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# 12V 100Ah Lead Acid Battery Charger Circuit

The proposed 12V 100ah lead acid battery charger circuit was designed by one of the dedicated members of this blog Mr. Ranjan, let's learn more regarding the circuit functioning of the charger and how it could be used as a trickle charger circuit also.

Update: For an Auto-Cut off Lead Acid Battery Charger, please refer to this Article

## The Circuit Idea

My self Ranjan from Jamshedpur, Jharkhand. Recently while googling I came to know about your blog, and become a regular reader of your blog. I learned a lot of things from your blog. For my personal use I would like to make a battery charger.

I have a 80 AH tubular batery and a 10 Amps 9-0-9 volts transformer. So I can get 10 amps 18-0 volts if I use the two 9volts leads of transformer.(Transfomer is actually obtained from an old 800VA UPS).

I have constructed a circuit diagram based on your blog. Please have a look on it and suggest me.  Please note that,.

1) I am belonging to very rural area hence there is a huge power fluctuation it varies from 50V ~ 250V. Also note that I will draw very less amount of current from the battery( Generally using LED lights during power cuts) approx 15 - 20 Watt.

2) 10amps transformer i think safely charges 80AH Tubular Battery

3) All diodes used for the circuit are 6A4 dides.

4) two 78h12a used as parallel to get 5+5 = 10 amps output. Although I think Battery must not draw full 10 amps. as it will be in charged condition in day to day use so internal resistance of battery will be high and will draw lesser current.

5) A switch S1 is used thinking that for normal charge it will be kept in off state. and after fully charging the battery it switched to on state to maintain a trickle charge with lower voltage. NOW question is that is this safe for the battery to kept in charge unattended for long time.

Please reply me with your valuable suggestions.

### Solving the Circuit Request

Dear Ranjan,

To me your 12V 100ah lead acid battery charger circuit design looks perfect and should work as expected. Still for guaranteed confirmation it would be advisable to check the voltage and current practically before connecting it with the battery.

Yes, the shown switch can be used in the trickle charge mode and in this mode the battery can be kept permanently connected without attending, however this should be done only after the battery has been fully charged upto around 14.3V.

Please note that the four series diodes attached with the GND terminals of the ICs could be 1N4007 diodes, while the remaining diodes should be rated well over 10amps, this could be implemented by connecting two 6A4 diodes in parallel at each of the shown positions.

Also, it is strongly recommended to put both the ICs over a single large common heatsink for better and uniform thermal sharing and dissipation.

Caution: The shown circuit does not include a full charge cut-off  circuit, therefore the maximum charging voltage should be preferably restricted between 13.8 to 14V. This will ensure that the battery is never able to reach the extreme full charge threshold, and thus remain safe from over charge conditions.

However this would also mean that the lead acid battery would be able to attain only around 75% charge level, nevertheless keeping the battery undercharged will ensure longer life for the battery and allow more charge/discharge cycles.

SHARING IS CARING!

### About the Author

I am an electronic engineer (dipIETE ), hobbyist, inventor, schematic/PCB designer, manufacturer. I am also the founder of the website: https://www.homemade-circuits.com/, where I love sharing my innovative circuit ideas and tutorials. If you have any circuit related query, you may interact through comments, I'll be most happy to help!

### 43 thoughts on “12V 100Ah Lead Acid Battery Charger Circuit”

1. Howdy, Friend! Interested to Learn Circuit Designing? Let's Start Discussing below!
2. The author mention on this article two 78h12a used as parallel to get 5+5 = 10 amps output. that mean if I parallel more 7812 I may get 5A more from each regulator ic?
coz i have a 8v-0-8v 40A transformer ( rewind a old MOT transformer) and Iam looking for a circuit to make a 13.8V battery charger from it without losing the transformers current value.

Regards.

• yes that’s correct you can add any number of ICs in parallel and get the added value for the max current, just make sure to mount all of them over a common heatsink, and in that case you can eliminate the output diodes….

3. Sir I want Arduino control invertor circuit

• Hari, I already have a few Arduino based inverter circuits in this website, please find them through the search box…

4. Pls I am finding it difficult in connecting my charging circuit to the inverter bcos when the inverter starts working its drows current from the charging circuit rather than to drop from the battery… Which courses the rectifier diodes to burn out …. Please help me solve it

• use a relay to isolate the (+) line of the battery….join the coil of the relay with the charger supply….connect the pole of the relay with the battery….N/C with the inverter positive input…and N/O with the charger supply (+)

5. Good day Swagatam I am a beginner and want to build a 12v 100ah battery charger. I have a transformer from a 650v UPS 1N5400 diodes and a 1000uf 35v Capacitors. But the Transformers and diode gets too hot when connected to the battery. Pls can you suggest a simpler setup? Have been trying to figure out the circuit above. Thanks

• Good day Charles,
it's because your transformer is trying to stuff as much as possible current into the battery which is making the devices hot and this might also damage your battery.

you will have t include a current controller stage in the middle.

you an use a simple transistorized current controller stage for limiting the charging current to the battery to 10 amps, using the following circuit

https://homemade-circuits.com/2011/12/make-hundred-watt-led-floodlight.html

you will simply need to replace the LED points with your battery points.

however the bridge rectifier diodes cannot be 1N5400, these will need to be at least 20 amp rated rectifier diodes.

6. Hi, you can easily do it with a 36V, 20 amp solar panel…..just plug it in, it will charge your battery within 6 hours (assuming the sunshine is optimal)

7. hi, can you help to design solar battery charger for 30vdc-100ah battery bank (6vdcx5-100ah) based on mosfet and opamp

8. Good day Sir, my mind still confused about this circuit,, we all know that 14.4v are needed to charge a 12v battery so why 7812?? i know that this is a 12v regulator? am i missing something?

• Joseph, the 4 diodes connected with the center pin of the 7812 elevates the output by 0.6 x 4 = 2.4V, that's equal to 12 + 2.4 = 14.4V

9. Please sir can it charge 160AH battery?

• you can, but the charging will be much slower and full charging could take 20 hours

10. good day mr. swagatam..i was intersted to built cgarger same as above diagram using two 78h12A and using 18v transformer.this diagram make me easy specialy begginer like me..but i want the output would be 30 to 50 amp.this will be very helpful to my shop..please give me diagram for this same as mr. ranjan diagram..and also correct material..tnx

• Good day lowie, for more current you may simply go on adding more number of IC stages with the shown circuit, may be 5 or 8 more ICs will ensure a 30 to 50 amp current from the design.

just copy and repeat the upper section ICs and diodes, the lower 4 series diodes does not need to be repeated

• tnx for replying mr. swagatam..desame two 9v and 10 amp transformer?how many diodes would be use as parallel?one more thing mr. swagatam,sometimes we cant avoid that – and + output connector touch each other.so, in this case is it posible to easily damage the ICs?

• hi swagatam,if the output – and + line will short the ICs will worn easily for this diagram?

• shorting should be avoided, but it won't necessarily harm the ICs because those are internally short circuit protected.

11. My 600va ups transformer secondary volt only 9v
can i make bettery charger for charging 100ah bettery.problem is beacause its give only 9v.

• if your battery is 12V then you would require a boost charger circuit for boosting the voltage to 14V….

12. Can i use 7812 in this circuit because 78h12a not availablein our place and what diffrence between in two component.

• yes it will do.

• …but it won't charge a 100 AH battery..

13. hi,swagatam.
how can i attach amp meter in my 125watt solar panel for measure amp.

• Hi Anish, just connect the meter in series with the positive wire of the panel….

(+) of the meter goes to the panel positive while the negative of the panel goes to the load positive….

14. how to measure secondary winding and primary winding in my ups transformer one side blue and red wire and other side yellow,blue,brown and black. i plug ac volt in blue and red wire but this is shorting and blow my board fuse.
its intex ups 600va.

• get an inductance meter and measure the values of the winding, the one which gives the highest value would probably be the primary mains…

• Can i use 7812 in this circuit because 78h12a not available in our place and what diffrence between in two component.

15. thanx swagatam.
your blog is best.

• you are welcome Anish!

16. i have a 600va ups transformer can i make bettery charger and how many amp give this transformer.

• yes you can, …divide 600 with the secondary voltage to get its amp rating

17. how can i make 12v 100ah bettery charger.the charger output power should be 10amp or more.
with digram.

• search for "high current charger" in this blog, you'll find it.

18. Dear Swagatam, please I need you to help me with a 12v self charge inverter of 2 and 5kva with 220v output. I mean without any input

• Dear Kazeem, that's not a feasible idea, and cannot be implemented on practical terms

19. Good job

20. "it can be replaced with a relay
and an associated circuit for obtaining
an automatic response"

Quoting you from above sir, Is there such circuit in your database that I can add to this circuit for such?

Another question Sir….

Please is there a reason you don't make SCR battery charger circuits?

I can't seem to find any on your blog sir.

I came across some chassis bolt mount scrs and I was hoping you might have made chargers with them.

If so, please do you have such circuit?

• Adding an auto-relay in the above circuit could make it much complex, you can make the following circuit for getting all the required automatic actions in one:

https://homemade-circuits.com/2012/07/make-6v-4ah-automatic-battery-charger.html
For implementing trickle charging actions just connect two 1N5402 diodes in series from the main +12V to the circuit positive rail with a 1K series resistor

The lower relay is not required it can be removed.

SCR concepts are not as efficient as relay/transistor chargers, therefore I did not find them useful enough to be included

21. What kind of switch would be employed here sir?
Could it be replaced with a relay and pots for setting trickle charge/batt full cut-off and low voltage start-up thresholds?

Hakeem

• the switch can be an ordinary spdt switch, it can be replaced with a relay and an associated circuit for obtaining an automatic response.