LED Malfunction Need help

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BTTFSpencer

Sr Member
I've built an AMT Batwing with 3 mm warm white led's installed in the wing tips and on the bottom of the model, however when I turn it on...one of the led's is actually brighter and more white then the rest of them.

They came from the same packet, all wired up the same. I used 2 resistors, and 2 AAA Batteries to get them running. I'd really like if someone could help me solve this problem, I am really new to wiring and electronics, frankly I have no idea what to do about this little issue...

Here are some pics, the led I'm talking about is on the LEFT WINGTIP. The rest of them fire up normally.

SDC15855-1.jpg


This is the power supply:

SDC15858.jpg


So if anybody could offer some suggestions, short of breaking that wing open. I'd be much obliged. :lol

Thanks,

-Spencer
 

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falcondesigns

Well-Known Member
I'm no expert but I think you need more power for whole set.LEDs take at least 4.5 and dont behave well at just 3 volts.I'd repeat the whole wireing set outside the model and use a 9 Volt.I'd also wait for some more responses.
 

exoray

Master Member
Buy more LEDs and color match... The color shift and brightness shift is very common from lot to lot, especially if you purchased cheap imports vs name brand...
 

BTTFSpencer

Sr Member
They were cheap imports yes, However when I originally fired them up they all looked identical.

It's a really weird thing.

Thanks, guys! Your advice is really appreciated, keep it coming. :D
 

star-art

Sr Member
How are they wired? If you wire them in series and the voltage is not sufficient, you can get a drop in brightness. Each LED causes a voltage drop. The next LED gets less voltage, and so on. (Yes, I know LEDs are current driven devices, but they can get dimmer down the line when wired in series.)

You probably need a higher voltage source. 12V is ideal, but a 9V wall transformer should work. Make sure you include resistors in series. ("In series" means connect the - lead from the first LED to the + lead of the second one, and so on, until you reach the end of the chain.) Choose a resistor that gives a current through each LED of 15-20ma. To find the correct value for the resistor, you will need to know the voltage drop of each LED.

A common way to wire LEDs is to connect to a resistor, then wire up to 3 LEDs in series with that. If you have more than three LEDs, place them in sets of no more than three in each set where all sets are wired in parallel with each other. If you get a reduction in brightness within the set of 3 LEDs in series, you need more voltage.

Hope that makes sense! :)
 

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exoray

Master Member
I will repeat what Star-Art asked, how do you have them wired up?

In parallel sharing a single resistor is a no-no and only works 'right' if the LEDs are all identical or very close, and as I have stated above in many cases they are not identical or even close... Thus differing LEDs in a parallel wired circuit can and will react differently... General rule of thumb is to avoid sharing a common resistor among LEDs, especially if color and brightness matching is a concern...

In series with 3 volts isn't going to get you that far either with white LEDs...

Your best bet is to wire each LED with it's own resistor in a parallel configuration to the battery if you want to use the 3ish volt supply... Since the white LEDs probably want at minimum 3 volts, you should use the smallest resistor you can get a 1 or 2 ohm just to act as a current buffer...
 

morrris99

Well-Known Member
You'll probably have to open her up and see what it is. If you have something shorted, it might do that. One of the leads may be bypassing a resistor. Had the same problem inside an HO engine once. I shook it around a little, and the light got brighter and dimmer. Upon further inspection, I had some bare leads that were touching. Insulated them, and went back to normal.
 

BTTFSpencer

Sr Member
Thanks guys for all your help! I'll need some time to go over your suggestions and improve the led's in my Batwing, for now I just misted over the led's with an acrylic transparent yellow to disguise it. Surprisingly it actually worked pretty well, and because it's water based I can strip it at any time.

Again, Thank you so much for your help. You guys are so talented and informative. :)

Best regards,

-Spencer
 

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BTTFSpencer

Sr Member
I have the Batwing finished actually, if you look above I stated that I pretty much corrected the problem using paint, for now. I'll start a new thread for the finished model as soon as I take some pics. :)
 

11B30B4

Well-Known Member
I would recommend wireing each led separately. Each having it's own resistor, this will insure that each will have the same draw from the power source. This becomes Very important when you start mixing colors or strobes vs non- strobes.
 

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