Lead acid batteries are normally used for heavy duty operations involving many 100s of amps. To charge these batteries we specially need high current battery chargers rated to handle high ampere charging levels for long periods of time. Here we discuss one such automatic lead acid battery charger with high Ah charging capacity.
This high power lead acid battery charger circuit can be used for charging large lead acid batteries in the order of 200 to 500 Ah, the design is perfectly automatic and switches of the power to the battery and also itself, once the battery gets fully charged.
Simulation and Working
Looking at the shown high current schematic for charging large batteries, we can understand the circuit idea through the following simple points:There are basically three stages in the shown configuration viz: the power supply stage consisting of a transformer and a bridge rectifier network.
A filter capacitor after the bridge network has been ignored for the sake of simplicity, however for better DC output to the battery one can add a 1000uF/25V capacitor across the bridge positive and negative.
The output from the power supply is directly applied to the battery which requires to be charged.
The next stage consists of an opamp 741 IC voltage comparator, which is configured to sense the battery voltage while it is being charged and switch its output at pin #6 with the relevant response.
Pin #3of the IC is rigged with the battery or the supply positive of the circuit via a 10K preset.
The preset is adjusted such that the IC reverts its output at pin #6 when the battery becomes fully charged and reaches about 14 volts which happens to be the transformer voltage at normal conditions.
Pin #2 of the IC is clamped with a fixed reference via a voltage divider network consisting of a 10K resistor and a 6 volt zener diode.
The output from the IC is fed to a relay driver stage where the transistor BC557 forms the main controlling component.
Initially, power to the circuit is initiated by pressing the "start" switch. On doing this, the switch bypasses the contacts of the relay and powers the circuit momentarily.
The IC senses the battery voltage and since it will be low during that stage, the output of the IC responds with a logic low output.
This switches ON the transistor and the relay, the relay instantly latches the power via its relevant contacts such that now even if the "start" switch is released, the circuit remains switched ON and begins charging the connected battery.
Now as the battery charge reaches about 14 volts, the IC senses this and instantly reverts its output to a high logic level.
The transistor BC557 responds to this high pulse and switches OFF the relay which in turn switches of the power to the circuit, breaking the latch.
The circuit gets completely switched OFF until the start button is pressed once again and the connected battery has a charge that's under the set 14 volt mark.
How to set up.
It's very easy.
Do not connect any battery to the circuit.
Switch ON power by pressing the start button and keep it depressed manually, simultaneously adjust the preset such that the relay just trips or switches OFF at the given rated transformer voltage which should be around 14 volts.
The setting is complete, now connect a semi discharged battery to the shown points in the circuit and press the "start" switch.
Due to the discharged battery, now the voltage to the circuit will drop under 14 volts and the circuit will instantly latch, initiating the procedure as explained in the above section.
Circuit Diagram for the proposed battery charger with high ampere capacity is shown below
Using two opamps:
An alternative way of achieving battery charging for a lead acid battery with high amperage can be observed in the following diagram, using a couple of opamps:
LM358 Pinout
At low battery level, the lower opamp output remains high disabling the upper transistor relay driver, which allows the battery to initiate its charging process through the N/C contact of the relay.
As the charging voltage rises, the potential at (-) input pin of the lower opamp exceeds its (+) input level, which switches OFF the lower BC547, however the upper opamp output being still at logic zero the relay sustains its N/C relay position and carries on charging the battery.
At the full charge level when the potential at (+) input pin of the upper opamps tends to exceed its (-) input pin, the output of the upper opamp goes high, switching ON the relay and toggling its contacts to N/O.
This action switches OFF the charging current for the battery.
In this condition, a positive feed back from the 1K/10K resistive divider is applied to the (+) input pin of the upper opamp, which latches the opamp hard, and this in turn latches the relay in the N/O position.
Now, if any intended load is operated through this battery, and as it goes through a discharging process....after a period of time the battery voltage tends to drop to a point wherein the potential at (-) input of the lower opamp gets lower than its (+) input pin....this instantly causes its output to go high, switching ON the lower BC547.
The BC547 grounds and breaks the feedback latching potential and also the base triggering voltage of the relay driver transistor.
The action switches OFF the upper relay driver transistor allowing the relay contacts to revert to its N/C position, yet again initiating an automatic charging of the attached battery.
Video Clip:
The set up of the above circuit can be visualized in the following video which shows the cut off responses of the circuit to the upper and the lower voltage thresholds, as fixed by the relevant presets of the opamps
Using a BJT only for high Ah Charging
The following explanation details how a battery may be charged effectively without using any IC or relay, rather simply by using BJTs, let's learn the procedures:
The idea was suggested by Mr. Raja Gilse.
Charging a Battery with a Voltage Regulator IC
I have a 2N6292 . My friend suggest me to make the simple fixed voltage high current DC power supply to charge the 12 v battery. He had given the attached rough diagram. I don't know anything about the above transistor. Is it so ? My input is 18 volt 5 Amp transformer. He told me to add 2200 uF 50 Volt capacitor after rectification. Is it works ? If so , is there any heat sink necessary for transistor or/and IC 7815 ? Is it stops automatically after battery reaches 14.5 volt ?
Or any other alteration needed ? Please guide me sir
Charging with an Emitter Follower Configuration
Yes it will work and will stop charging the battery when around 14 V is reached across the battery terminals.
However I am not sure about the 1 ohm base resistor value...it needs to be calculated correctly.
The transistor and the IC both may be mounted on a common heatsink using mica separator kit. This will exploit the thermal protection feature of the IC and will help safeguard both the devices from overheating.
Circuit Diagram
Circuit description
The shown single transistor high current battery charger circuit is a smart way of charging a battery and also achieving an auto shut off when the battery attains a full charge level.
The circuit is actually a simple common collector transistor stage using the shown 2N6292 power device.
The configuration is also referred as an emitter follower and as the name suggests the emitter follows the base voltage and allows the transistor to conduct only as long as the emitter potential is 0.7V lower that the applied base potential.
In the shown single transistor high current battery charger circuit, the base of the transistor is fed with a regulated 15 V from the IC 7815, which ensures a potential difference of about 15 - 0.7 = 14.3 V across the emitter/ground of the transistor.
The diode is not required and must be removed from the base of the transistor in order to prevent an unnecessary drop of an extra 0.7 V.
The above voltage also becomes the charging voltage for the connected battery across these terminals.
While the battery charges and its terminal voltage continues to be below the 14.3 V mark, the transistor base voltage keeps conducting and supplying the required charging voltage to the battery.
However as soon as the battery begins attaining the full and above 14.3 V charge, the base is inhibited from a 0.7 V drop across its emitter which forces the transistor to stop conducting and the charging voltage is cut off to the battery for the time being, as soon as the battery level begins going below the 14.3 V mark, the transistor is switched ON again...the cycle keeps repeating ensuring a safe charging fr the connected battery.
Base resistor = Hfe x battery internal resistance
paaker says
I thing there is a small mistake on this circuit.
PIN number 2 is mention next to PIN number 8. I think it should be pin 7.
Swag says
thank you paaker for pointing out the mistake, I have corrected it now, please check it
Paaker says
Both circuits work perfect,
I hav assemble and using it.
Thanks Swag.
Swag says
Thanks Paaker, I am glad it’s working!
Nkwenti says
again sir.
I am needing this automatic charge cutoff for my solar installations, if it can work well for both solar and windmill it would be great!
Swag says
yes it will work for kinds of sources between 3V and 30V, for higher voltages just make sure that the IC supply is restricted below 30V (for the last circuit)
Nkwenti says
Thanks for directing me here sir… now i have some questions, can i replace IC LM358 with TL072? can i replace transistor 8050 With any darlington pair or any high voltage transistor such as tip transistor? please i will take your advice from here if i have anymore questions.
thanks for the help sir.
Youre amazing teacher for real
Swag says
Thanks Nkwenti, yes you can replace LM358 with TL072, just make sure the pinouts are correctly exchanged.
The relay driver transistor can be replaced with other types but preferably it should be selected as per the rating of the relay, having said this any transistor such as a TIP122 will also work
josephxc says
hi sir, can this circuit be used to charge a 12v 60AH battery. thanks
Swag says
Hi Joseph, yes it can used!
Jude says
dear sir,
on the second circuit in the link you provided,i am asking if LM338 input is connected to battery input?
and what formular should i use when calculating resistor in parallel with the LEDS?
Regards
Swag says
Jude,
yes the input is connected to the supply source (+), the output is connected to the LED (+), the negative goes directly to the LEDs. The formula is
R1 = 1.25 / LED safe current (max current)
Jude says
Dear Sir,
is it proper to just connect all my bulbs(dc bulbs) directly to the positive and negative terminal of the battery without any damage to the bulbs? using the bottom charging circuit diagram.
or advise on how best i can handle this.
Thanks
Swag says
It will need to be calculated with formulas, give me the V and I specs of the LED and the supply input, I’ll show you how to do it.
Jude says
Dear Sir,
i have five(5) 12V , 4watts bulbs already, and i have 12V, 200AH battery for this purpose,
Thank you so much while i await your response
Swag says
Jude, the total wattage of your becomes 4 x 5 = 20 watts,
You may have to include a current limiter circuit in between the supply and the LED assembly.
You can opt for the following current limiter design and use it for the purpose
https://www.homemade-circuits.com/universal-high-watt-led-current-limiter/
This will allow the supply current to pass through the above circuit and limit current before entering your LEDs
Jude says
Dear Sir,
i appreciate so much for the kind responses.
i will be building the charger circuit at the bottom article this weekend.
i need a simple dc emergency light circuit diagram where i have to go straight and connect my load(i.e DC bulbs) through the charging circuit..
i just need to power five DC bulbs of 5Watts each.
Humble regards
Swag says
You are welcome Jude!
I wish you all the best!
Jude says
Dear Sir,
i want to build this circuit,but i want to use it to charge 12V, 200AH battery.
My questions are:
1-what are needed to be modified in the circuit to be able to charge this battery comfortably?
2-will the battery discharge after power outage when the battery is not in use,if yes,how do i prevent this?
3-how can i set up this circuit to power dc bulbs without having to build extra circuit for it.
4-i want it in such a way where i have to switch to DC for lighting in my home when there is power outage from the utility,how do i achieve this?
5-how do i wire it so that when the utility restores the light and i switches to utility,my battery starts charging automactically.
Best regards
Swag says
Hi Jude,
If you want to have an automatic load switch ON, then you can try the following concept
https://www.homemade-circuits.com/make-this-automatic-10-watt-to-1000/
Only the relay will be required to be changed with a 30 amp relay.
Jude says
Dear Sir,
thanks for your quick response.
i have checked the link and this questions to ask;
i am a newbie and i don`t want to make a lot of mistakes while building this circuit…does the circuit in the link has charging capacity?,
i want to build a kind of DC project where i have to power ten dc bulbs like 4watts each,through my 12V, 200AH battery.
i need a clearer explanation on how i can achieve this project in such a way that the battery will keep charging automatically when there is AC and won`t give out power except the AC is OFF.
Please note i don`t want the battery to discharge when it is not in use.
i appreciate your assistance.
regards
Swag says
Jude, if you are a newbie then I am afraid this circuit may not be suitable for you, it will require a good knowledge of electronics to finish it successfully. If possible I’ll try to find an alternative design which may be easier than this one, and let you know
Jude says
Dear Sir,
Newbie here does not mean i can`t finish it successfully,what i needed know is if the combination of the charger and the emergency light circuits can achieve the design i want and how to prevent discharging of the battery when not in use.
The emergency light circuit in the link does not have a charging unit and wanted to be clarified and how best i can integrate the charging circuit with the emergency light circuit to achieve my aim.
thank you again for the kind responses
Swag says
Jude, yes it will accomplish the required objectives. To stop the battery from self discharging when no load is connected you could add a small value resistor from the charging supply + directly with the battery +, this will enable a permanent trickle charging for the battery and never allow it to self-discharge. The resistor value could around 1K 5 watt
Mho says
Is the 741 used just as a comparator? Can it be replaced with any other regular comparator like lm393 which has two comparators as opposed to 741 which has just 1?
Swag says
LM393 is a comparator and the output might need a pull up resistor, but can be applied in the above concept, other opamps like LM321 LM358 etc can also be used
Prashant says
I have found one problem in this circuit Sirji.
Whenever circuit is in high cut mode, I discharged the battery at 11v. But the charging doesn’t start automatically. Then I set preset for low cut so led will not off of low cut led even at 14v. So set high preset so low cut problem starts. I used 42ah battery. So what can I do?
Please guide me sir.. ..
Swag says
Prashant, which circuit are you referring to?
the second circuit is tested, you can see it in the video how it correctly responds to the high and low voltage thresholds..
Swag says
Prashant, do one thing, just swap the input supply with battery and battery with input supply….meaning apply supply input from the relay side on the right…and connect the battery at the left side….
I’ll update this in the second diagram soon….
Prashant says
Dear swag sir,
I am requesting to you that l want to make 15-20 A charging current circuit. So please give me the components list for that including transformers and bridge circuit data.
Swag says
Dear Prashant, you just have to buy a 20 amp transformer, connect a 30 amp bridge rectifier with the output and a 10,000uF / 50V filter capacitor to get the required output, if you want to have any special design, please specify the details….
Prashant says
I have 1.5kva inverter with 24v dc and 5a charging Current circuit but I want to make 15 to 20a charging Current circuit and add it in that inverter and synchronized with it.
Can you give me details of transformer winding like primary and secondary winding gauge and no. of turns of charging transformer. Dear sir,
I want a Transformer data for 12v and 24v DC Battery charging with 15 to 20a charging current.
Swag says
Hi Prashant, I am sorry, I do not have the data for the specified transformer winding, you will have to consult a professional trafo designer for this…
Prashant says
OK no problem sirji
Aayan says
Hello, its not that simple as i thought. I just purchased all the items, 10k preset, 10k resistors, LM358, BC 547, 8050, 12v Relay, 1N4007 diode,1N4148 diodes, 6V Zener, leds. But after 2 days of completely attaching the components together I am not able to use it. “””” I want a Wiring Diagram of the Second Diagram””‘ so that i can remake it again. What happen to that i build? When i attached the input voltage of above 12v relay turns on and no output on the other side and even no led lights glow. On other side I have a 12v battery connected to the circuit, when i removes the input voltage the battery itself powers relay and makes zzzzzzzz noise.
Please provide me a Wiring diagram in which all the components are connected in simple manner and with pics…. Or u can also provide me a sketch of this too… Its my first time so please help !
Swag says
It is an extremely simple circuit idea but only if you do it with proper understanding, how did you set up the presets? did you use a variable power supply for this?
Give me two days I’ll make a working video of it and upload it.
Aayan says
I will be waiting for that video…. Please make that video as soon as possible… “” Talking about presets I didn’t setup them just soldered them into the board and thought I will rotate the screw at the top of them to set when I need it to turn ON and OFF but …… Problem persists…
Swag says
yes you have set it up after soldering only, so how did you do it….I’ll try to upload the video but can’t guarantee you whether it will be quickly or not because I have other work also, but I will do it for sure, it will be not just for you for but all other readers…
In the meantime you should try fixing your circuit by correctly setting up the presets
Aayan says
Okay at least for now You can Provide a drawing of Second Diagram/Schematic. Just show components instead of their symbols. It will make me clear about the connections. “””” Actually I am not sure about my connections and It is difficult for me to read schematic where LM358 is connected and where Relay is connected. I hope you will provide me a Wiring diagram of mentioned schematic.
Swag says
My breadboard set up is ready and the presets are responding perfectly, now only the actual battery charging procedure is pending which I’ll try to finish by tomorrow…I’ll update the diagram by inserting the pin numbers to the IC soon…
Aayan says
Im waiting for drawing or video. Please make me feel better as i haven’t slept from 2 days… Red eyes…. Figuring out solutions… Resolving schematic
Swag says
I have updated the circuit diagram with the IC pinouts, and also I have shifted the upper LED towards the base of the transistor since this showed a better response while testing my prototype
Aayan says
What is this 1234 5628 written on the above diagram. Is it the lm358 pin out numbers… Thanks for Replying fast
Swag says
those are IC pin numbers.
Prashant says
What should be the values of preset 1 & 2 ?
Swag says
10K, it’s mentioned in the diagram…
Prashant says
Yes, but how can set up this variable value?
suppose, I want to set high cut at 14v DC. So what should be the value between 2 and 3 lead of preset of both preset.
Swag says
you will have to set it up by piratical procedures, first keep the slider of upper presets to ground level, adn the slider of the lower preset to the POSITIVE level.
then feed the over charge voltage from the left side, say at 14.3V, now adjust the upper preset until the relay just clicks ON and the upper LED is ON. At this point the upper opamp will be latched.
Now reduce the input voltage slowly up to the lower discharge value, say at 11V, now adjust the lower preset until the lower LED is ON and the upper LED is OFF and the relay is also OFF.
That’s all your circuit is setnow…you can stick or glue the presets in that position.
Prashant says
Thanks for cooperation.
Now the circuit works.
How can increase or decrease charging ampere?
Swag says
I am glad the circuit is working for you…current will need to be adjusted from the input power supply side, the above designs are only for controlling the charging levels of the battery…
Prashant says
I am referring second circuit.
1. How many lm358 ICs are Used in that circuit ?
2. How many Supply voltage is providing to lm358?
3. Can I providing the capacitor in parallel with relay diode? What value?
Swag says
yes BC547 can be used if the relay coil resistance is not less than 200 ohms.
only one LM358 is used
LM358 can operate with max 32V supply
you an put a capacitor in parallel with relay coil, it can be a 100uF/25V
Prashant says
Can I use bc547 instead of 8050 transistor?
Aayan says
Sir, Im am a newbee… I wanted the simplified/wiring diagram of the Second Schematic diagram. Please provide me that, as i am unable to figure it out how to connect the components.
Swag says
Hi Aayan, If you are confused about the opamp then you can refer to the following diagram of the IC’s internal layout IC, you just have to match and assemble it as per the given pinout specifications, if you have any other doubts please let me know…
https://www.robomart.com/image/catalog/RM0067/01.gif
Saqib Lodhi says
Hi Swag,
Hope you’re doing well.
I have three questions.
1. Can this circuit be used to charge different amperage batteries? I mean if I want to charge 45 AH, 70 AH and 200 AH?
2. What is the best way to calculate input amp/transformer power rating for a battery, assume 100 AH?
3. Do you have any transformerless power supply circuit that can provide that kind of high amperage?
Swag says
Hi Saqib,
1) the circuit can be used for charging any preferred battery, by upgrading the transformer, diodes, and the relay accordingly.
2) for lead acid batteries the ideal rate of charging is always 1/10th of its AH rating, the trafo can be selected based on this rule.
3) sorry I do not have any high current transformeless SMPS circuit at this moment.
Saqib Lodhi says
OK thanks.
To avoid having multiple chargers for different amperage batteries, can we modify this circuit to automatically detect battery capacity and give out as required like Samsung adaptive charging technology which gives 5v 2amp output when required by cellphone otherwise gives some milliamps for normal cellphones.
Swag says
It may be possible, it will require some thinking, and the design can be little complex.
Saqib Lodhi says
If possible, whenever you get some extra time from your busy schedules please try to build this circuit.
Thanks for your quick help.
Swag says
sure, I’ll try to do it in my free time…
kelly says
Hello Sir,
I am a fan of your work. I am having a little problem. I need a circuit that will automatically cutoff supply from a charger to 3pieces of 200ah battery charging in parallel. I was thinking of using a comparator but I have not found anything useful. The maximum charge voltage for the batteries must not be above 14volts and I definitely would love one that works with MOSFETs or any other transistor you may prescribe. Thanks a lot sir
Swag says
Thanks Kelly, appreciate your feelings!
A conparator circuit is the most useful and the ultimate thing that should be used for any voltage cut off related circuit…so you must employ only an opamp based circuit for your application too!
you can try try the first circuit from the following article:
https://homemade-circuits.com/2014/04/48v-solar-battery-charger-circuit-with.html
if your battery is 12V you can remove the 22K resistors and the the pin#7 components, pin#7 can be directly connected with the positive line.
Swag says
I am sorry I have provided the wrong link, the correct one can be seen here
https://homemade-circuits.com/2012/08/make-this-48v-automatic-battery-charger.html
sharath says
please sir i have great challenge i need design a battery in the the battery capacity is 3.7V and overall battery capacity is 20A and a need a rechargeble circuit for that
Swag says
That’s not difficult,
you can use the second design from this article:
https://homemade-circuits.com/2013/12/usb-automatic-li-ion-battery-charger.html
replace the 2N2907 with an IRF9540, and calculate the 3 ohm accordingly for limiting at around 15 amp.
sharath says
my battery capacity is 20 amps if i connect to
that battery section that op-amp may damage i need a circuit with an IC specifically used for charging
Swag says
IC will not get damaged due to current, it will get damaged if the voltage is increased above 18V.
no special IC is required, it just needs to have a CC, CV and auto cut off.
But sorry a mosfet cannot be used here because the voltage is too low to trigger a mosfet, you can use an IGBT or use a 2N2907/TIP36 in Darlington mode.
Faith Jumbo says
Sir please I'm having serious challenge after making those changes and connect my power supply at the point were we have the battery connected still the led did not come up when varying, and when i measure, the voltage is not in line with the zener diode at pin#3 i have 13.16v, pin#7 i have 16.2v while pin#2 is 12.6v but when i apply the voltage sample in the opposite side i have at pin#3 4.7v, pin#7 15.18v then when i vary the 10k preset at pin#2 such that i have a voltage higher than that at pin#3 there will be no output at pin#6 but when i vary it such that voltage at pin#3 is greater there will be output at pin#6 which i have to 13.2v
But in all these varying i noticed that the led is on irrespective of fact that the voltage at pin#2 is changing its remain on
Then when i measure the voltage at the point were the battery will be it's 19.23v
Please sir what could possibly be the error and the voltage at the point were the battery will be connected i thought it should be my supply voltage and not less
If this is going to give me little problem please can you recommend another working 24v automatic battery charger please ur advice is seriously needed
Thanks and best regards
Swagatam says
Faith, in the previous link of 48V charger which you are trying, you must feed the voltage from the points where it is mentioned "48V"….you cannot apply from the other side for this design because the mosfet would be blocking the voltage….right??
therefore if you are applying the voltage from the left hand side then it is correct and your adjustment results also look perfectly correct.
when pin#2 voltage goes above pin#3 voltage then pin#6 must become zero (cut-off)…that's correct.
Now as for the LED being illuminated all the time, this could be due to the leakage offset voltage from pin#6 of the IC741. Did you connect the shown zener diode at pin#6 of the IC?? make sure you connect that to solve the LED switching problem.
And what did you use for the power transistor, is it a mosfet or a BJT, remember if it is a BJT then you will require a resistor at its base, and the LED shifted towards the zener side, and not at the base of the BJT.
this circuit is the easiest one, and you are almost near….if you are having difficulty with such an easy circuit then just imagine what you might have to face with the other relatively complex ones…actually all opamp designs are extremely straightforward it's just about understanding them patiently.
Faith Jumbo says
Please sir the first circuit in this article can i use it for 24v charger?
https://homemade-circuits.com/2012/08/make-this-48v-automatic-battery-charger.html
Swagatam says
yes you can use the same circuit for 24V also
Faith Jumbo says
I really appreciate your help and fast response please i build and tested the first circuit thishttps://homemade-circuits.com/2012/08/make-this-48v-automatic-battery-charger.html during setting when vary the preset the led never turn up, could it the 22k or any component i will remove from the circuit to make it work properly
Swagatam says
the pin#2 resistor must vary and become higher or lower than pin#3 reference voltage in order to change the output state, while adjusting the preset.
yes, you can try replacing the 22K with 1K, and remove the 4k7 attached with the pin#2/ground since your supply is not 48V rather 24V only
Faith Jumbo says
And what could be current rating of the relay that i Wil use at that transformer current rating
Swagatam says
I won't recommend the above circuit for a 68amp charging because the relay will need to be rated at 100A…which may be difficult to procure.
better to use the first circuit from the following article….but make sure to remove all the 22K resistors, and zener diode from pin#7 of the IC because we are using a 14V supply for your case
https://homemade-circuits.com/2012/08/make-this-48v-automatic-battery-charger.html
Faith Jumbo says
Wen i put my digital meter across the transformer and at the same time clap it with my clap meter and power it burn of my digital meter but the clap meter read 68A. My question is can this transformer be use to charge a three 12v @200A connected in parallel?
Swagatam says
68A is too high for any standard digital meter but will be OK for a 600AH battery (200AH x 3nos)
Faith Jumbo says
Sir please sorry to disturb please can 650va center tap transformer charge a 12v 200A battery?
Swagatam says
what is the current rating of the trafo…if it's 10 times less than the AH value of the batt, then it would be fine….
Faith Jumbo says
Please sir how do test the current of my power supply because when i use a clap meter to test the current at the positive line its reading 8. 5A could that be the current of my power supply
Swagatam says
Faith, you can connect you DMM prods directly with the trafo wires for a few seconds and check the reading which will inform you regarding the current rating of the trafo.
make sure the DMM is set at AC 10 amp or 20 amp range.
Faith Jumbo says
Please sir how do test the current of my power supply because when i use a clap meter to test the current at the positive line its reading 8. 5A could that be the current of my power supply
Faith Jumbo says
Again i noticed that if connect it to battery for charging the battery voltage rises to the transformer voltage as if its fully charged so please i want to ask it the charging voltage or the its fully charged once connected
Swagatam says
your power supply current(amp) rating must be 10 times lower than the battery AH rating….did you follow this rule?…if not then please make sure you do it.
Faith Jumbo says
Hi
i have built this circuit but when i try to set it the relay dose not flikers and it only works if the switch is connected pls what could be problem
Swagatam says
I have explained the setting up procedure using a few simple steps, just follow those and it will be fixed.
Rohullah Nazari says
Hi dear Swagatam thanks a lot with this good battery charger circuit. This circuit is for 10 to 20 ok. There five diodes 4 diodes are rectifier and 5 diode is used between bridge positive and battery positive and all diodes have the same value. Now if I charge a 50 ah or 70 ah batteries. should I change all diodes amp or only the bridge rectifier. Thank you very much with best regards. Rohullah.
Swagatam says
Dear Nazari, you will have to change all the diodes except the relay diode.
odeyinka azeez sunkanmi says
please how can i determine the amp of a transformer?
Swagatam says
connect AC ammeter directly across the secondary wires and measure
Agbontaen Elvis says
Dear sir, again my transformer with three terminal produce 14V between the last 2terminal and 7V between any of the last terminal and the center terminal. Is this the type of transformers you recommend?
Swagatam says
yes it will do, you can use the 14V for your 12V battery, and make sure the current of the transformer is 8 to 10 times less than the AH value of the battery
Agbontaen Elvis says
Dear sir,
Thanks for this circuit. I couldn't get 6V zener but 6.8V and 3V zener but 2.8V. will still give me a good result. my hope is the 10K pot. please put me through
Swagatam says
Dear Elvis, yes those zeners will also do, and 10k preset will also work….do not use pot.
Jade Mark Talaboc says
hello swagatam,
Is this a 3-state battery charger? if no, do you have any circuit that is 3-state and charges 300AH battery. Tnx
Swagatam says
Hi Jade,
No, the above is a single step charger, for a 3 step charger you can refer to the following article;:
https://homemade-circuits.com/2012/10/make-this-3-step-automatic-battery.html
Unknown says
Hi…I am confused that how are u producing dc output just after the bridge because u said in a comment that u can remove 100u capacitor.although if we continue with this capacitor I think it will discharge very quickly and produce huge ripples at output
Swagatam says
Hi, 100% pure DC is not essential for charging a battery, however in the other comment my recommendation about removing the filter capacitor in order to eliminate the relay chattering might not be correct.
the correct remedy to prevent relay chattering at the cut-off threshold is to add 100K hysteresis resistor across pin#6 and pin#3. This will latch the opamp at the cut off levels and enable a quick and complete switch OFF of the relay and the entire system.
Filter capacitor need not be removed.
Anonymous says
Hello Swagatam,
What are the modifications if I'm going to charge 300AH lead acid battery?
Regards,
Jade
Swagatam says
hello jade, only the transformer, the relay and the diode rating will need to be upgraded as per the battery charging current and voltage specs.
the charging current rate of a 300AH batt can be around 30 to 40 amps
erwin vistal says
hello sir.. still, the relay did not tripped after the battery is fully charged.. i also put and LED in series with the transistor base. there is no changes in the led too after the battery is fully charged. thank you for your response sir…
Swagatam says
Erwin, please tell me how did you set the pin3 preset?
did you do it exactly as explained at the end of the article?
Swagatam says
when you connect the discharged battery pin3 voltage is supposed to be lower than the pin2 voltage and when battery is fully charged pin3 should become higher than pin2….please confirm whether this is happening or not
erwin vistal says
sir.. is there any other way to test the circuit (if it is working) without using a battery?
Swagatam says
erwin, you can use a 5amp 12V power supply for testing it
erwin vistal says
sir after i finished making the circuit on the breadboard and tested it… the output voltage of my charger becomes 16~17 vdc even though my battery was discharged…when i pressed the pushbutton, the relay latched but when the battery is fully charged it did not tripped or turn off the charger… i followed your circuit in every detail…by the way sir thank you for your reply on my first question..
Swagatam says
erwin, connect an LED in series with the base of the transistor…anode to base and cathode 10K…this will give the exact idea how the opamp is behaving.
I am assuming you have done preset adjustment correctly as per the given instructions
erwin vistal says
sir…will the circuit still function even if my charger's output voltage is 16~17 volts dc? thank you for your quick reply sir..
Swagatam says
It will work, but the current should be significantly less than the battery AH, preferably 1/10th of it.
erwin vistal says
thank you sir…
King Dedon says
Pls sir, I need an auto-cut off 96volts/600amps car battery charger circuit diagram, tnx alot
Swagatam says
you can try this
https://homemade-circuits.com/2016/01/high-voltage-360v-battery-charger.html
SUDIP BEPARY says
Can I connect a fixed resistor without using variable resistor
Swagatam says
yes you can, after correctly calculating it..
kas says
Pls reply
kas says
What if I have to charge 7.5 v battery from wall?
Swagatam says
use a 10V DC input
Nabeel Ghori says
Hi Swagatam,
I need to change 50-64 amp car battery. Can I use this circuit? How much amp transformer I would be required. And also is there any other changes with capacitors and diode are need to be done here?
Swagatam says
Hi Nabeel, yes definitely you can use this circuit for charging a 50AH 0r 60AH battery, the transformer current rating should not be more than 8 amps.
the bridge rectifier diodes must be rated at 10amps each…or a single 10amp bridge module will also work at the indicated position
Hardi Susanto says
Sir, can I use this circuit for charging lead acid battery 24v?
Swagatam says
yes you can do it….
Hardi Susanto says
Oke. Thankyou sir, by the way I need to change that ic or not? Example that relay, comparator, or something else?
Swagatam says
yes, just forgot to tell you, you can use a LM321 IC as it's rated to work with upto 32V…the IC 741 IC will burn at over 22V so won't work with 28V inputs
Hardi Susanto says
oke, thankyou so much sir..
Sharanabsava says
Plz swagatam videos URL send me
Swagatam says
sorry sharanab, there's no video for this circuit.
popipo says
Hi, this system would serve me to charge a solar battery and 300Ah 24v?
thank you very much
Swagatam says
you are welcome popipo
Sharanabsava says
Plz swagatam 100 AH 12 V battery charg. And inverter system circuit send me
My mail : sharanbs.basava39@gmail.com
Swagatam says
you can use the above circuit for the charging the battery or the second circuit from the following link:
https://homemade-circuits.com/2011/12/how-to-make-simple-low-battery-voltage.html
for the inverter I'll need more info regarding its specs
Nirvikal Lal says
I have a modified pc smps that gives 14v and 20A
so I want a circuit that charges a 12v 100ah battery automatically ie it should turn off the smps when battery is full and turn on the smps when the battery is low
Swagatam says
you can try the second circuit from the following article:
https://homemade-circuits.com/2011/12/how-to-make-simple-low-battery-voltage.html
Tariqul Alam says
if i just avoid the rectifier portion and use a varying dc source, will the circuit work .please let me know
Swagatam says
i did not understad what you are trying to implement…pls make it clearer
daniel says
thank you for the replayed sir,no i did not make any modifications but one thing is that i use 1n5399 for the 4 diode showing there and also i used In540(16A4) the one that connect to the battery positive is it 6A or 6.4A? sir i build one of your circuit How to Make a Simplest 200 VA Uninterrupted Power Supply UPS Circuit i build only the charger it work very well but i don't think it can charge 24vDC battery two 12v battery? if it can chard what can i do sir help me with the circuit thank you jah guide you and hop to hear from you soon..
Swagatam says
Daniel, Referring to the charger circuit shown in this article:
https://homemade-circuits.com/2012/02/how-to-make-simplest-200-va.html
You can use it for charging 24V batt also…you just have to upgrade the circuit with a 0-24V transformer and 24V relays. R1 should be replaced with 10k resistor.
Remember the transformer current should 1/10th of battery AH.
Anonymous says
Mr,Swagatam i like your good work you been doing so far but one thing i don't understand is you answer to some people questions but you don't reply to me why sir or they are your family? ok please and again as soon as you received this message please i am burgin you to reply me allow me to be one of the your friend cos i am a electronic Hobie i do like your project.my firs quotation is this 12v battery charger circuit i build it but when i power the the circuit relay switch correctly but the problem is out put is 11v and if i calibrate 10k preset to left side it switch on the relay and it give 11v out put if i calibrate to right side it switch off the relay and give me 13v out put why sir any help? i will be glad for your assistance, looking foreword to hear from you thank you.
Swagatam says
Mr Anonymous, I reply to each and every comment and rarely miss any, may one in a million, or as long as it does not have an outbound link.
Anyway, did you make the circuit as it is shown in the diagram, with the start button or did you do any other modifications?
The DC input to the circuit should be 14V DC and the connections to the relay should also be exactly done, and the input current should be rated at 1/10th of the battery
Also did you follow all the instructions mentioned in the article??
It's just about setting up the opamp correctly that's all….the functioning is very starightforward
Naga's World says
Hi Swagatam,
Thanks for your prompt and positive response.
I just read, – Hire me for Designing Circuits – Circuit Ideas, Inventions for Sale – in your blog.
I have a special requirement for my set up, the details I will send to your email ids you have mentioned, would you be kind enough to reply whether there is any scope for making them and your charges as well?
Regards
NG
Swagatam says
Thanks Naga, I have replied to your email, please check it.
Naga's World says
Hi Swagatam,
I wish I had seen your blog earlier. In my set up, I need my charger, connected to the 220 Volts AC mains to start automatically to charge the battery when the voltage drops to 11 and stop the charger when the battery is charged to 14 volts.
Your advise and guidance would be of immense value.
Regards
NG
Swagatam says
Thanks NG,
you can try the last circuit from the following link:
https://homemade-circuits.com/2011/12/how-to-make-simple-low-battery-voltage.html
You will see two relays in the diagram, the lower relay is not required so you can just eliminate it from the design.
Anonymous says
Hi Swagatam am just so proud of you i also made this circuit at the bottom.i did not have BC 557 I used 2N2907, 6.8 Zener and for preset i used a 50k. when i connect it to my supply, the relay trips. the problem is in setting the cut off voltage.i tried adjusting but still it was on pliz help me thanx
Swagatam says
Thanks very much, you can do the following things:
Connect an LED in series with the transistor base 10k (anode to base, cathode to 10k) for indication.
Keep the transformer disconnected, and apply an external power supply of 14.4v across IC supply pins.
Now flick the preset to and fro until you find a point where the LED toggles ON/OFF, adjust this point to just switch ON the LED.
Your circuit is all set now.
Now carry on with its normal operations through the trafo.
While adjusting the preset do not connect the battery.
Swagatam says
…during normal charging operation switch ON the circuit only after connecting the battery to the shown points.
Anonymous says
Sir, I need this circuit to be automatic turn on, not manually with the push button. Can you help me with that subcircuit please? Thanks in advance.
Anonymous says
Hi sir can you add an automatic starting instead the push Butrón, please? Thanks in advance.
Swagatam says
remove push-button connections, connect the trafo directly to mains, and connect the battery positive to bridge positive via relay N/O and pole contacts.
Maung says
Sir,
Thank you very much for your quick reply. 10 amps would be enough for me , would you be able guide us for using ICs like 338, 196 etc on this circuit ? it would be very useful for you.
Thank you once again sir
With best regards
Maung Pru
Swagatam says
Hi Maung,
You can try the last circuit given in this article:
https://homemade-circuits.com/2012/07/making-simple-smart-automatic-battery.html
Replace the IC LM338 with LM196 for 10 amp specs.
Anonymous says
I haven't built this circuit, but may do so. Can I make a couple of comments.
It can be confusing for some of you readers to mix "ampere hours" with amps, as in you title and elsewhere.
With a very slow change of battery voltage the 741 circuit makes a poor comparator. Especially as constructors will have a variety of relays. Relays are notoriously slow at releasing and the 741 will behave unpredictably when the inputs are close to equal. Best practice surely would be to add a touch of hysteresis by adding a resistance between the output (pin 6) and the + input (pin 3). this would cause the 741 to snap quickly and give the relay a chance to close properly. I am no circuit designer might try 470K to start with.
Also please explain the purpose of the 100uf capacitor on the output. Wouldn't that add to the problem.
Finally, I think the circuit would work much more reliably if the relay (perhaps a stand automotive relay) were connected between the battery + and the comparator circuit, rather than on the mains input side.
Swagatam says
Thanks, I appreciate your attempt, here are more precise answers:
AH signifies the charge or the discharge rate of the battery. ideally it indicates the full charge or full discharge rate of the battery in an hours period.
Opamps are excellent comparators and they work very well in battery charge cut off applications.
hysteresis is surely needed so that the relay doesn't keep switching ON/OFF at the thresholds due to the extreme accuracy and sensitivity of the opamp.
Hysteresis delays the relay actions and makes the response slower so that it doesn't chatter…… without hysteresis the relay would snap rapidly producing rapid switching at the thresholds.
A hysteresis can be added in the above diagram to avoid the same.
In the above diagram the position of the relay switches OFF power completely, right from the transformer, so it becomes much safer and reiable.
Swagatam says
…the 100uF is not required, because its inclusion actually makes no difference, so it can be removed
Maung says
Sir,
Thank you once again.
would it be possible to add a charging current controller?
would you please kindly explain us what type of component need to be use ?
Thank you and with best regards
Maung Pru
Swagatam says
Hi Maung,
can you specify your current requirement, if it's upto 10 amps then it can be simply done using ICs like 338, 196 etc, otherwise it would become sightly complicated.
daz says
hi Swagatam,
a very promising circuits youve always share, actually Im always visit your blog coz im also electronics hobbyist from the philippines… i have read many your posted electronics designs especially on battery charging circuits 🙂 its very simple and yet reliable and efficient circuits, building those circuits using your designs works great and thank you so much swagatam! but until, i was thinking an solidstate automatic dual battery charging isolator for deep cycle agm 100ah batteries, i am using some of your design charging circuits and delay and relay techniques, but unfortunately, always got me an error… what should I do sir?. can you guide me with my issues? thanks so much.
here is the step of how the circuit may do…
1. before starting, the two agm batteries 1&2 will combine in parallel connections to use for starting the engine to provide more smooth and more power to start.
2.then, once the engine is started, the battery 1 will automatically disconnect and relay for automatic fast charging and to float mode ( dpdt relays to be used?)
3.while the battery 2 is connected,a voltage low level cut-off monitoring is standby for 11.5v,
4.so when the low volt reach as 11.5v the circuit will automatically trigger the relay of the fully charged battery 1 in parallel connection.
5. after the battery 1 connected in parallel, a delay relay cut-off circuits of battery 2 will engage for automatic fast charging and to float mode.
6.a continuation cycle of relays, monitor, charging. thats it.
I hope you understand of what i mean.
hoping to hear from your sir. i hope you can help me with this circuits to make.
Thank you so much and more power to you sir!
Swagatam says
Thank you Daz,
From the explanation what I understood is, you want to charge two batteries together having separate low and high voltage detection circuits…so when any of the batteries get fully charged it will get removed from the charging system and in case any one gets discharged below the set threshold it would get connected again…right?
Swagatam says
….and it will also be used for starting the engine together and once the engine initiates they will return to the detection mode.
daz says
yes you're right sir! thanks for the response! can you design that for me sir? thank you so much and more power!
daz says
it would be possible to you design that circuit? thank you so much swagatam
Swagatam says
Hi Daz,
Thanks!
I have noted it, will try to update the article soon.
daz says
thank you so much my friend… youre so very kind and very quick when it comes in response.. once youre circuit done and it worked for me, i will then donate something to you. i am very interested with this design to build. thank you so much and more power swagatam! please keep update me soonest possible. thanks again.
Swagatam says
Thank you Daz,
It might take some days to complete it, I'll inform you as soon as it's done.
daz says
thanks my friend.. looking forward in your design.
Swagatam says
Hi Daz, please check it out here:
https://homemade-circuits.com/2013/08/automatic-dual-battery-charger-with.html
Maung says
Sir,
what do i need to change in this circuit if i use for charging of a 150 Ah lead acid deep cycle battery? would you pls guide me.
Thank you
Maung
Swagatam says
Hi Maung,
just use a 20amp rated transformer, rest everything will remain as it is.
also be sure to select the diodes rated at 25 amps and the relay contacts also at 25amps
Anonymous says
Hello,
I want to make a car lead acid battery charger for a 72Ah and a 100Ah lead acid battery, could it be possible to use this charger circuit with to different settings for the current that loads the battery. And wich kind of diodes should I use to regulate these currents
best regards
Swagatam says
yes the above circuit can be used for your need.
72ah and 100 ah would almost require identical current levels for getting charged, so an added current regulator circuit wouldn't be required.
you may incorporate a 12V 10 ampere transformer for charging both the batteries with the above circuit.
be sure to use a 6800uF/50V capacitor across the bridge positive/negative terminals
Gertjan says
but doenst a 72Ah need to be loaded with 7,2A and a 100Ah with 10A? And about the potentiometer which resistance and which power should this component need?
thanks
Swagatam says
ideally it should be done in that way, you may add a LM196 circuit stage for that, it's not critical though.
The main thing is to switch OFF the charger when battery voltage reaches 15% more than its rated value….charging at slightly increased current rate won't harm the battery if it's switched OFF when fully charged.
Swagatam says
potentiometer is actually an ordinary preset, power rating is not critical, any type would work.
Basem Khrais says
Hello,
Thanks for this circuit I want to understand if I eliminate the switch as u said above how the relay shall be connected.
best regards
Swagatam says
Please check out the last circuit in the following article, it should be in this way:
https://homemade-circuits.com/2011/12/how-to-make-simple-low-battery-voltage.html
Sammy Eshun says
Hello,
Thanka very much for your response.
Regards
pk
Sammy Eshun says
hello Sir,
Are the 10k's all a variable resistor?
I want to use it to charge two 12v 200AH batteries connected in parallel.
what if I want to use it for 24v 200AH or 2V 400AH.
Regards
PK
Swagatam says
Hello Sammy,
only the one which is at pin#3 is the preset, others are fixed resistors.
for 24V replace 741 IC with IC 324…..
Sammy Eshun says
hello sir,
Thanks for the reply.
would the circuit be suitable to charge 12v 400AH battery.
I want to charge four 6v 200AH batteries in series parallel, thus two of the 6v 200AH IN series making 12v 200AH.
Two of the 12v 200AH in parallel, thus making total of 12v 400AH. I am using it to connect to an inverter, keeping it connected permanently. Thus charging the batteries when battery discharges and using the batteries when power outages occurs.
Would leaving it connected to the inverter damage the inventer?
Your responses are highly welcome.
Regards
pk
Swagatam says
Hello PK,
Yes you can charge them, just make sure the relay contacts are rated accordingly.
This circuit will not initiate automatically, you will have to press the switch for initiating the charging process.
If the battery is connected to the inverter via a cut off relay then it's fine.
Septian M Hidayad says
Hai swagatami want to make automatic battery charger (without switch) with cut off. I have battery 24v with 200AH. Would u like to show me how the circuit diagram? And the components? Thanks
Regards
Septian
Faridul Islam says
this circute use 24 volt battrey .if any chang please help me.
Swagatam says
use 24V relay and 24v transformer….
Anonymous says
hello sir,
i have build this circuit but my problem is the switch can i connect the circuit directly to the battery without using the switch or how do i do it.
secondly i connect circuit to 10v dc battery the relay is not energies but immediately wen i connect it to anything 12v dc or above it energies the relay
and am told to charge 12V 200AH battery with 13.5V supply so the relay energies even b4 the battery attain full charge so how do i overcome this problem
becouse normally 12V 200AH reaches i think about 14-14.5V b4 its fully charge
Swagatam says
You will have to read the whole article for understanding the operations.
Without switch the system will not cut of after the battery is fully charged.
The preset needs to be adjusted for setting the desired cut off voltage level.
mahroof mrf says
hii Swagatam,
good ckt.
actually am looking for a solar charge controller to charge 150 AH 12V battery. solar panel is 12v/225-250W/ and around 15amps current.
so can i use this circuit by replacing the power supply ckt (transformer,brdige ckt and filter capacitor) with the out put of solar panel?
if yes, what are the necessary changes which i have to do? is there any regulator ckt needs to regulate the voltage to the battery from solar panel?. because the out put voltage of the solar panel will vary up to 20V.
one more doubt,what is the value of potentiometer which is connected to 3rd pin of IC 741.
thanking you ,
mahroof
Swagatam says
Hi Mahroof,
The circuit will work with all types of solar panels provided the max voltage does not exceed 20V (if the IC is 741) and 30V if the IC is 1/4 LM324).
Yes you may connect the panel supply at the input of the bridge.
It's a 10K preset.
mahroof mrf says
thank you.
the solar panel open ckt voltage(Voc) is more than 20v as per specification.so any voltage regulator ckt i need to use?
if the voltage is below 20V,we don't want to use any voltage regulator for 12v battery? i mean for 12V battery if we charge by 19V, the battery will not damage?
as the voltage comes from solar panel it self 'dc' i need to use bridge ckt again?
thank fully,
mahroof
Swagatam says
A voltage regulator will be required for controlling the output voltage to around 14V, so anything above 14V will require a voltage regulator for 12V batteries.
Anonymous says
what is kind of diode i"ll use for this and how many ampere.
Swagatam says
what is the AH of your battery???
Auston says
What type of amplifier is it??…i mean is it inverting,non inverting, Differential??
Swagatam says
It's a comparater, not an amplifier….
Auston says
Thank you very much BRO!!!!!!!!!!!!!!!!!!
Auston says
can i use 14-0-14 transformer??
Swagatam says
for 12V battery you may use the 0-14 tap and for 24V you may use the 14-14 tap, but for 24V, the opamp must be replaced with 1/4th LM324 opamp
Auston says
hey…i connected a discharged battery which had a volrtage of 10Volt….n i used a 14-0-14 transformer….but the relay switches on and off as soon as i connect the battery….
Swagatam says
Did you follow the setting up procedure as given in the article?
Auston says
yup…..i did…..
Auston says
i understood…….there was a mistake in ma setup…..i didnt read the word simultaneously…..so….how can i make it trip off when battery voltage reaches 13.5..Coz i have used a 14Volts transformer…and it gives a output of 15.7Approx…..
Swagatam says
You will have to use an external 13.5 volt source. Do not connect the battery initially. Connect the 13.5V source across pi#7(+) and pin#4(-) of the IC.
Adjust the 10K preset such that the relay just activates at this voltage.
Seal the preset with some glue.
The setting is complete, now you can remove the external supply and power the circuit through the attached transformer.
Press the switch only after connecting a discharged battery having 5 to 10 times AH rating than that of the transformer current.
Auston says
Thanks……i will do that….
Auston says
but the relay fluctuates when i do this….
Swagatam says
Add a 470uF/25V capacitor across the relay coil….
Auston says
K….
Auston says
hey…..How can i make it fully automatic????…..like i wanna replace that switch so that i dont need to press it for charging….n it should detect BAttery Voltage n automatically start……
Swagatam says
The circuit will need to be changed significantly for that, I'll try to produce the modified circuit in the form of a new article soon…
Auston says
K…..thanks…..but can u do anything….like modify this…… is there any chances of changing this????
Swagatam says
Connect power directly to transformer, eliminate the switch.
Wire up the N/O contact with the battery to be charged.
Connect a variable resistor of around 470K across pin#6 and the preset center pin. This must be adjusted for setting the low voltage threshold.
That's all…. Now when the circuit is powered with a battery connected, the relay will activate, the battery will start charging charging via N/O of the relay, once it's full, the relay will disconnect and stay in that position until the battery voltage reaches the lower threshold….the cycle will repeat as long as the battery remains connected, charged and used up…
MD ARIFUL Islam says
hello, this is great, can i use it to my 50amps lead acid battery? If not so where get i 50amps charger cutter diagram. plz help.
Swagatam says
Thanks, yes you may use this circuit for charging 50AH battery, just make sure that the diode connected at the positive of the battery should be rated at 1/10th of the battery AH, means 50/10 = 5amp to 6 amp diode.
jreynolds09 says
I was wondering about a couple things on this schematic. Is the N/O under the start a switch or relay? Also, the 12v Relay, is it a N/C or N/O and how do you make the connections. I am using ExpressPCB to make the schematic and then transfer it to a pcb for printing. I am unsure about those two items in particular. Any help, preferably detailed and maybe pictures, would be greatly appreciated as I'm still a little bit new to all this. Thanks.
Swagatam says
The N/O is for the relay contacts. An SPDT Relay will always come with both the contacts in one package, here we have used an spdt relay, however only N/O has been indicated, the other contact is obviously is the N/C.
I would rather advise you to first test the circuit over a general purpose PCB and then go for making the final PCB layout.
The circuit shown at the bottom of this article would be perhaps a better option
jreynolds09 says
I was talking about the one at the bottom of the article. It shows the N/0 but then it shows a relay to the left of that with a ground coming out the left side and a diode looping from the left side(ground side) to the input from the transistor (BC 557). So I'm assuming that is the rest of the pin out hookup for the 12v relay after hooking up the N/O pins to the switch circuit? Sorry to ask so many questions but I'm rather new to this.
Swagatam says
OK got it….the box which shows "Relay 12V" is the relay coil, the wires coming from the transistor and the positive goes to the relay coil….where as the symbol at the left of the box are the contacts of the relay with the N/O and the N/C contacts.
Yes the supply needs to go through the relay contact such that the system shuts OFF completely once the battery charges fully and the relay trips.
Swagatam says
Actually I was referring to the circuit at the bottom of the following article, I just forgot to paste the link in yesterdays comment:
https://homemade-circuits.com/2012/07/making-simple-smart-automatic-battery.html
Babu says
The circuit for 10 to 20 amps battery charger is not clear and it is too small. Can you please send me an enlarged circuit diagram. It would be most useful.
Thanks,
Babu
Anonymous says
Does removal of filter capacitor affects the charging time?
Asif Usman says
Hi! Great site for amateurs like me. It will be great help if the printed circuit board is also added with ur projects. Many thanks.
Asif Usman
Ronald says
There are some simple software that can design PCB like Circuit Wizard or PCB Wizard. Easy to use. Just input Sir Swagatam's diagrams and it will design the pcb. Just make little rearrangement afterwards to make the design neat. Practicing it will enhance your knowledge.
Cheers!
Asif Usman says
Hi!Great to learn for amateurs like me. One thing which u should add to it is the Printed circuit board for your projects. This will be added benefit for people like me.
Asif Usman
asif.met16@gmail.com
Anonymous says
the relay turn off and on. turn off when reaching the cut off but turns on again immediately. what should I do?
Tom says
the primary coil trips but the battery is still connected to the circuit, a fraction of the voltage of the battery drops the moment the relay trips, the circuit senses the voltage of the battery again not yet at the cut off, powering the relay again…
King Dedon says
Pls sir, can u guide me to upgrade this battery charger to be able to charge my 96vols/400amps car battery, tnx!
Swagatam says
King, you can try the first circuit from this article:
https://homemade-circuits.com/2012/08/make-this-48v-automatic-battery-charger.html
Anonymous says
the relay turn off and on. turn off when reaching the cut off but turns on again immediately. what is the solution?
Anonymous says
the relay keep turning off and on. turn off when reaching the cut off but turns on again after about 2 secs. what shall I do?
Ronald says
The relay flickers when reaching the cut off limit, what shall I do?
Ronald says
Ok thanks, I'll try…
Anonymous says
pls how can i add led to dis circuit
Ronald says
wow! this is the simpliest autocharger circuit.