Li-ion Battery Charger





Introduction: Li-ion Battery Charger

When I bought a 7.4 V Li-Ion battery, little did I know that it would require a special charger for recharging.

While searching for chargers I found a simple circuit by Scott Henion that makes use of an LM317 Adjustable Regulator.

I found another interesting circuit by Bill Bowden which makes use of a 555 timer, LM339 comparator and TL431, band gap voltage reference.

This instructable makes use of Scotts design.

Step 1: List of Components

  1. LED x 1
  2. 470 Ohm Resistors x 3
  3. 47 Ohm Resistor x 1
  4. 2.2 K Ohm Resistor x 1
  5. 1 Ohm 5 W Resistor x 1
  6. 1 K Ohm Trimmer x 1
  7. 0.1 uF Ceramic Capacitors x 2
  8. 1N4004 Diode x 1
  9. LM317 Adjustable Regulator x 1
  10. 2N2222 NPN transistors x 2
  11. 7.4 V Li-Ion battery x 1
  12. 12 V wall DC adapter or Power Supply x 1

Step 2: Schematic

Here's my schematic and Layout designed in Eagle. The eagle files along with the layout as an eps file are available in the file ""

For details about the working of the circuit refer to Scotts Article

Step 3: My PCB

I transferred the layout to a copper clad board using the iron transfer method. Then I etched the layout using ferric chloride. The image shows my board after populating it with the components. I attached a heat sink to the LM317. The big white block is the 5 Watt 1 Ohm resistor.

Step 4: Testing the Circuit

  • Before inserting the battery to be charged, we need to set the charging limit.
  • Power on the circuit by connecting it to a 12 Volt power supply.
  • The trimmer is used to set the output voltage limit. To set the limit, measure the voltage at the output (without connecting the battery) and adjust the trimmer R4 till the measured voltage equals the limit. I set my circuits limit to 7.2 Volts.
  • Once the limit is set we can attach the battery to be charged.
  • While the battery has a low charge the LED will glow brightly.
  • Once the battery is sufficiently charged the LED will become dim and might turn off. The battery can then be disconnected from the circuit.

For more detailed instructions/modifications and safety instructions see Scott Henions article



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    Please be positive and constructive.




    dear frinds ..if any one have 3s circuit for 3.4v lithium battery charger ..send me please.....

    Hi i wanted to build a 12v lithuim battery charger, can i used this one? what changes do i need to make? my charger is 12v 1a

    dear can u send me this circuit at ..
    gulshan India

    I offger no crictism, just praise. This is a nice little circuit. I will breadboard it and use wire for the heavier current spots. I need a small 7.2 volt (2S) charder for a little QRP tranceeiver I use ( picxie II). This fits the bill and i can build it into my case for about 5$. Nice job !

    The age is of modular technology so unless you are an electronic hobbyist this project not for you. Even if you need a cheap / safe functional charger, this project is not for you especially if you do not have a pre-existing power supply of the right voltage. I am also not a big fan of making my own PCBs and usually get away using the general purpose ones when absolutely necessary. The only time I have made PCBs is when I am mass producing electronics. My quick suggestion would be therefore to buy a 2A switching supply ($8), a lithium protection module ($2) and a thermostat ($2) on ebay. You will then merely need to sequence them one after the other and bingo!... you just made myself an intelligent ultra fast charger that costs $75 in the market. Some of these circuits on eBay have fancy LCD display (of course at an extra cost) that will display the progress of charging. So go ahead and knock yourself out... P.S.: I am willing to post details if there are enough requests.

    ranjeevm, please do make an instructable if you'd like. I doubt anyone would come forward with such requests otherwise unless you give a decent teaser.

    Also the project isn't only for electronics hobbyists, it could serve any enthusiast. Although when buying something off the shelf, I'd prefer going for something modern and safer. If I saw something like this in a commercial product, I'd say "Bleh, this I could build at home using what I have".

    I just did in quite a bit of hurry...

    Hey nice to see that you did. Maybe you could also add the links to the modules you used in the instructable.

    Hello your project is awesome, but that 1 ohm resistor is necessary? Pleas write me back and sorry for my bad english :D

    Hi, The 1 ohm is used to monitor and limit the current to 1 amp (1V = 1A) . You could use a resistor with a 1 Watt rating. Lower rating resistors might burn out.

    See the link below for more detailed explanations