Two Automatic battery charger circuits

A lead-acid battery charger circuit  is most popular though it will very large size than others battery type. But them have advantage are : cheap, easy to buy and long life if correctly uses.

The charging is best importance.
When I had 10 year old ago. My father bought it to me in first time of my life. In 6volts size for that era motorcycle.
When power outage will charge at shop near the house. Which is quick charger with high current. While charging will Air bubbles inside the battery and high temperature. Which technician tell me no problem it high power.
But can be application 2-3 time only it is failed.

Which as usually this battery type if correctly charges wil can use for 4-5 years
Battery do not like hot!
At all time do not use or store them in too heat area. OR If while use may short circuit or high current use them will too hot.
An importance while charging do not quick charge with high current and high voltage.

1.  Simple Automatic battery charger circuit 

Principle working

This is an automatic battery charger circuit,  Which normally producer will tell at battery as follows:

Must charge with DC voltage only.

And neat voltage level not should more than 15-volts or 1.5 times of a battery voltage.
Most importance should use charger current 10 % of battery current for example 2.5Ah size use time for 10-12 hour.

In my site we suggest many battery charger circuit. You will love it, because use simple circuit,cheap so easy to build.

simple aciti battery charger which I use idea from…

First of all, I think “When…Charge? And When stop?”
Normally we should charge battery when voltage lower than 12.4 volts and voltage maximum of most battery is 14.4volts but someone guru tell me voltage saving of 13.8 or 13-volts approximately.

Secondly,Thus we need to use comparator circuit which in first times I often use IC-op-amp such as LM339,LM311,LM324,LM301 but sometimes we cannot buy them. And This our working is simple stye only.
When begin we learn basic principle of electronic parts, I like use Diode, Zener diode, which they are both valves for electrical currents. The Current will flow one way. But the zener diode is connected backwards. It then blocks current until the voltage exceeds a certain level.

I try to test them with the zener diode 12-volts the current will flow through it when voltage higher than 12V.
Therefore I use Zener diode for detects voltage over than 13V to control stop charger system.

Then, I use relay to control current to a battery. Because cheap and used easily.

Next, I use a SCR for uses as quick control switch.


As Figure 1 is perfect circuit diagram.

You can watch video below I test it. This projects will always cut off battery when voltage drop across it is 13.6V up. Then LED2 (yellow) glow brightly. While relay will pulls out from contact NC-C. Which no current to battery and voltage lower down.

Then you can charge again with pressing SW2 to reset, recharge them again.

Though This projects will easy technology but very useful for all.
Importance it cheaper! I love it.


If you want to read more: how it works,parts list and look full size circuit image.

You like my sites want to support me by buy this E-book.


2. Automatic OFF 12V Battery Charger by power SCR

This stop current give battery, when Voltage of battery tall arrive at the level that load with full speed already ahead for protect something charger too much poor distilled dry water. This circuit can is usable very wide can use with battery many model. By choose diode and SCR at can durable the trend loads topmost follow to want. Fining decorates while initial lead battery at charger until with full speed ahead already come to build reach at a pole for charger. Fine R1 – 500Ohm until Amp Meter begin be down be O as a result fully be usable already.

Automatic OFF 12V Battery Charger by power SCR

Note : above circuit is just basic ideal only we lets to see really uses below.

Auto dry battery charger using SCR

This projects is automatic dry battery charger that can use for many size such as 6V, 9V and 12V Depending on the changes, some devices only.

How this circuit works

As circuit below. To begin with an AC220V will flow to a transformer to transform to 15 volts, then flow to bridge diode to rectifier AC to DC is 15V. The LED1 is power indicator of the circuit.

dry battery charger circuit

Beginning SCR1 is working, because the 15V flow to R3, to limit the current to decrease, and flow through to diode D5 to To prevent the reverse voltage, Before bias to lead G of SCR1.

While SCR1 conduct, to make the 15V flow from lead K will feed to the positive battery terminal. Ideally SCR1 will conduct current and stop current alternately very fast with frequency of 100 Hz.

Since the 15V voltage from the bridge diode is full wave rectifier so output frequency of 50+50 Hz. The feature of current will be continuous positive half sine wave.

Which will differ with the voltage from capacitor filter that is smooth as a straight line. So will see that SCR1 do not conduct current all time. When have positive voltage to bias at lead G. Since waveform of voltage Not smooth enough in a straight line.

Theoretical of SCR, it will stop conducting current when disconnect the power supply output. Which in this circuit is do not have positive side of the power supply range. And when have positive voltage waveform new SCR1, it starts to currents again, this was reversed with a frequency 100 Hz.

Battery level monitoring

This circuit will get voltage from the battery positive through R2 to reduce current, and have C1 to filter current to smoothly. Then will flow through VR1 to divide voltage to feed to a zener diode ZD1 before send to bias lead G of SCR2.
A adjust level of VR1 will must make in full battery, adjust VR1 until voltage at negative of ZD1 have level more than 6.8V or about 7.3V.

Which will cause ZD1 to saturation voltage collapse flow through to ZD1 to feed lead G of SCR2, cause SCR2 conducting current by R4 is helper to SCR2 extraordinary stable work. When SCR2 work will cause negative voltage flow to lead K to A result to LED2 glow. And the same time SCR1 will stop conducting current.

Since lead G of SCR1 get negative voltage from SCR2 there. In the case of battery is lower voltage, cause voltage at negative of ZD1 have lower than 6.8V, makes lead G of SCR2 not get positive voltage but can get only negative voltage through R4 result SCR2 don’t conduct current.

The parts list
Resistors ½W 5%
R1, R5_____________2K
R3_____________560 ohm
VR1_____________10K Potentiometer
C1_____________100uF 25V Electrolytic capacitor
ZD1_____________6.8V 1W
LED1, LED2________5M LED as you want
PCB,and other, etc.

How to make and setting

After preparation equipment is ready, then we soldered it successfully on PCB as Figure , next checked again. For example The device has a positive – negative. Are they correct polarity?

the component layout of dry battery charger
The component layout of dry battery charger

soldering point of dry battery charger
Soldering point of dry battery charger

Complete assembly on PCB
Complete assembly all parts on PCB

Fully 12v battery 2.5Ah

To Safety, customization first step, to find full battery voltage fit, be connected to the circuit to correct polarity. Then apply AC220V , next adjust VR1 clockwise until LED2 go out. Then to rotate VR1 clockwise slowly until LED2 light up, then stop immediately, do not too much spin is strictly prohibited. The principles, LED2 will light when battery voltage until full. So the battery will be adapted for the first circuit has to be really full voltage.

Please watch video below to increase understand this projects.

Circuit modification

This saving dry the battery circuit, can charge voltage 3 size are 6V, 9V, 12V. We can change each value parts as neat charged battery.
For this circuit we use with 12V battery Look at the chassis battery is stated as 12V 20AH, mean, Battery voltage 12V currents supply 20 amps per hour. When you know voltage at the battery is charged, Now I have to choose the transformer to be used. currents transformers used can be selected from 3-5 A.

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The table below shows the change in each device. To fit the battery charger.

Battery Voltage

Transformers Voltage

Zener Diode voltage

R3 and R5

6 volts

9 volts

12 volts

9 volts

12 volts

15 volts

3.3 volts

4.7 volts

6.8 volts




We recommend:

Best 12V battery charger circuit using LM311

6V or 12V lead acid battery charger using LM317


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