Automatic 12V Lead Acid Battery Charger

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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

Part	Total Qty.	Description	Substitutions
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

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.

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.

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.

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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Comments

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soundar Automatic 12V Lead Acid Battery Charger Monday, May 20, 2013 5:17:23 AM

hi..... how to add 2 or 3 batterys to this same circuit........???

faz Automatic 12V Lead Acid Battery Charger Monday, April 01, 2013 6:36:41 AM

i can't found the TRIAC BT136 but can i use TRIAC BT139 instead of TRIAC BT136? and can i use BC548 or BC558 instead of BRX49 SCR? and can i use IN4004 diode instead of P600 Diode? please help me. i need to complete my project urgent.

anonymsamaduSAloussa Automatic 12V Lead Acid Battery Charger Monday, April 01, 2013 5:24:52 AM

i assembled a 12v charger only using 1no center tap 12-0-12 transformer 4amp and 8nos of power diode 4nos for each side and charged 120AH BATT WITHIN 8HOURS. CHARGING CURRENT FOUND 10AMP. NO MORE COMPONENT USED. WHAT WILL BE THE DEMERITS ON IT .

anonymous Automatic 12V Lead Acid Battery Charger Wednesday, December 12, 2012 8:07:15 AM

pls how can this circuit be reconfigured to charge two 12V/15Ah sealed lead -acid batteries using a 27 or 28 volts AC/DC converter

kimura Automatic 12V Lead Acid Battery Charger Thursday, November 08, 2012 4:46:08 AM

i made that cct n its working good, used full wave rectification coz D1 introduce high resistance, n BT151 for brx49,

Dileep Naik Automatic 12V Lead Acid Battery Charger Wednesday, November 07, 2012 6:21:09 AM

Dear sir, We try to make the circuit but at the output we are getting voltage between 6.3 v to 7.38v only. Connected LED D4 is not glowing. We are connected 3v red LED. Please guide us how to get complete 12 v for charging the battery. We also connected 12v chargable battery at output but we are not getting 12v at the output.

anonymous Automatic 12V Lead Acid Battery Charger Wednesday, July 11, 2012 2:31:03 AM

hi been wondering whether Vac or Vdc is used to power the device? i tried making it but it failed to power up. please send me an email. thanks!

emmanuel Automatic 12V Lead Acid Battery Charger Friday, May 18, 2012 4:26:23 AM

Dr. thanks for the good work, Please how long will it take to charge 12V 200AH battery and how will i change the design to charge the battery within 5hrs Please send me the reply if possible with the circuit diagram to my email

tjolle62 Automatic 12V Lead Acid Battery Charger Tuesday, May 08, 2012 5:45:05 PM

Hello, I'm going to build this nice gel charger and i womder what values and components do i need to change for a 24V feed ?

wempire Automatic 12V Lead Acid Battery Charger Saturday, April 28, 2012 4:48:55 AM

third class circuit dont try to assemble otherwise you will loos your mony and time

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soundar	Automatic 12V Lead Acid Battery Charger	Monday, May 20, 2013 5:17:23 AM
hi..... how to add 2 or 3 batterys to this same circuit........???
faz	Automatic 12V Lead Acid Battery Charger	Monday, April 01, 2013 6:36:41 AM
i can't found the TRIAC BT136 but can i use TRIAC BT139 instead of TRIAC BT136? and can i use BC548 or BC558 instead of BRX49 SCR? and can i use IN4004 diode instead of P600 Diode? please help me. i need to complete my project urgent.
anonymsamaduSAloussa	Automatic 12V Lead Acid Battery Charger	Monday, April 01, 2013 5:24:52 AM
i assembled a 12v charger only using 1no center tap 12-0-12 transformer 4amp and 8nos of power diode 4nos for each side and charged 120AH BATT WITHIN 8HOURS. CHARGING CURRENT FOUND 10AMP. NO MORE COMPONENT USED. WHAT WILL BE THE DEMERITS ON IT .
anonymous	Automatic 12V Lead Acid Battery Charger	Wednesday, December 12, 2012 8:07:15 AM
pls how can this circuit be reconfigured to charge two 12V/15Ah sealed lead -acid batteries using a 27 or 28 volts AC/DC converter
kimura	Automatic 12V Lead Acid Battery Charger	Thursday, November 08, 2012 4:46:08 AM
i made that cct n its working good, used full wave rectification coz D1 introduce high resistance, n BT151 for brx49,
Dileep Naik	Automatic 12V Lead Acid Battery Charger	Wednesday, November 07, 2012 6:21:09 AM
Dear sir, We try to make the circuit but at the output we are getting voltage between 6.3 v to 7.38v only. Connected LED D4 is not glowing. We are connected 3v red LED. Please guide us how to get complete 12 v for charging the battery. We also connected 12v chargable battery at output but we are not getting 12v at the output.
anonymous	Automatic 12V Lead Acid Battery Charger	Wednesday, July 11, 2012 2:31:03 AM
hi been wondering whether Vac or Vdc is used to power the device? i tried making it but it failed to power up. please send me an email. thanks!
emmanuel	Automatic 12V Lead Acid Battery Charger	Friday, May 18, 2012 4:26:23 AM
Dr. thanks for the good work, Please how long will it take to charge 12V 200AH battery and how will i change the design to charge the battery within 5hrs Please send me the reply if possible with the circuit diagram to my email
tjolle62	Automatic 12V Lead Acid Battery Charger	Tuesday, May 08, 2012 5:45:05 PM
Hello, I'm going to build this nice gel charger and i womder what values and components do i need to change for a 24V feed ?
wempire	Automatic 12V Lead Acid Battery Charger	Saturday, April 28, 2012 4:48:55 AM
third class circuit dont try to assemble otherwise you will loos your mony and time