Hello all! First post/LED problem!

[Abe Osman]

Hello guys!!!
Im very happy to be here. Thanks Gordon for fixing my log in problem!

Here is what i started. Its an array with 201 LEDs, 5mm. 152 are red, and the others are all blue.

I used the array wizard to calculate the resistors, and have it powered off of a 12v DC adapter.

The entire thing lit up perfectly...for about 30 seconds. Then, one by one, each of the RED series' (groups of 6) started burning out. I measured the mA, and each red led is only getting 8mA, and 1.99-2.05 volts. This is well within spec, and yet still after a few minutes, more and more of the LED batches started burning out. The blue ones are all fine.

I think it may be because i have the red and blue running off the same parallel config? Was i supposed to have 2 seperate parallel configs for the series batches of red and blue LEDs? I didnt think it would make a difference?

Anyway, ive burned out 6 batches of red LEDs, so ive lost 36 LEDs, and all i know is that the batch gets semi hot, and then stops lighting up.


Any help would be appreciated!!!!!!!!!!!!!!!!!!!!!!!

Abe

[Abe Osman]

well tonight, i seperated the circuits, and even removed the burnt out series' from the red array so that they wouldnt cause any problems, and im STILL getting red batches getting hot and slowly dimming and then turning off!

The blues continue to run as normal. I took measurements again, and the reds are seeing 1.99-2.05 still, and the mA is ~10.

I am so confused!!!

Abe

[minimum]

1st, make sure your supply is DC and 12V (with and without load).
2nd, if possible, make sure you're measuring (or reading measures) correctly. 2 volts and 10mA and still burning out doesn't make any sense.

6 red's in series, each series string having it's own resistor? What's the value of the resistor?

[Abe Osman]

hello,
The ac/dc adapter w/o any load is at ~13.9v, with all the LEDs connected its at ~12.1v.

I tested about ~10 leds, each is seeing only ~1.99-2.05 (the red ones). Blues are at 3.1-3.5v

Yes, there are 6 LEDs in series, and each set has a 1ohm resistor, as recommended by the wizard. There are 2 left over at the end of the set, which has a 470ohm resistor.

 

[BVnursery]

something is reeeally screwy.

Id do a test with 6 red leds.   Hook them up to your power supply and add a variable resistor.. of bout 100 ohms.

if they still blow with the variable set at 100 ohms.. Id say you have a bad batch of leds.

[Abe Osman]

i did a test connection of 3 red LEDs wired in series, with a 330ohm resistor and it stayed lit for hours!

[BVnursery]

Add 3 more leds.  Id say your reds are waaaay out of spec.

[Abe Osman]

47ohm resistors instead of 1ohms solved the problem!!!

What i learned:

There is a difference between a regulated 12v power supply, and one rated 12v at 1a. I think the extra ~.5v at the 700ish mA im drawing caused the reds to fry.

Now here is another question. LEDs from sites (including the ones recommended here) are approx $20-45 for 100 red. I found them for $3 for 100. Is there a large quality difference between the 2? brightness wise, my array of 201 LEDs lights up my neighbors house across the street at 10mA. Will my cheap ones not last as long?

I suppose if i could justify spending $45 just for 100 lights, i would. but then it doesnt make any sense to build a light rather than to just go buy one for $90 right?

Abe

[BVnursery]

With most electronics, if they last 72/96 hours, they just last.

[justDIY]

Now here is another question. LEDs from sites (including the ones recommended here) are approx $20-45 for 100 red. I found them for $3 for 100. Is there a large quality difference between the 2? brightness wise, my array of 201 LEDs lights up my neighbors house across the street at 10mA. Will my cheap ones not last as long?

when it comes to round bulb type leds, there is no such thing as quality.  Get the cheapest ones you can find.  $3 for 100 is a good deal, last batch of cheapies I bought, I paid $6 (+shipping) for 200 3mm red with 30 deg lens.