Old 01-22-2013, 04:40 AM #1
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Default LED desktop lamp, please help!

I am making a led lamp...and I have about 92 LEDS on it. The lamp is sort of like a tree it has lots of LEDS basically branching out from a base. I have them all wired up now (I had to use thin wire 30awg) and just testing them using a single panasonic 3100mah 18650 they all light up, but after a few seconds the wires themselves (In random places) start to smoke. But they LEDS still run. The LEDs run 3.0-4.5 volts @ 20ma. I am assuming the wires can't handle the current? I hope to power this using a 4v AC/DC adapter I have that's rated for 2000ma. I don't want to keep powering up because I don't want to cause more damage. Does anyone have any ideas on how I could fix this? Could adding a resistor or something stop it from smoking? Thanks any sort of help is appreciated!

EDIT: Turned out one of the LEDS shorted out...I replaced it and the lamp runs on the AC/DC adapter fine as well.



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Old 01-22-2013, 05:48 AM #2
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Default Re: LED desktop lamp, please help!

Well sheesh. That's impressive even for an 18650. You'll uhhh... have to start from the beginning.

Lets see... you'll need a more exact Vf on the diodes @ 20ma, because that could make the difference between being able to use that wall wart or using a different one. I'll do some math for you:

You need a current limiting resistor in series with each and every LED.

Here are some assumptions:

Wall Wart: 4VDC
LED: 3.5V @ 20ma

Resistor should drop .5V then, and also conduct 20ma each, so .5/.020 = 25 ohms for each resistor.

If your really have some ~184 wires in this thing, make sure all your wires are insulated from each other. If there is even 1 short, the battery will see it and send all the current through as is possible.

I'm also assuming you're not using 38 gauge wire.. maybe 20ma is a bit much for such wire... just a guess.
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Old 01-22-2013, 06:06 AM #3
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Default Re: LED desktop lamp, please help!

Quote:
Originally Posted by Meatball View Post
Well sheesh. That's impressive even for an 18650. You'll uhhh... have to start from the beginning.

Lets see... you'll need a more exact Vf on the diodes @ 20ma, because that could make the difference between being able to use that wall wart or using a different one. I'll do some math for you:

You need a current limiting resistor in series with each and every LED.

Here are some assumptions:

Wall Wart: 4VDC
LED: 3.5V @ 20ma

Resistor should drop .5V then, and also conduct 20ma each, so .5/.020 = 25 ohms for each resistor.

If your really have some ~184 wires in this thing, make sure all your wires are insulated from each other. If there is even 1 short, the battery will see it and send all the current through as is possible.

I'm also assuming you're not using 38 gauge wire.. maybe 20ma is a bit much for such wire... just a guess.


Thanks for the quick reply. This lamp I am making is for my friend and I am actually suppose to give it to them today, so thanks I need all the help I can get! Here Is a little more information...

The LED specs say "VF(V) If=20mA =3.5-4.5" for the led I have. They are 3mm RGB LEDS
The Wall Wart lol (I like that)...is 4V and 2A
And the wire I am using is 30 AWG

I really do have 184 wires on this! There are a ton running through it that's why adding resistors right now would be impossible really.

What do you mean by "If there is even 1 short, the battery will see it and send all the current through as is possible."

I was under the impression that the wall wart would limit the power to the LEDS. So that's why I did not put resistors on all the wires. I have not tried powering it using it yet, as I didn't want to do any damage. But maybe I should try it with that instead of the battery?

Last edited by r1Bro; 01-22-2013 at 06:07 AM.
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Old 01-22-2013, 08:10 AM #4
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Default Re: LED desktop lamp, please help!

Pictures. We definitely need pictures. If nothing else, 4 teh lulz.
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Old 01-22-2013, 08:26 AM #5
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Default Re: LED desktop lamp, please help!

Quote:
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Pictures. We definitely need pictures. If nothing else, 4 teh lulz.
I will try to in bit...right now its like a birds nest of wires and you would probably die laughing.
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Old 01-22-2013, 05:19 PM #6
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Default Re: LED desktop lamp, please help!

If your battery happened to find a short circuit (IE a current path of no resistance), it will send a ton of current through the short which can likely burn 30ga wire.

So... you're powering each anode of each RGB led then? All at the same time?
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Old 01-22-2013, 06:09 PM #7
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Default Re: LED desktop lamp, please help!

I just want to see this lamp! 'nother vote for pics!
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Old 01-22-2013, 07:03 PM #8
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Default Re: LED desktop lamp, please help!

Quote:
Originally Posted by Meatball View Post
If your battery happened to find a short circuit (IE a current path of no resistance), it will send a ton of current through the short which can likely burn 30ga wire.

So... you're powering each anode of each RGB led then? All at the same time?
Yes thanks you! One of the LEDS was shorted making the wire melts therefor thats why it smoked. I have been using the wall adapter to power it now and it seems to be fine. I measured volts and its running 4.27volts perfect for my LEDS! Yes that's correct, all 92 at the same time. Thanks!

Quote:
Originally Posted by BShanahan14rulz View Post
I just want to see this lamp! 'nother vote for pics!
I will take some pics when I finish it should be today or tomorrow, as long as I don't run into anymore problems. It's basically a mini tree, on a base. It looks like a tree, with a LED on every branch tip. It changes colors so its more just for fun then functional lamp. But either way it still lights up a room!

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Old 01-27-2013, 09:43 PM #9
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Default Re: LED desktop lamp, please help!

Quote:
Originally Posted by BShanahan14rulz View Post
I just want to see this lamp! 'nother vote for pics!

Yes! must have some ( I won't lulz ) ........
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Old 01-28-2013, 08:46 AM #10
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Default Re: LED desktop lamp, please help!

We don't want this turning into another EPIC TEA LASER thread.
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Old 01-28-2013, 04:53 PM #11
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Default Re: LED desktop lamp, please help!

hellz no! this sounds like a cool light. If only they made mini electrical flexible conduit in like, 2.5mm diameters or something. Would be neat to have that kind of flexibility and adjustment, i.e. if you wanted, you could bunch up all the warm white LEDs for some illumination, or all the greens and reds for a christmas motif, or just let them all float around randomly... You know, this stuff: http://www.monumentalelevatorsupply....ges/G-Flex.jpg but smaller
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