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G8MNY  > TECH     19.01.19 09:45l 103 Lines 4276 Bytes #7 (0) @ WW
BID : 55258_GB7CIP
Subj: Cheap Battery/12v LED Light
Sent: 190119/0833Z @:GB7CIP.#32.GBR.EURO #:55258 [Caterham Surrey GBR]

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By G8MNY                              (Updated Aug 13)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)

Recently I discovered the "99p shop" & "Poundland" discount shops are still
selling twin packs of 4.5V self contained 3 LED battery lights for 99p
(~1.5eu/$). Is this less than parts cost? I have seen these lamps in 3 packs
for far more in other shops!

Inside there is a proper locking "tack" switch, 3 bright LEDs, 10R, flexible
reflecting housing button spring, & stick up 3x AAA in the round battery box.

     clear press cover
       _..----.._              n  = LED
 /~~~~             ~~~~\        
 ~\.n./~~\.n./~ Ĵ
(bat)________(bat)      ~\. = Spring Reflector
===========================         = Switch
Bernet   ~~~~~~~~~~              
 Base      Sticky                ___ = PCB

White LEDs are about 3.5V, so a 10R is in series with a 3 paralleled LEDs on
4.5V to limit the current.

__            __  __  __
__ 3x    LED \_/  \_/  \_/

The lights are quite useful as they are. They draw some 90mA from the 3x AAA
cells. But I found the double sided sticky quite poor. So I intend to screw the
base in place & attach the body.

This is a fiddly job! The case is lightly glued around the edge & a small screw
driver/knife inserted between the cover & black inner & carefully worked around
will crack the glue, & separate 2 undamaged parts.

Putting the LEDs in series is done by tuning the middle one around & cutting 2
of the paralleling PCB tracks. Then remove the 10R & add a 150R to the -ve
lead. This will then give about the 25mA @ 13.8V. And by putting a diode input
after the switch, an Emergency lighting option can be added. Many of these low
power lights can easily be run from a floated battery on mains with a mains
fail relay.

Emergency oĴ>Ŀ
Lights +                                      ___    ~-_ 
            o\oĿ      E [o o]>ô(:)~-_ PCB
                        Ŀ  Ŀ           ] [          ~-_
     +12V o           __  __  __   +12V[o o]Ĵ  SW (:) >
                   LED \_/  \_/  \_/        ] [          _-~
                                  0V [o o]150(:)_-~
       0V o150                     ~~~    _-~

To makes room for a small 3 way block connection, with a soldering iron I
perforated & cut a hole in the middle of on of the AAA battery holders, to suit
the connector. With care the 3 holes for the bernet mounting plate still work.
The PCB is held firmly back in place on the cut battery mount with heat glue &
the lamp tested, then the whole lot is glued back together.

Running permanently these LEDs light have a short life, as the get quite a bit
dimmer after 6 months on!

Using some strip board pressed into the chrome holder, I replaced a hot dim
power hungry lensed lamp with 6 LEDs. I cut away the copper track away at the
edge to make sure there was no shorting to the case.
__________________       _____________________
Ŀ                  Ŀ 
   (o)_.--'''~~\         (o)_.--'''~~             o o  6 LEDs
   (_)_/\/\/Bulb   |        (_)_  Rs   ||LEDS          o   o
       ~---...__/             ~---...__             o o

As this is used for illuminating my radio while /M (14V battery), I used 2 120R
as the series Rs, one for each chain of 3 LEDs.

Make sure the 12V is fused (e.g. 1A) & there is no fire risk from trapped wires

If your find the light is too directional, just lightly scratch LED lens heads
or lamp cover to defuse more of the light.

Why Don't U send an interesting bul?

73 de John G8MNY @ GB7CIP

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