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G8MNY > TECH 22.11.11 09:44l 128 Lines 5217 Bytes #999 (0) @ WW
BID : 17845_GB7CIP
Read: GUEST
Subj: LED Bike Light
Path: IZ3LSV<IV3SCP<IW0QNL<IW2OHX<UA6ADV<GB7CIP
Sent: 111121/2357Z @:GB7CIP.#32.GBR.EU #:17845 [Caterham] $:17845_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EU
To : TECH@WW
By G8MNY (New Jan 10)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
After a recent club talk on these with several connection ideas...
No Current Resistive Current Constant Current Switch Mode Current
Control Control Control Control
ÚÄÄÄo\ÄÄÄ¿ ÚÄÄÄRÄÄÄo\ÄÄÄ¿ ÚÄÄÄÄo\ÄÄÄÄ¿ ÚÄÄÄÄo\ÄÄÄÄÄ¿
LEDs NiMH LEDs NiMH LEDs NiMH LEDs NiMH
³ Battery ³ Battery ³ Battery ³ Battery
ÀÄÄÄÄÄÄÄÄÙ ÀÄÄÄÄÄÄÄÄÄÄÄÄÙ \³Const ³ Output<-FB¿ ³
e/³ I ³ ÀÄÄÄÄÄRÄÁÄÄÄÙ
ÀÄÄÄÄÄÄÄÄÄÄÙ
This is the sort of LED current (light) graph with 3 LEDs powered from 9 cells.
Direct
LED I No R:short .'Typical
600mA ´ life:time ú Series R
³ : .' (5R)
400mA ´ : ú
³ ú .'
300mA ´ . ___:..----ÄÄÄÄ Max Rated LED Current
³ .' ú from constant current
200mA ´ '/ .' transistor's collector
³ ú/ ú
100mA ´ ./.'
³.ú/ú Just
0 ´Flat Norm Charged
ÃÄÄÄÄÄÂÄÄÄÄÁÂÄÄÄÄÄÂÄÄÄÄÄÂÄ Battery
9 10 11 12 13 Volts
MY CIRCUIT
Without going into loads of components if a switch mode design, I just used..
1 2 pole switch
3 1W White LEDs
1 Diode
2 Rs (select on test 1-10k)
9 AA NiMH
1 High gain power NPN
The transistor in a constant current mode to not only feed the 3 LEDs, but also
feeds the battery charging in this design...
ON OFF/
ÚÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄo /oÄÄÄÄÄÄÄ´<ÃÄÄÂÄÄÄÄoÄoÄÄÄo +13.8V
3 _³_ ³ ³ CHARGE D1 ³ fuse
ð\_/ ³ _³_+ ³ link
1W _³_(10V) ³ _Ü_ 9x AAs ³
ð\_/ ³ _Ü_ 2.9AH ³
WHITE _³_ R1 _Ü_ NiMh ³
ð\_/ ³ ³ (10.8V) ³
LEDs ³ ³ o ³
³ ³ OFF/ | Fuse ³
³ ³ CHARGE o link ³
ÀÄÄÄÂÄÄÄ)ÄÄÄÄÄÄÄo ³ ³
300mA ³ ³ \_³ ³
³ ³ ON o ³
\³ ³ ³ ³
NPNÃÄÁÄÄÄÄÄÄÄ)ÄÄÄÄÄÄÄÄR2ÄÄÄÄÄÄÄÙ
e/³ ³
ÀÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄo -VE
HOW IT WORKS
The NPN should be a high gain TAB transistor (not a darlington!). Although bias
voltage is quite temperature sensitive, current gain is not, feeding the base
with almost constant current results in a nearly constant collector current
down to about 0.1V drop emitter to collector. This is much better than the
usual series resistor used to reduce the current.
R1 sets the LED current & for a Transistor with Hfe of 100 it needs to be about
3k3 this will need selecting on test for your transistor with a charged up
battery! Best measured with the lowest resistance ammeter e.g. a DMM on 20A.
Different R1 values could be switched in, or a variable could be used (with
series R) allowing you to set the brilliance needed.
R2 sets the charging current for your battery, & if 290mA is wanted with 13.8V
then again with Hfe=100, then R2 will need to be about 4k7. Higher current can
be used, but only until the cells get hot!
Voltages less than 13.8V may not fully charge the battery as the cell voltage
can be as high as 1.35V/cell (12.15V for 9)! D1 can be a 1N4001, but a schottky
type 1N5817 may be better to get full charge with some batteries @ 13.8V
290mA charge for 14 hours should be the max rate for 100% charge on 2900mAH
cells & in use should give a good 8 hours discharge @ 300mA for 300 charge
discharge cycles of battery life.
Do not short out either R1 or R2 if presets are used! Use a series R of 1/2 the
total value with your preset.
The switch is any good 1A double pole slide/toggle type. With the switch in
CHARGE (OFF) position & no external power connection made, no current will flow
from the battery.
N.B. Do Not Switch to "ON" with 13,8V power connected. This will double the LED
current & shorten their life!
The battery pack & input supply need fuses, I suggest very thin 1A wire (relay
coil etc) be used to bridge PCB solder points at least 1cm apart, should
provide some short out safety (assuming, no inflammable material nearby!)
MOUNTING
The white LEDs need heat sinking or their lifetime is very short! At the talk
3x 3W LEDs (1Amp) were used with different lenses/reflectors to get a
reasonable beam spread, & were mounted in an aluminium U channel with special
sticky heatsink pads onto the back of the U channel.
ÜÜÜÜÜÜÜ
³Ú ||Þ _ Clips are mounted one the
³³\_||Þ/~ ~\. rear to fit the handlebar.
³³(±||Þ The battery pack was
³³/~||Þ\_ _/' actually separate in
³À ||Þ ~ a drinks canister.
ßßßßßßß
See my bul "Cheap Battery/12v LED Light", "LED Lights", "Windup Torch info",
"Recovering Old NICAD/NIMH Cells", & "7AH "F" NiCad Battery Pack".
Why Don't U send an interesting bul?
73 de John G8MNY @ GB7CIP
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