Car Battery Charger

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.

Schematic-

Parts List-
R1 - 1 - 500 Ohm 1/4 W Resistor
R2 - 1 - 3K 1/4 W Resistor
R3 - 1 - 1K 1/4 W Resistor
R4 - 1 - 15 Ohm 1/4 W Resistor
R5 - 1 - 230 Ohm 1/4 W Resistor
R6 - 1 - 15K 1/4 W Resistor
R7 - 1 - 0.2 Ohm 10 W Resistor
C1 - 1 - 0.1uF 25V Ceramic Capacitor
C2 - 1 - 1uF 25V Electrolytic Capacitor
C3 - 1 - 1000pF 25V Ceramic Capacitor
D1 - 1 - 1N457 Diode
Q1 - 1 - 2N2905 PNP Transistor
U1 - 1 - LM350 Regulator
U2 - 1 - LM301A Op Amp
S1 - 1 - Normally Open Push Button Switch
MISC - 1 - Wire, Board, Heatsink For U1, Case, Binding Posts or Alligator Clips For Output

Notes-
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.

5) 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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Automatic 12V Lead Acid Battery Charger Circuit

This charger will charge any 12V lead acid battery including flooded, gel and AGM. It is fully automatic and will charge at a rate up to about 4A until the battery voltage reaches a preset point at which it will switch to a very low current float charge. If the battery voltage drops again the charger will begin charging until the voltage once again reaches the cut off point. In this way it can be left connected to a battery indefinitely to maintain full charge without causing damage. An LED indicates when the battery is fully charged.

Schematic-

Parts List-
R1, R3 - 2 - 330 Ohm 1/4W Resistor
R2 - 1 - 100 Ohm 1/4W Pot
R4, R5, R7, R8 - 4 - 82 Ohm 2W Resistor
R6 - 1 - 100 Ohm 1/4W Resistor
R9 - 1 - 1K 1/4W Resistor
C1 - 1 - 220uF 25V Electrolytic Capacitor
D1 - 1 - P600 Diode Any 50V 5A or greater rectifier diode
D2 - 1 - 1N4004 Diode 1N4002, 1N4007
D3 - 1 - 5.6V Zener Diode
D4 - 1 - LED (Red, Green or Yellow)
Q1 - 1 - BT136 TRIAC
Q2 - 1 - BRX49 SCR
T1 - 1 - 12V 4A Transformer See Notes
F1 - 1 - 3A Fuse
S1 - 1 - SPST Switch, 120VAC 5A
MISC - 1 - Wire, Board, Heatsink For U1, Case, Binding Posts or Alligator Clips For Output, Fuse Holder

Notes-
1. R2 will have to be adjusted to set the proper finish charge voltage. Flooded and gel batteries are generally charged to 13.8V. If you are cycling the battery (AGM or gel) then 14.5V to 14.9V is generally recommended by battery manufacturers. To set up the charger, set the pot to midway, turn on the charger and then connect a battery to it's output. Monitor the charge with a voltmeter until the battery reaches the proper end voltage and then adjust the pot until the LED glows steadily. The charger has now been set. To charge multiple battery types you can mount the pot on the front of the case and have each position marked for the appropriate voltage.

2. Q1 will need a heatsink. If the circuit is mounted in a case then a small fan might be necessary and can generally be powered right off the output of D1.

3. T1 is a transformer with a primary voltage appropriate to your location (120V, 220V, etc.) and a secondary around 12V. Using a higher voltage secondary (16V-18V) will allow you to charge 16V batteries sometimes used in racing applications.

4. If the circuit is powered off, the battery should be disconnected from it's output otherwise the circuit will drain the battery slowly.

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