LM317 Battery Charger
According to the battery manufacturers, a battery should be charged with only 1/10 current (in ampere), of its Ah value.
For example, if a battery is of 7Ah value, then it should be charged with 0.7 Ampere current. Charging a battery using this rule, extends the battery life.
| PARTS LIST | |
| R1 | 0.56Ω 5W |
| R2 | 470Ω |
| R3 | 120Ω |
| R4 | 100Ω |
| VR1 | 220Ω |
| D1 | 5A Diode Bridge |
| C1 | 1000 µF 50V |
| C2 | 0.22 µF |
| C3 | 0.22 µF |
| T1 | BC140 |
| IC1 | LM317 |
| T1 | Secondary 15V, 3AMP Transformer |
| Other | Good Heat sink |
LM317 Regulator IC Pin Configuration
BC140 Transistor Pin Configuration
- Charging current is controlled by T1, R1, and R4. VR1 is used to set the charging current.
- As the battery gets charged, the current flowing through the R1 increases. This result in increase in the current and voltage from the LM317.
- When the battery becomes fully charged, charger reduces the charging current to the battery, and the battery is charged in trickle charging mode.
- The input at LM317 should be around 3 volts higher than the output voltage from the LM317. As this IC requires minimum 3-volts for its operation.
- As this IC gets very hot during operation, a good heat sink should be used with this IC.
Please send your ideas, those are very important for our success…
#1 by jawahar on July 15th, 2011
i think it would be more clear if you explain the working of T1,R1,R4 as current limitors.
thanking you.
awaiting your explanation