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 Post subject: IR LED Help Needed
PostPosted: 01.02.2011 18:45 
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Junior Modder
Junior Modder

Joined: 27.03.2005 21:25
Posts: 10
Location: Wilmington, NC
Hello,

I can create standard LED arrays without any problems, but for some reason IR LEDs are giving me a lot of problems.

Here is the problem. I am creating am LED IR array for night vision. I am using 10mm IR LEDs that have the following stats:
Voltage: 1.5V~1.6V
Current: 140mA
Peak(pulse): 700mA
Power: 200mW
Wavelength: 850nm

I am connecting them 4 in a series with a 47Ohm 1W resistor on a 12V power supply.

These LEDs should give my camera night vision of over 50' , but i can not seem to get more than 5 or 6 inches.

Any ideas and suggestions?

Thanks

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 Post subject: Re: IR LED Help Needed
PostPosted: 06.02.2011 11:49 
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Senior Modder
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Joined: 10.09.2004 12:08
Posts: 290
Location: Finland
Maybe one of them is broken, check them with a multimeter.

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 Post subject: Re: IR LED Help Needed
PostPosted: 06.02.2011 15:04 
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Junior Modder
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Joined: 27.03.2005 21:25
Posts: 10
Location: Wilmington, NC
Thought of that and all of them are working just fine...

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 Post subject: Re: IR LED Help Needed
PostPosted: 06.02.2011 15:21 
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Site Admin
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Joined: 24.01.2002 10:09
Posts: 4683
Location: Finland
These high power leds should be used with constant current sources rather than regular leds. But then again, these should still work... perhaps you should test one string at the time and see that they are all performing ok before combining them together in parallel. Point your camera towards the leds and you will see if they are outputting the same amount of light.


Perhaps something like this...
http://www.dealextreme.com/p/330ma-6w-p ... 265v-44008

Are you sure your current power supply can handle the load you are putting it on?


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 Post subject: Re: IR LED Help Needed
PostPosted: 06.02.2011 23:58 
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Junior Modder
Junior Modder

Joined: 27.03.2005 21:25
Posts: 10
Location: Wilmington, NC
Thank you for your input. Before I build the array, I use my bread board to test each series of leds to make sure they are all producing the same level of emissions. Then as I build the array, i test each series before I solder them.

The power source is 8 AA batteries that produce 12V with 2700 - 2900 mAh. This setup works great with every other led type I use but fr some reason, I do not seem to be about to get the range that the IR leds are reported to have.

Still confused. Still looking for suggestions...

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 Post subject: Re: IR LED Help Needed
PostPosted: 12.02.2011 16:41 
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Super Modder
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Joined: 28.01.2002 10:31
Posts: 941
Location: Tuusula, Finland
I think you must use pulsed current (near peak current) to achieve reported range. That constant current is only 20% of full power so you can't reach maximum range using it.


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 Post subject: Re: IR LED Help Needed
PostPosted: 20.05.2011 18:45 
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Regular Modder
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Joined: 26.05.2007 10:06
Posts: 128
Location: Texas
StiNgeR wrote:
I think you must use pulsed current (near peak current) to achieve reported range. That constant current is only 20% of full power so you can't reach maximum range using it.




I believe StiNgeR is correct. With rechargeable batteries and even some regular batteries they only put out the peak amount when they are first being used so even after just a small amount of time they will not be "up to snuff" any longer. I know it kinda defeats the purpose of what you're doing with the LED's but try using a transformer with a resistor of course and see what results you get. (I think this is how you did it before actually soldering it up, but just in case...)


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