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LED calculations causing burnouts - What am I doing wrong?

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tkheaven

Joined: Mar 25 2011
Posts: 4


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Post Fri Mar 25, 2011 9:36 am

'lo all... I'm hoping someone can help me with the following...:
I have 6 IR LEDs purchased with resistors to set up for night vision using +6V (4AA recharge batteries) for power. I have used both Oznium’s LED calculator as well as from LED Center (http://led.linear1.org/led.wiz). I followed the diagram but the battery pack starts to produce too much heat, resulting in smoking/burning the pack. I don't want to risk NOT adding resistors and burn out the LEDs as well.

NOTE: I'm also incorporating Radio Shack's SPST Micromini Toggle Switch where I wire red/black --> switch --> battery pack. I already have this exact toggle setup for another circuit board with 6 UV LEDs - they all light up, no issues, no burning batteries. Ultimately, I’ll be using both infrarerd and ultra violet LED boards (each with its own +6V power source) in a project box and using it as an IR/UV spectrum illuminator.

IR LED Info:
Voltage: 1.5V~1.6V
Current: 140mA
Peak (pulse): 700mA
Power: 200mW
Wavelength: 850nm
Angle: 30 degree
Diameter: Approx. 10mm

LED Center Calculation:
3 x 2 array uses 6 LEDs exactly, R = 12 Ohms

• each 12 ohm resistor dissipates 235.2 mW
• the wizard says the color code for 12 is brown red black
• the wizard thinks 1/2W resistors are needed for your application
• together, all resistors dissipate 470.4 mW
• together, the diodes dissipate 1260 mW
• total power dissipated by the array is 1730.4 mW
• the array draws current of 280 mA from the source.


Soooooo....what am I doing wrong?? icon_sad.gif
bad venge

Joined: Jul 28 2007
Posts: 3550


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Post Fri Mar 25, 2011 9:45 am

SWITCH is SHORTING pack just interupt the RED WIRE no black connection
tkheaven

Joined: Mar 25 2011
Posts: 4


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Post Fri Mar 25, 2011 12:49 pm

Forgive my lack of knowledge for these things... no black connection? How am I connecting the other switch prong? Sorry, having a moment here. Also, thsi is how I connected the UV LED board without any issues. Should I have the same concerns or is the difference in the varied wattage, etc? Would it help if I said I used the following resistor (idk, it looks huge compared to the other resistor connection I've used for the same type of project...)
tkheaven

Joined: Mar 25 2011
Posts: 4


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Post Fri Mar 25, 2011 1:23 pm

I also wanted to mention that I tested the LEDs without the switch and the pack was still burning up....so I'm not sure of it's the switch...
bad venge

Joined: Jul 28 2007
Posts: 3550


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Post Fri Mar 25, 2011 5:35 pm

the way you have it drawn there would be power to the leds when the switch is off when you turn the switch on it's a dead short across the pack...

reconnect the black wire to itself , then connect the red to each connection on the switch (I'm assuming it is not lighted)
corvettecrazy

Joined: Dec 17 2003
Posts: 4357
Location: moved (twice)


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Post Fri Mar 25, 2011 5:48 pm

Your switch needs to be wired like this:
User posted image

Not the way it is wired in your diagram.
Phil
Owner, Oznium.com

Joined: Feb 11 2003
Posts: 7719


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Post Sat Mar 26, 2011 5:49 am

I've re-drawn your diagram:

User posted image
tkheaven

Joined: Mar 25 2011
Posts: 4


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Post Sat Mar 26, 2011 8:46 am

Thanks! That seems to have worked. I'll post once i'm finished with the project...or if I run into another issue.. icon_biggrin.gif
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