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Topic: LEDs losig brithness at a different rate, am I damaging them somehow? (Read 8976 times) previous topic - next topic

byteofthat

@Chagrin: The shift registers/transistor arrays wouldn't have anything to do with it, considering the effected LED's are not connected through them, but are connected directly to the power and ground.

Maybe @cjdelphi is correct. I replaced one LED, and it was back to normal brightness. I had then just changed them all out for the effected letters and it seems to be working. I am going to see what happens after it runs for a while. Hopefully it was just bad LEDs. Time well tell!

Thanks for all the advice, everyone.

ChilliTronix

Did you re melt the joints as a test first? If not then the problem could still have been a dry joint issue... though it would be odd if it affected all in one run of LEDs and not randomly across the board.

MarkT

White LEDs fade with time, the datasheet for the particular device should be consulted.

White LEDs change colour balance too - the basic issue is that the fluorescent yellow
gel in front of the LED changes with time.  The LED is typically blue/indigo/UV and the
other colours are generated by fluorescence.  Its hard to engineer a fully stable fluorescent
dye - note that ambient daylight could be aging the dye more than the blue from the LED
itself even - only the manufacturer will have data on these processes as they are a property
of the dye.

The actual LED emitter itself can age too, but this is likely to be a smaller effect due to
crystalline semiconductors being more robust than organic dyestuffs.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

byteofthat

Did you re melt the joints as a test first? If not then the problem could still have been a dry joint issue... though it would be odd if it affected all in one run of LEDs and not randomly across the board.
I did with a couple of them, and nothing happened. I figured as much when I tried using alligator clips to see if a bad connection was the problem.

White LEDs fade with time, the datasheet for the particular device should be consulted.

White LEDs change colour balance too - the basic issue is that the fluorescent yellow
gel in front of the LED changes with time.  The LED is typically blue/indigo/UV and the
other colours are generated by fluorescence.  Its hard to engineer a fully stable fluorescent
dye - note that ambient daylight could be aging the dye more than the blue from the LED
itself even - only the manufacturer will have data on these processes as they are a property
of the dye.

The actual LED emitter itself can age too, but this is likely to be a smaller effect due to
crystalline semiconductors being more robust than organic dyestuffs.
I understand this, but it doesn't explain why they faded so fast in comparison to other lights on the clock that were on almost the same amount of time. The word "MINUTUR" was on 83% of the time "KLUKKAN ER" was. Considering the clock has been in operation for less than a month, after waiting for a week and not seeing the same behaviour in the word "MINUTUR", I found it unlikely that it was just a "wear and tear" issue.

ChilliTronix

I would be interested to see how it is in another month.

Grumpy_Mike

@Chagrin: The shift registers/transistor arrays wouldn't have anything to do with it, considering the effected LED's are not connected through them, but are connected directly to the power and ground.
And a resistor I hope.

It needs to be a higher value resistor than that connected through the transistor because there is more voltage across those than the transistor ones.

byteofthat

And a resistor I hope.

It needs to be a higher value resistor than that connected through the transistor because there is more voltage across those than the transistor ones.
Each LED has it's own 220Ohm resistor.

I would be interested to see how it is in another month.
The word 'MINÚTUR' gave out, it has now sunk in brightness. I wonder if I am simply running too my current through the LEDs? I would figure 220Ohms would be enough. At 5 volts that would be ~22mA, but assuming there has to be some voltage drop, it must be even less than that.

Any more ideas now that the effect seems to be spreading?

dlloyd

Regarding reply#14:

Right at the power input of the led strip, what value of capacitor did you connect?
I would recommend anything from 220µF to 470µF.

Right at the led strip and connected in series with the data line, what value of resistor are you using?
I would recommend 220Ω, 270Ω or 330Ω.

byteofthat

Regarding reply#14:

Right at the power input of the led strip, what value of capacitor did you connect?
I would recommend anything from 220µF to 470µF.

Right at the led strip and connected in series with the data line, what value of resistor are you using?
I would recommend 220Ω, 270Ω or 330Ω.
I am not having trouble with the LED strip.

Grumpy_Mike

Any more ideas now that the effect seems to be spreading?
It will spread if something is wrong. Can you make sure you have a 220 R resistor and that the voltage is 5V.

You need to subtract the forward voltage of the LED. Being white it might be as much as 3V so with that resistor you would get (5-3)/220 = 9mA. That should be well withing the limits of an LED, unless they are faulty or as I said the resistor or voltage is wrong, measure both with your meter.

dlloyd

Ahh, I originally stopped at the picture that mentioned "The RGB LEDs are a WS2812B strip".

Quote
I painted the back of this black, and at first it didn't wind up sticking too well or looking too good. It wound up working out though.
Note: Just to mention - some types of paint could be conductive or semi-conductive (however I don't think this is the issue).

Quote
And so begins the arduous process of gluing in all the LEDs. I ordered 150 of diffuse white LED lights on ebay for next to nothing.
Careful there are no shorts (it appears some resistors could be shorting out).



MAIN PROBLEM:
It truly appears that the resistance code is red/red/black with black (multiplier) and brown (tolerance). If so, then these are 22Ω resistors and the excessive current will cause the LEDs to fail.
The first 3 colors should be red/red/brown for 220Ω. EDIT: (I see Grumpy_Mike is a bit quicker than I)


byteofthat

It will spread if something is wrong. Can you make sure you have a 220 R resistor and that the voltage is 5V.

You need to subtract the forward voltage of the LED. Being white it might be as much as 3V so with that resistor you would get (5-3)/220 = 9mA. That should be well withing the limits of an LED, unless they are faulty or as I said the resistor or voltage is wrong, measure both with your meter.
The power supply is definitely 5 volts. I have measured it several times, and just did again. Maybe it's the source of the LEDs? I got them from a seller on eBay by the name of "Bright Components".

I seem to have blown the fuse on my multi-meter for low amp current readings, I will grab a fuse in the next day or two an update with an actual current reading.

Ahh, I originally stopped at the picture that mentioned "The RGB LEDs are a WS2812B strip".
Note: Just to mention - some types of paint could be conductive or semi-conductive (however I don't think this is the issue).
Careful there are no shorts (it appears some resistors could be shorting out).



MAIN PROBLEM:
It truly appears that the resistance code is red/red/black with black (multiplier) and brown (tolerance). If so, then these are 22Ω resistors and the excessive current will cause the LEDs to fail.
The first 3 colors should be red/red/brown for 220Ω. EDIT: (I see Grumpy_Mike is a bit quicker than I)


It is a 5 band resistor. Red + Red + Black + Black is 2-2-0 x 1 with tolerance on the end. I just measured too with my multi-meter, and they are inded 200ohm resistors. I think if you were right, they would have blown immediately, no? That would have been a lot of extra current with only 22Ohms.


For my own curious mind, would the following work. The LEDs are broken into 4 compartments regarding them sharing a positive power rail (all anodes connected), and I have a wire (4 wires total) that connect each of these sets to the positive power from the supply. Rather than changing out all the resistors, if I wanted to add lets say 50 ohms to all the leds, could I add a 50 0hm resistor to each of the wires so that way the resistance for each led would be effectively 270 ohms? I only have 1/4W resistors, so I am not sure if that would be too much load on the resistor.

Grumpy_Mike

Quote
I only have 1/4W resistors, so I am not sure if that would be too much load on the resistor.
No that will be fine.

A thought struck me, could it be that the LEDs are getting hot inside those unventilated compartments?

Coding Badly


Have you replaced any of the dim LEDs?

Have you extracted any of the dim LEDs then tested them?


byteofthat

No that will be fine.

A thought struck me, could it be that the LEDs are getting hot inside those unventilated compartments?
How do I treat that situation with the resistors? Because I then have a parallel/series thing going on. If each light was consuming lets say 15mA after adding that resistor, and it branched off to 10 lights, wouldn't 150mA be flowing through that one 50 ohm resistor?

I suppose they could be getting warm. I didn't think they would get all that hot though to be honest. Not really sure how to test that, since the face doesn't really come off and by the time I get one out, it likely will have cooled. I guess Ill try on a breadboard, but I am sceptical.

Have you replaced any of the dim LEDs?

Have you extracted any of the dim LEDs then tested them?

I have extracted and replaced some, as mentioned earlier in the thread. Though, I didn't test them on a breadboard, I just tossed them out. After replacing the LEDs for "KLUKKAN ER", the words were back at normal brightness. The problem has now spread to "MINUTUR".

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