2v Led
2v Led
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 Mini 3W 250lm Lumen CREE Q5 Focus Adjust Zoom LED Flashlight 1 Mode AA Silver  US $6.75
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 1600 Lumen Zoomable CREE XM L T6 LED 2x18650 Flashlight Torch Zoom Lamp Light US $30.38
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How long will this battery power this LED? What are the calculations?
Suppose the LED has these specs -
5mm/T1-3/4 568nM Green LED, 5mcd TPP brightness, Forward Voltage Drop: 2.2V. Max. reverse Voltage 5V, Max. Forward Current: 20mA
WT: .08 pack
Suppose I had a 1.5V battery at 150mah powering it. How long would it last?
What If I stacked both 2 of those batteries so I had 3v, how long would that last?
I do not plan on using any resistors.
What are the calculations so I can figure out the life with other battery/LED combination?
I should have been more specific, this is an alkaline LR44 type battery I am dealing with. I am aware they have strange curves as there power is exhausted.
and, a 1.5v battery should not fry and LED that is rated for that kind of voltage and current.
You always need a resistor, or you will burn out the LED.
the rest is just arithmetic. look at the units.
150ma-hour / 20 ma = 7.5 hours.
"and, a 1.5v battery should not fry and LED that is rated for that kind of voltage and current."
wrong.
First of all, Vf on a LED has a wide tolerance, and it is very temperature dependent. Second, the curve of I vs V is very steep, which means a small change in V causes a large change in I.
Yes, you may have an LED that has a rating of exactly 1.5 volts at 20 mA, and you connect a 1.5 volt battery to it, it will draw 20 mA. Initially. but as it warms up, Vf drops a bit, which causes the current to increase, which causes more heat, lower Vf, etc, until the current increases to the point where it dies.
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