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G8MNY  > TECH     03.05.25 17:56l 129 Lines 5220 Bytes #0 (0) @ WW
BID : 31758_GB7CIP
Subj: LED Bike Light
Path: JH4XSY<JE7YGF<LU4ECL<LU9DCE<EA2RCF<I0OJJ<GB7CIP
Sent: 250503/0845Z @:GB7CIP.#32.GBR.EURO #:31758 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
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
 ﾚﾄﾄﾄo\ﾄﾄﾄｿ       ﾚﾄﾄﾄRﾄﾄﾄo\ﾄﾄﾄｿ        ﾚﾄﾄﾄﾄo\ﾄﾄﾄﾄｿ        ﾚﾄﾄﾄﾄo\ﾄﾄﾄﾄﾄｿ
LEDs    NiMH     LEDs        NiMH      LEDs      NiMH      LEDs       NiMH
 ｳ     Battery    ｳ         Battery     ｳ       Battery     ｳ         Battery
 ﾀﾄﾄﾄﾄﾄﾄﾄﾄﾙ       ﾀﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾙ         \ｳConst   ｳ      Output<-FBｿ   ｳ
                                        e/ｳ I      ｳ        ﾀﾄﾄﾄﾄﾄRﾄﾁﾄﾄﾄﾙ
                                        ﾀﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾙ
This is the sort of LED current (light) graph with 3 LEDs powered from 9 cells.

          Direct
  LED I   No R:short     .'Typical
600mA ｴ   life:time     �  Series R
      ｳ       :       .'    (5R)
400mA ｴ       :      �
      ｳ      �     .'
300mA ｴ     .  ___:..----ﾄﾄﾄﾄ Max Rated LED Current
      ｳ      .' �             from constant current
200mA ｴ    '/ .'              transistor's collector
      ｳ   �/ �
100mA ｴ  ./.'
      ｳ.�/�               Just
    0 ｴFlat     Norm     Charged
      ﾃﾄﾄﾄﾄﾄﾂﾄﾄﾄﾄﾁﾂﾄﾄﾄﾄﾄﾂﾄﾄﾄﾄﾄﾂﾄ 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/
       ﾚﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄﾄﾄﾄﾄﾄﾄo  /oﾄﾄﾄﾄﾄﾄﾄｴ<ﾃﾄﾄﾂﾄﾄﾄﾄoﾄoﾄﾄﾄo +13.8V
 3    _ｳ_      ｳ          ｳ CHARGE   D1  ｳ    fuse
     �\_/      ｳ         _ｳ_+            ｳ    link
 1W   _ｳ_(10V) ｳ         _ﾜ_ 9x AAs      ｳ
     �\_/      ｳ         _ﾜ_ 2.9AH       ｳ
WHITE _ｳ_      R1        _ﾜ_  NiMh       ｳ
     �\_/      ｳ          ｳ (10.8V)      ｳ
LEDs   ｳ       ｳ          o              ｳ
       ｳ       ｳ   OFF/   | Fuse         ｳ
       ｳ       ｳ  CHARGE  o link         ｳ
       ﾀﾄﾄﾄﾂﾄﾄﾄ)ﾄﾄﾄﾄﾄﾄﾄo  ｳ              ｳ
   300mA   ｳ   ｳ        \_ｳ              ｳ
           ｳ   ｳ    ON o                 ｳ
            \ｳ ｳ       ｳ                 ｳ
          NPNﾃﾄﾁﾄﾄﾄﾄﾄﾄﾄ)ﾄﾄﾄﾄﾄﾄﾄﾄR2ﾄﾄﾄﾄﾄﾄﾄﾙ
           e/ｳ         ｳ
           ﾀﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄo -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.

  ﾜﾜﾜﾜﾜﾜﾜ
  ｳﾚ  ||ﾞ  _       Clips are mounted one the
  ｳｳ\_||ﾞ/~ ~\.    rear to fit the handlebar.
  ｳｳ(ｱ||ﾞ          The battery pack was
  ｳｳ/~||ﾞ\_ _/'    actually separate in
  ｳﾀ  ||ﾞ  ~       a drinks canister.
  ﾟﾟﾟﾟﾟﾟﾟ


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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