of the existing 3mm LED for maximum light transmission. If it's not bright enough, one SMD LED to light up the existing 3mm LED and another in parallel pointed the opposite direction. This may actually work.
My preliminary tentative thanks and undying gratitude if it works.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
O----+---|>|---+---|
I had thought of that but also noticed that the maximum LED reverse voltage and current might be exceeded. That's why I preferred the back to back diode approach.
Assuming 24VDC operating voltage and a 2.0V forward voltage drop on the LED, that puts 22VDC reverse voltage on the unlit LED which is rated at 5V reverse maximum. I don't know exactly how the LED with react when it enters the reverse breakdown region, but if it avalanches and conducts somewhere above 5V, there may be a problem. I found some vague references suggesting that the reverse avalanche voltage is about 20V or more, which might eliminate the problem.
Looking at some typical specs, it seems (not sure) that it will zener at something above 5VDC and will tolerate no more than 100 microamps. At a voltage of 24v - 2.0v - 5.6v = 16.4V (the 5.6v is my guess) the existing 5.2K resistor will produce: 16.4V / 5200ohms = 3.2ma which greatly exceeds the 100 microamp reverse current limit.
The maximum dissipation for green is 100mw. With this arrangement, the reverse polarized LED will dissipate: 2.0V * 0.0032A = 6.4mw which is much less than 100mw. So, it just might survive reverse conduction. I don't know exactly what will happen, so it's probably worth my time bench measuring the reverse breakdown voltage and testing the idea.
"What destroys a LED in the reverse direction?" "In my experience the standard 3mm and 5mm red LEDs can block 12V easily so I have used them as reverse polarity protection in 12V systems where current is about 10 mA DONT use them on a 24 Volt system some LEDs died at approx. 30V"
Thanks much for the suggestion.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
Looks like it just might work. I took a green 3mm LED, wired it in series with a 2.2K resistor, and connected it to an HP6235A variable voltage power supply. I connected a DVM across the LED. There was no indication of any reverse conduction or voltage limiting to 40V. So, it just might work. I don't have any of the 3 pin LED's in stock, so I'll order some immediately. Meanwhile, I get to ponder over why the LED manufacturers specify a maximum of 5V reverse voltage when it seems to be much higher. Any clues?
Thanks again.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
"Failure modes for LEDs" Almost all LEDs can withstand 5 V reverse voltage. (We rely on this to avoid damaging LEDs in Testing unknown LEDs.) If you try your own reverse voltage limit testing you may find that most have higher actual reverse voltage breakdown voltages of 12 to 70 V. It would be unwise to depend on this in a design project, however, as it is not guaranteed by the manufacturer and could change from batch to batch or vendor to vendor.
"what is the reverse breakdown voltage of a red or green 5 mm led ?" The breakdown voltage has been about 170V for the last 40 years at least for generic ones. You will see Chinese designs that connect them to the mains without a diode for 120V operation. I've been testing them periodically since then, placing them on the line for a couple weeks with a 47K resistor. There are some newer ones that have a really low breakdown voltage. (...) Various red, yellow and green: they seem to cluster around 30-40V, and >110V (some over 150V). Probably some die manufacturers / designs have softer doping profiles? (...) My understanding of the situation is that under reverse bias below the avalanche breakdown threshold, the leakage current is concentrated around existing lattice defects in the junction depletion layer and if the bias voltage is high enough, the resulting hot carriers cause the defects to grow.
And in summary red (N) mean 50.2 V std 3.2V green (N) mean 89V std 12.3V blue (N) mean 50.8V std 21.7V red (OS) mean 27.3V std 7.7V N = New LED's OS = Old Stock
Looks like high brightness red will be a problem at 24VDC, but green and ordinary red are will work:
Argh!
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
or the near-equivalent, using a silicon dual diode, common anode
5v is just a figure they're confident they'll all pass with no testing. They're not going to waste time/money testing a spec almost no-one is interested in ever using. Real breakdown v varies widely, some even do 100v.
NT
why not make it even easier & just solder an smd green led between the existing led's pins. You might even get it shining up into the existing led perhaps. Any green glow should work, doesn't need an ideal distribution.
NT
3 wire LED for 2 wire operation
// // A -+---|>|--+--|
guaranteed by design... vs need to test each batch?
I've seen LEDs die from 9v reverse.
-- When I tried casting out nines I made a hash of it.
You already suggested that and I already replied that I like the idea and that it will probably work. See: I would have tried it by now, except I can't find any 0805 green LEDs in my mess. I'll need to order some.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
in inverse parallel. Loads at 3mm x 1mm and smaller. This one's 2.1mm x 0.7mm, picked at random...
Cheers
-- Clive
Kingbright makes a few 5mm two-lead Green/Green LEDs:
Neither distributor page mentions that it's a bidirectional device, but both datasheets show it.
--S
-- sceptre@sdf.org SDF Public Access UNIX System - http://sdf.org
Also Lumex SSL-LX5093GGD:
Only stock is at Heilind:
-- sceptre@sdf.org SDF Public Access UNIX System - http://sdf.org
English version of Kingbright web page:
Having the exact right part would sure make my life easier. However, all the above are 5mm parts and I need 3mm for it to fit inside the relay. Looks like Kingbright makes one that's bi-color green/green in
3mm: The 60 degree viewing angle will be much better than the 20 or 30 degree LED's I've been buying.However, all the stocking distributors are too far away: It does list one jobber in the USA, but they want me to ask for a quote, which usually means sky high prices, large minimum quantities, or both.
Oh yes... I'm familiar with the problem. The device is called a "bi-color" LED, which translates to a "two color" LED. But, what does one do when both colors are the same? I have no idea, and apparently neither do the manufacturers and distributors.
Thanks much. I'll dig through the Kingbright web pile and see if I can find anything else that might work. It looks like I have an extra month to deal with the LED problem because the mill in question just destroyed some spindle bearings, a drive belt, a nylon gear, etc.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
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