Thursday, June 16, 2011

Car Battery Charger

  1. This charger will quickly and easily charge most any lead acid battery. The charger delivers full current until the current drawn by the battery falls to 150 mA. At this time, a lower voltage is applied to finish off and keep from over charging. When the battery is fully charged, the circuit switches off and lights a LED, telling you that the cycle has finished.

R1                         500ohm
R2                         3k
R3                         1k
R4                         15ohm
R5                         230ohm
R6                         15k
R7                         0.2ohm
C1                         0.1uF 25v ceramic capacitor
C2                         1uF 25v electrolytic capacitor
C3                         1000pF 25v ceramic capacitor
D1                         1N457 diode
Q1                          2N2905 pnp transistor
U1                          LM350 regulator
U2                          LM301A opamp
S1                          normally open push button switch
MICS                     wire,board,heatsink for u1,case,binding posts or alligator clips for output


  1. The circuit was meant to be powered by a power supply, which is why there is no transformer, rectifier, or filter capacitors on the schematic. There is no reason why you cannot add these.
  2. A heatsink will be needed for U1.
  3. To use the circuit, hook it up to a power supply/plug it in. Then, connect the battery to be charged to the output terminals. All you have to do now is push S1 (the "Start" switch), and wait for the circuit to finish.
  4. If you want to use the charger without having to provide an external power supply, use the following circuit.
C1             6800uF 25v electrolytic capacitor
T1              3A 15v transformer
BR1           5A 50v bridge rectifier
S1              5A SPST switch
F1              4A 250v fuse

The first time you use the circuit, you should check up on it every once and a while to make sure that it is working properly and the battery is not being over charged. 

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