# LEDs losig brithness at a different rate, am I damaging them somehow?

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.

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.

Grumpy_Mike:
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.

ChilliTronix:
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?

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.

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.

byteofthat: 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.

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

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).

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)

Grumpy_Mike: 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.

dlloyd: 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.

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?

Have you replaced any of the dim LEDs?

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

Grumpy_Mike:
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.

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”.

I thought you wanted to add one resistor to each of the existing resistors, that is why I said it would be fine. Yes with 150mA you burn just under 2W so you need a bigger resistor. However as I said before it looks like the LEDs, did you measure the forward voltage drop of them?

Grumpy_Mike: I thought you wanted to add one resistor to each of the existing resistors, that is why I said it would be fine. Yes with 150mA you burn just under 2W so you need a bigger resistor. However as I said before it looks like the LEDs, did you measure the forward voltage drop of them?

Well, I went and got a fuse today.

The I get ~9mA running through an LED in the phrase "KLUKKAN ER".

I get ~7mA running through an LED in the phrase "MINUTUR". I changed an LED and measure again, and still ~7mA.

I placed my probes on each side of an LED in both "KLUKKAN ER" and "MINUTUR". I get the same reading, ~2.9V. 2.95 in the former, 2.91 on the latter. This is the voltage drop/forward voltage right? I am not sure if the terms are synonymous, I am still trying to figure that out. Any chance you could clear up my confusion with this terminology? I get the impression forward voltage/voltage drop is the volts consumed by the component in question.

I wonder if the reason the amperage reading is different is because there is a small amount of resistance in the transistor arrays? I can't seem to account for the difference any other way.

I am starting to wonder if this is just a cause of lousy LEDs? These are the LEDs I bought: http://www.ebay.co.uk/itm/50-x-White-LED-5mm-Diffused-1st-Class-Postage-UK-/121419713404?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item1c452dcb7c

Just a reminder that "KLUKKAN ER" is not connected through the transistor arrays, and is simply just connected to ground.

Voltage is not consumed, that is current. The voltage across the LED is the forward voltage drop.

There is less spair voltage on the transistors because there is a permanent saturation voltage across the emitter / collector of about 0.7V, so you loose some there and so the current is less for the same resistor.

Well I guess we are back to square one then. I suppose it either has to be poor LEDs, or the junction temperature is too high. If the latter, not really sure how to test that. I suppose I would need to setup something on a breadboard and enclose an LED in a similar situation. Even still, not sure quite how to measure the temperature effectively.

If it were me, I would take everything else out of the equation and just go for Regulated 5V supply and 68R resistor per LED for say 2 or 3 LEDS and 75R resistor for another 2 or 3 LEDS and just run them constantly on a breadboard until/if you see any difference.

The Spec on the ebay advert says 3.2-3.8 forward volts 20-30mA forward current...

So :-

5 - 3.2 / 68 = 26.5mA // A little higher than typical but below max rating 5 - 3.2 / 75 = 24mA // A little higher than typical but below max rating 5 - 3.8 / 68 = 17.6mA // Approaching typical rating 5 - 3.8 / 75 = 16ma // Approaching typical rating

5 - 3.2 / 220 = 8.2mA // Expected to be quite dim 5 - 3.8 / 220 = 5.5mA // Expected to be even dimmer

This will at least drive them closer to their rated spec and prove if it is the LED's or something else....

Regards,

Graham

ghlawrence2000: If it were me, I would take everything else out of the equation and just go for Regulated 5V supply and 68R resistor per LED for say 2 or 3 LEDS and 75R resistor for another 2 or 3 LEDS and just run them constantly on a breadboard until/if you see any difference.

The Spec on the ebay advert says 3.2-3.8 forward volts 20-30mA forward current...

So :-

5 - 3.2 / 68 = 26.5mA // A little higher than typical but below max rating 5 - 3.2 / 75 = 24mA // A little higher than typical but below max rating 5 - 3.8 / 68 = 17.6mA // Approaching typical rating 5 - 3.8 / 75 = 16ma // Approaching typical rating

5 - 3.2 / 220 = 8.2mA // Expected to be quite dim 5 - 3.8 / 220 = 5.5mA // Expected to be even dimmer

This will at least drive them closer to their rated spec and prove if it is the LED's or something else....

Regards,

Graham

I actually happen to have my breadboard and resistor kit out, I think I will give that a try.

Is it possible to damage an LED by driving them with too low of a current?

byteofthat:
Is it possible to damage an LED by driving them with too low of a current?

No.

byteofthat: Is it possible to damage an LED by driving them with too low of a current?

Not only will you not damage them they will last a lot longer.

I came across this:

http://lumeniquessl.com/2008/11/30/5mm-leds-generally-unsuitable-for-general-illumination/

Maybe this is a heat issue? The writer seems to hint that the 5mm bulbs I was using aren't really for continuous use. I'm guessing we are talking at about the 600 hour mark when the light brightness started to dim.

The writer also suggest using "LED packages". If I was to do another project using LEDs in such a continuous use fashion, what packages might be suitable? Are all LED packages SMD that I might possibly use in a situation like this?

Able to recommend a better dealer of LEDs?

The writer seems to hint that the 5mm bulbs I was using aren't really for continuous use.

He has a axe to grind.

Are all LED packages SMD that I might possibly use in a situation like this?

There is no difference between an SMD LED and the ones he is talking about in this page.

He wants to sell you:-

Packaged LED devices, with proper thermal control,