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

Schematic of the 12V automatic battery charger

Parts
Part
Total Qty.
Description
Substitutions
R1, R32330 Ohm 1/4W Resistor
R21100 Ohm 1/4W Pot
R4, R5, R7, R8482 Ohm 2W Resistor
R61100 Ohm 1/4W Resistor
R911K 1/4W Resistor
C11220uF 25V Electrolytic Capacitor
D11P600 DiodeAny 50V 5A or greater rectifier diode
D211N4004 Diode1N4002, 1N4007
D315.6V Zener Diode
D41LED (Red, Green or Yellow)
Q11BT136 TRIAC
Q21BRX49 SCR
T1112V 4A TransformerSee Notes
F113A Fuse
S11SPST Switch, 120VAC 5A
MISC1Wire, 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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Comments

BAKARE OLUFEMI
Automatic 12V Lead Acid Battery Charger
Tuesday, May 13, 2008 9:23:44 AM
yeah i need to know how i can improve or simply step up my charger capacty cos 4A is very small to charge my device so i can i step it up i have built my inverter but i need to incorporate the charger circuit into it and the battery i used is 200Ahx 6 so help me out on how to get a suitable charger
frank
Automatic 12V Lead Acid Battery Charger
Saturday, May 10, 2008 8:24:47 PM
Can i use my 6A 12V transformer on this circuit? I need your advise sir, and reply me, Thank you.
Alejandro Bemporat
Automatic 12V Lead Acid Battery Charger
Monday, April 28, 2008 2:44:48 PM
Hi i will like to make a 36VDC charger 20AMPs if you can help me TKS
TAUQEER
Automatic 12V Lead Acid Battery Charger
Monday, April 28, 2008 2:32:15 PM
Sir Thanks a lot of your its a very helpful circuit.
mohy
Automatic 12V Lead Acid Battery Charger
Sunday, April 27, 2008 12:05:57 PM
it's very good inormations and design . what do you mean by U1? in last raw of part table
Alfred
Automatic 12V Lead Acid Battery Charger
Sunday, April 27, 2008 5:40:14 AM
Dear sir i am designing solar charger to charge a 12V Acid Battery with 185 AH (Amp per hour). the solar cell is 12V, i can run 12V energy saver with the cell. what kind of modifications will be done in above circuit to charge battery thanks
ashimas
Automatic 12V Lead Acid Battery Charger
Friday, April 25, 2008 1:40:54 AM
Sir, I am using this circuit for 6V battery.but the current flowing through the circuit is not as per our requirement.Please give the circuit diagram and working for 6V battery with current less than 0.2A.
GOPAL
Automatic 12V Lead Acid Battery Charger
Tuesday, April 22, 2008 6:22:47 AM
OK THIS CIRCUIT IS OLD TYPE.NO PROTECTION.
jawad
Automatic 12V Lead Acid Battery Charger
Monday, April 21, 2008 3:33:24 PM
Is this circuit workable for batteries from 50 to 175AHr? if not what changes required to do so, also how much harm this circuit can does to battery, is it reliable to work as first part of UPS.
Benjamin Naworio
Automatic 24V Lead Acid Battery Charger
Monday, April 21, 2008 10:29:20 AM
How do I modify automatic 12v lead acid battery charger to Automatic 24V Lead Acid Battery Charger.
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