Wednesday, February 1, 2012

How to Make an Automatic 12 volt Battery Charger Circuit Using IC LM 338

The IC LM338 is an outstanding device which can be used for unlimited number of potential electronic circuit applications. Basically the main function of this IC is voltage control and can also be wired for controlling currents through some simple modifications. Battery charger circuit applications are ideally suited with this IC and we are going to study one example circuits for making a 12 volt automatic battery charger circuit using the IC LM338.

Referring to the circuit diagram we see that the entire circuit is wired around the IC LM301, which forms the control circuit for executing the trip off actions. 

The IC LM338 is configured as the current controller and as the circuit breaker module. The whole operation can be analyzed trough the following points:

The IC LM 301 is wired as a comparator with its non inverting input clamped to a fixed reference point derived from a potential divider network made from R2 and R3.

The potential acquired from the junction of R3 and R4 is used for setting the output voltage of the IC LM338 to a level that’s a shade higher than the required charging voltage, to about 14 volts.

This voltage is fed to the battery under charger via the resistor R6 which is included here in the form of a current sensor.

The 500 Ohm resistor connected across the input and the output pins of the IC LM338 makes sure that even after the circuit is automatically switched OFF, the battery is trickle charged as long as it remains connected to the circuit output.

The start button is used to initiate the charging process after a partially discharged battery is connected to the output of the circuit.

R6 may be selected appropriately for acquiring different charging rates depending upon the battery AH.


Circuit Functioning Details (As Explained By +ElectronLover)

" As soon as the connected battery is charged fully, the potential at the inverting input of the opamp becomes higher than the set voltage at non-inverting input of the IC. This instantly switches the output of the opamp to logic low."

According to me:
V+ = VCC - 74mV
V- = VCC - Icharging x R6
VCC= Voltage on pin 7 of Opamp.
When The battery charges fully Icharging reduces. V- become greater than V+, output of the Opamp goes low, Turning on the PNP and LED.
Also,
R4 gets a ground connection through the diode. R4 becomes parallel to R1 reducing the effective resistance seen from the pin ADJ of LM338 to GND. 
Vout(LM338) = 1.2+1.2xReff/(R2+R3), Reff is the Resistance of pin ADJ to GND.

When the Reff reduces the output of LM338 reduces and inhibit charging.




  

95 comments:

  1. how many amp battery can dis be use 4?

    ReplyDelete
  2. You can build the following circuit:

    http://homemadecircuitsandschematics.blogspot.in/2011/12/high-current-10-to-20-amp-automatic.html

    ReplyDelete
    Replies
    1. What was the wattage of the resistors used in the circuit....?

      Delete
    2. All are 1/4 watt except R6 which may be around 1 watt.

      Delete
  3. how can i make a 12 volt DC output 7 to 10 amp current, out of 20 volts to 110 volts voltage input? can you help me plz.. tnx!

    ReplyDelete
    Replies
    1. You will have to incorporate an SMPS circuit for inputs that's more than 50 volts....

      Delete
    2. pls help how to make power supply charger, i'm using traspormer and 2 diode in5406 the problem is i forgot the diagram for this. pls help me.

      Delete
    3. Please refer the following article:

      http://homemadecircuitsandschematics.blogspot.in/2012/03/how-to-design-power-supply-simplest-to.html

      Delete
    4. This would work as a solar regulator/charger with the addition of a blocking diode to prevent losing charge at night, correct?

      Delete
  4. Hi there I'm Looking all over For a simple diagram for a charging circuit with a variable input from 24 volts to about 80 volts AC to a 12 volt 4 to 6 AH can you please help i looked every where on the internet and so far yours was the closest i could find on what I'm looking for..

    ReplyDelete
    Replies
    1. Hi, The above circuit won't be suitable because it cannot tolerate more than 32V at its input, the following circuit looks good, you can try it:

      http://homemadecircuitsandschematics.blogspot.in/2012/08/simplest-dc-cell-phone-charger-circuit.html

      The input can be from 24 to 80V DC.

      Delete
  5. hi swagatam , can i use 741 instead of lm301
    if yes then can u tell me the connections

    ReplyDelete
    Replies
    1. if we are using 741 instead of lm301
      where is the compensation pin(8-pin)
      is there any draw backs if neglect that pin connection
      thank you

      Delete
    2. yes due to the presence of the "start switch" a 741 will be difficult to replace the 301.

      but there are other options through which a 741 can be used for getting the same results as above.

      Delete
  6. Hello sir,
    Can u please help me on the capacity of the battery should be selected to store a power of 55W(1320Wh).

    ReplyDelete
    Replies
    1. Helo Rizmy,

      you may divide 1320 by the voltage to get the rating of the battery.

      Delete
  7. k sir. thanks alot.

    then I'm going to store half of this energy to the battery, using a 12V 60Ah battery. So can I use the above circuit to charge a 12V 60Ah battery?.. If not, what r the modifications needed.. please help me on this sir...

    Regards!

    ReplyDelete
    Replies
    1. use LM196 circuit for charging your battery. Refer to the LM196 datasheet you will get the circuit there.

      Delete
  8. thnk you sir.

    Can I charge a 12V 60Ah battery using this circuit?... If not what are the modifications needed?. could you please help me on this sir..

    ReplyDelete
    Replies
    1. Rizmy, The above circuit will not charge a 60 ah battery..... refer to my previous comment.

      Delete
  9. sorry for the inconvenience sir. I have typed the same message twice mistakenly.

    thanks a lot for your guidance sir. I'll look for it.
    thank you!

    ReplyDelete
  10. Sir,
    Cant I use your above circuit with LM196?.

    ReplyDelete
    Replies
    1. yes it can be replaced but R6 will need to be modified appropriately.

      Delete
  11. Thank you sir,
    Then please help me on calculating R6 according to my requirement sir.
    How did you arrive in 0.2ohm for the above circuit?.

    ReplyDelete
    Replies
    1. Hi Rizmy,

      What is your battery AH, is it above 100 AH? If it's below 100AH, R6 won't be required.

      Delete
  12. its obviously not above 100Ah. it's mostly a 60AH one. But sometimes I'll go for a 40AH one. If so is it not required to put a R6 resistor?.

    Then the above circuit without R6 resistor(S/C) con be used right?..

    Are the other components same as like your above circuit sir?. If I need to draw a current nearly 7-8A to charge the battery?.
    If any modifications needed please explain me sir.

    Regards

    ReplyDelete
    Replies
    1. then you can use it without R6.....but the input current should not be more than 1/7th of the battery AH.

      you may refer to the following article to know more regarding the IC specs.

      http://homemadecircuitsandschematics.blogspot.in/2013/04/15v-10-amp-adjustable-voltage-regulator.html

      Delete
  13. thank you sir!

    what about the input voltage then?. Is that should be more or equal 18V to charge the battery as you mentioned above?

    ReplyDelete
    Replies
    1. any voltage above 15V, and below 24V can be used.

      Delete
  14. If i am using a variable input from a turbine generator ranges from 5V to 15V, how should I use that input to charge the battery using this battery charger? what are the modifications needed?. please guide me on this sir.

    regards!

    ReplyDelete
    Replies
    1. the above circuit will not boost voltage

      Delete
  15. Thank you sir!
    To use this as a solar charger, a diode at the output is sufficient or any other modifications needed?

    ReplyDelete
    Replies
    1. According to me that would be enough, but it must be rated appropriately...

      Delete
  16. without R6 means sir is it short circuited or open circuited?.
    then how the comparator work to swith off the charging?
    can you please explain me sir.

    regards!

    ReplyDelete
  17. it cannot be open circuited for sure. so then how the comparator works without R6. if shorted always the inverting input voltage will be high and it outputs logic zero, isn't t sir?
    I was confused sir. please help me on this.

    ReplyDelete
    Replies
    1. It means, the R6 points should be replaced with a wire link.

      Delete
  18. then how lm301A works as a comparator?. according to your explanation above R6 only determines the voltage level of inverting input. so if we remove it how the comparison is done?

    ReplyDelete
    Replies
    1. check the article now....is it OK now?

      R6 is only for setting the charge current.

      Delete
  19. "According to me:
    V+ = VCC - 74mV
    V- = VCC - Icharging x R6
    VCC= Voltage on pin 7 of Opamp.
    When The battery charges fully Icharging reduces. V- become greater than V+, output of the Opamp goes low, Turning on the PNP and LED."

    you have mentioned this in your article. According to this R6 is controlling and adjusting the voltage according to the current drawn and making the inverting input high after charging.

    Then without R6 how LM301A operates as a comparator?

    ReplyDelete
  20. I dont see any changes in the article sir. Could you please help?

    ReplyDelete
    Replies
    1. don't worry about the article details, it was submitted by some other reader.

      pin#2 of the IC detects the battery high level, while pin#3 is fixed with a reference. when pin2 level goes beyond the pin3 level, the circuit latches up and stops any further charging of the battery.

      Delete
  21. Swagatam thanks. can i charge 12 volt 30 ampere battery with this circuit charager ?? help plz

    ReplyDelete
  22. Hi Swagatam,

    Im going to use this circuit to charge 12V, 35A battery by using input voltage, 20v-60V AC , what are the modification i need to do?

    Varuna

    ReplyDelete
    Replies
    1. Hi Varuna,

      No modifications would be needed, but the input voltage must not exceed 32V, the only precaution you need to observe, and also the input source must not generate more than 5 amps for the specified battery.

      Delete
    2. Sir,
      Tnx for the repply.

      Actually i hope to use this circuit to charge a 12V-35A battery by using charging input of the Diesel THREE WHEELER that made by Bajaj.
      Bcoz the original rectifier falty and not avialable in the market. I mesured the charging voltage of the output and its avilable about 20V an idel, and up to 60v when accalarate. plese give me a modyfy version of this or any other circuit for this issue.

      Tnx a lot.
      Varuna.

      Delete
    3. OK, then you can try the following circuit:

      http://homemadecircuitsandschematics.blogspot.in/2013/08/simple-zero-drop-solar-charger-circuit.html

      but it's not a tested design, according to me it should work.

      Delete
  23. Sir,
    Thx for the repply.
    I already made following circuit, and think to use my above mention application

    http://homemadecircuitsandschematics.blogspot.com/2012/05/make-this-voltage-stabilizer-circuit.html#uds-search-results

    Is there any wrong with this?
    what is

    ReplyDelete
    Replies
    1. The above link circuit will not tolerate more than 35V, so again it won't suit your application.

      Delete
  24. Sir Swagatam,
    I could'nt find 1N457 Diode. What can use else instead of it ??? is there any substitution ?? Plz help!

    ReplyDelete
  25. hi swagatam,
    hoe it can be possible that Vout=14V? for me the right expression when pnp is off is Vout=1.2+1.2(R1/R2+R3)
    and this results 15.9V right?

    ReplyDelete
  26. hi swagatam,
    how can it be possible that Vout=14V? when pnp in off the righ exression is Vout=1.2+1.2(R1/R2+R3) and this results 15.9V right?
    thank you

    ReplyDelete
    Replies
    1. Vout = Vref(1 + R2+R3/R1) + Current ADJxR1

      Alex, please solve the above formula which the correct one.

      Delete
  27. hi swagatam

    you sayd that when the pnp is on vout=14V is this true? but when pnp is off Vout=15.9V (V=1.2+1.2(R1/R2+R3)
    so when Reff reduce the voltage charger it change from 15.9 to14?
    tell me if something is wrong
    thank you
    alex

    ReplyDelete
    Replies
    1. Hi Alex,the PNP is only for illuminating the LED, it has no relation with the IC. Please refer to the formula presented in the previous comment by me.....it's according to the datasheet and is correct
      the formula which you have used could be incorrect

      Delete
  28. my last question is how can I find output current?

    thank you so much!!

    ReplyDelete
    Replies
    1. the output current will depend on the load, connect an ammeter in series with he load for finding the output current.

      Delete
  29. can use lm317 for this circuit? i only want to charge 12v 4amps battery.

    ReplyDelete
  30. hello sir! how can i know if the circuit is charging the battery or not? how can i add a charging indicator in this circuit.., please help me!

    ReplyDelete
    Replies
    1. hello eric, the led will light up once the battery is charged.

      Delete
  31. how can i modify this to charge both 6v and 12 battery and make a select button(switch) so i can chose wich battery to charge

    ReplyDelete
    Replies
    1. use two cacuated resistors in place of R1, make one of their ends common and connect the joint to the IC while terminate the lower free ends to a selector switch such that the switch selects and connects the resistors to ground for getting the desired 6V or 12V at the output

      Delete
    2. sir plz help me where I have to connect second wire of input and input is ac or DC ??

      Delete
    3. the negative wire should be connected to the common line which connects with pin4 of the IC, the input should be rectified and filtered DC

      Delete
  32. Hi Swagatam,

    Please advise the formula to calculate the value of R6. Alternatively, please advise the value of R6 for the Charging Current (Constant) of 500mA with 24V.

    Thanks for your kind help.

    Rajneesh

    ReplyDelete
    Replies
    1. Hi Rajneesh,

      R6 = V/I = Voltage/Chrg. current

      Delete
  33. hello Sir........I want to know Does this circuit work??? If yes then can I use for charging 3-5 Amp ,12 volts battery for charging if my supply(input) is 12 volt D.C.

    ReplyDelete
    Replies
    1. Hello parashar, yes this circuit will work, you can get 3 to 5 amp output from this charger but for charging a 12V batt you will need to apply a minimum 15V input to the IC

      Delete
  34. hi sir
    can i charge 12 volt 3 amp battery using this circuit , if no then what i have to change this circuit ?

    ReplyDelete
  35. hello sir,
    can i zinc carbon batteries using this circuit??

    ReplyDelete
  36. sir i have used 1ohm resistor instead of 0.2,will it make a difference??and i hav kept 12v rechargeble lead acid battery from ups to check the o/p,will it work??please let me know asap

    ReplyDelete
    Replies
    1. 1 ohm will do,
      the input amp should be rated at around 1/10th of battery AH, only then it would work correctly

      Delete
  37. Sir can i charge rechargable batteries of digital camera using this circuit,it has 2.5AH,will it go???

    ReplyDelete
  38. Sir can I use 741 instead of 301? i don't have a 301 with me now, but i have 741

    ReplyDelete
    Replies
    1. jamey, i don't think 741 would work in the above circuit because of pin1 and pin8 specs which are used here from the IC 301.

      Delete
  39. Dear sir im going to make above charger.
    i have following problems please answer
    1.how i can put "still charging" and "charging completed" LED's to above circuit?
    2.R3 230 ohm is not available 220ohm will do or not?
    3.what is the value of R6 , 0.2 means ?

    ReplyDelete
    Replies
    1. Dear Jayanth,

      the above circuit is not so advanced, please make the last circuit given in the following article:

      http://homemadecircuitsandschematics.blogspot.in/2012/07/making-simple-smart-automatic-battery.html

      Delete
  40. Dear,sir I want to build one IR remote control as design by you for the first time to control remotely my ceiling fan.Can you please help from where I can buy the parts and then to begin?

    ReplyDelete
    Replies
    1. Dear Partha,

      you can begin with the following circuit, it's fairy simple so would suit you:

      http://homemadecircuitsandschematics.blogspot.in/2012/02/how-to-make-simple-infra-red-remote.html

      Regarding parts, you will need to inquire with your local electronic spare parts dealer, he'll know better

      Delete
  41. Hi Swagatam, Can op amp LM301A be replaced by uA741? I have a number of these lying with me.

    ReplyDelete
    Replies
    1. Hi aquarius, in the above design it can't be used, because of pin1 which is not compatible with IC 741

      Delete
  42. Hi, What should br the wattage of 500E resistor ?

    ReplyDelete
  43. 7 ampere for battery charger I just need the LM317. whether it can be used as a substitute for LM338. and whether it can be replaced with the LM741 to LM301. thank you :)

    I am from INDONESIA.

    ReplyDelete
  44. very difficult to get LM301.
    LM301 with what code can be replaced.

    ReplyDelete
    Replies
    1. 301 cannot be replaced with 741 in the above design,

      you can try the following circuit:

      http://homemadecircuitsandschematics.blogspot.in/2012/02/how-to-build-automatic-6-volt-12-volt.html

      LM317 can be used in place of LM338 and 741 instead of LM324

      Delete

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