Car Battery Charger

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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

Part	Total Qty.	Description	Substitutions
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

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.

A heatsink will be needed for U1.

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.

If you want to use the charger without having to provide an external power supply, use the following circuit.

This is the schematic of the Car Battery Charger Power Supply

Part Total Qty. Description Substitutions

C1 1 6800uF 25V Electrolytic Capcitor

T1 1 3A 15V Transformer

BR1 1 5A 50V Bridge Rectifier 10A 50V Bridge Rectifier

S1 1 5A SPST Switch

F1 1 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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Comments

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Max Car Battery Charger Friday, June 25, 2010 1:15:25 PM

Thats a great circuit ! I am gonna use it as a storage battery charger. Thank You

siamak Car Battery Charger Sunday, June 20, 2010 11:41:25 PM

the circuit that u suggested has 18v input i think it should be DC voltage and as you know a 12v AC transformer after passing throgh a diode bridge give 18v DC( 12x2 root squire). so i think a 12vAC transformer with 3 amp current are enough for this circuit, is it ok?

Spooge Car Battery Charger Friday, May 28, 2010 8:38:17 AM

Nice circuit. what needs to be changed if i want to make it charge a 140 amp battery quckly. I need a 10A to 20Amps charger at least, For my ups, we get 4-5hrs blackout here every day.

fabieville Car Battery Charger Tuesday, March 16, 2010 7:57:01 AM

how do you wire several LM350's in parallel to use with this circuit? I tried wire 3 in parallel but it didn't work. So can u either show me a circuit with several wired that can use in this circuit or just explain as to how to do it please.

mojtaba Car Battery Charger Wednesday, March 10, 2010 2:45:25 PM

can you Substitute R1 500ohm with a 510? and R5 230 with a 220 i am unable to find them. thank you

gajah_gendut Car Battery Charger Wednesday, February 03, 2010 10:22:10 PM

for higher current about 5A, you can replace U1 with LM138/LM338

georgi Car Battery Charger Wednesday, January 20, 2010 2:24:24 PM

R1 1/4W ??? Out 3A R7 10W ???

baraa Car Battery Charger Friday, January 08, 2010 6:47:26 AM

what is the current output rating of this charger? cuz all of these equipment have current rating of milli amps i am an electrical engineering student but i haven't dealth with car batteries much, are all of them 12V (i mean to ask about the output voltage rating) thx a lot

brockster Car Battery Charger Monday, December 07, 2009 11:17:37 PM

@Woody: Oops, my error. The LM350 limits the maximum charge rate to 3 amps, not 2 amps. Running at 3 amps, you will need to heat sink the LM350 fairly well, even if the input voltage is only 18 volts or so.

brockster Car Battery Charger Monday, December 07, 2009 11:04:58 PM

Thanks for posting this useful circuit! @Randy: Yes, you can substitute 510 ohms for the 500 ohm resistor. Better yet, just use a diode, such as a 1N4006. The cathode side should point toward the "in" terminal in the schematic. @zizo: Yes, you can substitute any similar "small signal" type diode as long as it can handle 200 ma of current and 70 volts of repetitive reverse voltage. The popular 1N4148 ought to work. @anonymous: Use the momentary switch as indicated. This is just a "force to start the charge cycle" button. The cricuit may start charging even without pressing this button. You can find momentary switches at Radio Shack or any electronics parts shop. @Woody: The maximum charge rate is limited to 2 amps. This is set internally by the LM350 voltage regulator. @Martins and Umar: To get more output current you would need to add a "current pass" transistor to the circuit or use several LM350's in parallel. You would be better off not using this circuit and simply using another circuit rated at 10A. See the application circuits in the LM350 datasheet (link below) for ideas. @All: This circuit is from the LM350 datasheet. See this circuit, and other charger ideas, in the datasheet at http://cache.national.com/ds/LM/LM350.pdf

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Max	Car Battery Charger	Friday, June 25, 2010 1:15:25 PM
Thats a great circuit ! I am gonna use it as a storage battery charger. Thank You
siamak	Car Battery Charger	Sunday, June 20, 2010 11:41:25 PM
the circuit that u suggested has 18v input i think it should be DC voltage and as you know a 12v AC transformer after passing throgh a diode bridge give 18v DC( 12x2 root squire). so i think a 12vAC transformer with 3 amp current are enough for this circuit, is it ok?
Spooge	Car Battery Charger	Friday, May 28, 2010 8:38:17 AM
Nice circuit. what needs to be changed if i want to make it charge a 140 amp battery quckly. I need a 10A to 20Amps charger at least, For my ups, we get 4-5hrs blackout here every day.
fabieville	Car Battery Charger	Tuesday, March 16, 2010 7:57:01 AM
how do you wire several LM350's in parallel to use with this circuit? I tried wire 3 in parallel but it didn't work. So can u either show me a circuit with several wired that can use in this circuit or just explain as to how to do it please.
mojtaba	Car Battery Charger	Wednesday, March 10, 2010 2:45:25 PM
can you Substitute R1 500ohm with a 510? and R5 230 with a 220 i am unable to find them. thank you
gajah_gendut	Car Battery Charger	Wednesday, February 03, 2010 10:22:10 PM
for higher current about 5A, you can replace U1 with LM138/LM338
georgi	Car Battery Charger	Wednesday, January 20, 2010 2:24:24 PM
R1 1/4W ??? Out 3A R7 10W ???
baraa	Car Battery Charger	Friday, January 08, 2010 6:47:26 AM
what is the current output rating of this charger? cuz all of these equipment have current rating of milli amps i am an electrical engineering student but i haven't dealth with car batteries much, are all of them 12V (i mean to ask about the output voltage rating) thx a lot
brockster	Car Battery Charger	Monday, December 07, 2009 11:17:37 PM
@Woody: Oops, my error. The LM350 limits the maximum charge rate to 3 amps, not 2 amps. Running at 3 amps, you will need to heat sink the LM350 fairly well, even if the input voltage is only 18 volts or so.
brockster	Car Battery Charger	Monday, December 07, 2009 11:04:58 PM
Thanks for posting this useful circuit! @Randy: Yes, you can substitute 510 ohms for the 500 ohm resistor. Better yet, just use a diode, such as a 1N4006. The cathode side should point toward the "in" terminal in the schematic. @zizo: Yes, you can substitute any similar "small signal" type diode as long as it can handle 200 ma of current and 70 volts of repetitive reverse voltage. The popular 1N4148 ought to work. @anonymous: Use the momentary switch as indicated. This is just a "force to start the charge cycle" button. The cricuit may start charging even without pressing this button. You can find momentary switches at Radio Shack or any electronics parts shop. @Woody: The maximum charge rate is limited to 2 amps. This is set internally by the LM350 voltage regulator. @Martins and Umar: To get more output current you would need to add a "current pass" transistor to the circuit or use several LM350's in parallel. You would be better off not using this circuit and simply using another circuit rated at 10A. See the application circuits in the LM350 datasheet (link below) for ideas. @All: This circuit is from the LM350 datasheet. See this circuit, and other charger ideas, in the datasheet at http://cache.national.com/ds/LM/LM350.pdf