Sunday, December 18, 2011

Self Regulating, Automatic Lead Acid Battery Charger Circuit

Te post explains how a neat little self regulating automatic battery circuit can be made using just two inexpensive transistors.

Setting up this automatic self regulating automatic battery charger circuit is very simple and may be done in the following way:
Initially, do not connect the fixed transformer power supply; instead connect a 0-24V, variable supply voltage to the circuit.

Remove the anode of D6 from the relay contact and connect it to the positive of the power supply.
Keep both the presets somewhere at the center position,
Switch ON the power and adjust the voltage to 11.5 volts or lower.
Adjust P2, so that the relay just activates.
Now increase the volts to about 13.5 volts, and adjust P1 so that the relay just deactivates.
The setting procedure of the circuit is now complete.
Check the whole procedure by continuously varying the voltage up and down.
You may now remove the variable power supply and connect the fixed transformer, bridge power supply to it.
DON’T FORGET TO RECONNECT THE ANODE OF D6 BACK TO THE RELAY CONTACT OR THE BATTERY POSITIVE.
The battery connected to this circuit will be charged only as long as its voltage is in between the above "window" level.
If the battery voltage crosses the above "window", the relay will trip and stop the battery from charging.

Parts List for self regulating automatic battery charger circuit.

R1, R2 = 10K,
P1, P2 = 10K PRESET,
T1, T2 = BC 547B,
C1 = 2200uF/25V
C2 = 47uF/25V (Please connect this capacitor across the relay coil)
D1---D4 = 1N5408,
D5, D6 = 1N4007,
RELAY = 12 VOLT, SPDT,
TRANSFORMER = AS PER THE CONNECTED BATTERY AH (DIVIDE BY 5)

The following diagram shows the instructions which needs to be followed while setting-up the circuit with the desired cut-of thresholds, using a variable power supply unit:




The above self-regulating battery charger circuit was successfully built and tested by Mr. Sai Srinivas, who is just a school kid but nevertheless has an immense interest in the field of electronics. The following images were sent by him which displays his talent and intense dedication in the field.






91 comments:

  1. Hi Swagatham
    Can this ckt can be used for 6volt battery charging if so what should be the voltage setting

    ReplyDelete
    Replies
    1. Hi Balram,

      Yes this circuit can be used for charging all types of batteries, just the relay and the transformer needs to be matched with the battery voltage rating.

      Regards.

      Delete
  2. for inverter battery charging what changes required in this ckt.....???

    ReplyDelete
  3. madurai chandrasekarOctober 15, 2012 at 11:48 AM

    I want to charge 12V - 100 or 150Ah battery. Can I use this circuit? What is the relay and transformer amp. to be used sir?

    ReplyDelete
    Replies
    1. Yes you may use it, just make sure the relay contacts are appropriately rated.

      Delete
  4. hi sir i want 24Vdc 7amh battery auto cutoff charger please guide me
    thank you

    ReplyDelete
    Replies
    1. You may try the following circuit:

      http://homemadecircuitsandschematics.blogspot.in/2012/08/make-this-48v-automatic-battery-charger.html

      Delete
  5. Hi,
    Just checked, few questions,
    1. The circuit and battery using 6 volts, but in this circuit, i thought using 12 v, any suggest for using 6 volts?
    2. How to set up p2 dan p1 for using 6 volts? And how to change the voltage value for set up, coz i don't see any P except P1 and P2.
    Thanks, sorry for disturbing you always.

    Regards,

    ReplyDelete
  6. hi, just sent question this noon, but dunno may be didn't sent. I have a few questions:
    1. I think this one was for 12v, how to change it to 6v?
    2. to set the relay, with lower and upper value, how to adjust the voltage? Coz i only see P1 and P2 for setup relay activation, not for adjust the voltage.
    Sorry for my bad english, i'm Indonesian.
    Thanks for your innovation, i like it very much.

    Regards,

    ReplyDelete
    Replies
    1. Hi,

      1) This circuit will work for 6V applications also.

      2)You will have to use a variable power supply for setting the voltage thresholds. Once the settings are completed a normal transformer power supply may be replaced in place of the variable power supply.

      The battery should be connected first before switching ON the transformer power supply while using the circuit.

      Regards.

      Delete
    2. Thanks, should i change the relay with 6v? Thanks a lot

      Regards,

      Delete
    3. Oh yes, the relay needs to be changed to 6V and the transformer too...

      Delete
    4. Hi Swagatam,

      I could not find 6v relay, do you have any suggest or other options?
      Thanks.

      Regards,

      Delete
    5. Hi Menanti,

      You will have to get a 6v relay, i am afraid there's no other option for this circuit.

      Delete
  7. hi sir what circuit can i use to control or cut off the battery load to prevent battery from over discharging

    ReplyDelete
    Replies
    1. You may try the last circuit shown in the following link:

      http://homemadecircuitsandschematics.blogspot.in/2011/12/how-to-make-simple-low-battery-voltage.html

      Delete
  8. swagatam the battery needs to charged at 1/10 ah then why transformer with ah/5

    ReplyDelete
    Replies
    1. A battery can be charged at C/5 rate also, but when it reaches near full charge, the rate must be reduced to C/10 manually, not a very critical requirement anyway.

      Delete
  9. Swagatham If i connect 100AH battery and 230/12 2A transformer whether it will charge?

    ReplyDelete
    Replies
    1. 2 amp will not be enough, you will have to use a 12V/10amp transformer at least.

      Delete
  10. Hi Swagatam, why I can't set the different voltage between low and cut off more than 0.5v? so, if I set low voltage is 12.0v then cut off voltage is 12.5v and I can't change that. Any suggestions? I want set 12v for low and 13.5 for cut off voltage. thanks

    ReplyDelete
    Replies
    1. Hi Steven,

      You will have to adjust it somehow through some means by yourself, like you may connect s resistor of some high value across the base of the left transistor and ground....and then check, it may take some time because the above circuit is little tricky to adjust.

      Delete
  11. Thankyou Swagatam, I'm completely newbie. Maybe, just maybe you can give me some advice about the sample value of resistor you talking about? Lets says voltage range about 2 volt between low and cut off voltage. Thanks for your unvalueable advice Swagatam.

    ReplyDelete
    Replies
    1. Actually even if I try adjusting the levels, it would take quite a long time, so may be it's not something that can be fixed visually, you will have to try hard practically for getting the correct optimization....

      Delete
  12. respected sir,
    i want to charge 12v battery which are automatically controlled .If yes then what would be the value of transformer and relay.

    ReplyDelete
    Replies
    1. use a transformer with a current rating = 1/10 x battery AH

      Delete
    2. relay will be 12V/400 ohm, spdt

      Delete
  13. sir, I like your diagram, but i was wondering how to connect the
    C2?, is it the same way as the D5...across the coil?

    Thanks!

    ReplyDelete
    Replies
    1. yes, connect it parallel to D5 or simply over the points of D5, positive of the cap will go to the positive rail...

      Delete
  14. sir,

    I have assembled the circuit as per your schematic,P1 and P2 at the center position,connected variable power supply set at 11volts,,,but when i switch it on, the power supply trips off. I set to 10volts and trips off again. What seems to be the problem? Should i include the bridge in the circuit before connecting the var power supply? Little help please!.. and by the way i'll be using a 16v/5-6amp transformer for this circuit to charge a 12v/5ah motorcycle battery...is it okey?

    Thanks a lot!

    ReplyDelete
    Replies
    1. first of all you are using a hugely wrong transformer which is not suggested in the article. It is clearly mentioned that the transformer current should be AH/5, that means 5/5 = 1 amp

      your transformer should be rated at 0-12V/1amp

      connect this transformer, the output will show around 14V after rectification.

      don't use a variable PS, simply connect the above trafo, set the presets such that the relay just switches OFF at 14V without any battery. That's all, your circuit is set.

      Delete
  15. hello good day i just something about my type of my charger is cannon 12v 15a what can i do to assemble for fast charger thank you hope u understand me.

    ReplyDelete
    Replies
    1. hello,

      sorry you cannot make it fast, it's not feasible.

      Delete
  16. Sir can you explain me resistor and pot calculations of this circuit please. You have used bc 547b this has hfe of 100 that means base current is 1mah and voltage about 0.7 to turn on. Am I right? For the both transistor R1 ,P1 and R2, P2 acts as voltage divider. When voltage is 11.5 we have to adjust p2 so that we get 0.7v and 0.001 amp current to the base of t2 activate right? and at the voltage 13.5 then also we have to adjust the p1 to get 0.7v and 0.001amp current to the base of t1 and when t1 turns on. then the voltage comming from r2 connected to ground hence voltage accross base of t2 decrease then t2 turns off therefore relay deactivate. But I am confused here that when voltage 13 t1 can be turn off then then t2 turns on? Please apply me

    ReplyDelete
    Replies
    1. yes, that's why I have attributed the word "self regulating" to it, meaning as soon as the battery voltage drops at a certain value the circuit will again start the charging process and never allow the battery voltage to fall below a specified lower level.

      Delete
  17. Hello sir,

    Can i use this circuit for my UPS battery charge control. It charges at 10amp but there is a problem in the UPS built-in charge controller and it does not trip automatically when the battery is fully charged. I'm asking if i can install this circuit in this system.

    Regards

    ReplyDelete
    Replies
    1. Hello Muhammad,

      Yes you can use it, but you will have adjust the presets very carefully for getting the desired cut-offs.

      Delete
  18. Swagatam, i have a 1000VA IPS that uses 24v, 14AH sealed lead acid battery. It was brought for backup computer. Is it possible now to use the IPS with a 24v, 70AH battery for longer backup as I want to drive it a fan and 2 light?
    Pls suggest me what can i do at this time.

    ReplyDelete
    Replies
    1. Hi Debashish, yes it's possible, as long as the voltage is not altered or exceeded beyond the specified limit AH won't matter, it will only help to provide higher backup time.

      Delete
  19. this is relly work , i like this circuit , very simple , thanks

    ReplyDelete
  20. this circuit is really work , very simple and low cost , i like this circuit , thanks bro , can u tell me how to make temperature sensor 0-1000 degree

    ReplyDelete
    Replies
    1. thanks! presently i do not have 0-1000 degree circuit, if i get i'll surely post it for you.

      Delete
  21. @Swagatam Majumdar,
    good work...
    my question is this....
    will this circuit diagram cut-off the voltage when the battery is fully charge?
    thks. hope to read your reply soon.

    ReplyDelete
    Replies
    1. thanks! Yes the relay will cut-off as soon as the voltage reaches the set upper threshold and stop further charging of the battery

      Delete
  22. Hi swagatam
    Thanks to your post i make this circuit and its work...how can i add 2 led bulb for charge monitoring..i plan to place 1 red led for charging status and 1 green led for full charge status..how can i connect this to the circuit?

    ReplyDelete
    Replies
    1. Hi Flhex,

      Thanks, however here only one LED would work effectively across D5.

      Connect it with a 10k series resistor, it will indicate "battery full and disconnected", another "power ON" indicator LED can be added directly across the positive/negative line with a 10k series resistor.

      Delete
  23. Hi sir,

    I want made 12v & 24v single transformer. Variable current rating. How I design cut off circuit. Please help me.

    Thank you

    ReplyDelete
    Replies
    1. Hi Suresh,

      Try the first circuit from this link:

      http://homemadecircuitsandschematics.blogspot.in/2012/07/make-6v-4ah-automatic-battery-charger.html

      Delete
  24. hello
    pls i dont understand that relay part. NO and COMMON are nit joined inside relay but you joined them in ur diagram. i understand that NC is not connected. pls clarify the connection of NO and COMMON. thanks for your response!

    ReplyDelete
    Replies
    1. The diagram shows the relay in activated mode while charging the battery, therefore the N/O is connected to pole, when deactivated it will connect with N/C

      Delete
  25. Hello Swagatam, please can dis circuit output voltage be regulated so as to charge the battery at thesame rate as it is discharged?
    Using d appropriate transformer amperage how long will it take to charge a 12v 100amps battery?

    ReplyDelete
  26. Please can this circuit output voltage be regulated so as to charge the battery at thesaurus rate as It's discharging?

    ReplyDelete
    Replies
    1. Hello Mega blessing,
      yes it can be done simply by using an appropriately rated transformer.

      for any lead acid battery the ideal charging time is around 10 to 14 hours.

      Delete
  27. Hello swagatam, i like ur circuit,easy to understand, i want to charge 3v battery(2x1.5v) can i change D5,D6 to 3v zener diode,to trigger the relay.hope u understand

    ReplyDelete
    Replies
    1. hello mohammad,
      all the diodes shown in the diagram are 1N4007, these are not zener diodes but ordinary rectifier diodes, you can use them as given.

      Delete
  28. dear sir 1 want to charge 12v45ah battery i have 5A20v ups transformer. this will work?

    ReplyDelete
    Replies
    1. Dear Jayanth, use a LM338 IC based charger to drop the 20V to 14V for charging your battery.
      I have published many LM338 IC chargers, you can search them through the search box at the top

      Delete
  29. ok sir,,,,How to Make an Automatic 12 volt Battery Charger Circuit Using IC LM 338
    im going to make above one. please answer my question on that comment forum.

    ReplyDelete
  30. sir, for c1, can i use a 1000v,25uf capacitor? and for c2, can i use a 100uf 25v capacitor? and for d1-----d4, can i use 1n4007 diodes, sir? please tell me sir....

    ReplyDelete
  31. sir, i want to use this circuit with a 12v 7ah battery. can i use a 12v, 1amp transformer, sir?

    ReplyDelete
    Replies
    1. yes, it's fine, you can proceed.

      Delete
    2. sir, i assembled the circuit and it switches on relay when i connect power supply. and when i adjust the presets, the relay stays in on position only(in both cases i.e., in adjusting cut off and adjusting switch on of relay). please tell me whether i should connect power supply including bridge or directly to capacitor? also please tell me if i should connect battery while setting the circuit, sir? please help me...
      thanks.

      Delete
    3. Battery should not be connected while setting up the circuit.

      you must use a variable power supply for setting-up the circuit as instructed in the article.

      I'll update the diagram with the required information shortly.

      Delete
  32. sir, please tell me where i should connect variable power supply when setting up the preset resistors and the circuit before connecting the battery and fixed transformer? thank you for your help.......

    ReplyDelete
  33. sir, thank you very much for your help. im sure this would help others also......by the way, this circuit WORKED on my breadboard..thank you again.......

    ReplyDelete
  34. Dear sir, ive been using this circuit for more than a month now....works great I sent the photos of circuit to your mail(homemade circuits@gmail.com)......
    Regards
    Ss.

    ReplyDelete
    Replies
    1. That's great SS, thank you, I'll check them out soon.

      Delete
  35. Sir, could you please help me in designing an automatic 24 V battery charger circuit having the following spec.

    - it should be capable of charging a 24 V 80 Ah battery bank

    - higher voltage cut off and lower voltage turn on facilities

    I have a 300 W inverter transformer with me which is a 230 V / 15-0-15 type... So the primary winding can handle a maximum current of 20 A........ So is it possible to use the primary terminals of this transformer ( end taps excluding the mid one,showing a voltage of 30V total ) to charge this battery ?????

    ReplyDelete
    Replies
    1. Arun you can try the second circuit from the following article:

      http://homemadecircuitsandschematics.blogspot.in/2011/12/how-to-make-simple-low-battery-voltage.html

      You can use the 30V/20Amp transformer as the input, but don't use a filter capacitor, just connect a single rectifier diode for rectification, and use it as the input with the above linked circuit.

      Delete
  36. Is the second schematic (testing setup) accurate?

    It seems to conflict with text as to the connections around D6.

    The text indicates the +VDC to be connected to the anode of D6 but the schematic shows it connected to the cathode and the coil and NO connection of the relay.

    ReplyDelete
    Replies
    1. Actually D6 is not crucial and could be removed, I placed it initially just for a psychological comfort, practically it serves no purpose.

      Therefore the circuit actually becomes very simple now, remove the entire D6 link and connect the R1/R2 junction with the positive line.

      The setting up procedure may be done by supplying the external variable voltages across the positive/negative lines of the circuit, without any battery connected and also without the mains input to the circuit transformer.

      Delete
    2. Thanks for the info.

      I have completed the circuit without a D6, but used PN2222 NPN transistors instead, as I had them here and their characteristics are similar to the 547B ones.

      I can setup the charge on cycle, but I cannot get the off adjust to work at all. The relay stays locked on through the entire range of P1. In fact once the relay engages, the only way to get it to go off is by removing the power. Once power is restored, it immediately engages again. If I drop P2 back to center, it will stay off until I adjust it as per spec.

      Any thoughts on this?

      Delete
    3. Additional info:

      I found one of the resistors I used was way out of tolerance, down to about 700 ohms or so.

      I replaced it and the circuit seems to work as stated, but I am having a lot of diffiuculties getting the levels dialed in as both affect the other. Adjust one to the proper level will bring the opposing one off of it's level and vice versa.

      It seems to me the critical one to get accurate is the off limit, as this one is the key to stop over charging.

      I found the point was so finely tuned that just touching the pots would cause them to flip the relay state. Maybe multiturn pots would make setup easier.

      I also found that the lower setting has little effect. When the upper one is set at say 13.8 volts (normal for a fully charge 12V lead acid cell), any voltage below 13.3 will cause the relay to engage and start the charge cycle again. The voltage would never get down to 11.5 volts, even though that level had been set first.

      I gave up tweaking after 45 minutes, as it is just too sensitive to get dialed in properly.

      Delete
    4. I agree with you, setting up the lower threshold could be a bit difficult with this circuit...you could probably try one simple modification for achieving the desired lower threshold activation to a reasonably accurate extent.

      Try adding a high value resistor from N/C of the relay to the base of T1....the value of the resistor will need to be experimented, may be a 1M could be the starting value and lowered down until the right one is found.

      The mod will basically add a bit of hysteresis to the design which is actually missing in the here and needs to be added for the intended results.

      you can also add a capacitor in parallel to the relay coil to stop the relay from chattering at the thresholds

      Delete
    5. I have the 47uf cap already in place.

      I will try the resistor mod when I get back to bench later on, and let you know hos it goes.


      Delete
    6. It ended up being an 820k resistor that gave the best results.

      It is still very sensitive to tweak, but it got easy enough to tune it in quite close to were I wanted it to be.

      There is still a fair amount of variance in the cut in voltage, but the cut out is quite stable.

      Thanks for the help!

      Delete
    7. That's great! Thanks for confirming it, this update will be quite helpful for the other readers.

      Delete
    8. I just noticed something about the circuit. When you said to remove D6 and connect the R1/R2 to +, was that correct?

      It seems it will not detect the battery state unless the relay is enaged, so the charger will never start when hooked up to an actual battery.


      I think the R1/R2 should be connected to the COM (Armature) contact of the relay that is connected to the battery.

      Delete
    9. Oh yes, I seemed to have missed it completely.

      R1/R2 should be connected with the relay pole, as rightly indicated by you.

      Delete
  37. Hi M Majumdar,

    Please could you help me !!! I can not make the setting of your circuit. I don't understand what you means with " connect this point temporarily" on the second drawing? Is there 2 points for the positive input for the variable supply? The line in dot ???
    And where do you set the resistor of 820K in the circuit?
    Thanks

    ReplyDelete
    Replies
    1. Hi Willy,

      " connect this point temporarily" means join those points together with a wire link (wire link shown as red dotted line)

      Join 820 k resistor from the "normally closed" contact of the relay to the base of T1

      Delete
  38. Well, I could never get this circuit to work properly. Even if I got it to calibrate, in the real world when connected to a battery, the system either does not start a charge or hammers the relay like a buzzer. I am going to have to scrap it and find another charger. This one is just too finicky.

    - Tim -

    ReplyDelete
    Replies
    1. As per the title, the circuit is specified to keep the battery always in a topped up condition by regulating its voltage within the top 5% margin, meaning a 12V battery would never be allowed to fall below 13.5V and rise above 14V, so I think the circuit should be allowed to work under these specs only and nothing more should be expected from such a simple design.

      Delete
  39. hi Swagatam again..
    I have a sonnenschein a612/150 gel cell battery.. I charge it using a "SUOER MAD-1220A" 20amps charger that should have 4 steps charging modes..
    the question is.. when a green light turned on that means floating mode is on.. but when I apply multimeter on the battery during floating mode charging.. it gives 14.3-14.5v.. is that good?? because I know that floating mode volt should be 13.8v..
    is my charger stop charging when green light turns on ?
    or this green light means that floating mode is started?
    or is my charger is broken and it's never stops charging and never enter floating mode ??

    thank you for your patience

    ReplyDelete
    Replies
    1. Hi Ahmed, applying float charge at 14.3V is OK, but whether the charger is getting into a trickle charge or not at this volatge can be confirmed only by practical testing.

      if your charger is specified to produce float charge once the green light comes ON then it should be initiating the process with the green light turned ON.

      Delete

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