Introduction: 24V Battery Charger Schematic

Picture of 24V Battery Charger Schematic

The battery charger is originally designed by me to meet the need of some who want a 24V battery charger.
The charger is in three stages; the power source, current limiting and float charge stage.

In this design, 240/24Vac(rms) transformer was used. After rectification and filtration i got about 30Vdc.Therefore the transformer and diode rating should be well chosen to meet your demand

At the current limiting stage , transistor U1,Q1 and resistor R1 plays the vital roll in the current limiting; When U1 switches on it short circuits the gate voltage of Q1 thereby restricting current flow through the battery under charge. U1 will only switch when Voltage across it's base-emitter Vbe is up to 0.7V. the voltage drop across R1 determine this,if the voltage drop across R1 is up to 0.7V then U1 switches on then, I(current thru batt)=0.7/R1(sense resistor). Ohms Law.

The float charge stage come to play when the Battery Voltage builts up to 28Vdc. In this design once the voltage gets to 28Vdc, it is considerably large enough to make the zener diode reach it breakdown voltage. And once this is done U2 switches on and consequently short circuit gate voltage of Q1. The charger is now said to float charge.

The LED comes on when the battery is full.

Note: In most cases D6 is chosen to be 10v but, 6v can be chosen for logic MOSFETs. And this current limiting circuit only allow N-channel MOSFETs


MajorMotion (author)2017-06-23

Where can I get a replacement transformer? There are no identifying numbers on the transformer itself.

Hicks1579 (author)2017-04-11

Can anyone tell me if its possible and how I could modify this circuit to become a pass thru charger. So that I can charge two 12v BB-2590 batteries while connected to shore power and run the system and when I disconnect from shore power it kick to the batteries.

Opanin17 (author)2016-10-16

Thanks for your nice idea. I saw a circuit in this post that can charge any battery size.

can you please advice me?

mohameda465 (author)2016-04-20

I have 4 batt each 2 conected in series and each group(2 series batt)conected in parrellel each batt is 12v 110amp and my source 115 ac volt 60hz how can i use this circiut to charge my batteries

MuhammadA49 (author)2015-05-16

NelsonC1 (author)2014-10-16

Hi! > Max, can ask something regards for this circuit, what is the maximum input voltage for this schematic diagram?

novice29 (author)2012-10-07

i am a novice as for as electronics is concerned.
I have built a charger on bread board. it does not work . I have following observations ;

1.the LED comes on as soon as charger is switched on with or without load
2.there is no output on mosfet drain. i used IRFP260N
3.voltage accross the base and emmiter of U1 is 0. voltage across emitter and collector is 0.7 v.
4.voltage across R3 is34v(my input is 35v rectified and filtered )i
5. my C2 is a 100 nf capacitor. 10nf was not available.
6.what is the function of 6v zener diode

i do not know how to trouble shoot can you guide me please

alvin.deleon.12 (author)novice292014-07-30

10volt zener is switch on the moment 24volts appear in its battery terminals

in effect, the mosfet Q1 is already @ Floating mode meaning a very small amount of current is fed to the battery even though @ battery terminal is only 24v when we take a voltage measurement.

Now to fix this problem , replace zener diode with 12v rating, and the R5 should be replaced with the exact value or close to 9835 ohms.In this values ,as the voltage of the zener reaches 12v across its terminal U2 will be turned on, LED1 Lights on indicating that @ battery terminal 28volts is reached and the circuit is now in float mode with very minimal current flowing to the battery

i am also make a 24v 7amp battery charger but i have also same problem i am using irf250. also r1 0.1om how many wats resister using please sent me replay about this problem in my gmail account. my gmail address is can u send this immediately.

Dyk (author)2014-07-29

what do i need to do to be able to use this charger to charge a 100A 12V SLA battery?

jackthelad (author)2013-09-30

I have a DC 24v 5amp electric motor taken from an old mobility scooter that had been powered by lead-acid batteries. I need a power supply to run off the mains to drive this motor for a new application. I would like to build my own power supply therefore can I use something like the 24v charger designed by 'maxolous'?

grateed (author)2013-09-05

hi sir i want to build this charger but i have a small problem can i use the same inverter transf to charge and can i replays 450 ohms resister with 470 ohms?

grateed (author)2013-09-05

hi sir i want to build this charger but i have a small problem can i use the same inverter transf to charge and can i replays 450 ohms resister with 470 ohms?

asa1964 (author)2013-08-10

How can I Cross-connect this circuit with the inverter transformer, in other to use the same inverter transformer to charge the 24Volts battery.

asa1964 (author)2013-07-31

Hello Maxolous,
please, can you send to my mail a circuit diagram of how to incorporate this 24 volt battery charger you design into your inverter circuit diagram to be able to use the inverter transformer to 24v-0-24v tapping to charge the 24volts battery. my mail is Thank you very much. Please I am still expecting your reply. God bless you.

sanmlight (author)2013-04-06

Hi Max,

Can i use irfz44n instead of irf250 for 12v and 24v?
what diode/ampere should i use for 6 and 10 amps transformer?

Mike L

rameez44 (author)2013-02-07

can we use IRF250 Mosfet instead of IRF250 in 24 v battery charging circuit??

asa1964 (author)2013-01-04

Hello Maxolous,
please, can you send to my mail a circuit diagram of how to incorporate this 24 volt battery charger you design into your inverter circuit diagram to be able to use the inverter transformer to 24v-0-24v tapping to charge the 24volts battery. my mail is Thank you very much.

tsitsios (author)2012-12-29

Good morning,
I am interested in building a 24V charger implementing the hand sketching diagram.
Have you built the charger following this diagram?
Will this charger be able to pump 30Amps on my battery bank of 200AmpH?

Best regards

macdinhchi99 (author)2012-12-05

Hi max,
for 12v changer, are you mean that D7 replace by 6v zener diode?

nazirm (author)2012-11-08

Hi Maxolous:
1. You mentioned that during float charge stage U2 switches on and short circuits gate voltage of Q1 - but there is a diode D1 which is isolating base of Q1 from U2 and so how will U2 short circuit Q1?
2. Also, in current limiting stage U1 shorted the Q1 gate and in float charge stage U2 has shorted the Q1 gate. Then I would expect Q1 to behave in the same manner in both phases. Please help me understand here. Thanks

nazirm (author)2012-11-08

Hi Maolous:
I have one more question. In your notes aobe you have mentioned that U1's Vbe will be 0,7 if the volatage drop across R1 is 0.7 volts. Should we not add the voltage drop across R2 which is 20K and even a low current will give significant voltage drop.

nazirm (author)2012-11-08

Dear Maxolous:
Thanks for sharing the circuit. I have few questions:
1. Can I use IRFz44N instead of IRF260? Looking at the datasheets it does not look like a problem.
2. In the text above in your formula I=0.7/R4 -- when I look at your circuit I think it should be R1.
3. In your circuit you have indicated R1 to be 0.1 Ohm. So using the formular 07./0.1 gives 7 AMPs. I am assuming the 24V battery is 100-150 AMPh. If 50% of the available power is drained, then the battery will take 7- 11 hours to charge. Is this calculation correct?

piragash (author)2012-03-19

hi every body i am piragash form srilanka so i have solar & battery i wont solar battery charger controler

i have 150amp*2battery total 300amp i need charge solar to battery
plz help me i wont charger circuit

tplim (author)piragash2012-10-31

Go to this link
Think this is what you want.

tplim (author)piragash2012-10-29

Hi piragash, go online ask uncle Google. Used keyword "charge controller".

novice29 (author)2012-10-19

can some please throw some light

computek272 (author)2011-09-27

This circuit looks like something that would work for my project...

Three questions:
1. Can this circuit be made to run from a 24 VDC regulated power source that is already supplied?
2. Can an LED be added to indicate if no battery is present?
3. Can an LED be added to indicate the battery is charging?
I'd also like to add a relay to #2 and #3 to turn on two pins on a microcontroller when the proper statuses are reached.


maxolous (author)computek2722011-09-27

1. Yes
2.Yes at the terminals of batteries and has to be given current limiting resistor.

lacus2000 (author)maxolous2012-08-22

Hi Max,

If I plug it in before connect it to the battery, it will not charge it. I guess because the input voltage is about 30-33V without load. Do I miss something?


computek272 (author)maxolous2011-09-28

Cool! How would I tweak the schematic to do #1 and add #3? Thanks.

maxolous (author)computek2722011-09-29

If you want to run it from 24V regulated power supply, you need to remove the transformer and Rectifier Diodes only

There are so many ways you can achieve this , the simplest is to put LED across the charging terminals,also put a 2k2 resistor in series with the LED to limit current. you will observe that when it is not charging the LED will not glow reason is that MOSFET is not switched.Otherwise, u2 had switched to short cct the gate of mosfet to earth. see the text above.

computek272 (author)maxolous2011-09-29

One more thing: Is there a equivalent to the BZV80 diode that I can use? I can't find that diode anywhere.

maxolous (author)computek2722011-10-02

That is a 6V zener Diode.

computek272 (author)maxolous2011-09-29

Alright, thanks! I'll have to order parts and give this circuit a try.

la5tia (author)2012-06-26

Hi Mr. Can you please help me to change the components so this circuit will charge a 32 volt 150AH battery bank. (I suppose it should be charge current of max 15 amps) In advance Thank you.
Kind regards, Terje.

sarco (author)2012-03-31

How to add delay rc timer for about 15 seconds to this circuit to use the same h bridge of the inverter for charging without burning the bridge

maxolous (author)sarco2012-04-22

your delay timer has to be switched on by your 220v or 110v relay that you had before now installed in your inverter, (so when making choice of your 220 or 110v relay ,make sure you get the one with multiple throws) by helping you pass your batteries voltage to the delay circuit, it also depends on the numbers of batteries you are using.if you are using battery voltage higher than your delay cct voltage then, you need to regulate it.

Your delay timer which of-course has a relay should pass your mains into your center tap of the high voltage side of your inverter transformer when in operation. I believe you know what i mean.

asa1964 (author)2012-04-10

Hello Maxolous, can you give to us a modifications circuit that can work for 48V and 60V battery charger.

Thanks for your good Jobs.

stephan007 (author)2012-03-10

Hi Maxolous
Could you please modify this circuit for operating at 26V 4A.
As i have a battery which needs a charger of this rating.
I would be grateful if you help me out.

arjan_al (author)2012-02-12

Hi Max,
Can i use this schema to charge a 24 v 80 AH battery?

maxolous (author)arjan_al2012-02-15


arjan_al (author)maxolous2012-02-16

Hi Max,
I have a Deca CLASS 16A charger:

It seems that isn't an automatic charger(have only a zener diode) but i want to use it all the time(the battery 24 v 80AH will stay connected always).
I would like that when the battery is fully charged, the charger should not continue to charge it.

How can i modify it using your schematic?

Thanks in advance

maxolous (author)arjan_al2012-02-17

Arjan_al ,

The only way i can help you modify is when i see the schematic of your said Deca 16A charger.

kcgeorge (author)maxolous2012-03-04

max i have been follwowing ur responses and also your images of the inverter, I am inlove with your design. But pls I will like to request from you a low battery warning circuit for a 2KVA/24VDC inverrter which i can incorporate into the PWM inverter circuit posted by nick. Thanks

maxolous (author)kcgeorge2012-03-06

Hello Kcgeorge, I have today 6th mar,2012 designed a circuit for you to meet your need. You can use it for 12v or 24v inverter low-battery alarm. To set this you need a variable Dc power source up to 20v. For your 24v inverter , put 20v source across +ve & -ve of the circuit and vary pot. to the point you hear the buzzer. for 12v inverter put 10v across +ve & -ve and vary pot. to hear the buzzer.

Or run Inverter and monitor with voltmeter across inverter batteries till inverter battery drain to 20.5v then, vary pot to the point you hear buzzer sound lowly

741 is a Voltage comparator pin 3 is the non inverting input while pin2 is inverting input
if the voltage in pin 3 is higher than pin 2 the o/p will be high which ofcourse cannot switch PNP transistor. but, when the i/p in pin 2 which is preset by R4&R5 is higher than i/p @pin 3 due to the fall on battery voltage , the o/p will go low thereby transistor is switched and buzzer comes ON

arjan_al (author)maxolous2012-02-27

Dear Max,
In order to change "The float charge stage come to play when the Battery Voltage builts up to 28Vdc" float charge stage from 28 Vdc to 27 Vdc,which resistor shoul i change(R6),and how should be the value?
I builded your schema but led comes on although the battery is not connected,is it ok?

maxolous (author)arjan_al2012-02-28

use variable reaistor 1K to find out by replacing R6 with it. Read the Ohmic value and put a fixed resistor. LED will always come up when open the batt connector is open unless your o/p voltage is less than 28Vdc.

arjan_al (author)maxolous2012-02-20

Dear Max,
Below is the schematic (i tried to draw it,sorry if it's not displayed that well)
My charger is very simlple, it has a kbc2508 silicon bridge rectifier,an ampermeter and a switch that changes voltage to 12 or 24 (i am intersted in 24 v)
Can you check please how can i modify it (maybe the following schema is not clear for you)
Thanks a lot!

asa1964 (author)2012-02-18

Hello maxolous, people seems to have gotten enough informations about this charger since last year.
Please, I wish people in the forum understand that, your transformer should be able to deliever the required voltage and current you want. That is that.

My questions is, can someone use a transformer caliberated as 28 volts ac in the circuit.

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