White LED flashlight conversion for 12Volts

 

I keep noticing these new white LED flashlights which run on one or two
1.5V batteries.  I want to build some efficient lighting into my RV
camper, that charges a 12V battery with a solar panel.
Has anyone here tried to configure these for 12 Volt use?
I picked up a neat 7LED light for $5 that runs on 3AAA cells (4.5V),
and assume I could put three of them in series (4.5 x 3 = 13.5V), but
was hoping to drive each on directly on 12V with a dropping resistor or
similar.
 I tried to measure the current flowing to it but had some trouble
getting it to register on my multimeter for some reason.

 


robvann wrote:

robvann--

Give www.superbrightleds.com a try (although I've never purchased from
them)--they have led assemblies made up to fit a variety of 12 volt
sockets.

Tut

 

WOW, thanks (and to everyone else who replied), there are some great
sites out there about this.  I think I will order a few to try out.

I found the problem with my multi-tester - it had an internal fuse that
was blown for the current measurement.

Most of the LEDs that are on the sites referenced seem to provide 10
Lumens per watt.
I see that 12V floursecents provide about 50 Lumens per watt, so it
appeared that LEDs would be preferred mainly from a vibration
perspective (I suspect they will endure road vibrations of a camper
better than the glass tubes).

BUT, then when I measured my $5 7-LED headlight, I found it to be MUCH
LOWER power consumption, (but with unknown Lumens).  From my seat of
the pants testing it looks pretty bright and it would seem that if I
installed 30 of them (not that I plan to) that would way brighter than
a single 15Watt flourescent light bulb!

FYI,
with 7 LED's on 125mA at 4.5V = 1/2Watt!
3 LEDS at 75 mA = 1/3 Watt
1 LED at 40 mA = 0.2 Watt

I was surprised to observe that there is NOT a linear relationship
between the number of LEDS on and the power consumption, which leads me
to believe they are using some kind of pulse mechanism to improve the
efficency.  I have seen adds claiming 200hours of use on one set of AAA
batteries.

So, now my original problem becomes more complex, it appears to not be
a passive electronics circuit that I can just add a resistor to limit
the current, compounded by the availability of the 3 settings (1 3 7
LED's).


cnctutwiler@wmconnect.com wrote:

 


robvann wrote:

robvann

If you plan to due some engineering work a LED spec sheet would be
helpful--and probably save you some diodes. ;-))  The forward current
through the diode is not linear with respect to the voltage across it,
nor is the forward current linear with respect to relative intensity.
Simply--a small change in the voltage can dramatically affect the
current. Also, operating temperature is also a determinate of the max
current the diode can handle before it goes south.

Superbrightleds.com provides spec sheets for diodes they sell if you
choose to go that root.

Check out Big Lots--I bought several solar powered 6 LED lights for
about $8 each. My wife and I use these in the RV when we are remote
camping.

Did you ever decide on a suitable tower for the AirX? The wife and I
put up an old telephone pole and attached a 1.5 inch steel SCH 40 pipe
on top of that at our remote site. With some wind, our AirX keeps the
main battery charged fairly well.

Good luck,

Tut

 

Gee you have a great memory.
Well its still up top of the tree in our front yard.  It nicely
survived the winter snow storms!
We are moving into town in the next month, so I will finally have to
retire it from the tree, untill I find some cottage lot to put up a
proper tower.
- Rob


cnctutwiler@wmconnect.com wrote: