Saturday, July 21, 2012

Making a Simple, Smart Automatic Battery Charger Circuit - Universal Battery Charger Circuit

The following automatic smart battery charger circuit was exclusively designed by me in response to requests from two keen readers of this blog, Mr. Vinod and Mr.Sandy.
Let's hear what Mr.Vinod discussed with me through emails regarding the making of a smart battery charger circuit:

"Hi Swagatam,
My name is vinod chandran. Proffessionaly i am a dubbing artist in malayalam film industry but i am an electronic enthusiast too. I am a regular visitor of your blog. Now i need your help. I just built an automatic SLA battery charger but there is some problems with that. I am attaching the circuit with this mail. The red LED in circuit is supposed to glow when battery is full but it glows all the time .(my battery shows only 12.6v). Another problem is with 10k pot. there is no difference when i turn the pot left and right. . So i request you to either correct these problems or help me to find an automatic charger circuit which gives me a visual or audio alert when battery is full and low . As a hobbyist i used to make things from old electronic appliances. For the battery charger i have some components. 1. Transformer from an old vcd player. out put of 22v, 12v,3.3v. And i don't know how to measure ampere. My DMM has only the ability to check 200mA. It has a 10A port but i can't measure any ampere with that.(meter shows "1") So i assumed that the transformer is above 1A and below 2A with the size and requirments of the vcd player. 2. Another transformer -12-0-12 5A 3. Another transformer - 12v 1A 4. Transformer from my old ups(Numeric 600exv). Is this tranformer's input is regulated AC ? 5. couple of LM 317's 6. SLA battery from old ups- 12v 7Ah. (Now it has a 12.8v charge) 7. SLA battery from old 40w inverter - 12v 7Ah. ( the charge is 3.1v) One thing i forgot to tell you. After the first charger circuit, i made another one (i'll attach this too). This is not an automatic one but it is working. And i need to measure the ampere of this charger. For that purpose i googled for an animated circuit simulation software but didn't get one yet. Atlast i found one in this link (http://www.cs.technion.ac.il/~wagner/index_files/ckt_anim/). But i can't draw my circuit in that tool. there is no parts like LM317 and LM431(variable shunt regulator). not even a potetiometer or led. So i request you to help me to find a visual circuit simulation tool. I hope you will help me. regards


vinod chandran"










Hi Vinod, > > The red LED should not glow all the time and turning the pot should change > the output voltage, without the battery connected. > > You can do the following things: > > Remove the 1K resistor in series with the 10K pot and connect the pot's > relevant terminal directly to ground. > > Connect a 1K pot across the base of the transistor and ground (use center > and any one of the other terminals of the pot). > > Remove everything that's presented at the right side of the battery in the > diagram, I mean the relay and all..... > > Hopefully with the above changes, you should be able to adjust the voltage > and also adjust the base transistor pot for making the LED glow only after > the battery is fully charged, at around 14V. > > I don't trust and use simulators, I believe in practical tests, which is the > best method of verifying. > > For 12v 7.5 ah battery, use a 0-24V 2amp transformer, adjust the output > voltage of the above circuit to 14.2 vollts. Adjust the base transistor pot > such that the LED just starts to glow at 14V. Do these adjustents without > the battery connected at the output. > > The second circuit is also good but is not automatic....is current > controlled, though. > > Let me know your thoughts. > > Thanks, > Swagatam


Hi Swagatam Your Idea is graet. The charger is working and now one LED is glowing to indicate the charging is in progress. but how can i configure the charge full indicator LED. When i turn the pot to ground side (means lower resistance) LED starts glowing. when resistance goes high LED will be off. After 4 hours of charging my battery shows 13.00v. But that charge full LED is off now. Plz help me.

I am sorry disturb you again. The last email was a mistake. i didn't see your suggestion correctly. So please ignore that mail. Now i adust the 10k pot to 14.3v(it's quite difficult to adjust the pot, because a slight variation will result a bigger voltage output. ). And i adjust the 1k pot to glow a little. Is this charger supposed to indicate a 14v battery?. After all let me know the danger level full charge of the battery. Once again thanks. regards vinod chandran
Hi Swagatam, As you suggested, everything was alright when i test the circuit from breadboard. But after solder into PCB thing are happening strangely. The red LED is not working. charging voltage is ok. Anyway i am attaching the image that shows the present condition of the circuit. plz help me. After all let me ask you one thing. Could you please give me an automatic charger circuit with a battery full indicator. ?.
Hi swagatam, Actually i am in the middle of your automatic charger with hysteresis feature. I just added a few modifications . i will attach the circuit with this mail. plz check this out. If this circuit is not ok then i can wait for you to tomorrow . regards vinod chandran






I forgot to ask one thing. My transformer is about 1 - 2 A. Idon't know what is the correct. how can i test with my multimeter?. Besides if it is a 1A or 2A transformer, how can i reduce the current to 700mA. regards
Hi Vinod,
The circuit is OK, but won't be accurate, will give you a lot of trouble > while adjusting.
A 1 amp transformer would provide 1amp when short circuited (check by connecting the meter prods to the supply wires at 10amp range and set to either DC or AC depending upon the output). Meaning the maximum power of is 1amp at zero volts. You may use it freely with a 7.5 ah battery, it won't do any harm, as the voltage would drop to the battery voltage level at 700ma current and the battery would get safely charged. But remember to disconnect the battery when the voltage reaches 14 volts.

Anyway, a current control facility would be added in the circuit that I would be providing you, so there's nothing to worry Regards.
Hi Vinod,
I'll provide you with a perfect and easy automatic circuit, please wait >> > until tomorrow.
Hi swagatam, I hope you will help me to find a better solution. Thank you. regards vinod chandran




In the meantime, another keen follower of this blog Mr.Sandy also requested a similar battery charger circuit through comments......

So finally I designed the circuit which will hopefully satisfy the needs of Mr.Vinod and Mr.Sandy for the intended purpose.
The following figure shows an automatic 3 to 18 volts, voltage controlled, current controlled, double stage battery charger circuit with standby charging feature.


For circuit explanation please read the comments.....



130 comments:

  1. hi swagatham
    thanku very much

    can i use this charging circut with 5ow inverter circuit and low voltage cut off circuit collectively?

    where i can get pcb boards of this circuits?

    ReplyDelete
    Replies
    1. Hi Sandy,

      Yes you may use it.....PCB will need to be procured from a PCB maker only.

      Delete
  2. Hi swagatam,
    Thank you for this amazing circuit. I am waiting for your circuit explanations. There is no LM338 in my local shop. what if i connect LM 317 ?. And i only got a 6.8v 1W zener. Once again thanks.
    -vinod chandran

    ReplyDelete
    Replies
    1. Hi, Vinod,

      Thank you!

      You may use LM317 here for charging a 12v 7.5 ah battery but for other bigger batteries you will need LM338.

      Zener diode is not crucial, you may use any value from 3 to 9v

      I'll update the explanations soon...

      Regards.

      Delete
  3. Hi Swagat
    Zener diode is not crucial because of the op-amp,isn't it ?.Last day i just try to learn about this op-amp. What i understand is, when the pin 3 goes higher than pin 2, this ic will produce output in pin 6. So we have to adjust the pot to a position which gives a voltage little more than the zener breakdown voltage. I am i right swagat ?. What about the two diodes ?.that part of this circuit is still an enigma for me. please explain ..
    Regards
    vinod.

    ReplyDelete
    Replies
    1. Hi Vinod,

      You are absolutely right.

      The two diodes are kept to let the battery get charged at the stand-by voltage even after the relay has tripped. This will keep the battery topped-up all the time and will not allow it to discharge after the relay has tripped.

      Actually the two diodes should be replaced with a high watt resistor of some calculated value for charging the battery at lower current rather than lower voltage as with the diodes.

      Regards

      Delete
  4. Hi Swagat,
    I hope the two diodes in series with each 1k resistors are LED's. aren't they connected to output pin of IC ?. Why i am asking this because you clearly illustrated the junctions with a dot and non junctions (like in between zener and 10k resistor)with a gap.

    ReplyDelete
    Replies
    1. Hi Vinod,

      Yes they are connected to the output of the IC, and are there for indicating the relevant charging status.

      Delete
  5. Hi Swagat,
    I am confused about that the two diodes in the positive terminal. After tripping the relay the battery get charged a voltage of 1.4- actual input voltage . are you sure the battery won't be overcharged ?. The second idea is comparatively good lower current means it is a trickle charger...But how to calculate the value.?. I need to charge the battery with 500-700mA. After the relay tripped this current should be 100 mA or something like that. Am i right swagat..

    ReplyDelete
    Replies
    1. Hi Vinod,

      You are right.

      We can use ohm's law to calculate the resistor value:

      R = V/I = 14/0.1 = 140 Ohms...around a 3 watt resistor will do.

      Regards.

      Delete
    2. Actually the float charge should be much lower than that, probably at around 20 mA.

      So R = V/I = 14/0.02 = 700 Ohms 1/4 watt will be better.

      Delete
    3. Hi swagat, I am planning to add a 1 ohm resistor as the current limiter. By your formula 0.6/0.6A=1. But what will be power rating of that resistor ?.In this circuit you are illustrated a regulated power supply. my question is about the value of R1 and R2.My Electronics2000 software shows that R1=240 ohm and R2= 2.5 for 14.2v output.So swagat plz confirm these values.
      regards

      Delete
    4. Hi Swagat,
      Do i need 1 diode there for protecting the circuit ?.If so Do i need to increase the charging voltage to 14.9 ?

      Delete
    5. Yes your all calculations are correct...wattage may be found by using the formula:

      W = V*I = I^2*R

      Regards.

      Delete
    6. Yes you may add one diode (1N5402) for better safety and increase the voltage from the IC to 14.9V.

      Delete
    7. You are talking about adding this diode at which place? Is this diode necessary?

      Delete
    8. Hi everyone
      A little late, but a common mistake in charging lead acid batteries is too low a charge voltage. LA batteries (12 volts ones) require a charge of 15.2 volts to get fully charged. This is difficult to achieve without boiling the batteries though. Only going to 14.2 volts will shorten the life of the battery because it does not return sulphates to the electrolyte and eventually the plates will increase the sulphate buildup- This is accumulative (it is never completely removed at the standard 14.2 volt charge). HOWEVER, getting to 14.2 volts must be done very carefully and slowly - high current, low voltage. This is usually only accomplished with some sort of a "pulsed" current so the batteries get a short rest between pulses and do not get a chance to boil.
      Having said that, getting to 14.2 V is pretty standard for most chargers (meaning that most are not very good for your battery). Even if you just do the standard 14.2V most of the time and once every 10 cycles or so give them a 15.2 volt boost it should be OK. Just keep in mind that 1) 14.2 volts will not allow your battery to last as long as it should AND, 2) be careful not to boil the battery when trying to get to 15.2 - that is also bad for the battery and if it cannot be achieved, just go as high as you can without boiling.
      Things are generally not what they seem in the world of "standard".
      I wish I could give you a circuit that would do the 15.2 volts reliably but I am not an electrical design engineer.
      Cheers
      Joan

      Delete
    9. Thanks Joan! however I don't agree with you.

      The standard spces are always the correct and safe.

      Delete
  6. Hi swagat,
    Thank you . So i need to connect a resistor instead of that diodes. But i think the resistor should be 1/2W. because the power in that point is 284mW.(14.2*0.020). Anyway i am going to build this circuit.Once again thanks for this circuit.
    regards.

    ReplyDelete
  7. Hi swagatam,
    Can you please explain how to adjust the level which the relay turned on this charger ?. That means this charger will turned to a trickle charger when the battery gets a particular high voltage. But when will it turned to natural type charging. How can i adjust that level.?. please explain

    ReplyDelete
    Replies
    1. Hi Vinod,
      The circuit is not equipped with a low voltage detection facility. Actually if you remove the two diodes the battery will start discharging the moment relay trips, and after the voltage drops a few millivolts the relay will again switch OFF, this will keep on repeating giving rise to a rapid ON/OFF of the relay. The addition of the two diodes restricts the battery from discharging quickly, the same will happen if the diodes are replaced with a resistor, and thus this stops the relay from chattering at the cut off threshold.

      So this how the opamp in the above circuit would basically function. For making it detect the low voltage situation of the battery, say at around 11.5V we would have to add another opamp or add enough hysteresis to the present opamp, such that once the relay switches ON and cuts the battery, it would again switch OFF to restart the charging process only when the battery voltage reaches 11.5volts.

      Regards.

      Delete
  8. Hi Swagat,
    I was modified your charger with hysteresis feature. Because i failed to build your smart charger today. So i decided to modify the old one. This is the modifications: 1)added 5 diodes(1N4007) to increase the hysteresis. Now the charger should turn on when the battery voltage reach 12v. 2)The relay is DPDT relay. So i just connected a 270 Ohms resistor to the charger output and when the relay gets off the current will pass through this resistor( about 30mA). Thus this charger will be a trickle charger.And a red LED will indicate the charging mode. Anyway i can't test accuracy of the hysteresis level because my battery never gets 12v yet. By the way could you please post a subwoofer filter circuit with frequency adjustment and volume controller ?. Single power supply is desirable .

    ReplyDelete
    Replies
    1. Hi Vinod,

      That's nice.

      A subwoofer filter will be difficult for me to design because it requires too many calculations, however you can find plenty of good circuits over the net if you just google a bit.

      I'll try to figure out a better one, though, if I find one I'll post it in this blog.

      Regards.

      Delete
  9. Sir, Can I use this circuit with 15-24 V 0.5 amps dc circuit

    ReplyDelete
  10. can u tell me the resistor value across BC547 emitter. in -ve line.

    ReplyDelete
    Replies
    1. You will have to calculate it using the formula 0.6/charge current.

      The charge current is ideally 1/10th of the battery AH.

      Delete
  11. Thank you very much. I will complete the ckt for 1.2 AH BATTERY , i.e. I have to use -5E, 1.5watt resistor. Am i wright.

    ReplyDelete
  12. this is nice circuit SWAGATAM sir...but my LM317 is dissipiating much heat within 2-3 minutes..i used some heat sinks but couldnt account it...i have used 220/24v 1amp transformer for supply...could you suggest something sir???...

    ReplyDelete
    Replies
    1. Hi Bishal,
      Thanks!

      The heat dissipation from the IC will primarily depend on the connected load at the output, it shouldn't go beyond 1amp....however putting a larger heatsink is the only option for controlling the heat dissipation here.

      Delete
    2. yes.....heat sink worked sir..You had suggested 1N5402 as a safety diode...this diode is rear here..cant we use 1N4007 for that purpose??...and,right now i am initiating the tickle mode for the battery voltage nearly 13V..,what actually should be the cut off voltage sir??

      Delete
    3. For trickle charging, 1N4007 will do.

      Make the cut off voltage to 14.3V for achieving near optimal charging.

      Delete
    4. beg your pardon sir but i m a bit confused here...do u simply mean that relay should be tripped once BATTERY VOLTAGE reaches 14.3V??...IF i have understood wrong,what that voltage should actually be??..thanks again...

      Delete
    5. yes 14.3V is the voltage at which the battery should be stopped from charging further. The IC741 preset should be adjusted such that the relay activates at this voltage.

      R2 should be replaced with a 4k7 pot so that the output may be adjusted to 14.3V (without any battery connected).

      Delete
    6. hi SWAGATAM SIR,ur circuit is going nice and simple for me..haha..today i have multiple queries if you dont mind..
      1.sometimes the voltmeter measures around15.7 volt as LM317 output(WHEN CIRCUIT NOT CONNECTED),HOWEVER IT IDEALLY GOT TO BE 14V...i am quite concerned about the lonlivity of the battery,so how can i account it???
      2.is there any adverse effect if we charge the 7ah battery at low current around 0.35 amps,considering that ideally it got to be near 0.70 amps,RIGHT SIR?

      thanks in advance sir,have a nice time...

      Delete
    7. Hi Bishal,

      The output should not fluctuate with a 317 IC, it should very constant.

      Adjust the 2k2 resistor for getting a perfect 14V.

      However at 0.35amp, 15V will not harm the battery, so there's no problem,

      Regards

      Delete
    8. hi swagatam sir,
      my LM317 still get much heated after 1-2 hour use...i am afraid if it get over heated and get damaged during charging process,HOW DOES IT AFFECT TO THE CIRCUIT AND THE BATTERY???
      (THOUGH,i have used heat sink of CPU POWER BOX for LM317..)

      Delete
    9. If it's getting too much hot means you are pulling more than 1.5amps from it, you can replace the 317 IC with LM338, or add even a bigger heatsink.

      All these ICs are thermally protected so there's no danger of getting damaged, however the performance will suffer.

      Delete
  13. i completed the design, can u pls tell before going to connect what are the adjustments i have to do. i tryed and no current is flowing into battery, and if input 15v is removed relay is continuously on and off. pls give some sujetions.

    ReplyDelete
    Replies
    1. Check the voltage at the output of LM338, it should be above 13.5V. Adjust the preset such the relay just trips at this voltage.

      Now switch OFF the power, connect the battery, switch ON power.... battery will start getting charged and the relay will trip once the charge reaches the maximum output voltage.

      Delete
  14. hi sir, this is sekhar. can u explain the transistor working across lm338. pls

    ReplyDelete
    Replies
    1. Hi sekhar,

      The transistor conducts and grounds the ADJ pin of the IC when hi current is detected. This shuts the output voltage restricting the short condition.

      Delete
  15. Hi Sir, This is sekhar. I have a doubt, when by connecting ammeter in series with battery, there is no current flowing through it, why it is happen.?, is there any wrong in my ckt.?, we are using dc only, but whit out i/p power, why the relay is switching continuously.? what is the reason.?

    ReplyDelete
    Replies
    1. Hi Sekhar,

      Check the voltage at the output of the IC, it should be 14V (for charging 12V batt). For confirming, connect a 12v automobile bulb at the output, it should l;ight up brightly.

      The above confirmation is enough for charging the battery.

      You'll have to set the preset 10K appropriately, so that the relay just trips when the battery voltage reaches 14V.

      Delete
  16. hello,every one....this circuit is simply the best among all available circuit....i have implemented it quite well....THANKS TO SWAGATAM SIR...

    ReplyDelete
  17. HI SWAGATAM SIR,ur circuit is doing great for me....but i am still not well cleared about the TRANSISTOR BC 547 action and 100 ohm at base terminal....could you plz help me?

    ReplyDelete
    Replies
    1. Hi Bishal,

      you are most welcome!

      BC547 and it's base resistor along with the emitter resistor form a current limiter circuit which restricts any current that might rise above a predetermined value set by the emitter resistor value.

      Delete
  18. hai, swagath i have a doubt ,can this circuit used to charge a 12v 10AH battery ,becoz R=.6/1=6 ohms ,is this resistor is available ? if yes,what modification we should do?

    ReplyDelete
    Replies
    1. Hi Nimesh,

      R = 0.6/1 = 0.6 Ohms, you may use any close value for it like, 0.66, or 0.56, or you may use two 0.3 Ohms in series etc.

      These will be available in 1 watt and higher types of resistors...

      Delete
  19. Hi sir
    How can i add low voltage detection to this circuit
    Means when relay turns on after full charge say at 13.5V and cut the supply
    What should be added so that it should turn when battery voltage reaches 12.6V and again starts charging ?

    ReplyDelete
    Replies
    1. Hi Shaurya,

      The 10K resistor connected across pin6 and preset is meant exactly for that.

      However for adjusting the lower threshold, connect a 100K pot in series with this resistor, then adjust this pot for setting the desired low point restart.

      Delete
    2. Thank you for prompt reply sir
      But i have one doubt that ic741 only gets activated when battery voltage goes above 13.5v
      so by adding 100k pot at point 6 of ic how can it help in keeping low threshhold voltage because ic will be deactivated once the voltage gets 13.4V or below
      Please explain ?

      Delete
    3. when pin6 goes high it provides the needed positive potential to the sensing pin and keeps it latched, until the battery voltage falls to a level where this voltage from pin6 becomes lower than the reference point...and the output flips to low logic again.

      Delete
  20. hi sir
    i have made this circuit successfully
    Can you provide pcb layout for this circuit ?

    ReplyDelete
    Replies
    1. Hi Sohan,

      It will difficult for me to provide the PCB design, I'll try, though....

      Delete
    2. Kindly if you make it. Send it to me as well. I have made the circuit but i want to confirm it.
      So kindly send it to me as well, sir.
      09beeojaved@seecs.edu.pk

      Delete
  21. Hello Sir,
    I have gone through this circuit, but I want a charger for 12V 12Ah sealed lead-acid battery. Would this circuit be good enough for this battery specifications? And I have to charge 24 batteries which are in series how could I do that with this circuit?
    Can you guide me a bit?
    Thanks.

    ReplyDelete
    Replies
    1. Hello Osama,

      The last circuit is good for all types of 12v lead acid batteries.

      For 24V battery you can try the following circuit:

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

      You will have to charge the 24v batteries separately and not in series.

      Delete
    2. Sir, Can i get your e-mail or anything? I want to discuss it with you. Actually I am working on Hybrid Electric Vehicle. My part is to deal with "Battery Bank" and its charging.
      I have a battery bank of 28 batteries with each battery of 12V. Now I have to charge all these 28 batteries which are connected in series. How can I do that? Can you explain me that.
      If you need any more detail I can send you more details.

      Delete
    3. We can discuss it here, no problem , others will also become enlightened....

      Batteries should be ideally charged separately and never in series or in parallel, because if there's an imbalance between the discharge levels of the batteries may result in uneven charging of the batteries.

      So I think you use a multiple output charger for charging them.

      However many people don't follow this rule and directly charge all in series, you can also try it, it might work for the time being....

      28 x 14 = 392 volts.

      That means you will need a charger capable of generating 392 volts @ 1/10th of the batt AH, for charging the 28 batts in series.

      Delete
    4. Yeah that's the main issue! So can you kindly tell me how to modify your own circuit above to 'multiple output charger' to charge all the batteries at a time.
      How can I do that? And would that be feasible for charging 28 batteries?

      Delete
    5. First of all you will have to select a transformer with current rating at least 50% of the total battery AH.

      Next you can make the DC chager section.....for a simple one just make 28 separate bridge rectifiers with 1000uF capacitors, so that you can connect the outputs of all these bridge to the 28 batts separately.

      If you intend to build a current controlled charger then you may have to add a LM338 IC stage after the bridge network.

      However for charging the 28 batts you will have to everytime first remove their series connections and then connect with the above charger.....

      Delete
    6. Sir, this way of charging a 12V 12Ah battery is secure enough? I mean that is very lay-man thing to do. The above main circuit that you have drawn is working perfectly in Proteus. I thought that I could make 28 such battery chargers as above and connect each one of them separately to each battery. Is that way correct?
      Because in the rectifier circuit you described above is without any battery-cut off + without any recharge voltage etc.. it is just simple way of charging. I don't think that would be good enough for charging batteries?
      What do you say?

      Delete
    7. And i have made the above circuit in Proteus ISIS Professional and run the simulation. Can you just check that circuit if send you?
      And my exact requirement is to charge a battery of 12V 12 Ah sealed lead acid battery, so can you just check the values of my resistors and other connections and current values. The current in the simulations is turning out to be very low.
      Before implementing it on hardware pcb i want you to check my working circuit.
      Thanks.

      Delete
    8. If you can monitor the charging manually then even a simple method is good enough, however if you want a sophisticated circuit, and cost doesn't matter to you then it is best to build the above circuit with auto cut-off feature.

      You may build 28 circuits separately, the inputs can be connected to a common transformer/bridge/cap assembly (appropriately rated)

      Delete
    9. The last circuit in the above article is correct and will work efficiently if everything's done correctly, so you can be sure of it....

      for 12ah the value of R = 0.6/1.5 = 0.4 Ohms, the value of the resistor across pin#6 and preset center pin should be made 100K instead of 10K.....rest everything can be kept as it is.

      Delete
  22. Doesn't your above circuit includes the cut-off feature and auto-recharge as soon as it sense the desired voltage (14.3V) is reached and then starts recharging when its voltage drop to approximately 11V?
    it is not included in your above circuit?

    ReplyDelete
  23. Okay I have modified the circuit accordingly, but still the current just output of voltage regulator LM317 is 48.2mA. Shouldn't LM317 have an output current around 1.5A? Because this current (48.2mA) is very very low for charging of battery. The charging current should be around 1.5A so that battery is properly charged. How can i increase the current in my circuit?

    ReplyDelete
    Replies
    1. The 10K preset is used for adjusting the high cut off and the resistor across pin6 and preset center pin is for adjusting low voltage restart threshold.

      It's LM338 and not LM317.....I have explained the current setting procedure (R) with formula in my previous comment.



      Delete
  24. If I don't have LM338 can i use LM317 instead? Would it affect any resistor values or anything else? If I am using LM317, would i need to change anything else?

    ReplyDelete
    Replies
    1. You may use a LM317, it will be just marginal, but will do the job, R will not be required then....you can short it. No other changes will be required.

      Delete
  25. If you have some time can you look at my circuit on proteus? It's all running, just to confirm can you just have a look at it for a while kindly?

    ReplyDelete
    Replies
    1. Actually I don't trust software results, they are mostly wrong with their simulations, so it won't be of any use for me.

      Delete
  26. Is this circuit using the switch mode technique?
    That is first constant current charging, then constant voltage and then float charging. Is the circuit above implementing this mode of operation or not?

    ReplyDelete
    Replies
    1. No it's a auto shut-off/constant current controlled charger circuit, not a 3 step charger.

      a three step charger is shown here:

      http://homemadecircuitsandschematics.blogspot.in/2012/10/make-this-3-step-automatic-battery.html

      Delete
  27. hi swagatam sir,it is already 4-5 months and your circuit is going nice without any maintenence required... however,i am still not clear with BC547 here(limiter portion)...i think it is in switching mode...also i found that removing that transistor have no effect on the amount of current flow..does that mean only that registor (0.6/amp) can act as limiter???..please,help sir.

    ReplyDelete
    Replies
    1. Hi Bishal,

      Thanks,if you remove BC547 the current limiting feature will completely vanish and the circuit will not be current controlled, the transistor controls by shutting off the IC 338 whenever the current rises above the safe level.

      Delete
  28. good day sir i made this ckt,i use for my battery inverter to charge automatically .The charger automatic off when full but when the voltage drop from the battery to minimum level charger will not activate?it will not charge automatically. plz help me sir.

    ReplyDelete
    Replies
    1. Add a 100k preset in series with the 10k resistor that's connected across pin#3 and pin#6 of the IC, adjust this preset such that the relay deactivates at 11.2V or at the desired low battery threshold.

      Delete
    2. Good day again sir,thanx for reply.I put already 100k preset in series to 10k resistor but my charger wont automaticaly charge again.i examin the diagram i notice that the b+ supply is connected directly to the circuit of ic 741 .I think the b+ supply of circuit 741 connect to positive terminal of battery not to ic lm338 so that it can detect minimum voltage for the activation of the relay?thanx for any help sir.

      Delete
    3. Good day,

      The voltage at the output of LM338 will also drop proportionately when a discharged batt is connected.....so the 741 (+) connection can be connected to the 338 or to the battery, it won't make any difference.

      remove the resistors across pin6 and pin3 completely and then see wahat happens.

      Delete
  29. Sir, what is the difference between 1st and 2nd circuit? Can 2nd circuit prevent over charging? How can I add lid indicator on 2nd circuit? and What is voltage that i have to adjust for 12v 7ah sealed lead acid battery?

    ReplyDelete
    Replies
    1. mrsilicon, the bottom circuit which involves an opamp is the most efficient circuit and will prevent overcharging accurately.

      The upper circuits are not efficient.

      The full charge voltage for 12V batt is 14.3V

      Delete
  30. Hi Mr. Swagatham.,

    In this circuit can I use 24V, 1A transformer Instead of 15-24V, 3A to charge 12v, 7.5A lead acid battery....if it's ok how long it'll take for charge as full...

    ReplyDelete
    Replies
    1. Hi Abdul, yes you may use it.

      it will take about 10 hours to get fully charged.

      Delete
  31. hi swagatam sir,your circuit is doing nice.but i am having some sort of problem.my battery is taking around 24 hours to get charged up to 14.2v.I found that the charging current goes on decreasing and reaches around 50MA at the battery voltage of 14v and above.is this natural or my circuit malfuntioning???.thanks in advance............

    ReplyDelete
    Replies
    1. Hi Bishal, use a transformer with little higher current rating, that will charge your battery faster, but it should not be above 1/5th of the battery AH rating.

      Current will decrease as the battery attains full charge, so it's fine.

      Delete
    2. ok then..and sir i wanted to know if this prolonged charging period(with low current) as mentioned in my query affect the longivity of the battery??..

      Delete
    3. No it will not affect the battery life.

      Delete
  32. Hi Mr. Swagatham

    Im rizmy. this type of circuit is what I'm searching. But need to clarify one thing. can I use this cct for fluctuating voltage inputs like solar panels or wind turbines?. What are the modifications needed for this cct to do so?. could you please help me

    ReplyDelete
    Replies
    1. Hi Rizmy,

      Yes the above design will work with varying voltage sources, but the max voltage should not exceed above 20V if a 741 opamp is used, and 30V if a LM324 opamp is used.

      Delete
  33. hey man, since quite some time never post my problems to you hahax!~
    today i wanted to ask you about the 9volt battery charger, can you pls help me by showing me the circuit about voltage and current needed to charge a 9v? equip with auto cut off... i'll try to find the source myself...and by the way, still remember the hair blower? the 17v DC? i found it i think..haha. but i havent disassemble it to obtain the coil only...

    thanks . all the time :)
    regards

    ReplyDelete
    Replies
    1. hey ben,

      the charging current should be 1/10th of the battery AH,so the input current should be equal to this value. The charging voltage can be around 11V for a 9V battery.

      Delete
  34. The note about transformer current is not quite right, the current rating of the transformer is at the rated voltage. I would suggest putting a load like some 12 v bulbs if you do not have a high wattage power resistor, in series with the multimeter on the 10 Amp range. (make sure u change ports on the meter)

    ReplyDelete
    Replies
    1. for an smps your suggestion might be true, but for transformers it might not be, try drawing 500mA from a 1 amp rated transformer and check the voltage, you would find it drop substantially.

      anyway I appreciate your involvement, thanks very much!

      Delete
  35. hi swagatam, can i use this charger for a 100ah battery? what adjustment should i make? thanks.

    ReplyDelete
    Replies
    1. yes, replace LM338 with LM196, that's all

      Delete
  36. hi swagatam, i am irwin. i would like to ask if this charger can charge up to 120AH battery? Pls show also how to calibrate and adjust the Pot. Thanks in advance.

    ReplyDelete
    Replies
    1. Hi Irwin,
      No the above circuit is not rated for charging a 120ah battery.
      you can try the following circuit instead:

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

      Delete
  37. Mr Swagatam, good day. can i use a 40A SPDT automotive relay in this circuit? can you show the connection and changes to be done? i'm not familiar with relays and automotive relays is common. Thanks...

    ReplyDelete
  38. hi swagatam, what is the maximum AH rating of battery that can be charge using this charger? thanks.

    ReplyDelete
  39. say what IC was uesd in this design?

    ReplyDelete
  40. hi swagatam,
    i have made smart auto charge bat with your scematic reference and worked.
    i have 12v 5ah lead acid bat.
    i got problem with adjusting voltage at pin out of ic338. volt resulted max 9,3v before i used vr 2k2 replaced res 2k2 to adjust voltage and the res i used is 1.2ohm 1/2watt (R=0.6/0.5). you say 14,3v is ideally for charging 12v bat. so what solution to get 14,3v?
    regard,
    Dedy

    ReplyDelete
    Replies
    1. Hi Dedy,

      2K2 is an incorrect, i don't know why the datasheet itself shows the wrong values on many occasions, I practically found that it should be a 10K pot for getting a range of 1.25v to 24V variable option. Please replace the 2k2 with a 10K preset or pot, you will be able to fix the desired 14.4V mark with it

      Delete
  41. i use a 10k preset replaced 2k2 preset. and resulted 13,40v at max adjust. the following problem is while 12v battery was connected with pcb smart auto bat terminal out + and - . the relay repeating trip (on off) quickly. how to fix it?
    regard,
    Dedy

    ReplyDelete
    Replies
    1. Please do not connect the battery while setting the preset, also the 10k feedback resistor from pin6 should be kept disconnected while adjusting the preset, once its adjusted this resistor should be connected back into position.

      For the charging operation, the battery should be first connected to the circuit and then power should be switched ON.

      The transformer current must be rated at 1/10th or not more than 1/5th of the battery AH value.

      Delete
  42. thanks for your fast respond.
    i have did as like you talked about it. disconnected 10k res in pin 6 then adjusting preset resulted green led light on brightly and red led light very dim (a little light). if i do adjust opposite the preset resulted green led light very dim and red led light brightly. it the same happened while i adjust 10k preset (pin6) which 10k feedback resistor connected into position.
    next the charging operation, battery connect to smart auto battery with no current from transformer (power off). And the same problem appear again, relay vibrate trip rapidly.
    so that, i think replaced 12v relay with 24v relay can solve the vibrate trip problem so i did it, then i adjusting again and connected battery first without current. and yeah, the relay not vibrate. While i powered transformer, the relay vibrate trip rapidly again huff.
    i use transformer 3A 0 - 20v, battery 5Ah 12v, relay 12vdc, dioda zener 6,8v 1 watt. i have already recheck the trace pcb, and i feel no wrong traced.

    ReplyDelete
    Replies
    1. Did you set the 10k preset at the opamp pin#3 for 14V relay activation?
      After setting R2 to get 14V at the output, you must set the opamp 10k preset to just activate the relay.
      Do this without connecting any battery and the 10k link disconnected.
      After the above setting is done, adjust P2 to vary the voltage from 12 to 15V, and confirm the relay activation at 14V by repeating many times.

      For 5ah battery the chaging current must be around 600ma or 0.6amps select BC547 emitter resistor as 0.6/0.6 = 1ohm.

      The above settings will produce a perfectly smooth charging and over voltage cutoff, without any relay vibration

      Delete
  43. what the scematic smart auto battery which focused line between pin v out of lm338 and n/c of relay is correct? why pin v out lm338 not connect at threshold of relay? because i think logically, the current flow in out pin lm 338 to N/C relay become not do job as function of relay. when the coil relay active. It trigger threshold to N/O but the current still flowing in battery. it should be cut off current to battery. sorry if i wrong.

    ReplyDelete
    Replies
    1. I could not follow what you are suggesting, the diagram is correct, as long as the upper threshold is not reached the battery charges via the N/C contact, once the over threshold is reached the relay activates and breaks its N/C contact cutting off supply to battery.
      The two diodes at battery positive ensures that the battery level never falls below 13V mark.

      Delete
  44. Can this circuit be used for a 60 Ah 12 V deep cycle lead accid battery( it is a bank of three 12V 20 Ah batteries in parallel ) ? If it can be, what are the modifications needed?
    What will be R value for the battery rated here?
    Another doubt too. Can this circuit be used for all low ang high Ah batteries?

    ReplyDelete
  45. Hellow sir have a good day
    Hoping that you will reply to ma previous comment. Now i am back with a question that ,whether this circuit can be used with the single transformer inverter/charger/changeover circuit ( which you posted one year before in this blog ) as an automatic charger section ?
    I am using a higher watt transformer ( about 300 W ) which is supposed to draw current more than 20 A

    ReplyDelete
    Replies
    1. The single transformer inverter/charger can be added with a current limit feature just by adding a calculated high watt resistor in series with D6, the above circuit is not necessary.

      Delete
  46. Dear sir,
    Is this charger a completely automatic one ? Means will it be able to stop charging after a higher threshold and also able to start charging when the battery voltage reduces down to a MINIMAM THRESHOLD ?
    How this circuit can be caliberated for these two THRESHOLD LEVELS ? Can u plz explain it. You didn't even mention about it in this article

    ReplyDelete
    Replies
    1. Dear Ramsree,

      yes the above circuit is completely automatic, the 10k preset at pin2 determines the upper cut off while the feedback resistor value across pin6 and 10k preset center lead decides the lower restoration point. This feed back 10k resistor should be replaced with a 100k preset for enabling the lower threshold setting-up option

      Delete
  47. This circuit cannot be used for 60AH battery, it can be used for charging all types of batteries rated at below 50AH

    ReplyDelete
  48. Hello, mr swagatam
    i have been following your blog just of recent. about two days ago. amd i have been following your comment with keen interest. i need your help/assistant concerning the circuit for battery charger that i want to construct( Automatic battery charger for acid lead battery be it smf/ deep circle etc.) that is as high as 200AH. pls is this cct okay for it if not is there any midification or is there any one that that i can use for that project. and i want it to be smart battery charger. if none smart charger i will prefer anyone that has been tested and constructed by one of the blogger and is working fine.
    sorry for asking this too much question as i have read through your comment on one of your Automatic Lead acid battery charger using NE555 you said the modify circuit is below the page of the blog but i could not find it . i need your assistant concerning that.
    thanks

    ReplyDelete
  49. hello sir,
    i will be expecting your reply as soon as possible. keep it up with the good work.

    thanks

    ReplyDelete
    Replies
    1. Hello Mr. Day,

      I will recommend you the IC 741 circuit that's been discussed in the above article, because it's extremely accurate and is a tested design, the one using 555 IC is still a bit controversial and hasn't been tested by me yet.

      Delete
  50. hii mr swagatam, i just built last schematic on this article, i want to know is ..that's N/C contact is in default state when in charging mode ?or when charging mode, the relay will activate..??? because i really confuse, what's condition the relay will activate , in charging mode will activate or in default state will charging?? and one thing.. when reaching voltage/near supply voltage, the relay will fluctuating ...

    ReplyDelete
    Replies
    1. Hi hui,

      yes N/C means Normally Closed or closed at the indicated N/C contact in the deactivated or default state.
      when switched ON, the relay will not activate and the battery will get charged from N/C default state of the relay, once fully charged the relay will activate and switch from N/C to N/O disconnecting the battery from charging.

      Delete
    2. the 10k feedback resistor from pin6 of the IC is introduced to prevent fluctuations at the threshold cut off points, did you connect it properly?

      Delete
  51. i've checked the resistor 10k resistor to make sure connected to the pin 6 of IC but still fluctuating, and i already checked on the internet what is normally closed means on the relay pin, the 87a called the N/C and 87 is N/C so i connected as schematic for N/C and the other.., i ve forgot to say on my last post, i used TL071, because i dont have LM741, did this ic caused the relay fluctuating?? transistor i used was D438 .when charging state, red led will off and red led will glow if charging is stopped.. correct me if im wrong...

    ReplyDelete
    Replies
    1. TL071 is fine, but the circuit shouldn't fluctuate if everything's done correctly.
      Your power supply amps should be rated at 1/10th of the battery AH, or should be much lower than the ah of the battery.

      remove the battery and check the response by flicking the preset to and fro. if the relay clicks would indicate your circuit is good.

      Delete
  52. sir this ckt work for 12v 40ah batry ?

    ReplyDelete
  53. can i use 12v 3A transformer ........... and 0.6/ .6A= 1 ohm 1/4 w resistor ???

    ReplyDelete

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