On Sun, 15 Apr 2018 16:39:14 -0700, Mike S wrote:
I was given a broken LED light (on a headband) that takes 3 AA
batteries, can't find the lumen spec as there is no company name or part
number on the ct. board.
I'll assume that there was only one LED in the headlight. Lumens are
fairly easy to guess. The commodity LED du jure is the Cree T6
series. It produces about 100 lumens/watt of power consumed (minus
whatever the optics attenuates). There are LED's with higher efficacy
available, but you won't find them in commodity lights. The LED will
be mounted on a COB (chip on board) which also acts as heat sink.
Somewhere in the package, either on the COB or on the on/off/dim
switch, will be some electronics to control the light. These also
include a current source to regulate the current drawn by the LED. You
should not need any additional current limiting resistors. On the
really cheap junk LED lights, there might be one or two tiny chip
resistors on the COB to provide some current limiting. Three AA
alkaline cells in series is about typical for powering a low end,
single LED light.
If I just run the 3 batteries directly to the
LED will the batteries drain too fast or will I damage the LED? I don't
know if I have to limit the current for either case.
I don't know. Take it apart and see what's inside. Most battery
compartments include a label or molded description of the type of
battery to install. Look for it. Unless you were given a bag of
parts, it's unlikely that you'll need to add anything to make the
light work. Start with three alkaline cells and measure the current.
If the LED burns about 1 watt or less as in:
voltage_across_LED * current through LED = watts
it should work.
Also, while it might be possible that your headlight runs on LiIon
cells, I doubt it. The lights that use AA size cells (14500) tend to
use alkaline or NiMH, while the one's I like use one (or two in
parallel) 18650 LiIon cells. I haven't seen any 14500 LiIon cells
used in headlights yet, although such a light might be possible.
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060
http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558