hey, jsut wondering if its possible to run a LED off a small watch battery (or something similar) im thinking a little dimmer, not ultra bright... would this work? what type of setup, led, battery...would i need to use? thanks, lazy
3v Li-Ion battery would work best for blues and whites, and *may* work on reds and greens, depending on how much internal resistance is in the battery (my calculations say 45ohms for a 2.1v@20mA LED). If not, a resistor would be needed for those lower voltage LEDs. Anything that normally operates above 3v can work fine directly wired to the battery.
thanks! how long do you recon the battery would last for if it was running a single led all the time...
Depends on the mAh rating. mAh stands for Milliamp Hours. A typical AA battery has a rating of about 1500mAh, which means that a draw of 1.5A will deplete the battery in an hour. A draw of 750mA, will deplete the battery in two hours, and so on and so forth. The thing to remember though is that batteries also decrease in voltage the longer they're used. IIRC, Lithium-Ion batteries maintain their nominal voltage for fairly long before it starts to decline. Just remember that watch batteries aren't designed to hold a lot of juice because their used in devices that don't draw a lot of current.
The cheap key-ring torches work without a separate resistor, directly across Li cells like the 3v 2016. Reds light mega-bright, and probably wouldn't last forever, but the cell is only 75mAh so they'll flatten it in under 90 minutes. The blues and whites run mega-bright on 2 cells, but my blue from one (it's a standard 3.7v @ 20mA ultrabright type) lit fine (though much dimmer ) on a single cell. I tried a 2.1v ultrabright red on a 1.5v LR44 Duracell button, lit good enough for an indicator, but they're only low-capacity batteries so it wouldn't last all that long.
Ok, along the same lines of the first question, how would i figure out how long a couple 1.5v AAA batteries will run 2 LEDs? I saw the mAh post and looked at my batteries (they are duracell MAX) and could find no such rating. Is that rating just for lithium batteries?
I'd still be putting a resistor on it, I've managed to kill LED's by putting them on a watch battery without a resistor. It's not so much for dropping the voltage, but for sinking the excess current.
you can also run leds of lower voltage cells using a constant current source For Example Unfortunatly, ive never got this to work i even ordered a kit from japan for the components, and it still doesnt. Let me know if any one does get it to work.
