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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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

Tim Car Battery Charger Sunday, December 06, 2009 4:41:52 PM

I'm a mechanical engineering student working on a senior design project. All the electrical stuff is a little out of my element. I'm needing a circuit to charge a 12v car battery from a DC generator. Would this circuit be what i'm looking for?

Randy Car Battery Charger Friday, November 06, 2009 6:20:15 PM

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

anonymous Car Battery Charger Saturday, September 12, 2009 9:54:40 AM

can i replace this switch with a non momentary switch

zizo Car Battery Charger Thursday, September 03, 2009 8:42:33 AM

I could'nt find D1 1N457 Diode. What can use else instead of it ??? is there any substitution ?? thank you.

woody Car Battery Charger Thursday, July 16, 2009 9:09:10 PM

I like your circuit but the info does not state the maximum current charge rate. please state same. thanks.

umar Car Battery Charger Saturday, July 11, 2009 3:12:11 AM

Thank's for your circuit. I need a battery charger that can charge 12 V 10 A. what can I do for that problem, can You send me circuit for that? Thank's....

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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
Tim	Car Battery Charger	Sunday, December 06, 2009 4:41:52 PM
I'm a mechanical engineering student working on a senior design project. All the electrical stuff is a little out of my element. I'm needing a circuit to charge a 12v car battery from a DC generator. Would this circuit be what i'm looking for?
Randy	Car Battery Charger	Friday, November 06, 2009 6:20:15 PM
can you Substitute R1 500ohm with a 510? and R5 230 with a 220 i am unable to find them. thank you
anonymous	Car Battery Charger	Saturday, September 12, 2009 9:54:40 AM
can i replace this switch with a non momentary switch
zizo	Car Battery Charger	Thursday, September 03, 2009 8:42:33 AM
I could'nt find D1 1N457 Diode. What can use else instead of it ??? is there any substitution ?? thank you.
woody	Car Battery Charger	Thursday, July 16, 2009 9:09:10 PM
I like your circuit but the info does not state the maximum current charge rate. please state same. thanks.
umar	Car Battery Charger	Saturday, July 11, 2009 3:12:11 AM
Thank's for your circuit. I need a battery charger that can charge 12 V 10 A. what can I do for that problem, can You send me circuit for that? Thank's....