High Current Li-Ion Battery Charger Circuit

The post explains a high current Li-Ion battery charger circuit which can be used for charging any high current, high AH rated Li-ion battery from a car or a truck battery. The idea was requested by Mr. Neil

High Current Li-Ion Battery image

Charging a 8800 mAh Li-Ion Pack

This is perhaps very cheeky of me to ask for your help, but my design skills are limited in electronics and as a volunteer my budget is limited.

I am a volunteer for a local Search and Rescue organisation (Suffolk Lowland Search and Rescue), we are on call 24hrs a day 365 days a year, our work involves finding anyone who has gone missing in Suffolk (and bordering county’s).

Search often take place during the hours of darkness and we have a particular need for good torches, which need to be ready for action at a moments notice.

I am part of the mountain bike rescue team, we cover ground very quickly and can search paths much faster then foot teams, lights are again very important and I hope this is where you can help.

I have recently bought a Cree LED light for my bike, it is powered by a 8.4v Li-ion 8800mAh battery pack, I have 2.

These units came with a mains powered charger (240v UK) and what I would like is to be able to charge them in the car where the bike is kept.

I noticed you have already designed some charging circuits for this type of battery and I wonder if you could modify your design to be able to charge from a 12v car circuit to these specification batteries.

The car circuit will be switched with the ignition. I am very capable of constructing the circuit, it’s just my design skills that are limited!

I very much appreciate anytime you spend on this, it will help not only me, but potentially any lost sole in Suffolk.

Kindest regards,


The Design

The shown high current Li-Ion battery charger circuit is featured to charge any Li-ion battery upto 5 AH with the shown IC2, or for 10AH batteries if IC2 is appropriately replaced with a LM396

The LM338 IC2 is a versatile voltage regulator IC which can be specifically configured for charging Li-Ion cells with the essential features such constant current and constant voltage.

The above design is configured as a constant voltage Li-ion charger, since we assume that the input supply to be a constant current.

However in case the input supply is not current limited, the IC2 can be enhanced with an effective constant current feature. We will discuss this at the end of this explanation.

The design consists of two fundamental stages, the IC2 voltage regulator stage and the IC1 over charge cut-off stage.

IC2 is configured in its standard voltage regulator form, where P1 functions as the control knob and can be adjusted to generate the required charging voltage across the connected Li-ion battery at the output.

IC1 pin3 is the sensing input of the IC and is terminated with a preset P2 for facilitating the over charge voltage level adjustment.

The preset P2 is adjusted such that when the battery reaches its full charge value, the voltage at pin3 just becomes higher than pin2, resulting in an instant high at pin6 of the IC.

Once this happens the high from pin6 latches on to pin3 with a permanent high via R3, D2, freezing the circuit in that position.

The above high is also delivered at the base of the BC547 which immediately grounds the ADJ pin of IC2 forcing it to shut down its output voltage thereby cutting off the voltage to the Li-ion battery.

The Red LED now illuminates indicating the full charge level and the cut off conditions of the circuit..

Circuit Diagram

High Current Li-Ion Battery Charger Circuit with LM338

Warning: The supply pin polarity of IC 741 opamp are incorrectly configured. Please make sure that you connect pin#4 of the opamp with ground line and pin#7 with the positive supply line.

PCB Design

PCB Design Li-ion high current charger

Parts List fro the proposed high current 12V/24V li-ion battery charger circuit

R1, R5 = 4K7
R2 = 240 Ohms
P1, P2 = 10 K Presets
R3, R4 = 10K
D1, D5 = 6A4 diode
D2 = 1N4148
D3, D4 = 4.7Vzener diode 1/2 watt
IC1 = 741 opamp for 12V input, LM321 for 24V input
IC2 = LM338

How to Set up the circuit.

  1. Initially do not connect any battery at the output, and rotate P2 so that its slider touches the ground end, in other words adjust P2 to make pin3 to zero or ground level.

  2. Feed the input voltage, adjust P1 for getting the required level of voltage across the output where the battery is supposed to be connected, the green LED will be lit up in this position.

  3. Now very carefully move P2 upwards until the the red LED just illuminates and latches in that position, stop moving P2 any further, confirm with green LED shutting of in response to red LED illumination.

  4. The circuit is set now for the required high current Li-ion charging from a  car battery or any 12/24V source..

Adding a Constant Current Feature in the above Design

As shown below, the above design can be further improved by adding a current control feature, which makes the proposed high current Li-ion charger circuit perfect with the features of CC, and CV, that is with constant voltage and constant current attributes.

High current Li-Ion Charger with Current Control Facility

Warning: The supply pin polarity of IC 741 opamp in the above diagrams are wired incorrectly. Please make sure that you connect pin#4 with ground line and pin#7 with the positive supply line.

Simplified Design

While the above explained circuits are great with their features and working, the use of LM338 makes the design a bit complex, and costly.

A little tinkering reveals that the application could rather be implemented using only a single opamp and a BJT based current control as shown below:

High Current Li-IOn charger with single opamp

The concept has been tested thoroughly, the video proof can be seen here.

Need Help? Please send your queries through Comments for quick replies! And please Bookmark my site :)


Faizan Hamayun said…
Hello regarding this circuit.
Can it be modified for 4.2V,1200mAH while charging current should be 0.5A.In place of LM338 LM317 can be used? and in place of Lm741 can we use LM358 or Lm393?

And if i put a LED flasher in this circuit when in standby and it will go off when battery is connected how that be possible?.(i have flasher circuit just need connection)
Swagatam said…
yes you can use it for the required purpose with LM317 IC

i could not understand the operational details of your flasher, pls explain again properly.

alternatively you may also try connecting the last circuit from the following link with the battery terminals:


Faizan Hamayun said…
I have finalize all circuitry just need this scenario to be fulfilled:

I want slow flashing =Standby mode
Fast flashing= When charging (When battery connected)
Solid = Fully charged.
Faizan Hamayun said…
Waiting for the reply.
Swagatam said…
the circuit will become complex and elaborate with 3 opamps, and many transistors.
Faizan Hamayun said…
I just need a battery sensing switching circuit.All other i have.
Swagatam said…
you can try the second circuit from the following article:

Faizan Hamayun said…
How it can sense the battery and switch the flasher circuit to charger circuit when battery is connected?
Swagatam said…
I explained the sensing procedure of opamps it in the following article, if you remember

Sunil Kumar said…
Hi pls let me know what is the value & number of T1
Swagatam said…
T1 is BC547 transistor
Shuddhatam Jain said…
respective sir happy diwali
to day i read High Current Li-ion Charger Circuit from your site can this circuit protect battery from over charge or over discahare? pl tel me because low battery cut -off and overload protection circuit not work in bike my 6 li-ion battery is shot for this circuit
Swagatam said…
Happy Diwali to you too Shuddhatam,

yes the circuit is equipped with an automatic over charge control and cut off

But, you must know all the basics of electronics and should be able to implement the circuit correctly as explained in the article, otherwise you may not be successful with the results

Shuddhatam Jain said…

in this circuit have over discharge cut off?

is it recommend just for 1 Li-Ion battery or also possible for 4 ?

With kind regards,
Swagatam said…

yes it can be used for one Li-ion preferably which are rated with higher AH, but not for 4, because Li-ion batteries are not recommended to be charged in parallel or in series unless the charger is specially designed to handle this
rajesh g said…
Respected Sir, Happy NEW YEAR.I am Rajesh GS.Working as an service/repair technition.I need a help from you.I want to build a charger for Li-ion V-Lock Fxlion BP2000 14.8v/9AH/130Wh .It need 16.8v/2Amp chrger(as per their charger catalog)I saw your great idea "high current li ion chrger' circuit.Is this circuit good for it,or need any change in parts/circuit.I think li ion battery need cv,cc,to charge?so can i add your another CV,CC (using LM338)circuit before this circuit?Please help me withyour great advice ASAP.Thank you very much...
Swagatam said…
Happy new year to you too Rajesh!

You can definitely use the above concept but make sure you understand the building and the set up procedures correctly and implement them correctly.

If your transformer or the input power source is rated at 2amp for the mentioned 9AH Li-ion battery then I think you won't need to add anything before the shown circuit, you can use it as given above.
rajesh g said…
Thank you very much sir for your replay.I am planning to use 19v/3.6amp Laptop adaptor as power supply.(is it OK ?)so i asked to add CC.CV circuit.Sir i built this chrger,but it is not cutt off sharpily(i think,that is lack of my understanding this circuit/set up).I tested with a 12v/9Ah SLA battery and LM741.Is it ok?. I have one doubt also,D5 6A4 diode have its on voltage drop(.7v) is it affect the sharp cuttoff/output volts?Sir can you please explain detailed set up procedure simply again for me.(I know you are a very busy man)Once again thank you...
Swagatam said…
Rajesh, initially you mentioned that your battery was Li-ion but now you are specifying it as SLA....for 9SH SLA battery 3.6amp will be quite high but not for Li-ion...so please specify the correct one that you are using.

any opamp circuit will produce extremely sharp cut-offs so even the above circuit will do the same undoubtedly, if you have not understood the concept then I am afraid you'll continue having problems with this designs.

for compensating the 0.7V drop you can make the LM338 output at 15V.

You can study the following article for more info:

Unknown said…
Hello sir, I can't understand the last picture Rx explanation (Rx=1.4/current limit (amps)). If I want to limit my current at 1 ampers or 1000ma, I need a 1.4 ohm resistor?
how can I choose the suitable resistor in Watt? (I mean 1/4W,1W or higher?)
another question is that setting up the last picture circuit is the same as what you explain for earlier circuit?
Please help me.
Swagatam said…
Hello, yes the pot setting up procedure will be identical to the first circuit.

the Rx wattage can be calculated as follows:

watt = 1.4V x 1amp = 1.4 watts
Unknown said…
Hello sir.
I want to build a 9volt-30ma ni-mh battery charger with auto cut off(stop charging when the battery gets to its full charge). But I don't want to use integrated ics. I want to build a reliable, cheap circuit that just uses opamps and other simple things like transistors and cte. I want to have a circuit like what you explain in this page for a li-ion battery charger.
Thanks. Please help me sir.
Swagatam said…
You can try the following circuit for your requirement

Curtis Newton said…
Hi, I really dont understand D2 D4 & D5 purposes
and in the second diagram, the two added 4148 ???

everytime I see a diagram I feel like I dont understand anything, and I have been doing electronics for years now :-)
Swagatam said…
Hi, D2 makes sure that R3 does not form a potential divider with the preset as long as the output of the opamp is 0V, and this D2/R3 loop only becomes relevant and active when the opamp output becomes positive, and lathes the pin3 of the IC permanently.
D4 helps to block any leaking offset voltage from the opamp output and prevents false triggering of BC547
D5 cuts down the 5V to 4.3V which looks more suitable for charging a 3.7V Li-Ion cell.

the two 1N4148 in the second design are for isolating the Rx voltage from the opamp output voltage.
sunny said…
Hello sir,
I need to build up 12 v 8800 mah li ion 3s4p charger with protection circuit.I have a supply of 12 v 2amp of smps circuit can i use it?And i also need a circuit which automatically switch to this battery supply when there is no ac power.I have used 12 v 2amp smps . So how can i make circuit for charging a 12 v 8800mah li ion 3s4p battery using this smps supply with protection circuit and auto switch to battery mode incase of power outage with path isolation of ac mains and battery supply path.
Swag said…
Sunny, yes you can use the above circuit for your application,, but a 12V supply will not charge a 12V battery, change it to a 14V supply input.

for changeover you can simply use a relay with the input supply and wire the battery positive with N/C, input supply with N/O and pole with the load....negative line can be common with the battery, input supply and the load
sunny said…
Thank you sir for your valuable reply. But sir where do i connect relay circuit for switchover and charging circuit after smps circuit ? How can i increase smps output voltage from 12v to 14v with same 2 amp rating.I am confusing about relay connection so please sir guide me about this. And I have used nema 17 motor 200 steps/revo. Ao what will be the maximum current it will draw at very low speed. Battery selection will be depends on this current. I have chosen 12v 8800mah li ion battery. This battery can give longer backup capacity? (aprox. 6 hr.)
Swag said…
Sunny, You can connect the relay coil with the SMPS output. and connect the contacts as explained in the previous comment.
if your SMPS has a preset facility to tweak the voltage then you can use it, otherwise you may have to open the SMPS and do some serious modifications as explained in the following article:


sorry I cannot suggest about the current consumption of the motor, you will have to find it from the motor's technical specs
Dean Esprez said…
Hello Mr. Swagatam
I would like to use the above design to charge a 36 v dc 17 AH Lithium battery for an electric bike application.
The source is 120 v AC step down to 40 v dc after the full wave bridge rectifier and (1/5 of 17A) 3.4A of secondary supply current capacity. What design change do I need to do to make it work for a 40 v dc supply? I assume the parts above will work as it is. My concern is the supply voltage for LM321 and LM338. Could I use a zener diode instead to drop the supply voltage of 321 to 24v and 338 to 32v? No rush to reply. Great website and enthusiasm for all electronics hobbyist. Thank you for sharing your time and talent. Dean - Vancouver BC Canada
Swag said…
Thank you Dean, I am glad you liked my site.

A 36V battery will require 42V to get charged fully, while the maximum permissible input to a LM338 IC is lower than 40V, therefore the LM338 section cannot be used for charging your battery.

You can perhaps try the second last design from the following link and customize it for your purpose:


You can eliminate the Q4, R2, D1 stage, as it may not be necessary.
R5 may be calculated as follows:

R5 = 0.7 / safe charging current

This resistor could be replaced with a link and the Q5 stage eliminated if the input supply from the transformer is selected to be around 3 to 5 amps.
The battery may then be directly charged from the output of the above circuit, however it must be ensured that the output is precisely set at 41V, that's 1V less than the actual full charge level, this will prevent the battery from getting fully charged to the edge, and an extra auto cut-off circuit could be avoided.
sir I want to controll 14.8v li poly battery charging, is the above given circuit is tested?Is this circuit will be suitable to use for 4s li_poly/li-ion battery for 14.8v? if yes pls reply as soon as possible?
Swag said…
Anil, the above circuit is tested, but it will not charge the cells separately, rather the entire series module together, end to end
Abraham said…
Thanks a million! Please IF need circuit diagram of 24volts 12amps charger circuits.
You are doing a great job.
S.Sharma said…
Sir,I want to simulate the above circuit..Can u please tell me which simulation software i can use for simulation???
Swag said…
Hi S.Sharma, sorry I never use simulator so I can't suggest about them, you can build them practically and verify...all will work with 100% perfection.
Marcus Bawa said…
Sir pls i want to charge 7.4v 8ah lithium ion battery
Swag said…
Marcus, you can use the last circuit for your need, use 8.4V, 5 amp or lower as the input
Marcus said…
Thank you sir,can i use 12v 5amp as my input to charge 7.4v 8ah ?
Swag said…
The input should be 8.4V strictly, do not use 12V
marcus said…
sir thanks for your assistance but pls help me my 741 is heating.thanks
Swag said…
How much voltage have you used at pin#7 of 741, make sure it's not over 15V
Marcus said…
I use 12v as input sir
Swag said…
at 12v 741 will never become hot, there could be some other fault in the connection, or the IC itself could be faulty, so please check everything accordingly.
Marcus said…
Sir i check,there is no error,please if you can enlighting me why pin7 is going to ground and pin4 to ground.thank i appreciete your site
Swag said…
Hi Marcus, I am very sorry, the diagram is showing wrong supply polarity across the IC pins of 741...pin#7 should go to the positive, and pin#4 to the negative line. I think your IC might have already burnt, so please use a new IC and change the supply pins accordingly.

I'll write a warning message under the diagram immediately.

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