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




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18 thoughts on “Automatic OFF 12V Battery Charger by power SCR”

  1. Pls. send me circuit diagram with details. send me also the value of all resistors diode and all the components of the charger. Thank you.

  2. ZD1 is a 12 V.
    Note the absence of filter capacitor, only the circuitry related with the sample output voltage (220 nF). This design (double wawe rectifier) implies a “zero crossing” reset for the two SCR.
    Only when the SCR controlled by zener ZD1 conducts, disactive the SCR that charges the battery (also named SCR1), and the current leaves to flow, leaving charching Battery. ZD1 resistor divider (47 Ohms- 500 Ohms pot) adjust the voltage level for the Pb battery nominal Voltage (suddenty 13,8 V)
    I haven’t proved it, but evidenty, a little more splain from the deisgner will bw appreciate.

    Best ragards.

    Pedro Fco. Hermosilla
    Hermosilla Ing.
    Barcelona (SPAIN)

  3. Gostaria de com vc se da pra fazer um desse para
    carregar uma duas bateria ligada em serie 24 volts
    e 20 amperes, o trafo eu ja tenho e so para fazer o controle de desligar a entrada esse seu ai eu ja fiz, deu certo mas oque precisanmos mudar para funcionar em 24 volts.

    de momento muito obrigado.

  4. Pls give me a circuit which I explain below.

    A 12 v battery charger. It is now charging. Volt is now 12.0. It increases. At the level of 14.2 or 14.5 or near, I need stop charging now. OK. Now I discharging the battery. V level decreases 14v, 13.9, 13.5, 13, 12.8, 12.5. Now I need to start charging. Can You help me.

    With thanks. Ahmed

  5. Hi,Salim Khan
    Thanks for your feedback.
    I am sorry, I have not been that high charging currents.
    But In principle, we need a charging current, about 0.1 times of the current use.

  6. when i rotate the potentialmeter the green led ligth up…..but when a change a weak battery green led stilll light up..also with no load it light up..what should i do sirr…

  7. Dear sir,
    The scr’s used in this circuit are not availavle anywhere in my place,also it is hard to get the substitute scr’s so it would be nice. If
    you could provide me the scr’s 2N6397 & 2N5060 with the pcb.or elsejust substitute scr’s and the pcb of this circuit .
    Mail me or ship me the following parts,i will pay for it.
    Thanks in advance.

  8. Please Sir, you have a nice work. I need a car battery charger, but I believe your circuit can work very well. but the challenge am having is getting the resistor 2N5060 and 2N6397

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