A very simple single transistor automatic battery charger circuit is described in this article, which uses just a single transistor for the voltage detection as well as for automatically disconnecting the battery from the supply when it gets fully charged.
Simulation and Working
As shown in the diagram we can see a straightforward configuration where a single transistor is connected in it’s standard operating mode. The circuit functioning may be understood with the help of the following points:
Considering the battery to be charged is a 12 volt battery, we know that it is advised to charge the battery until it reaches between 13.5 and 14 volts.
The transistor base voltage is adjusted using the preset P1, such that the transistor just conducts and operates the relay at around 14 volts.
How to Adjust the Cut of Thresholds
This adjustment becomes the high voltage trip point of the circuit and is used to switch OFF the charging voltage to the battery when it gets fully charged or its voltage reaches around 14 volts.
The lower trip point of the circuit cannot be adjusted as this circuit is too simple and does not incorporate the low voltage detection feature.
However the transistor is itself equipped with a switch OFF feature in case its base voltage becomes too low.
Typically a general purpose transistor like the one which is shown (BC547) when adjusted to switch ON at 14 volts may have the lower threshold of around 10 volts, when it might get just switched OFF.
This wide voltage difference between the high set threshold and the lower natural threshold is because of the involved big hysteresis with the design. This acts like a natural hysteresis in the design.
The lower threshold of 10 volts is dangerously low and we cannot wait for the circuit to restart the charging process until the battery voltage falls to this dangerous 10 volts level.
Allowing the battery to discharge down to 10 volts can make the battery flat permanently and reduce its life. . Therefore to eliminate this issue the circuit needed to somehow reduce the hysteresis level. This is done by introducing a couple of diodes at the emitter of the transistor.
We know that normally a 1N4007 diodes would drop around 0.7 volts across it and two if them would make a total of 1.4 volts. By inserting the two diodes in series with the emitter of the transistor, we force the transistor to switch off 1.4 V earlier than its normal specified limit of 10 volts.
Therefore now the lower operating threshold of the circuit becomes 10 + 1.4 = 11.4 volts, which may be considered just OK for the battery and for the automatic restart of the charging process.
Having both the thresholds updated as per the standard charging requirements, we now have an automatic automotive battery charger that’s not only cheap to build but also smart enough to take care of the battery charge conditions very efficiently.
Circuit Diagram
Parts List for the proposed one transistor automatic battery charger circuit
R1 = 4K7
P1 = 10K preset,
T1 = BC547B,
Relay = 12V, 400 Ohms, SPDT,
TR1 = 0 - 14V, current 1/10th of the battery AH
Bridge diodes = Equal to the current rating of the
transformer,
Emitter diodes = 1N4007,
C1 = 100uF/25V
PCB Design
Adrian says
Are the two capacitors electrolytic or normal capacitors? I’m going to get the components today
Swag says
They should be electrolytic type.
Adrian Sassin says
Thanks and voltage ratings?
Swag says
any value that may be equal or higher than twice the supply voltage
Adrian Sassin says
Hey I added the transformer of greater rating and circuit worked but now I see that my transistor has blown aka Base emitter is open… If I were to place a resistor in series with the Base would it prevent damage to the transitor? also the relay buzzes even with a flywheel diode
Best regards Adrian Sassin
Swag says
Hi, the transistor can never get damaged because R1 is already present. R1 will restrict the current in case the preset adjustment is shorted accidentally.
The transistor can possibly burn if the flywheel diode is not good. You can try changing the diode with a good quality 1N4007 diode.
To stop buzzing you could try adding a 10uF capacitor across base/emitter of the transistor and and also a 100uF capacitor parallel to the relay coil.
Adrian says
Greetings I used a 15V 1A transformer to charge the battery for the circuit but when I charge the circuit noting I get 0.4 mA on the Dc side and my battery starts to make hissing noise… It cuts off at 13.7 but after and hour or two it goes to 13.4V what is the reason for this hissing and the discharge and what can I do to rectify the problem? I’m using this circuit in conjunction with and emergency light… my battery is a 12V 7ah
Swag says
Hi Adrian, that looks quite strange, because at 1 amp a 7Ah battery will never hiss. Try adding a current control stage using the following circuit and set the current to 500mA:
https://www.homemade-circuits.com/universal-high-watt-led-current-limiter/
If still you hear the weird sound then the problem could be in your battery.
the one transistor cut off circuit explained above may not be very accurate since the preset adjustment could deviate slightly overtime, giving rise to errors, you can try using fixed resistors instead of the perset to get reasonably consistent cut off response from the circuit
Adrian says
Hey I wanted to ask I’m getting 0.45mA when the battery chargers.. How can I increase current flow to 0.7A to change lead acid 12V battery 7ah… Transformer I’m using is 15V 1A and is quite warm after a few hours
Regards Adrian
Swag says
Hey Adrian, your transformer may not be actually rated at 1 amp, because most transformers usually print slightly higher rating than its actual capacity. Try some other slightly higher rated transformer, may be upto 2 amps and see the response.
If still the current does not increase then your could be having problems.
Osvaldo Destro says
Circuito não esta funcionando….tem um erro no R-1 e tambem no C-1 negativo, …. estão sem coneção ( Design do PCB ) só funcionou depois de fazer mudanças
Swag says
Obrigado por apontar o erro no design do PCB, ele foi projetado por uma pessoa externa, não eu, mas de qualquer maneira, estou feliz que você possa corrigi-lo e fazer com que ele funcione para você
Adrian says
Greetings if I use a 12V 7ah lead acid battery… What will the charging current be that will charge the battery?
Swag says
Hi Adrian, it should ideally 0.7 amps, but 1 amp will be just fine!
Adrian says
Hi I wanted to ask.. The Base voltage I measured when it starts conducting (when charger cuts off) is 1.45V? why is this voltage so high? Regards Adrian Sassin
Swag says
Hi, it is because of the combined voltage drops from the two emitter diodes and also the transistor itself
Adrian says
But so far I only connected on emitter diode not two
Swag says
so it is 0.7V for the diode and 0.7V for the transistor, resulting in 1.4V
manish Manikuttan says
sir can I use this circuit to charge my 60ah battery.. if yes. what are the changes required in the circuit
Swag says
Manish, you can do it just make sure to select a relay with contacts rated at 10 amp
Aminu Yahaya I says
Sir,
I built a battry charger using a step down tranfo and this circuit. The challanges am facing is that, If our Main AC is above or below 220v the DC output is varying either above 13v or below 11v and this may damage my battery.
So an Idea came to my mind and I changed transfo with a UPS tranfo that has 175v, 195v, 220v and 250v primary and 7v-0-7v secodary and am using outer taps that gave 14v to charge battery.
I used four (4) switches, 1st switch From Main to 250v of tranfo, 2nd swtch from main to 220v of transfo, 3rd swtch from main to 195v of transfo and the last one to 175v, If the Main AC power drop below 220 am switching either 195 or 175 switch so that the output will be okey for charging the battery and if the Main is 220, I off all the switch and On 220v switch. I am doing the same, to others depending on the Main AC voltage reads on the analong metre. At that moment, I realised that, since our Main power is either above 220v for many hours and sometime dropped below 220v for many hours, then I have to introduce a circuit that can do this changes of Main AC input to my tranfo automatically so that my battry will charge and remain safe. I need your help.
Thank you Sir.
Swagatam says
Aminu, if your step down trafo is 0-12V rated, and if you use a bridge rectifier with a high value filter capacitor, that will be enough to raise its output 14.5V at 220V.
Or alternatively you can use a 0-24V trafo and use an LM338 regulator to regulate the output at 14V
If you are thinking of employing a voltage stabilizer circuit that will be an overkill..
Aminu Yahaya Ibrahim says
Sir I did it, and it's working fine.
The transfor is 12v 5A
The bridge rectifier is 10A
The Diode i.e +recitifier to battery+ is 6A 400V
And the Caps is 4700uf 25v.
The output I got is around 14v to 16v.
Now, How can I set the above circuit for autor cut-up?
Thank you very much for your kind help.
Swagatam says
Aminu, first adjust the preset such that the slider completely touches the ground side of the preset.
now apply the supply voltage to the circuit….now very carefully and skillfully adjust the preset upwards until the relay just switches ON.
that's all your circuit is set.
Swagatam says
…while practically charging the battery make sure the discharged battery is connected first and then power is switched On
the power supply current must be 1/10th of the lead acid battery AH
Aminu Yahaya Ibrahim says
thanks for the reply sir.
So, do you means, I cannot charge other battery type than lead asid (as you have suggested in last reply) with is circuit?
Swagatam says
you can use any form of battery, lead acid is not compulsory, but the charging current can be different for different types of battery, for example if a Li-ion batt is used then the charging current could be as high as its AH value, but for lead acid it is recommended to be 1/10th of its AH
Aminu Yahaya Ibrahim says
Good Day Sir,
I am done with this battery charging circuit. But the diode you suggested me to use between rectified positive power from transfo to the positive to battery is getting hot. And it is a 6A diode. I tried finding higher current in the market but I didn't get one.
So, can I use MBR20100CT, which is 20A 100v three pin diode in form of transistor?
If yes, I need your help on how to coonect it.
Thanks very much Sir.
Swagatam says
Aminu, you can clamp the diode with an aluminum heatsink for cooling it. you can innovate the clamping method by some thinking
Aminu Yahaya Ibrahim says
Okey, thank you very much sir.
I will try this.
that means MBR20100CT cannot be use, which is very simple to clamp on the heatsink?
Aminu Yahaya Ibrahim says
Sir, can I connect two or three 6A diodes, in parallel, to double the current?
Swagatam says
Aninu, diodes should not be connected in parallel. the heatdink method will be more effective
Aminu Yahaya Ibrahim says
Sir, KBPC2504 It's a 25A diode brigde.
Swagatam says
Aminu, connect a 2200uF/25V filter capacitor and then check the response.
also check whether the bridge is getting warm or not, without load….if it is then your connections could be wrong.
Aminu Yahaya Ibrahim says
Thank you Sir.
If I got you right, connecting a diode from a 12v tranfor to a positive of 12v battery can charge the battery to 14v?
Swagatam says
Aminu, the diode needs to be connected after the bridge/capacitor network, if you use only the diode without the bridge then the output voltage will not reach even 13V
Aminu Yahaya Ibrahim says
Okey Sir.
Sir, Can I use KBL406 diode bridge and 12v 5A transfo with this circuit to charge a car battery. i.e 12v 50A battery?
Again, I had once connected KBPC2504 to a 14.2v transfo and the voltage at + and – output of the tranfo at diode dropped to around 11v. What mades the voltage dropped to 11v?
Thanks for the help you are offering us Sir.
Swagatam says
Hi Aminu, what is KBPC2504, please specify….
Aminu Yahaya Ibrahim says
Okey Sir.
Sir, could you help me on how to rectify 12v to 14v? And, How/Where do I connect the 60ohm resistor and of what watts?
Thanks for the help.
Swagatam says
connect a diode instead, in between with the charger positive and battery positive, this will drop 0.7V and never allow the battery to reach 14.4V or over
Swagatam says
charger(+)—–>|——-battery(+)
1n5408 or 6A4
Aminu Yahaya Ibrahim says
Thank you Sir.
Sir, If am using 12v tranfor, is there any harm to battery if it is fully charged?
So that, no need to use battery charge circuit for battery full cut off.
thanks one again.
Swagatam says
12V after rectification/filtration will become almost 14.5V…although it won't harm the battery much, it is not recommended to keep the battery connected with a 14.5V supply after it is fully charged. use a low ohm resistor around 60 ohm in series this will allow you to keep the supply connected permanently.
Aminu Yahaya Ibrahim says
Sir,
Using the above circuit, can I replace the relay with DTDP, so that, I can configure it to off the charger from main power when the battery is fully charged.
And, If I apply transfo with any volts above 14 (as specify) will it damage the battery? let say the transfro volt is 18 to 20 while the current remain 1/10th Ah of the battery.
Thankd you Sir.
Swagatam says
Aminu, you can do it but you may to incorporate an ON/OFF push-switch in parallel with the contacts which is wired with the mains, this push-switch will be used to switch ON the circuit initially.
18V will damage the battery once it's fully charged even if the current is 1/10th…so make sure the voltage is not above 14.5V
Rajagilse says
Sir, could I use this circuit for 110ah 110ah 110ah 12 volt D.C. battery?
Swagatam says
Hi Raja, yes you can connect the mentioned battery by suitably upgrading the relay to a 20amp relay and by replacing the BC547 with a 2N2222
Dewkaran says
Hi,
Please share the 3 and 6 volt auto cut battery charger circuit.
Regards
DEV
Swagatam says
you can try the following design:
https://homemade-circuits.com/2013/12/usb-automatic-li-ion-battery-charger.html
Anonymous says
Hi admin
is it easy to add some charging/full charge LED's ??
thank you
Swagatam says
no there's no proper place to add LED indicators in this cirucit…
Anonymous says
Hello Sir
i've created this wonderful circuit but i have a problem
battery voltage should be 11.4 or below in order to relay works and starts charging process !!
so lets assume my battery voltage is 12 , 12.5 or ….. i it's just half-charged but charging process doesn't start !!
Swagatam says
hello, try adding a few more diodes with the existing emitter diodes D5, D6 and see if it makes any difference..
Anonymous says
Hi swagatam
How to replace relay with a transistor or mosfet
Swagatam says
Hi, replace the relay coil with a 1K resistor…connect the gate of the mosfet with the collector of the BC547….connect the source with the ground, and connect the battery across the positive supply and the drain of the mosfet
ainsworth lynch says
Can you design a circuit to automatically charger 3 batteries at a times assuming that not all the batteries have thebsane amount of charge so they should be able to shut off individually when they reach full charge
Swagatam says
simply make 3 separate chargers and connect them separately to the batteries…I have discussed many automatic 741 battery charger circuits which can be replicated 3 times for the desired results.
saurabh nimavat says
14 volt transfirmar not available any market please help…..
Swagatam says
use 0-12V bridge rectification and filtration will finally produce 14V
saurabh nimavat says
Not work and my battery is 12 volt 12 ah so what is capable AmpeR to fast and safe battery chRge and wich type value of using bride center capasitor
Swagatam says
use a 2 amp 12V transformer, bridge using 1N5408 diodes and capacitor 2200uF/25V
saurabh nimavat says
What is a full charge 12 volt battery voltage
Swagatam says
14.3V
daniel adusei says
sir
this circuit is work very well for me i have tried a lot of 12v charger circuit but if i conpair this is the best for me thank you ok,but sir i want to put led where it should be put to indicate the battery is full charge? thank you.
Swagatam says
OK thanks! for a full charge indication you can connect a red LED across the relay N/O contact and the negative of the circuit via a 1K resistor.
daniel adusei says
sir please i don't really know the AH i asked the seller man he said it American gell battery it don't have AH but it a 21plate battery.
Swagatam says
your battery could be drawing large current beyond the capacity of the diodes, increase the diode rating to say 10amps each or more.
daniel adusei says
sir
please i build this circuit but when i it start charging the rectifier diode got hot almost damage if i didn't switch off,i used 1n5399diode same problem sir i have used three type of rectifier diode but not succeeded sir please any help? thank you.
Swagatam says
daniel, what's the battery AH??
biannz says
sir please can you show me boost circuit using IC555 to generate 28V if you have designed one.thank you
Swagatam says
you can try the one shown in the following article:
https://homemade-circuits.com/2012/09/led-emergency-light-circuit-using-boost.html
biannz says
sir please i have two 12v batt 200AH and i want to use 12v charger circuit to charge the two of them but sir i want ask you that if series the two 12v batt 200AH which is 24v batt i have automatic 12v charger so i want to use it charge this 12v 200AH,i have series them 24v so sir im going to send you that 12v automatic circuit please publish it for me so that i can use it to charge my 24v batt 400AH thank you
Swagatam says
you will need to make a boost circuit using IC555 to generate 28V and use it to charge the series 24V battery.
you cannot use a 12v charger to charge the series connection
biannz says
sir please to set btt cut off using variable power supply it plenty difficult for me so i want you to explain it simply for me to understanding if i use variable power supply do i have to remove the transformer from the bridge rectifier and connect variable power supply to the bridge rectifier and remove after set and connect the former or not that way? thank you.
Swagatam says
you can keep the transformer connected but do not plug it in to mains.
now you can use a variable power supply whose output must be connected to the circuit's positive and negative terminals directly.
After this the required voltage may be fed to the circuit and the preset adjusted for setting the desired cut off thresholds.
biannz says
ok sir thank you for accepted my request my prayer is that god will give you strewth than you once again im looking forward.
Swagatam says
i have published it, you can see it here:
https://homemade-circuits.com/2014/01/extracting-single-phase-voltage-from.html
biannz says
hi sir please i need something i been searching everywhere but not avail so please im appealing to you if you can do it for me, this is special request,that thing is in my country we have 3phace meter and single phase meter so if you use single phase meter you will get one power and negative from the electricity pole but sometime one phase go off and also low current so sir what i burgin you to design for me is 3phase change over i will bring all the 3 power from the electricity pole for single phase meter so that when one power go off or low current then it change to another phase,i have use this circuit for changing 2phase but when one phase go off it change but if it come back again while the other one is not off. so i will be glad if you can design me one 3phase change over thank you sir looking forward to hear from you.
Swagatam says
hi biannz, i'll try to do it soon, if it's possible for me
biannz says
hi sir this circuit Simplest SMF, Automotive Battery Charger Circuit Diagram Explained can i use 15v transformer? so the relay going to switch off when the batt reach full? thank you looking forward to hear from you.
Swagatam says
Yes you've got to adjust the preset accordingly for getting the desired cut-off
Preston Jose says
What can. Be added to the circuit for an led indicator?
Can I change any one of the diode and add an 1watt LED?
Please instruct me sir.
thanks in advance
Swagatam says
you can remove both the diodes and replace the position with a 1 watt LED, but the indication will not be instant rather gradual, rather you can use the N/O contact of the relay and connect an LED across it and ground via a 1k resistor.
Rajagilse says
sir i want this circuit in such a way thaT relay should active at 14.4 and deactive at 13.5. so I connect total 5 diode to the emmitter of the BC 547 . But the relay won`t active in any position of wiper of preset. could it be possible to do so ? how it could be done please help me
Swagatam says
Remove R1 from the shown position and connect it at the base of the transistor and then check.
network advise says
hi swagatham
this is srinivas naidu
you did a great job and ihave a problem
ihad a two transformers one is 12-0-12 and another one is 0-24 volts .how can i use with this circuit can u sugest me please.
great job
thanks & regards
Swagatam says
Hi Srinivas, thanks very much!
It depends on the battery voltage that you are using, if it's a 12V then you may use the 0-12V tap as the input, if you are using a 24V battery then the 0-24V would become suitable.
However for 24V make sure the relay is also upgraded to 24 rating and R1 increased to 10k.
krishna kumar says
hi swagatham
this is Krishna
I've a 1kw inverter (18-0-18 primary,0-230 v secondary & 24 V battery)how can i use with this circuit and which current rating transformer are using.plz help me.
Swagatam says
Hi Krishna,
What is the ampere of the transformer? and what is the AH of the battery? Pls specify them so that I can provide my suggestions.
krishna kumar says
yeah sir
i'am using 40 A Transformer and 100 Ah battery, and that inverter circuit using 8 IGBTs (IRF 250N).
krishna kumar says
sir
i want one more help, i also use 100 W,24 v solar PV with this ckt,how could interface with it.
Swagatam says
You will need to add a voltage regulator circuit using the IC LM196 for limiting the current upto 10amps. Connect this circuit before after the bridge network in the above design.
The bridge diodes must be rated at 15amps each.
The input can be then either from the mentioned trafo or solar panel.
That's all, this is enable to charge your 100 ah battery safely.
Swagatam says
….connect LM196 stage after the bridge, the IC configuration can be seen here:
https://homemade-circuits.com/2013/04/15v-10-amp-adjustable-voltage-regulator.html
krishna kumar says
sir,
Thank you very much sir, now i try to this circuit. sir and than wich current ratting transformer i used in above circuit sir.
Swagatam says
for charging the battery you can use the transformer that you have with you presently(40amp), the IC will restrict it to 10amps.
Courage says
Hi Swagatam,
Still experimenting on this circuit and here is my observation:
When I plug the battery into the circuit the relay contact vibrates (Note, my battery voltage is 12.5) and when I supply the charging voltage (Between 10VDC – 13.59VCD) it stops vibrating and the realy stays active regardless of how low the supply voltage is. I have used a 35uf and 47uf capacitor interchangeable as you earlier advised and tuned the 10K pot over and over still the same result.
Do you have any idea of what's going on?
Swagatam says
Hi Courage,
It is difficult to understand the situation in your circuit, because the circuit actually has nothing complicated in it.
It's works like that: pin#3 goes high when pin#2 voltage is less than 1/3rd of supply voltage, which can be set by the preset at pin#2.
And pin#3 goes low when pin#6 is 2/3rd of the supply voltage, which can be set by adjusting preset at pin#6
I'll do the circuit practically myself, and tell you the results soon.
Courage says
I am talking about the circuit with the single BC547B transistor in this blog and not the one with the 555. Although I'm experiencing issues with the both of them.
Any way, if you can build both of them and tell me the results for both I sure will appreciate what I may have done wrong and correct suit.
Swagatam says
I confused it with your previous comment which was related to the IC 555 battery charger.
The above circuit is very crude and the operations may get influenced with many factors like the resistance of the relay coil, transistor hFe, number of diodes at the emitter etc..
You may remove the diodes from the emitter and check the results, it should hopefully rectify the issue.
Courage says
I'll try…Thank you
Ajith says
In this site it is mentioned that " transistor is itself equipped with a switch OFF feature in case its base voltage becomes too low.".Please tell me that low voltage value.
Swagatam says
This lower threshold can not be accuratey fixed and may differ from transistor to transistor and also with the relay rating…..the number of diodes placed at the emitter of the transistor may be increased or decreased for altering the low voltage cut off threshold
Courage says
Hi Swag,
Once again, thank you. Just finish building the circuit and it seems to work except that there's a continuous buzz/vibration from the relay once it senses 14v input without the battery (Still waiting for the battery to arrive though). My question is: "Is the vibration normal or could there be something wrong? Please advice.
Swagatam says
Hi Courage,
Try adding a 33uF or 47uF capacitor across the relay coil, this will hopefully arrest the buzzing effect.
Menanti Selamanya says
Hi Swagatam,
It is possible put led when charging (red) and when stop (green)? If yes, how is it?
Thanks
Menanti
Swagatam says
Hi Menanti,
one LED can be added at N/O of the relay across ground for indicating battery charged condition.
Menanti Selamanya says
Ahhh, that's right. Thanks Swagatam…
Courage says
Good job Swagatam. I really appreciate what you are doing here. I came across this forum because I'm looking for suitable circuit/s for my project.
Kindly educate me: I have a power generating system that produces between 27 – 31VAC on the high voltage terminals and 7 – 9VAC on the low voltage terminals. How do I cleanup the high volt output to be suitable for charging a 12V battery (or say, as supply to the circuit you've given)?
Also I intend to use the low voltage output separately to control some actuators in the system. So, how do I regulate it to 7 volts?
Thank you.
Courage
Swagatam says
Thanks very much Courage,
You can probably use an IC LM338 circuit for regulating both the voltages, you would need two of them separately for the two sources.
please check out the first circuit in this article, the 5K pot may be adjusted for getting the required voltage levels:
https://homemade-circuits.com/2012/04/ic-lm338-application-circuits-explained.html
Courage says
Real big thank you for your speedy response.
I have seen the circuit, but one question: Do I have to connect the output of the circuit in this article to the input of the charger above? I think that should be the case but still need clarification.
Swagatam says
it's my pleasure courage!
you will have to first rectify and filter your generator AC source using bridge/capacitor network, like the one which is employed in the above circuit(D1—-D4, C1), then feed the DC to the input of the LM338 circuit, the output from the LM338 circuit then may be fed to the above circuit across the cathode of D1 and cathode of D6.
The D1—D4 and C1 stage then will not be required in the above circuit.
Courage says
Ok, got it… The buzzing stopped when I switched the terminals. my bad.
viral desai says
hi sir….
i tried to make the circuit but not getting voltage after the rectifier..i guess i have problem at preset or rather at transistor.so may be i ll desolder it n try again…….n i didnt get how to adjust the preset…..at first it will be at low but then how will i know battery is charged n how to adjust it………
Swagatam says
connect a battery, and let it get charged, when the voltage reaches 14v, adjust the preset such that the relay just activates.
the setting is complete.
glue the preset setting to fix its position.
Unknown says
Hi Swagatam sir,
I just tried this circuit, I have a 0-12V 1 amps transformer, 12 V 7.5 Amps battery. Output I got was 16-17 V, from the transformer when you place the capacitor c1.and the same out was fed to the battery. Is it right or wrong. Why I'm I getting 17 V when I connect the capacitor 100mf 25V
Ram
Swagatam says
Hi Ram,
The voltage will automatically adjust to lower levels once you connect a discharged battery to it. If it doesn't then you can try a 0-12V 750mA or 0-12V 500mA transformer for charging the 12V7.5ah battery.
Johnny Mehanna says
Hi
Thank u 4 ur wonderfull circuits.
what must i do if i want to recharge not 12v battery but 6 volt battery?Does this circuit do the job, or i must change somthing in it?Or i need a whole different one?
Thanks
johnny
Swagatam says
Thanks! You will have to change the transformer rating to 0-6V, it would provide an output of 7V after rectification…. and next you will have to set the preset such that the relay deactivates at 7V
Anonymous says
Salute sir, Happy new year and I wish u the best in 2013. Could a relay be incorporated in an UPS for switching devices when the mains power is off? If so, wouldn't the connected device (like computer) switched off for a sec before the relay execute the switching action. Thanks Abdulganiy
Swagatam says
Happy New Year to you Abdulgany,
Relays are normally pretty quick with their switching speeds, it happens within milli-seconds, at that speed a computer wouldn't switch off, yet for more reliability you may try SSRs instead of relays.
Anonymous says
Dear Sir,
on your diagram the relay at high voltage will cut off the battery completely from the cirquit. So when the battery voltage drops the cirquit will not detect it and will not charge again. I think that the switch should be before resistor R1 ( ..or it's obvious).
Have a Merry Christmas and prosperous New Year 2013
Swagatam says
Thank you, I have the corrected the diagram according to your suggestion.
Wish you too a Merry Christmas and a very Happy New Year.
bino says
Hi Sir.
I just found your great work.
Kindly please tell me what to do if I want this circuit to work for 24V batery and dc-loads at minimum of 20 Amps
Swagatam says
Thank you Bino!
You will have to change the relay to 24V and the transformer should be rated at 24V, 10 amps.
What load are you referring to??
Anonymous says
hie swagatham,
how to connect capacitor across the relay coil
Swagatam says
Connect the positive of the capacitor to the positive line and the negative of the capacitor to the collector of the transistor….
savyasachi says
Hi swagatam,
what if i connect a DPDT relay to this circuit and connect my LED array to the same relay ?.
savyasachi says
Hi swagatam,
I am sorry i didn't see the reply. anyway please ignore the above comment.
savyasachi says
Hi Swagatam,
what will be the transistor's base voltage for the circuit to turn off charging while battery gets 14 or 13.7. ?
savyasachi says
Hi , I am planning to make this charger. plz tell me about how to adjust the p1. I mean how could i know that this relay will off the circuit when battery voltage comes to 14V. And i want to connect a LED in this circuit which glows when battery fully charged.
Anonymous says
Can I use this in charging Car battery
Anonymous says
Can a mosfet/transistor switch replace the relay? How to connect it?
Anonymous says
Thanks for this nice circuit. I wish to replace the relay with a transistor for cutting of the charge to the battery on full charge. A relay would be bulky in a portable application.
faithgonuel says
OK. Got your message.
faithgonuel says
Thanks for the quick and clear response to my request. I truely understand your position.
Moreso, can you furnish me with your e-mail address as I have two electronic circuits I would like you to help analyse for me and others who may be interested in them.
Thank you.
faithgonuel says
Dear Engineer Swagatam,
I really appreciate your efforts on electronics hobbyst circuits. I have learnt alot from your tutorial and comments. Please, can you do a tutorial on practical transformers(especially those used for building inverters and battery chargers)could be design and fabricated
thank you.
kaluyam says
Thanks Engineer Swagatam,
Your one out of the few , who can manage to educate people of my nature. Now I can assure you that I will not give up until I get it. but still I need a lot of support from you as usual. Also I have seen very many useful circuits from your web site which are useful to very body in day to day life. so please help me engineer, I might become useful one day, like you in this world. lastly, please!! can you help me with your tel number.
regards kaluya moses.
kaluyam says
Dear engineer Swagatam,
Actually the led lights up having followed your instructions, there is voltage output at pin number 6 of the IC, which i measured using the the digital meter to conform and it was 14volts. by the means of adjusting the preset connected to pin 3 .
BUT, within less than 4 minutes the IC heats up and die i have tried to follow up but all in vain
so please!!!!! engineer just help me with a purely working circuit diagram instead I pay money. Because am like about to fail getting to the designation .!!!! Regards kaluya moses.
kaluyam says
Thanks engineer Swagata,
AM going to up your Instruction please sir
regards kaluya moses.
kaluyam says
Dear engineer Swatagatam,
I would like to help me about about the two inputs of the IC because I don't know whether you mean the inverted and non inverted i.e pin(2 and 3)or (7and 4) according to circuit diagram. I wish you a happy and prosperous new year 2012.
regards your student
kaluya moses.
kaluya says
Thanks, engineer Swagatam,
I have just received my modification, guideline for the auto charger. now let me get on,to correct those mistakes i made.
so i will keep in touch with you.
regards kaluya moses.
kaluya says
Hi Engineer Swagatam,
Congratulations for new site, am really so excited to hear that from you again. and now I have hope that I will be able to complete my project within this year. after that i hope to do so many business more things with you if you accept my request
In fact engineer, I was so shocked when I discovered there were some changes in our communication, Yet my project remain with few small mistakes to get ready. " Automatic High current battery charger 200AH"
Please!!!, advice me I got confused a bit because of that after failing. to in touch with you.
Now I saw some of your staff on fiverr web, all the way looking for you.
. so please help me by either selling to me that already tested circuit diagram or in any way in order to complete project and am ready to pay for it. or else any other way possible.
i will be very very grateful to get any news from you
regards kaluya moses your Informer Student
From Uganda East Africa.