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 "eagle_files.zip"

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

<p>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.</p>
<p>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. </p><p>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 &quot;Bleh, this I could build at home using what I have&quot;. </p>
<p>I just did in quite a bit of hurry... </p>
<p>Hey nice to see that you did. Maybe you could also add the links to the modules you used in the instructable.</p>
<p>Hello your project is awesome, but that 1 ohm resistor is necessary? Pleas write me back and sorry for my bad english :D</p>
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.<br><br>See the link below for more detailed explanations<br>http://shdesigns.org/lionchg.shtml
<p>I have never seen someone write 1V = 1A so let me be more explicit...what ****snail means that if a 1 ohm resistor has 1V across it, it is letting 1A through it.</p>
<p>Thanks ranjeevm, that's what I actually meant. I'm lazy sometimes to give explicit explanations. Thanks for putting it out there.</p>
<p>NP...We all are!</p>
<p>I'm not getting any extra current draw when adding the battery in and I set the open circuit voltage drop to 4.1 V. Any ideas?</p>
i tried this. but in my case i can't change the voltage using that trimmer.why is that..? HELP ME<br>
<p>i want a automatic charging cirtute for 4.7 volt lione battery....when the voltage will raise up to 4.5/4.7 the circuite will stop charging and when the voltege wiill be less then 4.3 volt it will automatically start charging again..........is it possible to modify your cirtuit for my requerment ??? @punkisnail</p>
<p>how should i charge 6V battery with this instructable ?</p><p>is there any full charge indicator in this circuit?</p>
<p>hi .. As dominick mentioned you can use a multimeter to first adjust the voltage. 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. After setting the limit you may then connect the battery to be charged.</p><p>Also, the LED goes off when the battery is sufficiently charged.</p>
<p>Adjust your trimmer or Potentiometer at the out put voltage with a multimeter and that will be your desired voltage </p>
<p>Hello,</p><p>the list of components does not mention the NPN trans. We do need them, right?</p>
Hi <br>Yes you would need the NPN 2N2222 transistors. Thanks for pointing it out. Shall update the list.
<p>can we use BC547 instead of 2N2222 transistor?</p>
<p>I think a BC547 should work</p>
<p>when i made a circuit in breadboard....i found some smoke coming out ....and when i check the components..i found that transistor(BC547)attached with trimmer is blown up.....hows it is possible?i have given 12v supply.....</p>
<p>hi .. sorry about that. Did you use a 5 watt 1 ohm resistor for R1? The BC547 has a collector current of 100mA while the 2n2222 has 1 A but I'm not sure if these matter as the transistor draws current from the voltage divider. But R1 would need a high watt rating as the battery migth draw 1 A which flows through R1. So the problem could be R1, a faulty transistor or a wiring error?</p>
<p>Hi...</p><p>Is it possible to use your setup on smaller input and output voltage. I need to charge 3.7v Li-on battery with 5-9v source?</p><p>Thx...</p>
<p>Hi,</p><p>I feel if you remove R2 from the circuit and instead connect the end of R4 (adjusted to about 880 Ohms) directly to the base of T1 you might be able to charge a 3.7 V battery with the above circuit. Source of 5-9 V should be fine.</p><p>Calculations Vo = 1.25 * ( 1 + R4/R3 ) = 1.25 * ( 1 + 880/470 ) = 3.6 V</p><p>I haven't tested this, so be careful and let us know how it goes.</p><p><a href="http://electronics-diy.com/electronic_schematic.php?id=729" rel="nofollow">here's an alternate design to charge 3.7 V batteries</a></p>
<p>Hi man, thanks for sharing! :) Would it be possible to use a circuit like the one below, or is it necessary to build a battery charger like yours? Is it possible to buy them cheaply pre-made? Many thanks.</p>
<p>Hi. It's not necessary to build the charger like mine. I built mine for fun to experiment and coz I didn't want to spend on a charger. Eventually I bought a cheap TP4056 based charger to charge 4.2 V Li-ion batteries from <a href="http://www.evelta.com/other-components/power-products/tp4056-module" rel="nofollow">http://www.evelta.com/other-components/power-produ...</a></p><p>You could try some local stores for pre-made chargers. Also, Many IC's are available to build more efficient chargers. I have shared the eagle files in case you want to make a PCB of the LM317 based charger.</p>
<p>Hi, thanks for the reply. I have a few of those charging boards that you linked, theyre great! Do you know if its possible to get something like them but for a 2 cell/3 cell battery? I want to be able to put them in a speaker enclosure, that would have to stay sealed, so the 1 cell charger is perfect, but I would need a 2/3 cell equivalent. Any suggestions? :) </p>
<p>Hi. Yep the tp4056 mudules great :-D regarding the 2-3 cells I haven't looked much into this and struggle with the same problem. I considered buying <a href="https://www.sparkfun.com/products/10473" rel="nofollow">this</a> but it might not be nice for your project. There are IC's like LT3650, LM3420, BQ2057WSN, BQ24004, MCP73842 which might be useful. But I was unsuccessful in using a TI sample due to a QFN package. Good luck :)</p>
<p>Hi, thanks for the suggestions :) I've been finding a lot of 'battery protection circuits/charging protection circuits'. Eg. http://goo.gl/MDWS41 Do these carry out the right function? Like could I hook up a charger directly to these, or is there other circuitry that needs to be in place too? Also does this circuit carry out the same function as the one I linked above, but just for 3 cell batteries? http://goo.gl/BHWaeE Cheers :)</p>
<p>Hi:</p><p> Nice work done.</p><p>What should I do If I need to set two thresh hold points. For Example I would like to charge a 6V 5Ah Li Ion battery, Circuit should start charging Li ion when voltage decrease from 4.5 V and stop charging when it equals to battery terminal voltage that is 6V. </p><p>This circuit immediately starts charging even when voltage drops 0.1 V from thresh hold. As If I add a relay in this circuit to cut off charging when voltage will be equal to terminal voltage/thresh hold voltage. When this circuit decrease 0.1 V from thresh hold relay again triggers and start charging. So A Tick Tick Tick Tick of relay will be there all time. Please suggest with your ideas. I really like this that is why I am writing some more on this. Thanks</p>
<p>Very nice.</p>
<p>Hi,<br>Have you tried to charge 1 Li-ion chell with it?<br>Is it possible to set charge voltage to about 3,7V?</p>
<p>This circuit is for a 2 cell Li-ion battery pack and successfully charged my 7.4V battery. Using the current setup I was able to set the limits from 7.08V to 9V. </p><p>To charge a 3.7V cell you might have to change the value of R2. See if <a href="http://shdesigns.org/lion-opt.html" rel="nofollow">this link</a> helps. I have to confess that I'm faced with the same problem and feel changing R2 to 1K might be the solution. I haven't tested it with the 3.7 V cell, Hopefully somebody guides us further before we blow up the batteries :-P</p>
<p>If it had possibility to safely charge single Li-ion cell, with use of microcontroller it would be great addition to recently added to i'bles Li-ion Capacity meter: <a href="https://www.instructables.com/id/Arduino-cell-capacity-meter/" rel="nofollow">https://www.instructables.com/id/Arduino-cell-capac...</a><br>to make automatic capacity meter. Microcontroller should just check when cell is fully charged, and then start the measuring procedure, and show measurement results ;)</p>
<p>Thanks ... I shall try building that :)</p>
It would be cooler if it had a cut off circuit..
<p>Totally agree. I just trusted scotts statements <em>&quot;</em><em>However it does not turn off the charge. Testing has shown that the current drops to almost zero anyway.&quot;</em><br>Anyway I keep monitoring the setup as I don't fully trust lipos</p>

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