Re-Purposing Your Old Laptop Charger

by santu.sanucupid19

27K10314

Intro: Re-Purposing Your Old Laptop Charger

In my other instructable, I described on how to repurpose a

old laptop screen which is not working due to some hardware issues. Refer to link https://www.instructables.com/id/Convert-You-Laptop-LCD-to-External-Monitor/

In this instructable I will be showing you on how I repurposed my old laptop charger which is sitting idle for a very very long time now. Below is the list of items used for this.

1. Old Laptop Charger (Working but not being used for anything)

2. LM2596 Step Down Voltage Regulator

3. Multimeter

4. Wires

5. Wire Cutter

6. Wire Stripper

7. Screw Terminal DC Power Connector

8. Solder Iron and some lead

9. Insulation Tape

STEP 1: Know Your Requirement

First Lets check if the Charger is working fine. Plug in the charger to the mains and check the voltage at the output pin of the charger. The inside pin is positive and outer cover is negative. My charger output specification is 19V DC with 3.2A max. The external monitor I made which is provided as an instructable previously required a 12V DC to power the monitor. So now I am going to convert this charger to a 12V DC power supply.

STEP 2: Preparing the Cable (Input)

Now that I know my requirement, I started with slicing off the existing output connector of the charger. The cable is a single cable with 2 covers. Carefully strip the outer cover to expose the aluminum strings covering an inner white wire. Separate the strings from around the inner wire and wind them together. This is our negative lead. Now the white inner wires is the positive terminal and strip this wire and wind the strings together. Take care so as the positive and negative terminals don’t short.

STEP 3: Understanding the Voltage Regulator

As my requirement is 12V DC, I need to bring down the 19V DC to 12V DC. For this I used a LM2596 Voltage Regulator. It has 2 points for connecting the input and 2 points for connecting the output as shown in the image.

This LM2596 is a voltage switching regulator providing capable of driving a 2A (max.3A) load with excellent line and lad regulation. A assemble circuit with minimum components provides simple various output controlling with internal frequency compensation and a fixed-frequency oscillator. Features: - Dimension: 52 (L) * 20 (W) * 14 (H) mm (with potentiometer) - Input voltage: 4.5-40V - Output Voltage: 1.5-35V (adjustable) - Output current: Rated current 2A maximum 3A (Additional heat sink is required) - Conversion efficiency: Up to 92% (O/P voltage higher the higher the efficiency) - Potentiomenter adjustment direction: Clockwise (increase) Anti-clockwise (decrease) - Switching Frequency: 150KHz - Rectifier: Non-Synchronous Rectification - Module Properties: Non-isolated step-down module (buck) - Short circuit protection: Current limiting since the recovery - Operating temperature: Industrial grade (-40 to +85 ) (output power 10W or less) - Full load temperature rise: 40 - Load regulation: ± 0.5% - Voltage regulation: ± 0.5% - Dynamic response speed: 5% 200uS - Connection mode: Welded plus pin can be directly soldered PCB. - Output ripple: Input 12V Output 5V 3A 60mV (MAX) Input 24V Output 12V 3A 120mV (MAX) Package includes: €1 x DC-DC Step Down Converter

STEP 4: Preparing the Output Connector

Now that we have sliced the charger and prepared the positive and negative input terminals, it’s time to prepare the output connector. For this I used a 10 cm dual wire (black and red) and soldered one end of the wire to the output connector. The image shown for that will be self explanatory. Now strip the other end of the wire to connect to the output terminals of the voltage regulator.

STEP 5: Connecting the Voltage Regulator

Now that we have a positive and negative terminal from the charger which we will connect to the input side of the voltage regulator and a positive and negative terminal from the DC Connector and solder them to the output terminals of the Voltage regulator.

STEP 6: Setting the Required Voltage

Now connect the multimeter across the output DC connector. This should show the voltage reading. To set the required voltage, use the screw present on the blue color preset either clockwise or anti-clockwise until you arrive at the desired output voltage.

STEP 7: Wrap Up THINGS

Now that you have the desired voltage at the output DC connector, wrap the open circuit with insulation tape, starting from input sliced wires to the output wires that we soldered at the voltage regulator.

After connecting this power supply to the external monitor, I observed that there is some amount of heat being generated by the voltage regulator. So I have poked some holes into the insulation tape wound around the regulator. I feel this should help some heat to dissipate from the regulator circuit.

13 Comments

Apolo8 6 years ago

You can obtain the very same result with just a potentiometer (just for testing the needed resistor's value), and the resistor itself

daveharnett 2 years ago

how is a single resistor going to do dc-dc step down?

rosekreuze 4 years ago

i have thoughts of reusing my old laptop charger as a 3s bms charger. which requires 12.6v to 13.6v. a question though about the LM2596, does it heat up lets say im using it at max 3a at 12.6v? does it mean it requires proper heatsink or ventilations?

santu.sanucupid19 4 years ago

I observed considerable heat up in my build which I am using as a 12v adapter. Buts its not to be worried about. Considering that you are using it for 3s BMS charger, I suggest add a small heat sink and case it with proper ventilation. please post your build here once done.

rosekreuze 4 years ago

i used LM317 instead, i think i would need a taller heatsink than the pre installed one. mines pulling 1.8 amps on lithium polimer and 4 amps on 18650s

rosekreuze 4 years ago

will do. thanks for the advice

3366carlos 7 years ago

Very nice, where can I buy the lm2596 module?

arthur_muh 7 years ago

the laptop charger is a Switched Power Supply... have no problem using an step-down switched power supply in serie?