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.

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

Mike S Car Battery Charger - what's the switch for? Saturday, May 10, 2008 7:01:53 AM

Hi, I was wondering if anyone's built this ct. and had it working 100% correctly - following the schematic exactly. Also, what's the switch for? It looks like it temporarily stops charging but I'm not sure about that. And why doesn't the author reply to any of the questions that have been asked here? Thanks, Mike

anonymous Car Battery Charger Monday, May 05, 2008 8:16:54 PM

can anybody please explain how the circuit works? i'm a beginner in electronics

naleli macclay Ni-Cd checker Friday, April 25, 2008 8:36:53 AM

its my first time, to visit this site so i guess am impressed.

anonymous Car Battery Charger Monday, April 21, 2008 12:45:37 PM

This circuit is "old" and right out of National Semiconductors LM138 "Typical Applications". It works well... ~20 years ago I built a 40A version... and it's still running today.

Tom Car Battery Charger Friday, April 18, 2008 12:04:35 PM

Hey, I am looking to build a battery charger, but my application is for a battery powered welder. So I will be pulling approximately 100 amps off of the batteries. Will it hurt this charger to be connected when drawing 100 amps off the batteries? If so, is there a clever way to make the battery charger disconnect when the battery amperage is high? Thanks

Ilya Car Battery Charger Tuesday, April 15, 2008 3:26:31 PM

What changes should be made to the circuit in order to use it for a 12V battery. Also, the battery I am planning to use is a higher current battery than an average car battery. Should I consider making any changes to the circuit? Thank you.

anonymous Car Battery Charger Friday, April 04, 2008 7:01:58 PM

jotham - "quote from the author" "When the battery is fully charged, the circuit switches off and lights a LED, telling you that the cycle has finished." vicky - id check the transistor Q1, it has to be PNP and properly connected so the led works properly, also check the ouput of the OP amp, it should be connected to the base of Q1, maybe thats it... Anonymous (Feb 19) - well duh , go to walmart or something, this site isnt meant for that Anonymous (Feb 8) - (N1/N2) = (V1/V2) so the turn ratio should be directly proportional to the given voltages, but considering current calculations (wich i dont have at hand now) getting the laminated nucleus, etc... you are better off buying one than making one, they are usually sold in voltage and current rating, like " a 120 VAC to XXVAC XAmps transformer" Anonymous Feb01 - it is most likely to work, i mean... voltage isnt much of an issue as long as its higher than 14 volts or so, however as you can see in the power supply he suggests a 5A bridge rectifier, if the circuit draws that much current and your solar panel doesnt handle at least that much current things might not work out, id like to know the maximum current the circuit draws

Olebak Car Battery Charger Friday, April 04, 2008 4:50:02 PM

I'm a bit confused about this charger . 1 the LED is always on when power is applied to the circuit, 2 how does this comparator operate and what is it comparing. could you please elaborate a bit more on how the circuit operates please. Any one who can help please do.

Chris Dreyer Car Battery Charger Sunday, March 23, 2008 5:19:17 AM

HI, THANK YOU FOR A VERY USEFUL ARTICAL. SOMEWHAT A NOVICE WITH CERTAIN ASPECTS OF ELECTRONICS AND CHARGERS, I NEED TO ASKED A QUESTION OR TWO. IN SOUTH AFRICA WE EXPERINCE A LOT OF POWER FAILURES AND HAVE TO FIND ALTERNATIVES TO ATTEND TO THE ESSENTIALS, LIKE MY MOTHER BEEN ON OXGESION. 1. CAN THIS CHARGER CHARGES TWO BATTERIES SIMILTANEOUSLY? (TWO 12 V BATERIES IN PARALLEL) 2. WHAT ARE THE MAXIUM O/P CURRENT THE CHARGER GIVEN THE FACT I WANT TO CHARGE TWO BATTERIES SIMILTAIONSLY. YOUR FEEDBACK WILL BE APPRECIATED. REGARDS CHRIS

santhosh Car Battery Charger Wednesday, March 12, 2008 10:17:03 AM

I have a battery but i don't know the Ah of the battery.It is a motorcycle battery.can i charge it with this circuit.What will be cost of this project?

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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

Mike S	Car Battery Charger - what's the switch for?	Saturday, May 10, 2008 7:01:53 AM
Hi, I was wondering if anyone's built this ct. and had it working 100% correctly - following the schematic exactly. Also, what's the switch for? It looks like it temporarily stops charging but I'm not sure about that. And why doesn't the author reply to any of the questions that have been asked here? Thanks, Mike
anonymous	Car Battery Charger	Monday, May 05, 2008 8:16:54 PM
can anybody please explain how the circuit works? i'm a beginner in electronics
naleli macclay	Ni-Cd checker	Friday, April 25, 2008 8:36:53 AM
its my first time, to visit this site so i guess am impressed.
anonymous	Car Battery Charger	Monday, April 21, 2008 12:45:37 PM
This circuit is "old" and right out of National Semiconductors LM138 "Typical Applications". It works well... ~20 years ago I built a 40A version... and it's still running today.
Tom	Car Battery Charger	Friday, April 18, 2008 12:04:35 PM
Hey, I am looking to build a battery charger, but my application is for a battery powered welder. So I will be pulling approximately 100 amps off of the batteries. Will it hurt this charger to be connected when drawing 100 amps off the batteries? If so, is there a clever way to make the battery charger disconnect when the battery amperage is high? Thanks
Ilya	Car Battery Charger	Tuesday, April 15, 2008 3:26:31 PM
What changes should be made to the circuit in order to use it for a 12V battery. Also, the battery I am planning to use is a higher current battery than an average car battery. Should I consider making any changes to the circuit? Thank you.
anonymous	Car Battery Charger	Friday, April 04, 2008 7:01:58 PM
jotham - "quote from the author" "When the battery is fully charged, the circuit switches off and lights a LED, telling you that the cycle has finished." vicky - id check the transistor Q1, it has to be PNP and properly connected so the led works properly, also check the ouput of the OP amp, it should be connected to the base of Q1, maybe thats it... Anonymous (Feb 19) - well duh , go to walmart or something, this site isnt meant for that Anonymous (Feb 8) - (N1/N2) = (V1/V2) so the turn ratio should be directly proportional to the given voltages, but considering current calculations (wich i dont have at hand now) getting the laminated nucleus, etc... you are better off buying one than making one, they are usually sold in voltage and current rating, like " a 120 VAC to XXVAC XAmps transformer" Anonymous Feb01 - it is most likely to work, i mean... voltage isnt much of an issue as long as its higher than 14 volts or so, however as you can see in the power supply he suggests a 5A bridge rectifier, if the circuit draws that much current and your solar panel doesnt handle at least that much current things might not work out, id like to know the maximum current the circuit draws
Olebak	Car Battery Charger	Friday, April 04, 2008 4:50:02 PM
I'm a bit confused about this charger . 1 the LED is always on when power is applied to the circuit, 2 how does this comparator operate and what is it comparing. could you please elaborate a bit more on how the circuit operates please. Any one who can help please do.
Chris Dreyer	Car Battery Charger	Sunday, March 23, 2008 5:19:17 AM
HI, THANK YOU FOR A VERY USEFUL ARTICAL. SOMEWHAT A NOVICE WITH CERTAIN ASPECTS OF ELECTRONICS AND CHARGERS, I NEED TO ASKED A QUESTION OR TWO. IN SOUTH AFRICA WE EXPERINCE A LOT OF POWER FAILURES AND HAVE TO FIND ALTERNATIVES TO ATTEND TO THE ESSENTIALS, LIKE MY MOTHER BEEN ON OXGESION. 1. CAN THIS CHARGER CHARGES TWO BATTERIES SIMILTANEOUSLY? (TWO 12 V BATERIES IN PARALLEL) 2. WHAT ARE THE MAXIUM O/P CURRENT THE CHARGER GIVEN THE FACT I WANT TO CHARGE TWO BATTERIES SIMILTAIONSLY. YOUR FEEDBACK WILL BE APPRECIATED. REGARDS CHRIS
santhosh	Car Battery Charger	Wednesday, March 12, 2008 10:17:03 AM
I have a battery but i don't know the Ah of the battery.It is a motorcycle battery.can i charge it with this circuit.What will be cost of this project?