Help with jumbo leds - Page 1
Forum section: electronics / beginners

author: Atom_slayer
author_rank: Newbie
timestamp: November 03, 2024, 05:15:02 pm
content: I purchased some dome leds from Electronix Express (part number 08c20zug). They are 20mm with 4 leads. The datasheet shows that there are two banks of 3 led's in the dome but doesn't show what voltage they should operate. First I tried to use the diode mode on my multimeter to check continuity. I tried each combination of the leads;left two leads changing the polarity of the leads , right two leads changing the polarity, front leads changing the polarity and back leads changing the polarity. Then I tried all the combinations with volts, then 9 volts. I am not getting a light. My first question is what am I doing wrong. My second question is where can I get different leds since these seem not to be working. I have tried searching the internet and evidently I'm not asking the right question. Thanks in advance.

author: xvr
author_rank: Frequent Contributor
timestamp: November 03, 2024, 06:32:45 pm
content: QuoteBut it shows maximum current it could operate - 30mA. LED forward voltage drop can be in 1.5-3V range. So you should get 10V (or more) laboratory power supply, add current limiting resistor and connect to LED. Set voltage to 0, turn on and slowly rump it up.QuoteIf you connect your LED directly to power supply (without current limiting resistor) it could be dead now.

author: u666sa
author_rank: Frequent Contributor
timestamp: November 03, 2024, 10:00:36 pm
content: Quote from: Atom_slayer on November 03, 2024, 05:15:02 pmYou can't. Voltage drop is too big.Quote from: Atom_slayer on November 03, 2024, 05:15:02 pmThey are either 12 volts or 24 volts. No, you should not get a light if you give them 9 volts.Give 12 volts to pin 1 and 2. If that don't work. Give more volts, up to 24 volts. Set current on your PSU to 100 milliamps.

author: tooki
author_rank: Super Contributor
timestamp: November 03, 2024, 10:13:32 pm
content: Since the datasheet is clearly a modified one (to remove the original source), I searched for the product title used within it, “20mm round single color light bar”.That immediately found this:https://betlux.com/led/LED-light-bar-20mm-big-LED--BL-AC1Z20.htmI can’t be 100% sure, but I strongly suspect it’s the same product line.The tables on the page don’t list a voltage either, but the PDF datasheet does:https://betlux.com/product/LED_light_bar/BL-AC1Z20.pdfI can only assume those voltages are per LED die, because if those needed to be divided by 3, they’d be extremely low.Who knows for sure which green you have, but from the color codes listed in your original datasheet, I assume it’s either “ultra green” or “ultra pure green”, which have a Vf of 2.2V and 3.8V (!) respectively.If you applied 9V and it was the ultra green (or the regular green not listed on your datasheet), then they may have fried. But if it’s ultra pure green, then 9V might not be enough for them to light up, since they’d want 11.4V.With that said, inconsistencies within the betlux datasheet also make me suspect its data. So more experimentation may be the only thing to do. Use a lab supply with current limiting, but turn the voltage up slowly. Dim your ambient light so that you can see if the LED is beginning to glow at a lower voltage.However, observe the polarity from the datasheet and don’t try applying higher voltages in reverse!! LEDs are not good in reverse, and both datasheets list an absolute maximum reverse voltage of 10V. If that LED actually needs 11.4V to light, and you apply 11.4V in reverse, you may damage it.

author: tooki
author_rank: Super Contributor
timestamp: November 03, 2024, 10:16:48 pm
content: Quote from: u666sa on November 03, 2024, 10:00:36 pmWhat? Where do you get this idea? You didn’t look at the datasheet, did you!! They are not 6 LEDs in series, but two strings, each with 3 in series.100mA?? The datasheet shows an absolute maximum non-pulsed current of 30mA. Applying 24V/100mA will fry them for sure.OP, do not do what u666sa says, it’s bad advice.

author: Atom_slayer
author_rank: Newbie
timestamp: November 04, 2024, 01:23:48 am
content: Thank you to everyone who responded. I took advice and dug out my variable power supply and a 330 ohm resistor. I am making a miniature traffic light, so I have 3 green, 3 red, and 3 yellow dome leds (I may make more and since shipping was the same, I ordered more than I need at the moment). I connected the lead from positive lead of the power supply to one leg of the resistor, the other leg of the resistor to a lead of the led, the other lead from the led back to the negative . I then turned on the power supply and starting at zero turned up the voltage of the power supply to over 12 volts. There was no output of the led. Then I turned off the power supply, reversed the leads on the led and turned on the power supply starting at zero and raised the voltage again to over 12 volts. Still no output. I did this on 4 of the leds with the same results. If I need more than 12 volts, then I won't be using these leds. I just ordered some 10mm leds and will be using these if the 20won't work. Thanks again.

author: floobydust
author_rank: Super Contributor
timestamp: November 04, 2024, 01:51:05 am
content: You might be applying voltage to the wrong pins? There's more than two permutations to try with the pins, rotate 90 degrees.The LED has 4 pins, two strings of 3 LED's in series. I read it's AlGaInP green about 2.3V each, so a string of three needs at least 7V or so.

author: Atom_slayer
author_rank: Newbie
timestamp: November 04, 2024, 01:00:51 pm
content: Thanks. Yes, I tried all the ways with the power supply. Left side top positive, left side bottom negative . Left side top negative, left side bottom positive. Left top positive, right top negative, left top negative, right top positive. The I tried the right side and bottom pins the same as the left and top and still nothing. Either the leds are bad, or I need more voltage.