12V Battery Absorb and Float Charger. 12v battery charger circuit

V Battery Absorb and Float Charger

Most battery chargers stop charging the battery when it attains its maximum charging voltage set by the circuit. This 12V battery charger circuit charges the battery at a particular voltage, that is, absorption voltage, and once the maximum charging voltage is attained, the charger changes the output voltage to float voltage for maintaining the battery at that voltage. Absorption and floating voltages are dependent on the type of battery.

For this charger, voltages are set for a sealed lead-acid (SLA) 12V, 7Ah battery, for which absorption voltage is 14.1V to 14.3V and floating voltage is 13.6V to 13.8V. For safe working and to avoid overcharging of battery, absorption voltage is selected as 14.1V and floating voltage is selected as 13.6V. These values are to be set as specified by the battery manufacturer.

V battery charger circuit

Circuit diagram of the 12V battery absorb and float charger is shown in Fig. 1. It is built around step-down transformer X1, adjustable voltage regulator LM317 (IC1), op-amp comparator LM358 (IC2) and a few other components. The 230V AC primary to 15V-0-15V, 1A secondary transformer used in this circuit steps down mains voltage, which is rectified by diodes D1 and D2 and smoothened by capacitor C1. This voltage is given to the input of LM317 for regulation.

The basic circuit is a regulated power supply using LM317, with a control on output by changing resistance at adjust pin 1. A good heat-sink is required for LM317. LM358 is a dual-operation amplifier that is used here to control overcharging of the battery. Capacitor C4 should be as near as possible to pin 1 of IC2. Jumper J1 is used for calibration (set-up). While setting the charging voltage, remove the jumper and connect it back after calibration.

For initial setup, remove jumper J1, switch off S2, switch on S1 and adjust potmeter VR2 to get 13.6V at test point TP2. Adjust potmeter VR3, so that LED2 begins to glow. Adjust potmeter VR1 to read 0.5V (difference of 14.1V and 13.6V) at test point TP1. Adjust VR2 to read 14.1V at test point TP2.

With these settings, TP2 should read 14.1V when there is low voltage at test point TP3, and 13.6V when there is high voltage at test point TP3. Connect jumper J1. The charger is now ready for use. Connect the 12V battery under charging (BUC), with correct polarity, at CON2. Switch on S2; one of the LEDs out of LED2 and LED3 will light up (most likely it would be LED2). If neither of these light up, check the connections; battery could be dead. Switch on S1 for charging. Fully charged status of the battery will be indicated by glowing of LED3.

Do not worry if you forget to switch off the charger. The charger is on floating voltage (13.6V) now and it can be kept in this charging mode forever.

Construction and testing

A single-side PCB for the 12V battery absorb and float charger circuit is shown in Fig. 2 and its component layout in Fig. 3. Assemble the circuit on the PCB, except transformer X1 and the battery under charge (BUC).

battery, absorb, float, charger, circuit

Download the PCB and component layout PDFs: click here

Enclose the PCB in a small box. Fix the battery terminal on the front of the box for connecting the BUC. Connect switches S1 and S2, potmeters VR1 through VR3, etc on the body of the box.

EFY notes

  • Switch off S2 or disconnect battery terminals to avoid unnecessary discharge of battery when not charging, that is, when S1 is switched off.
  • Connect the battery with correct polarity.
  • Casing of IC1 should not be connected to ground, so use insulation.

Fayaz Hassan is manager at Visakhapatnam Steel Plant, Visakhapatnam, and is interested in microcontoller projects, mechatronics and robotics.

66 Комментарии и мнения владельцев

Sir, Thanks for sharing this circuit design. Can it charge my Alto K10’s battery also, which need more current? I have a 12-0-12 5A transformer. Could you help me use it build the charger which can charge my car battery as well as my my bike battery which is 12V/9AH. Many thanks in advance. Regards, Jay

A 12V battery requires about 14VDC for charging. About 2VDC will be dropped across the voltage regulator IC. So, 12-0-12 transformer may not sufficient for charging 12V Lead acid battery. Please refer the project 12V BATTERY CHARGER CUM VARIABLE POWER SUPPLY published in November 2016 EFY edition for higher AH battery charging.

What if the transformer is used with Full Bridge Rectifier? I think, 12-0-12 2Amp Trafo is good. The Full Bridge should use the 2 end terminals and keep the center tap unused. Please confirm if this is true.

battery, absorb, float, charger, circuit

This circuit already uses rectifier. You always need to rectify an ac current to turn it into a nice dc current. Bridge rectifier gives the same output as this rectifier. 2 of the 4 diodes are not used in bridge rectifier, I mean, they are there to prevent voltage from running the wrong way. By the way, 12V trafo ac gives about 16.8V dc (121.4) that goes in to lm317. Lm317 takes 3V to itself (check datasheet) so the whole circuit uses around 13.8-14V. Since there is D3 in the path to battery, under 1 amp load it drops 1V (check datasheet) so the voltage that goes in the battery is 12.8-13V, and that is not enough to fill any kind of 12V battery. But if you have 15-0-15, the voltage that goes to battery will be 15.8-16V which is good.

That’s why I asked what if I use end terminals of 12-0-12 trafo which would be around 241.4 volts. I won’t use the center tap. Instead I will draw current from the 2 end terminals. That should work, right?

Dear Fayaz Hassan, Is it possible to use a 18-0-18, 20A transformer that I already have, instead of the 15-0-15 1A described as X1? I would like to charge a 12V 14ah lead acid battery for a motorcycle but i would like to use it as well for 12V car battery. Thanks and Regards Sal

when charging current is more than 1A, the IC1 will start heated up. since your transformer is able to supply more than 1A (where 20A is felt as infinite current in this case), I think, the IC1 will be damaged within no time, if a highly discharged battery is connected for charging. you can try by connecting about 3.3 ohm, 10W resistance instead of series resistance R7 and reduce to a safe value ( it is trial and error method only ).

Is it possible to use this circuit for 6V battery (instead 12V)? I was thinking about leaving the in power the same, and only adjusting the circuit with the potmeters with the help of test points, as described in the article. Is this enough or do I also need to change some other components? By the way, love the led solutions to show each charge state! Very professional. Instead of guessing what’s happening, the leds are here to show us. Love it!

@Sal Actually, you can’t move 20A through LM 317 because it has a cap of 1.5A. So, in my opinion, LM317 will pull 1.5A in which case you don’t have to change the circuit just add a 1-5C/W heatsink on LM317 or it will shut down. The right c/w for heatsink should be calculated. To keep heatsink size lower, you can add a small circuit to reduce amp size that will go through ic1 to 1 amp. Basically, amp is what the load will draw, so even with 30amp transformator, you can only use 1.5A max.

Maybe I’m mistaken, but the 1N4007’s used for rectification only allow 1A to pass through them, so wouldn’t this prevent the use of anything more than a 1A current draw to the LM317? If I’m mistaken, please, show me my error. Thanks.

Hello, I’m planning on using 15V-0-15V 1,67A 50VA transformer in this project for charging a 7Ah 12V SLA battery. Should I increase the value of R7? Best regards.

Dear sir, Alls of 3 leds are always light up in my circuit…Pls tell me How to setting them ? Thanks for advance.

That is the case when you attach a full battery, or the charger finished charging. If that’s not the case, than you wired something wrong. Led1 – will always light up because it is connected between the main line and – line so it always is under power. Led2 – will light up when you put in a battery to charge. No matter if the battery is fully charged or not, the led will light up and stay on because the battery completes the circuit and now the led is connected between the main and the OUT2 which acts as a When charging is over, power flows from the OUT2 and goes to LED3 (because it can’t go through LED2 – it’s still a diode and diode rules still apply), but power also flows (actually, it never stopped flowing) to LED2 from main supply (red line) and that’s why LED2 will always glow and LED3 only glows when charging is finished. Led3 is the ONLY led that will not glow all the time!

For whoever is watching this circuit: A little improvement can be done to it to make LED2 off when LED3 is on. What you need to do is add another comparator. Instead of using LM358, you can use any other chip that has 4 comparators in it. Basically, it doesn’t matter how many comparator you have in a chip, because you only need to use as much as you need. With this circuit a 4x or 3x chip would be better because you have room for upgrades. Any 4x comparator chip will work. So, here is how to connect it, but before you do, remove R8 and LED3 from the above circuit: IN on a new chip (or IN3 if you use a different chip instead of LM358) should be connected to IN2- on this circuit. IN- (or IN3-) should be connected to IN2. The OUT (or OUT3) should be connected to R8. R8 connected to LED3 and LED3 to ground. That’s all. Now this will work as it should without any confusion. @Fayaz I know it’s an old post, but your circuit is still the best one out there that is easy and cheap to make and still works as it should! Great job!

I have LM324. Could you please show me in drawing what will be the new connections if i use it. Thanks.

Can we get an update of dis circuit as u explained? U can send a link so dat everyone can benefit also Tnx

There is something that I don’t understand in this circuit. If VR3 is just is adjusted when TP2 is 13.6V then how can TP2 get more than 13.4v when it is in charging mode. I think when TP2 get more than 13.6v TP2 will get high voltage and T1 will be open and TP2 never get more than 13.6v. May be I am saying a silly thing, can someone clarify me. Thanks

Nice circuit and good explanation. But sir, Can I attach a diode at the battery positive line to Avoide the battery been discharged Wen switch s1 is off?

Dear Sir, We need battery back up system for temperature indicator with some modifications in above circuit. Can you give your e-mail ID so that we can give specifications for our requirement.

dear sir i want to charge my bike battery 12v 17ah what changes are need to be done with this circuit and where can i get the pcb.

i need a charger circuit for 12v and 12 ah battery. i am just a hobbyist. please provide me with an easy solution thank you very much.

Sir i want to make my own outdoor speake (trolly type) With Tda7388. So i need 15v 5amp supply with 12v 7amp sealed battery. Pls suggest how can i arrange this 12v battery charger with 5amp supply pluse online standby battery backup. Thx. [email protected] 9216791118, 7888829660

Hello Sir, I would like to charge a 12V 1.3Ah battery so, in order to limit the charge current to 0.394A, I should change the R7 to 3.2 Ohms right?? If I’m wrong then what is the solution for a 12V 1.3Ah battery?

I want to create a charger for 12v 7ah battery which will charge battery using solar energy. Normal 230V AC will be used as backup battery charging voltage incase solar energy is not available. Can i use same circuit ? Any modifications to be done ??

Sir can u send me a design of this circuit to my mail plz sir it is very urgent and nesesary to me sir

Is this circuit only applicable for automobiles and 2 wheelers ? If yes then what changes should be made to make it applicable only for mobile and other electronic handset charging? Please give me a clarification on this.

Can I use the same circuit to charge 2 x 12 V Lead Acid Batteries [7 AH] connected in series? – Require 24 V to drive my garage door motor.

PCB mount transformers are easily available from various online stores such as mouser.com, aliexpress.com, etc. But please note that in this project, we do not use PCB mount transformer.

can we use the battery for powering other applications with sw2 in on state and also the sw1 in on state?? like battery under continuous charging and also being used for powering other applications?

The author Fayaz Hassan replies : YES. The battery can be connected to the load while charging. But, REMEMBER that the discharge rate (current to the load) should be less than the Charging Rate. So, the discharge current (to load) should be less than 1 amp. The charger may be kept continuous ON state, which will change its state to either Float or Absorb state automatically.

How can this circuit be used for charging higher amperage 12 Volts batteries like 10 Ampere, 20 Ampere and lower Amperage batteries like 5 Ampere ?

The author Fayaz Hassan replies : The charger can charge any 12V Lead acid battery having charge rate more than 1A. (please check the charging rate printed on the battery). The problem with the higher AH batteries is, it takes very long time to fully charged. For e.g, w.r.t. 7 Ah battery, the 10 Ah battery requires 1.5 times charging time, 20 Ah requires 3 times charging time, and so on. The total time for fully charging depends on the voltage of the battery before charging and age of the battery.

Hello Sir, I have built this Battery Charger, it is working fine… Now, I need to charge 6V battery, Let me know the modification and voltage settings details Thanks Vinod C

Good day sir, Pls how can i upgrade this charger to charge 24v battery of 200to 500amp. And also to incorporate relay and polarity protection

Good day reputable engineer, How do I modify the charger to charge 24v battery 200-500amp. and also to incorporate a relay for cutting off.plshelp me out

Please share with me the purpose of diode D4 and resistor R7. Normally when you see a low resistance resistor in series with a current source it is to develop a voltage drop that can be sensed for foldback or crowbar protection circuitry. I don’t think I’m seeing that here. And I am really not understanding the reason for diode D4. Sincere thanks, Tom

I took lot of effort to make PCB and etching. finally, this is not working, the red LED is not gloving it gets only 1.4v in the LED terminal. Green light is always switched on.

You have not mentioned whether you are testing the circuit with or without BUC (battery under charge). Please connect the BUC and try again.

I made this with LM339 (with 4 opms) and works perfectly alright, thanks for the wonderful circuit. I wanted to connect my 12v Wi-Fi router as well, so that router works when the power goes off like a ups. When I connect the router in parallel to battery, the voltage drops 0.3 to.5 v and it varies. I am not sure whether the battery charges correctly or not. How can i calibrate it with this setting?

I made the circuit in a PCB. when After calibrating and reconnect the jumper back, the charger output is showing only 13.6v. When I connect to battery the charging indicator glows but the voltage reaches only till 13.6 and not going up, and the green led is not glowing even after many hours. Is it expected to be charged till 14.1v right ? Not sure what’s wrong with. I rechecked, and all the connection looks correct. I followed the same step mentioned in the article. no luck

Isolate R8 and R9 junction and provide two diodes from pin 7 of ic one forward biase to R8 and one reverse biase to R9

Can I use LM 338 instead of LM317 for charging higher capacity battery and change the value and wattage of R7to suite the charging requirement and also the transformer rating and the rect rating

Reg the tp2 voltage check zd1if it is of lower value tp2 voltage will go down.check R1and vr1and vr2 values check bc547 for collector to emitter short.check the dc voltage across the main filter if every thing ok change Lm317 blindly with a different make. Good luck

for 48 Volt /10 Amp bettery i can use this Circuit by Just replacing Transformer? Also Here which circuit used for Current limitation?

It is always safe to limit the input voltage of Lm317 to a max of 35 Band current to a max of 1 amp even though it can supply up to 1.5 amp above 1 amp and above 35v the ic will get over heatedand it can go defective very soon.in this case you may get around 42v.

I have DC power source of 18v 6~7 A. I want to charge 2 12v7a batteries connected in parallel. what is the current output of this circuit. how can i get 1.4 a at battery charging terminal.

it is an unreliable circuit … leave it alone it does not maintain stability, and it is very difficult to obtain the variation of the two voltage thresholds 14.1 and 13.6 volts … the LEDs always light up and in the best hypothesis there is a risk of always having about 13.6v output in any condition.

v battery charger circuit diagram

This diagram shows how to make a 12v battery charger circuit diagram. In this circuit diagram, we use a 14v step-down transformer, four diodes a ceramic capacitor, a 25v capacitor, an LED light, a 1 k resistor, and a 12 v battery. First, we connect the transformer to the diode and from the diode to the battery-positive terminal. Then make the connection between the capacitors and the ceramic capacitors with the battery. And lastly, we connect LED and resistor to the battery. Now this circuit is ready for use. Please check our YouTube video below.

Components needed For this Project:

You can get the components from any of the sites below:

  • Resistor [See Buy Click Amazon]
  • Capacitor [See Buy Click Amazon]
  • Diode [See Buy Click Amazon]
  • 14v Step Down Transformer [See Buy Click Amazon]
  • LED Light [See Buy Click Amazon]
  • 12v Battery [See Buy Click Amazon]

Please note: These are affiliate links. I may make a commission if you buy the components through these links. I would appreciate your support in this way!

Components used to make the 12v battery charger circuit:


A Resistor is an electrical component that controls the flow of electricity in an electrical circuit. Or we can say in this way that the material or component Which is used to block the flow of current in electronic equipment is called Resistor. And, because of the characteristic of the resistor or conductor that Prevents the flow of current through the conductor, that characteristic or religion is called resistance, where resistance Means the ability to block. The main function of a resistor is to cause a voltage drop to impede the flow of current in the circuit. In this case, the question may arise as to which circuit or which Parts need to be protected from low voltage or current flow.


Capacitor is a Two-Terminal passive component having the Property of Capacitance. This Property Electrifies (charging with electricity) Capacitors with input Voltage. Capacitors Condense Electricity, Hence it is also known as a Condenser. It consists of two Electrical Conductors that are Separated by Distance. The Capacitor Stores Charge and can act like a Battery. It is necessary for filter Circuits to Minimize voltage spikes, and Smoothing changes in voltage.

A diode is an Electronic Device that allows current to flow in one direction only. Diode has two ends. The end where there is a line of silver color is called the cathode. The other end is called the anode. A diode basically allows current to flow in one direction and prevents current from flowing in the opposite direction. Such a tendency of current to flow in one direction is called rectification. When a circuit is connected with an anode positive and a cathode negative it is called a forward bias diode.

Designing 12V Lead-Acid Battery Constant Voltage Limited Current Charger for UPS (Part- 2/17)

In this tutorial, a constant voltage charger for the 12V lead acid battery will be designed. The lead-acid batteries can be charged in different ways or modes. In this tutorial, a constant voltage charger will be designed for charging the lead-acid battery. The battery is required to be supplied limited current which saturates once the peak terminal voltage is achieved in the charging process. Depending on the per cell voltage of the 12V battery, the maximum rated voltage of the battery varies from 13.5 V to 14.6 V.

In this tutorial, the charger circuit is designed for charging a lead acid battery having peak terminal voltage of 14.4 V. So, this charger circuit charges the battery with a constant voltage of 14.4 V and provides a maximum current of 1.25 A.

Components Required –

Fig. 1: List of Components required for 12V Lead-Acid Battery Constant Voltage Limited Current Charger for UPS

Block Diagram –

This charger is easy to design and has the following circuit blocks where each block serves a specific purpose –

AC to AC conversion –

The voltage of Main Supplies (Electricity fed by the intermediate transformer after stepping down line voltage from generating station) is approximately 220-230V AC. This voltage needs to be stepped down by using a step-down transformer to the required voltage level. A step-down transformer having a rating of 18V-0-18V/2A is used in the circuit. It is capable of providing 2A current which is well suited for an application having a current requirement of 1.25 A. This transformer step downs the main line voltage to 18V AC.

It is important that the current rating of the step-down transformer and bridge rectifier diode must be greater than or equal to the required current at the output. Otherwise, it will be unable to supply the required current at the output. The voltage rating of the step-down transformer should be greater than the maximum required output voltage. This is due to the fact that, the LM317 IC used in the circuit takes a voltage drop of around 2V. In this circuit, two LM317 ICs are used so input voltage from transformer must be 4 to 5V greater than the maximum output voltage required and should be in the limit of the input voltage of LM317.

The stepped down AC voltage needs to be converted to DC voltage through rectification. The rectification is the process of converting AC voltage to DC voltage. There are two ways to convert an AC signal to the DC one. One is half wave rectification and another is full wave rectification. In this circuit, a full wave bridge rectifier is used for converting the 18V AC to 18V DC. The full wave rectification is more efficient than half wave rectification since it provide complete use of both the negative and positive sides of AC signal.

In full wave bridge rectifier configuration, four diodes are connected in such a way that current flows through them in only one direction resulting in a DC signal at the output. During full wave rectification, at a time two diodes become forward biased and another two diodes get reverse biased.

In this circuit, KBPC-3510 is used as bridge rectifier. It is a single phase bridge rectifier that has a peak reverse voltage of 1000 V and average rectified output current of 35 A. So, it can easily block 18 V in reverse bias and allow 1.25 A current in forward bias situation. Instead of using KBPC-3510 directly, four SR560 diodes can also be used to make a full wave bridge rectifier that will allow maximum 1.5 A current and in reversed bias will be capable of blocking 18V supply.

Smoothening –

Smoothening is the process of filtering the DC signal by using a capacitor. The output from the full-wave rectifier is not a steady DC voltage. The output from the rectifier has double the frequency of main supplies but still containing ripples. Therefore, it needs to be smoothed by connecting a capacitor in parallel to the output of full wave rectifier. The capacitor charges and discharges during a cycle giving a steady DC voltage as output. So a capacitor (shown as C1 in the circuit diagram) is connected at the output of full bridge rectifier.

A ceramic capacitor ( shown as C2 in the circuit diagram) is connected in parallel to this electrolytic capacitor to decrease the equivalent output impedance or ESR. At the output of the charging circuit, there should be a capacitor for absorbing any unwanted ripples. But in this circuit, the battery is connected at the output, which acts like a capacitor itself. So there is no need to connect any capacitor at the output terminal of the charging circuit.

The capacitor used in the circuit must be of higher voltage rating than the input supply voltage. Otherwise, the capacitor will start leaking the current due to the excess voltage at its plates and will burst out. It should be made sure that the filter capacitor should be discharged before working on a DC power supply. For this the capacitor should be with a screw driver wearing insulated gloves.

Voltage Regulation using LM317 –

For designing a constant voltage charger for 12V lead-acid battery, a constant voltage source and a current limiter are required. The voltage source should provide a constant voltage equal to the maximum voltage rating of the battery. Considering the charging current of the lead acid battery it should be half or less than the maximum current rating of the battery. In this circuit, LM317 IC is used as constant voltage source of 14.4 V as the 12V battery used in the circuit has a peak terminal voltage of 14.4 V. For charging current, another LM317 IC is used as a constant current source. This current source will limit the charging current to 1.25A so the battery never draws current greater than this value.

LM317 is used for the voltage regulation. LM317 is a monolithic positive voltage regulator IC. Being monolithic, all the components are inbuilt on the same semiconductor chip making the IC small in size having less power consumption and low cost. The IC has three pins – 1) Input pin where maximum 40 V DC can be supplied, 2) Output pin which provides output voltage in the range of 1.25 V to 37 V and 3) Adjust pin which is used to vary the output voltage corresponding to the applied input voltage. For input up to 40 V, the output can vary from 1.25 V to 37 V.

For using the IC as a constant voltage source the resistive voltage divider circuit is used between the output pin and ground. The voltage divider circuit has one programming resistor (Rp) and another is output set resistor (Rs). By taking a perfect ratio of programming resistor and output resistor a desired output voltage can be drawn. The output voltage of the IC Vout is given by the following equation –

The typical value of Programming resistor (Rp) can be from 220E to 240E for the stability of the regulator circuit. In this circuit, the value of Programming Resistor (Rp) is taken 220E. As the output voltage should be 14.4 V, the value of the output set resistor (Rs) can be determined as follow –

Automatic Battery Charger Circuit for 12V 6V Battery


In this electronics project, I have explained how to make automatic battery charger circuit for any battery on the zero PCB. You can easily make this auto cut off charger circuit for charging a 12V battery or a 6V battery.

First, you have to set the cut-off voltage, then you can supply 220V or 110V AC supply at the input and connect the 12V battery at the output.

The charging will automatically stop when the voltage across the battery crosses the preset cut-off voltage.

Circuit of Automatic Battery Charger

The circuit is very simple, You can easily make this project with some basic electronics components.

PCB Layout for Automatic Charger Circuit

Download the PCB layout, then print it on an A4 page. Please check the PCB size while printing, it should be the same as mentioned.

Required Components:

  • 1k Resistor 1/4 watt (2no)
  • 10k Potentiometer (1no)
  • 10k Resistor 1/4 watt (1no)
  • 10uF 35V Capacitor (1no)
  • 1000uF 35V Capacitor (1no)
  • 1N4007 Diode (1no)
  • 1N5408 Diodes (5no)
  • LED 1.5V (2no)
  • BC547 NPN Transistor (1no)
  • 12V SPDT Relay (for 6V use 5V relay)
  • Connectors
  • 15V 2A Step-down Transformer
  • Zero PCB or Cardboard

Tutorial Video for Auto Cut-Off Charger

In the tutorial video, I have shown all the steps to make the Auto Cut-Off Battery charger circuit. So please watch the video for a better understanding.

How to Make the Automatic Battery Charger PCB

Steps for making the Automatic Battery Charger circuit on PCB

  • Print the PCB Layout and stick it on Acrylic sheet or cardboard
  • Drill the holes for the components as shown on Layout
  • Connect all the components as shown on the layout
  • Solder those Components as shown in the circuit
  • Now, the Auto Cut-Off Charger PCB is ready

Setting the Cut-Off Voltage

Now, to set the cut-off voltage, you have to connect a variable DC power supply at the DC input and connect a multimeter (voltmeter) at the battery side as shown.

For example, to set the cut-off voltage at 13V, you have to give 13V at DC input.

Then rotate the potentiometer until the red LED turns on.

After setting the cut-off voltage disconnect the variable DC supply and connect the step-down transformer at the AC input, as shown in the circuit diagram.

Please take proper safety precaution while working with 220V or 110V supply.

Finally, Auto Cut-Off Battery Charger is ready

Connect a Lead Acid Battery at the Battery side (as per the circuit.)

Then give the 220V or 110V supply, the green LED will turn on, which indicates the battery is charging.

When the voltage across the battery cross the cut-off voltage, the relay will turn off and the battery will be disconnected from the supply.

Please share your feedback on this mini-project and also let me know if you have any queries.

You can also subscribe to our newsletter to receive more such useful electronics projects through email.

I hope you have liked this projects, Thank you for your time.

Automatic street light using LDR and BC547

April 15, 2020

Automatic Water Level Controller for Submersible Pump circuit

May 28, 2021

Using a car battery charger

Frequent short trips, with constant stopping and starting, make your battery work very hard, especially in winter when heater, headlights. heated Windows and wipers may be working most of the time.

Eventually, because more current is being drained from the battery than the alternator can put back, the battery will not have enough power left to turn the starter motor. A battery in that state of discharge is said to be flat.

A flat battery can be avoided if you have a battery charger. a relatively cheap, but worthwhile accessory.

It uses mains current to replace the battery‘s lost charge through positive and negative leads that clip to the corresponding battery posts.

battery, absorb, float, charger, circuit

An average car battery has a capacity of around 48 amp hours which means that, fully charged, it delivers 1 amp for 48 hours, 2 amps for 24 hours, 8 amps for 6 hours and so on.

A basic charger usually charges at around 2 amps. and so needs 24 hours to deliver the 48 amps needed to fully charge a flat, 48 amp hour battery.

battery, absorb, float, charger, circuit

But there is a wide range of chargers with different charge rates on the market. from 2 to 10 amps. The higher the charge output, the faster a flat battery is recharged. Fast charging, however, is undesirable as it can buckle the battery plates.

The loads imposed on your battery may be gauged from the amount of current used by the various electrical components: headlights take about 8 to 10 amps, a heated rear window about the same.

Theoretically, a fully charged battery, without taking in current from the generator. should work the starter for about ten minutes, or the headlights for eight hours, and a heated rear window for 12 hours. As the battery nears full discharge, the lights gradually grow dimmer and finally go out altogether.

There are also causes other than short trips and cold weather which can affect the state of your battery. Failure is more common on cars equipped with a dynamo rather than an alternator. because the alternator produces more electricity and charges better at low engine speeds (See How the charging system works ).

The answer in all these cases is frequent testing with a hydrometer (See Checking the batteries ) to see how much capacity is left in the battery, and using a battery charger to top up its charge when necessary.

Connecting a battery charger

Always check the electrolyte level before connecting the battery to the charger. Top up if necessary (See Checking the batteries ) and clean the battery posts.

If there is a power point handy, the battery can be left in the car, so long as the charge rate is only 3 or 4 amps.

However, if the car has an alternator, disconnect the battery terminals beforehand: otherwise some alternators. generally the older type. can be damaged.

If separate cell caps are fitted, remove them for ventilation. Leave a trough cover on, unless the charging rate is high. Clamp the positive lead from the charger, usually coloured red, to the positive battery post. Clamp the negative (-) lead, usually black, to the negative terminal.

Plug the charger into the mains and switch on. The indicator light or gauge ( ammeter ) will show that the battery is being charged.

The gauge may show a high charging rate at first, but this drops gradually as the battery becomes charged.

If it was very flat, charging is likely to take a long time; check periodically with a hydrometer, while continuing the charge.

In the final stages, the cells bubble and give off gas. If any of them begin gassing before others, or do so more violently, the battery is probably defective and should be checked by a garage or battery specialist.

Types of car battery charger

A basic home battery charger incorporates a transformer and rectifier, to change the mains 110/220 volt alternating current to 12 volt direct current. and allows the mains supply to provide a charging current at a rate determined by the state of the battery.

In the case of a battery in good condition, the rate of charge may be around 3 to 6 amps with a normal home charger.

A battery at the end of its useful life may not accept any recharging, and will not, in any case, hold a charge.

Some chargers are fitted with a high and low (Hi-Lo) switch to give a choice of two charging rates. typically 3 or 6 amps. in case you want to give the battery a short overnight boost at 6 amps rather than a longer charge at 3 amps.

Many have a charge indicator which may be a warning light, or a gauge showing the charge rate in amps.

Read more

How to test a car battery

If your car’s instrument panel includes an ammeter. it will tell you how well the charging syst.

Checking the batteries

Most car batteries are sealed for life. apart from a small vent hole which allows gas to e.

Checking a starter circuit

If the starter does not turn the engine although the car battery is in good condition, the.

How to test electrical circuits

If there is trouble without an obvious cause in any electrical component, test the circuit to f.

We’re making the ultimate video course.

You can preview the video course here

Leave a Comment