IR led hookup

[revres75]

If I hooked up 7 IR leds (1.6 forward voltage, 60ma) in parallel each how long could I run them on 2 AA batteries (3 volts)??

Also what value resistor should I use??
I used this site http://ledcalc.com/#calc to calculate the resistor value but it said that the leds would only be getting a current of 51ma with the resistor it suggested.

 

[Illum]

resistance needed = [(input voltage) - (voltage drop across LED)]/(desired current, in amps)

Parallel leds you add the current necessary together 7x60 = 420ma, 420/1000 = 0.42 amps

[3-1.6]/[.42] = 3.3 ohms...it'll run a bit hot though, you sure you want to drive your leds at 60ma each?
last time I werked with IR LEDs, I drove two 4 5mm LED banks in parallel [2V, 30ma per LED]using a 10 ohm 1/4 watt resistor on each bank, works very well for its purpose

the runtime will depend on the battery capacity of your AAs

 

[revres75]

I guess Ir leds require a higher current than other leds, because while looking at various sites online all the IR leds they were selling require between 50-100ma

 

[Illum]

infrared LEDs have varying driver requirements depending on which wavelength you plan to use, thats above my expertise on the matter though

the LEDs I used were 940nm 5mmLEDs spec'd at 1.2V 29ma, but I choose 2V because resulting 10 ohm resistance are the smallest value radioshack sells