DIY battery chargers: when it comes to a 12 V battery

About DIY battery chargers, Batteries are an essential component in many devices as they accept, store and release current as and when needed. 

They store energy in the form of chemical energy and release it in the form of electrical energy. 

Some rechargeable batteries can be recharged when they lose all of their energy.

You need battery chargers that are readily available in the market. 

However, you can make your DIY battery charger more performing and cost-effective than the readymade one. 

So, in this article, we will go over step-by-step instructions on how to make a 12 V battery charger.

What is a battery charger?

A battery charger is an electronic device that forces electric current into a battery or a secondary cell to generate energy. 

Different types of battery chargers include trickle chargers, pulse chargers, and fast chargers. 

Irrespective of the charger type, almost all chargers follow the same schematic scheme. 

There is a step-down transformer connected in series with an X-rated capacitor, and this connection helps lower the AC to the usable level. 

Further, a bridge rectifier converts the AC into rippling DC signals.

If you use a smoothing capacitor in the rectifier output, you can get rid of external noises.

Different types of battery chargers 

Different types of battery chargers 

Benefits of a DIY battery charger:

Battery chargers are standard in the market, but you can also build them at home, and they will share the following benefits.

Lower cost:

Buying chargers from the market will be more expensive than making one at home. 

While you buy chargers from the market, you pay for the material, labor, and other fees. 

Building chargers at home saves you from labor charges.

Higher performance:

Companies make battery chargers for business; thus, they tend to generate a maximum profit using low-quality components, which mainly applies to the less popular brands. 

However, the same may not be true for high-end companies. But every company wants the maximum possible profit, so they compromise on the component quality.

When you build a charger at home, you can choose any quality independently. 

Even if you choose the best quality, the money you save with a DIY battery charger offsets the high price of these quality components.

Much more flexible:

When you build your DIY battery charger, more than likely, you may need an adjustable voltage regulator. 

It may be a current constant boost converter or a current constant buck converter. Either way, it will have settings that make it a multifunction device for many types of batteries.

Turn the current settings of the regulator to the maximum level. Once you do this, it will work as a constant voltage regulator.

Suppose you have set your battery charger at 12 volts; you can charge a 12 V device with this charger. You can also set it to 5 volts and charge any USB device.

You can use your DIY battery charger to charge any battery with any chemical composition in its voltage limit.

Jump-start a car

Jump-start a car

Material and tools needed for a DIY battery charger:

All the tools and materials required for building a battery charger depend on the voltage, chemistry, and other factors of the battery to be charged.

Power supply:

Any battery charger will first need an AC to DC power supply

You can choose different options, like a dedicated AC-to-Dc High-wattage power supply, an ATX computer power supply or a low-cost USB PD supply.

 The battery charger is a combined form of power supply and a regulator.


Next, you will need a constant current regulator to manage the current flow. When the power supply voltage exceeds the battery voltage, you must use a constant current buck converter. 

On the contrary, you will need a current boost converter if the power supply voltage exceeds the battery voltage.

It’s suitable and advisable to start with a higher voltage and use a buck converter to adjust the voltage as needed. 

This way, you can adjust the charger to any voltage between zero and the input voltage. With a boost converter, you will have a limited band of voltages.


The wire is required to connect all the battery charger components, and you can choose either an 18 or 16-gauge wire.


With a multimeter, you can set the regulator’s output voltage and monitor the battery’s current voltage.

 Most multimeters have continuity beeps, which ensures an electrical connection between two conductive points. 

But not all have continuity buzzers, so while buying a multimeter, look for this.

Current meter:

You can use a multimeter to check the current; however, it is not convenient as you cannot check both voltage and current simultaneously. 

With current meters, you can check the current while you check the voltage on the multimeter.

Laptop charger

Laptop charger

Steps for a DIY battery charger( take the 12-V battery charger, for example)

Follow these steps to make a 12V battery charger, which features 2-step Charging: Constant Current and Constant Voltage.

Step 1: Getting things you need 

Alligator clip wires;

DC to DC step-down converter;

  • The DC-to-DC step-down converter can convert 19 V to 14 V for charging the battery. 
  • It offers constant current and voltage indicated by red and green light, respectively, and the third or blue light shows the load;
  • Features of DC-to-DC step-down converter:

The Output voltage range: 1.25-36 volts DC adjustable

Output current: 0-5 amperes

Output power: 75 watts

Input voltage range: 6 to 38 VDC (input voltage does not exceed 38 V)

Efficiency up to 96%

Built-in current limit function, thermal shutdown function, and output short protection function


Laptop charger;


Preparing the adapter

Cut the adaptor’s jack and remove the outer shield with the help of a blade. There will be red and black wires for positive and negative, respectively.

Setting connection

  • Observe the labels on the board and connect the adapter’s red wire to the board’s “IN+” positive and black to the “IN-.” Tighten the screw terminal properly.
  • After connecting the adapter, connect alligator clip wires; red clip wire to the board’s “OUT+” and black clip wire to the board’s “OUT-” negative.


  • Firstly, plug in the adapter to a power source. 
  • Then, connect the alligator’s black clip to the multimeter’s negative lead and the red alligator clip wire to the positive lead.
  • Now the board has two potentiometers, one for current and the other for voltage. 
  • Select the DC voltage on your multimeter and turn the potentiometer to get a 14 V reading on the multimeter. Next, select the current reading on the multimeter and turn the potentiometer to get two amps on the multimeter display.

Good to go

Once you set these readings, you can use this on the battery. 

Connect the red alligator clip wire to the battery’s positive terminal and the black to the negative, and keep the power on.

 You will see that a blue LED turns ON, which indicates that the battery is charging. 

After some time, you may notice the green light turning ON, showing the battery is fully charged.

 If red and blue LEDs light up simultaneously, it indicates constant current charging.

Things to consider

Of course, an AC-to-DC step-down converter can also work, offering a 220 V AC signal that passes through the X-rated capacitor connected to the live AC line and drops the voltage.

 The outgoing signal with a low voltage passes through the non-CT step-down transformer, whose output signal (AC) then passes through the bridge rectifier circuit.

 You can use this DC output to charge a 12-volt lead-acid battery.

Car battery chargers

Car battery chargers


So, now you know how to make a 12 V battery charger with a step-down converter (AC/DC). 

Try making it at home by following the above instructions. 

As we said, use high-quality products for making your battery charger.

 If you want high-quality chargers, Cloom is here to help you. 

We manufacture superior-quality cable assemblies and wiring harnesses that suit different applications.