Resistor Calculation trouble...

[kosPap]

Guys I need some help here....
I wish someone verified my calculation....

it is about a 4AA adapter tuned into a low output light with a 5mm white LED and a 5mm blinking one too...

I will use a 3-position switch to connect resistors for these battery configurations:
- 4AA Energizer Lithiums FULL (4x1.7=6.8Volt)
- 4AA Alkalines or 4AA Energizer Lithiums Partially Depleted (4x1.5=6Volt)
- 4AA Alkalines Partially depleted (4x1.3=5.2Volt)

Here is an example of my calculations: (3.2Vf & 20mA output)
V drop=I*R => 6.8-3.2V=0.02A*R => 3.6=0.02*R => R=3.6/0.02 => 180 Ohm

But using the FireStorm Resistance Calculator & the LED Pro Resistor & Convertor Calculator I get a suggested value of 1800 Ohm!
BUT using this calculator I get a value of 180 Ohm..

What is wrong?

 

[Justin Case]

LED Pro gives me 180 ohms, not 1800 ohms. Looks like operator error to me.

 

[JohnR66]

180 ohms is correct. Probably easier to find a 150 ohm resistor which gives you 24 ma. It is generally a better idea to overdrive the LED a bit in battery use for more light as long as the LED is good quality.

BTW, 6 volts is not a good voltage for powering white (InGaN) LEDs because the power of one cell is totaly wasted in the resistor. It is better to use 3 cells or a buck type switching regulator.

 

[kosPap]

aha! but I am making an emcoom companion light taht will use batts partially depleted from my handhaled radio....so no worries here

24mA is a good idea to consider.....BTW I do have some room and I am thinking using 2 resistors in line for a 180 value. LEDs will be faxton ones of course!

Justin I really do not know...I typed 20 on the calculator