3 leds

[yclo]

I just got 3 white leds hoping to make a small flashlight that uses the mn21/23... however I soon found out that this little battery doesn't have enough current to power up 3 batteries.

Has anyone seen a small (mag solitaire size) torch that uses 3 leds? What kind of battery has enough current to power up 3 leds?

 

[RonM]

Three AAAs should do the trick. Can't imagine any button batteries would work to well for 3 LEDs, plus the cost of use would be quite high.

 

[MrAl]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by yclo:
What kind of battery has enough current to power up 3 leds?<HR></BLOCKQUOTE>

The first decision you have to make is
what size flashlight you want to build
the 3 LED's into. It is the size that
determines what kind of battery you can
use, and therefore the run hours are
pretty much determined by the size of
the flashlight and the number of LED's.
For a large size flashlight, you can use
large batteries and so you get lots of
run hours on a single battery or set of
batteries. For a very small flashlight
you have to use very small batteries and
since small batteries dont run as long as
large batteries, you get less hours in
general with a small flashlight.
For example, if you have the room for a
good 6v alkaline lantern battery you could
power two LED's for a month 24 hours a day
at full brightness (and then some).
If your limited in size to say, the
AA mini mag then the space for keeping the
batteries is much smaller, so you cant expect
to get as long a run time as with the 6 volt
battery. This is like the first rule of
LED flashlight conversions: size=runtime.

There are some things you can do to get
longer run time. For example, you could
go to lithium batt's at increased cost,
or you could run the LED's at reduced
current and extend battery life much longer.

The choice is up to you, but even in
this day and age even the best battery
technology takes up some significant space.

Also, did you consider the possibility of
running two LED's in series with the MN21
12 volt battery? You wouldnt have the
three LED's, but you would still have two.
With two LED's in series the battery might
last longer, but i havent actually tryed
this yet. Perhaps someone else did?

Good luck with it,
--Al

 

[yclo]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR> Also, did you consider the possibility of
running two LED's in series with the MN21
12 volt battery? <HR></BLOCKQUOTE>

Actually I have tried that, both leds dim as I connect an extra led starting from one.
And the funny thing is the total brightness (if that's the phrase for it) is the same...

 

[MrAl]

Oh ok, well thanks for posting that im sure
there are other people out there who want to
do similar things also.
I cant find any of those batteries anyway

Oh yeah, i misquoted the info about the
6v lantern battery: a better discription
would be that one Energizer 6v lantern
battery can keep a single LED running
at 20ma (full brightness) for over
2 years! 24 hours a day! The deal there
is that a very small current drain like
that on such a humongous battery makes it
look better then it really is (when used with
'normal' loads). Pretty amazing i think.
Too bad small batteries cant do as well.

--Al

 

[PeLu]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MrAl:
Oh yeah, i misquoted the info about the
6v lantern battery: a better discription
would be that one Energizer 6v lantern
battery can keep a single LED running
at 20ma (full brightness) for over
2 years!<HR></BLOCKQUOTE>

That means (assuming the LED just uses a resistor for limiting current) the lantern battery has some 360Ah at 20mA? Which kind of lantern battery is this? The 'usual' square (about 7cm square and 11cm high)?
Hard to believe.
Even if you use a red LED and an almost perfect boost regulator it has to have more than 100 Ah.

PS: Mral, is it possible that you don't put in a CR/LF every 40 or so characters?