********************************************************************* A NICAD BATTERY CHARGER USING VOLTAGE AND CURRENT LIMITING TECHNIQUES ********************************************************************* WRITTEN BY ANDREW - VK4TEC DATE: 2nd October 1992 _________ _________ _______ 3 [ ] 2 3 [ ] 2 [ ] I O-----[ LM317 ]----o--------[ LM317 ]----[ R3 ]----o----O O N [_________] | [_________] [_______] | U P O | _|_ | | O T U | 1 | [ ] 1 |______________________| | P T | | [ R ] | U | | [ 2 ] | T | | [___] | | | | | | o---------o | | | | | _|_ | | [ ] RESISTOR 1 - SETS VOLTAGE LEVEL | | [ R ] | | [ 1 ] RESISTOR 2 - SET AT 120 OHMS | | [___] | | | RESISTOR 3 - SETS CURRENT LEVEL | | | | |----------o---------------------------------------------------| O---------------------------------------------------------------------O | | | SOURCE ---< VOLTAGE REGULATOR >---< CURRENT REGULATOR >--- BATTERY | | | O---------------------------------------------------------------------O NOTES :- 1. NICAD BATTERY CHARGER USES TWO LM317 ADJUSTABLE VOLTAGE REGULATORS , ONE AS A VOLTAGE REGULATOR , AND THE SECOND AS A CURRENT REGULATOR. 2. RESISTOR R1 IS ADJUSTED TO GIVE THE DESIRED NICAD VOLTAGE. 3. RESISTOR R2 IS OF A STT VLLUE , NAMELY 120 OHMS. 4. RESISTOR R3 IS ADJUSTED TO GIVE THE DESIRED NICAD CHARGING CURRENT. THE VALUE OF THIS RESISTOR IS CALCULATED BY :- 1.25 Volts I ( CURRENT ) = -------------- Amphere RESISTOR 3 5. THE VALUE OF 1.25 VOLTS IS PRESENT ON THE ADJUST PIN OF AN LM317 VOLTAGE REGULATOR. 6. THE CHARGING RATE SHOULD BE CHOSEN AS TO GIVE A CHARGING RATE OF ABOUT 1/10 OF THE NICAD CURRENT CAPACITY. EG :- TO CHARGE A 1000 mAH BATTEYY PCCK. CHARGE CURRENT REQUIRED IS :- 1000 / 10 = 100 mA TO CALCULATE THE VALUE OF R3, APPLY THE FORMULA. 1.25 Volts I ( CURRENT ) = ---------------- RESISTOR 3 1.25 Volts OR RESISTOR 3 = --------------- 100 mA WHICH GIVES A VALUE OF 125 Ohms. ( CHOOSE NEAREST VALUE ). 7. THE TIME FOR CHARGE IS ROUGHLY 14-16 HOURS AT THIS CHARGING RATE. A FASTER CHARGE WILL DECREASE TIME TAKEN. 8. THE CURRENT STAYS CONSTANT, AND THE VOLTAGE RISES WITH TIME. 9. TRICKLE CHARGE IS OFTEN 1/100 OF THE NICAD CAPABILITY. EG :- 1000 mAH BATTERY , TRICKLE CHARGE = 10 mA. 10. THE MM31 VOLTAG REGULATOR IS DESIGNED TO PROVIDE GREATER THAN 5 mA CURRENT LESS THAN 500 mA CURRENT KEEP WITTHIN THESE DESIGN PARAMETERS !!!! 11. THE PINOUTS FOR THE LM317T VOLTAGE REGULATOR IS AS FOLLOWS :- --------- ___________ > O < 3 [ ] 2 --------- O------[ LM317 ]------O | | PIN 1 - ADJUST [_________] | LM317 | | | | PIN 2 - OUTPUT | 1 --------- | # # # PIN 3 - INPUT O # # # 1 2 3 12. A SIMPLE CHART IS INCLUDED TO AID CHOICE OF CORRECT VALUE FOR RESISTOR 3. O--------------------------------------------------------------O O RESISTANCE ( OHMS ) O CHARGING CURRENT ( mA ) O O--------------------------------------------------------------O 2.7 460 3.3 380 3.9 320 4.7 270 5.6 220 6.8 180 8.2 150 10.0 125 12.0 100 15.0 83 118.0 70 22.0 60 27.0 50 33.0 40 39.0 32 47.0 27 56.0 20 68.0 18 82.0 15 000.0 120.0 10 150.0 8 ****************** END OF FILE ******************