6V, 12V, 24V Battery Charger Circuit


A simple yet accurate automatic, regulated 6/12/24 volt lead acid battery charger circuit is explained in this article. The circuit switches off the current to the battery as soon as the battery reaches full charge. An illuminated LED at the output indiacates the fully charged condition of the battery.

The circuit diagram may be understood from the following points:

Fundamentally the voltage control  and regulation is done by the versatile, work horse IC LM 338.

An input DC supply volt in the range of 30 is applied to the input of the IC. The voltage may be derived from a transformer, bridge and capacitor network.

The value of the 4k7 preset is set to get the required output voltage, depending upon the battery voltage to be charged.

If a 6 volt battery needs to charged, R2 is selected to produce a voltage of around 7 volts at the output, for a 12 volt battery it becomes 14 volts and for a 24 volt battery, the setting is done at around 28 volts.

The above settings take care of the voltage that needs to be applied to the battery under charge, however the tripping voltage or the voltage at which the circuit should cut off is set by adjusting the 10 K pot or preset.

The 10K preset is associated with the circuit involving the IC LM324(1/4) which is basically configured as a comparator.

The inverting input of the IC 324 is clamped at a fixed reference voltage of 6 via a 10K resistor.

With reference to this voltage the tripping point is set via the 10 K preset connected across the non inverting input of the IC.

The output supply from the IC LM 338 goes to the battery positive for charging it. This voltage also acts as the sensing as well as the operating voltage for the IC 324.

As per the setting of the 10 K preset when the battery voltage during the charging process reaches or crosses the threshold, the output of the IC 324 goes high.

The voltage passes through the LED and reaches the base of the transistor which in turn conducts and switches off the IC LM 338.

The supply to the battery is immediately cut off.

However the moment voltage is switched OFF across the battery terminals, the battery voltage tends to fall rapidly to some lower value, normally this would trigger the opamp back into its original position and the power would be restored to the battery giving rise to a rapid switching of the output at the threshold levels. The introduction of the 470K resistor eliminates the above possibility and latches the system to a switch OFF position even with the fall in the battery voltage level....however this position is sustained only for some fixed lower level of the battery depending upon the value of the resistor (470k), increasing the value will make the difference less and vice versa.

(presently the 470K is replaced with a 1n4148/1K diode resistor, making the circuit a one-shot latch up device....so it won't respond to battery low level threshold, and will need to be manually reset in case the battery voltage falls below the lower threshold.)



The illuminated LED indicates the charged condition of the connected battery.

This 6V, 12V, 24V automatic battery charger circuit can be used for charging all lead acid or SMF batteries having voltages in between 3 and 24 volts.



6v, 12v, 24v battery charger circuit with automatic cut off and shut off using LM338 IC


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237 comments

comments «Oldest   ‹Older   1 – 200 of 237   Newer›   Newest»
March 27, 2012 at 8:40 PM delete

its really cool I already needed one like this

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April 1, 2012 at 7:46 PM delete

Hi,

The IC CA3140 can be directly replaced with the IC 741.

Regards.

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Anonymous
April 2, 2012 at 4:51 AM delete

Thank you very much.

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Anonymous
April 2, 2012 at 10:19 AM delete

By the way, is the transistor will be ok with 741? What would you recommend?

Thanks again..

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April 2, 2012 at 10:22 AM delete

If it works with CA3140, it will well work with 741 also.

Regards.

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Ronald
April 2, 2012 at 10:03 PM delete

Hi!

I'm interested at your automatic battery charger. But I'm confused with LM388. I couldn't find it in my circuit wizard's voltage regulators. I saw it on google as 14pin IC and what does 2 in R2k2 and 7 in 4k7 means?

Thank you.

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Ronald
April 3, 2012 at 7:35 AM delete

Hi!

I'm interested in your new automatic charger. What do 2 in 2k2 and 7 in 4k7 means?

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April 3, 2012 at 8:29 AM delete

Hi!

It is LM 338 (not 388)! 2K2 means 2.2K and 4k7 means 4.7K...

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Anonymous
April 3, 2012 at 9:51 PM delete

I tried to used IC741, there's a little current passing through the transistor making the LED glow a little while the relay is off.

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April 3, 2012 at 9:59 PM delete

That shouldn't happen, clean the PCB with thinner and then check, their might be leakages.

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Anonymous
April 4, 2012 at 5:49 AM delete

ok, thank you.

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Anonymous
April 4, 2012 at 6:07 PM delete

can dis be use 4 150ah battery?

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Anonymous
April 5, 2012 at 3:53 AM delete

ok.can u post d one dat can work 4 80ah to 150ah.pls wot program can i use 2 convert your schematic to pbc

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April 5, 2012 at 2:15 PM delete

You may try the circuit given in the following link:

http://homemadecircuitsandschematics.blogspot.in/2011/12/high-current-10-to-20-amp-automatic.html

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Anonymous
April 5, 2012 at 4:16 PM delete

thanks pls what program can i use to turn most of your schematic to pbc layer

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April 5, 2012 at 5:36 PM delete

Sorry, I don't have any idea regarding it....

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Ronald
April 5, 2012 at 7:19 PM delete

you can use PCB or Circuit wizard of New Wave Concept

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Anonymous
April 7, 2012 at 6:53 PM delete

thanks@ronald

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Anonymous
April 16, 2012 at 3:40 AM delete

I just want to thank you on your effort and congratulate, i've found your work very useful

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May 4, 2012 at 7:25 PM delete

Hi Swagatam.
I have gone thru all the battery charger circuits posted in your blog spot.. It great.. but most of the charger are related to lead acid battery chargers.. can you get Lion (lithium ion)battery charger circuits..

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May 4, 2012 at 8:04 PM delete

Hi Balram,

i'll try to design one such circuit and publish it soon.

Thanks for suggesting.

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May 15, 2012 at 5:55 PM delete

hi,

what is the C1 volts.

reply plz

thanks

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May 15, 2012 at 9:03 PM delete

Hi,

C1 is a disc cap which are always rated at over 50 volts.

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Anonymous
May 16, 2012 at 4:51 PM delete

hi Swagatam.
This is when the circuit can be used directly in 12V battery?
when the input voltage would I use 21V DC from the solar panels ..

Thanks.. :)

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May 16, 2012 at 5:31 PM delete

You may feed the voltage from the solar panel into the circuits input

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Anonymous
May 16, 2012 at 6:24 PM delete

thanks for the answer..
if I have problems later on ask for your help.
thank you swagatam..

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Anonymous
May 18, 2012 at 2:11 AM delete

If a 6 volt battery needs to charged, R2 is selected to produce a voltage of around 7 volts at the output, for a 12 volt battery it becomes 14 volts and for a 24 volt battery, the setting is done at around 28 volts.
Hi Swagatam,
How can I made possible to use this circuit by immediately selecting needed voltage say; if the battery to be charged is 6v, then after that, there is a need to charge a 12V battery, and lastly, if the need arises to charge a 24volts battery?
Can you possibly elaborate the connections on how to do it? maybe my question would be also a great help to others who wanted to have this circuit simply and clearly modified for convenient use.
More power to your new site
Edgardo
e-mail address : edgardodiolola@yahoo.com

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May 18, 2012 at 9:04 AM delete

Thanks Edgardo,

With R2 = 2k5, gives 14 volts,

with R2 = 1k2 gives 7.5V

and with R2 = 5k1 gives 28 volts.

So the above resistors may be suitably arranged and selected using a selector switch for getting the desired output voltages.

Thanks and Regards.

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bima sinar
May 31, 2012 at 10:12 AM delete

Swagatam, I want to ask again.

why the LED indicator is not lit when the voltage of the battery has exceeded the threshold .. and when the light is on, it also as an indicator when the voltage used to charge the battery disconnected as well?
I also checked the condition of the LED can still be used.

do you think is the problem I face now

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May 31, 2012 at 6:56 PM delete

Hi Bima,

I have modified the diagram, please see it at the end of the article, this will certainly work as desired by you

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james
June 5, 2012 at 8:23 PM delete

Hi,

pls i need just full battery cut-off circuit for 12v battery.

thank you very much in advance

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June 6, 2012 at 3:51 PM delete

Please check out this circuit:

http://homemadecircuitsandschematics.blogspot.in/2011/12/high-current-10-to-20-amp-automatic.html

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June 16, 2012 at 6:05 AM delete

Hi Swagatam, need to be clear on one thing, the output of charging circuit (i.e output of 338) is connected to the 741 comparator and keeps a constant voltage of 14 voltage around 14 volt right? I know that the voltage across the battery increases with charge but if the constant output is connected to the comparator how can the non-inverting end of 741 get a increasing voltage with charging? I'm little confused. Please need guidance.

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June 16, 2012 at 12:18 PM delete

Hi ahnurbd,

The voltage at the output of 338 will immediately drop to the level of the discharged battery voltage and will gradually increase as the battery gets charged.

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June 16, 2012 at 3:41 PM delete

can I use a 317 coupled with a high current transistor instead of 338?

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June 25, 2012 at 7:39 AM delete

Can i Incorporate this circuit with the current one
http://homemadecircuitsandschematics.blogspot.in/2012/04/how-to-make-solar-battery-charger.html
with this circuit for current control
what changes are needed for changing lm 338 to 317
Waiting for your reply

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July 11, 2012 at 12:14 PM delete

sir
i have 16v 12amp transformer i need charging circuit to charge a 150ah lead acid battery.

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July 14, 2012 at 7:19 PM delete

You may try the following circuit:

http://homemadecircuitsandschematics.blogspot.in/2011/12/high-current-10-to-20-amp-automatic.html

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ravindar
August 10, 2012 at 4:49 PM delete

Thanks for such good circuit,swagatam, whether this circuit is protacted from short circuit?
waiting for reply

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August 10, 2012 at 5:30 PM delete

Thank you Ravindar,

Yes the ic is internally protected against short circuit.

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Anonymous
August 26, 2012 at 9:38 PM delete

sir , i have 10W solar panel delivering 21V , 0.57A and i want to charge 12V 7Ah SMF battery. can you please replace the 10K trimpot with a specific rated resistor because it is difficult for me to adjust. i have to construct 31 peices like this for a rural electrification project. charge controllers casts me 800 rupees and itr is not so ecnomic. please reply as soon as possible. i reqiure very badly. and how much is 104 50V capacitor rating. waiting for ur reply.

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August 27, 2012 at 11:32 AM delete

The 10K preset needs to be adjusted and set through practical monitoring, a prior fixed value will be difficult and incorrect to assume.

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Anonymous
August 27, 2012 at 4:22 PM delete

sir please instruct me how to set the preset , and where shud i take the output whether just before pin 3 or at pin 6.

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August 27, 2012 at 6:02 PM delete

Temporarily disconnect the 4k7 resistor from the base of the transistor and connect it to ground, then without connecting any battery, adjust the preset until the led just lights up.

Now reconnect the 4k7 to the base of the transistor.

The charger is ready.

When using the circuit for charging Always connect the battery first before switching ON power.

Before setting the preset change R2 to 2.5K value.....

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Anonymous
August 28, 2012 at 8:00 AM delete

thank you very much sir. will try it out and let you know. if i have doubts i would surely ask you. thank you once again.

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August 28, 2012 at 3:30 PM delete

Hi Sir i am impressed from u and ur knowledge! Sir i want to take a start in Circuts and their uses! i want to Charge 6 volt 4.5 Am Dry bettry and i have a Transformer of 6 Volts and 5 Am will u plz guide me and give me a circuit according to my need... thanks i m w8ing!

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August 28, 2012 at 6:35 PM delete

Will you plz explain the ratio between
Battery Voltage:Transformer Voltage
Battery Am : Transformer Am
and shy we cant attach the positive of transformer with the Positive of battery and Negative respectively. to charge a battery i mean why we need a Circuit :( plz explain Bro i am just taking start in this field

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August 28, 2012 at 10:50 PM delete

sir i need the circuit diagram of
auto battery charger ic 741 ,7912,7812
70 amp
48v

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August 29, 2012 at 1:00 PM delete

Hi Muhammed,

You can refer the LM338 datasheet, you will find many interesting battery charger circuits as per your needs....

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August 29, 2012 at 1:05 PM delete

The explanation can be very long, difficult to cover here...

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August 29, 2012 at 1:06 PM delete

Please provide specifications separately.....

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Anonymous
September 14, 2012 at 10:29 PM delete

hi swagatam. how to simulate this circuit in ISIS? thank you

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September 15, 2012 at 12:40 PM delete

Mr Swagatam, in my Livewire software. I could not find LM338 , what kind of IC can be replaced?

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September 15, 2012 at 12:56 PM delete

hi mr. swagatam.if i wanted to insert another led in this circuit to show that the battery is still charging,where must i put the led?is it before the potentiometer or after it?or is there anyplace else that i should put it?

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September 15, 2012 at 1:16 PM delete

The function is 100% guaranteed, no need to simulate.

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September 15, 2012 at 1:34 PM delete

Mr Ubai,

LM338 has no direct equivalent according to me.

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Anonymous
September 17, 2012 at 10:08 PM delete

sir, what is 15-24 VDC? can you explain to me about it?

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September 18, 2012 at 7:44 PM delete

It's the input supply voltage to the circuit from a DC source

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September 23, 2012 at 3:23 PM delete

hi

i want Battery status checking Circuit for battery 1.5v to 12v
plz reply

thanks

wasim

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September 25, 2012 at 12:19 PM delete

Hi,

1.5v is quite low to be sensed, yet I'll try to find a suitable circuit and post it for you....

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Kostas
October 28, 2012 at 7:46 PM delete

Hi and thanks for sharing this great circuit! I need some clarifications though.. I am totally new with electronics (besides soldering and desoldering stuff) and would like to know the following:

(all mentioned components are all available through a local store and they have a bunch of stuff to pick so here goes...)

1) when u say LM338 do you mean LM338M or LM338T or any other?

2) when u say IC741 do you mean LM741CN 8Ρ, UA741CH ΤΟ5, UA741, ΜΑ741Ν, LM741CH (METAL) or any other?

3) when u say IC 7812 do you mean 7812CV (LM340T12), L7812CT, or I.C.7812 (SKU: 800003003002)?

4) R1 240 means a 240 ohm resistor?

5) 104 50V means 104 ceramic 50V capacitor?

6) C1 you say 0,1uF... how many volts is this? is it electrolytic?

7) the capacitor after the 741 IC (100uF/25V) is electrolytic?

8a) The variable 15-24 VDC in; shouldn't it have a possitive and negative?
8b) if yes, where are they in the diagram?
8c) and how do they connect to the cicuit?

9a) does it make a difference if you feed 15 VDC or 18,5 VDC or 24 VDC or any other value in between 15-24 with respect to the R2 resisor so we can charge 6V,12V,24V ?
9b) I mean if you input 15VDC could you charge a 24V lead acid battery with selection of proper R2?
9c) and if yes without modifying R2, if you input 20VDC could you still charge the same battery?
9d) whould any input voltage between 15-24VDC make a difference for the same battery with the same R2?

10) in your second diagram you have substituted 6V 400mW thingy for a 10K

11) 10K means 10.000 ohm resistor?

12) lastly, how could I add another led (ie yellow) to indicate that the circuit is currenlty charging the battery?

I told you I am totally new so if you could be so kind as to enlighten me with your answers, I would gain a better understanding of things...
Hope I wasn't too much of a hasle and thanks in advance :-)

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October 29, 2012 at 9:41 AM delete

Hi, here are the required specs

1)LM 338 in TO-3 package, any type will do.

2) IC 741 in DIL (dual in line) 8-pin package, any type will do.

3) IC 7812, in TO-220 package, any type will do but it should have the 7812 print.
4) 240 means 240 Ohms, 1/4 watt will do.

5)104 means 0.1uF/50V, any type will do as long it's 0.1uF

6) see point 5)

7)100uF/25V is obviously electrolytic

8)Obviously the positive will go to the input of the IC and negative to the ground marked line.

9) When it's written 15-24V it means all voltages between them will work. All voltages in the given range will produce almost the same voltage at the output.

11)10K means 10,000 Ohms

12) connect it across 100uF/25V, with a series 1K resistor, anode of the LED will connect with the ground or the negative line.

Regards.

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October 29, 2012 at 9:52 AM delete

correction:

The "charging" indicator LED must be connected across pin#6 and positive of the battery.

anode to positive, cathode to 1K, 1K to pin#6 of IC 741

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November 6, 2012 at 12:39 PM delete

Hi Swagatam, Thanks for sharing this circuit. I have a doubt about the IC 741, is this a General Purpose Operational Amplifier ??? (LM741 or UA741).....Thank's in advance.

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November 6, 2012 at 1:43 PM delete

Hi LKlunder,

All opamps will work here, LM741 or uA741 it won't make any difference....

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November 7, 2012 at 2:30 PM delete

Mr Swagatam, I want to use as power supply of this circuit an old switching power supply of 30v 2A and convert it on an automatic charger for 24V. can I use a LM338T (TO-220) and this will require a dissipator ???. Thank's in advance

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November 7, 2012 at 3:08 PM delete

Yes Mr.Lklunder, you may proceed with your plans, LM338 is the best option you have, TO-220 will do since the current is moderate... a heatsink will be required though, for managing better efficiency.

Regards.

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November 10, 2012 at 5:28 AM delete

Hi Mr. Swagatam, I need your help.
I have finished the circuit and tested but don't work well, the input voltage is 30.2v, I have used a resistor on R2 a 5.6k to give a 28.8 volts output, but the led from pin 6 don't lit , I could see the voltage polarity are inverted (-1.5v) therefore the led don't lit , neither cut the voltage charge.
When I try to adjust the trimpot, the voltage output vary from 28,8v to down, I guess that's normal when trimpot polarizes the voltage to GDN, but the LED never lit:. ( tested with battery lit).
I have reviewed the circuit and I don't find the error, all connections is ok.
Could you help me please,

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November 10, 2012 at 8:13 AM delete

Hi Lklunder,

I am sorry, I think there are some mistakes in the circuit.

First of all the IC741 will get damaged above 20 volts, so you will have to use a LM324 IC (1 opamp out of the 4)

I'll correct the circuit so that you can build it again.

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November 10, 2012 at 11:35 AM delete

Hi Swagatam, I have reviewed the circuit and now works with a 12v battery. If I vary the trimpot the output voltage goes from 7v to 28.8v ... I have adjusted the trimpot reading 12,6v at output, but when the battery has reach 12,8v the voltage output is don't cutted, is this normally ?...The led indicator of the battery is charged lit when I set the trimpot to a voltage minor to the battery. I have installed the LED charging indicator, (R 1K to pin 6 and + to output, the voltage output drops to 6V. (??)
Now I have adjusted the trimpot to 26,0v voltage output and I connected two battery 12v on serie, but the R1 (240) was burn.
What's changes needs this circuit in order to charge 24V batteries ???
Thank's in advance

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November 10, 2012 at 5:42 PM delete

Hi Lklunder,

Please make the circuit as in the above new diagram.

After you make this then I can tell you how to proceed, please see my previous comment also.

Regards,

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November 11, 2012 at 3:30 AM delete

Hi Mr. Swagatam,
Sorry for so many questions but I am very interested in this circuit.

In your new diagram, I can see that the LM324 pin connections are different to the datasheet of LM324 pins, eg. pin 7 in your diagram is connected directly to Vout of LM338, and on the datasheet the pin 7 corresponding to Output 2, same with pin 4, on datasheet correponding to Vcc+ and pin 11 to Vcc-.I think it would not work if LM324 is connected in this manner.

When I made the above circuit, I put the 7812 regulator to power the IC741, so has not been damaged.
Thanks and best regards.

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November 11, 2012 at 9:14 AM delete

Hi MrLklunder,

when i relaced the diagram with LM324 circuit, i just forgot to change the previous 741 pin numbers for the 324 IC.

Now I have corrected it please check it.

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November 13, 2012 at 3:59 PM delete

Hi againg Mr. Swagatam,
Having got the new components, I have finished the new circuit, but before to test it, I want to know how to set the preset of 10K, I understand I have to adjust at 28V the preset of 4K7 for output voltage.
Could you help with this setup and how to include a charging indicator led ?.
Thank's in advance.

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November 13, 2012 at 5:40 PM delete

Hi Lklunder,

First make only the LM338 section, give an input of 30V.
Now adjust the 4k7 preset to produce exactly 28V at the output.
Seal the preset with some glue.
Now make the 324 section, connect with the lm338 output as shown in the diagram.
Initially keep the 470 k resistor disconnected, adjust the 10K preset such that the relay just activates at the 28V output.
Connect the 470K back in place.

That's it the setting is done. Your 24V battery charger is ready.

ForLED connection, please refer the following article:

http://homemadecircuitsandschematics.blogspot.in/2012/07/making-simple-smart-automatic-battery.html

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November 13, 2012 at 5:42 PM delete

I am sorry, in the above diagram, set the 10K preset such that the red LED just lights up at 28V.

Then connect the 470K resistor in place.

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November 14, 2012 at 2:25 PM delete

Hi Mr. Swagatam,
I just have done the LM338 section (the connections are :Vin 30v, Vin C1 to gdn, Vout to R240 to adj 4K7 to gdn) without other connections and only I got 26.5v max on the output (the 4K7 preset regulates from 1.5v up to 26.5v) inclusive I have increased to 32V the input but the output voltage will not was increased. I think 26.5v is a bit low to charge 24v batteries. The 4K7 preset works fine and it have a resistence of 4K7 ohms. What's you think about this ???. What changes will be needed ???.
Thank's in advance.

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November 14, 2012 at 5:12 PM delete

Hi Lklunder,

Use a 10K preset or pot in place of 4k7 and it will surely work, keep the input voltage to 30V only for safety reasons.

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November 16, 2012 at 3:12 PM delete

Hi Mr. Swagatam,
I have changed the preset 4K7 to 10K and works fine, now I have 28V. Following was connect the LM338 to LM324 and setup the 10K preset without R470K, but when I try to adjusting the preset and the center connection of the preset reaches 6V-6.1v, the red led is lit but very very little, almost invisible (is a 3V led), in this moment the output voltage drops to 26V and, if I continue turning clockwise, the output voltage continues to fall, but the led don't shines more.
I can see that the voltage power supplied to the red led is just of .5v max.
Is normal that the output voltage drops when the led was turned on ??.... The use 3v led is correct. ?? .
What's you think about this ???. What other changes will be needed ? ..
Thank's in advance.

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November 16, 2012 at 4:18 PM delete

Hi Lklunder,

Disconnect the 4k7 from the transistor base initially and connect it to ground.

Connect a 3V zener in series with the LED.... band side will go to the IC output and the other side to LED anode.

Now repeat the adjustment until the LED just lights up.

Once the setting is done, reconnect the 4k7 to the base of the transistor.

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November 19, 2012 at 4:11 PM delete

Hi Swagatam,
Following your instructions I done the setting using the zener diode, the LED brightness was fine during the setting, and the output voltage remained at 28V, but when is reconnected the R4K7 and is removed the zener, the voltage drops to 26V and again, the LED brightness is very very little.
After adjustment, the output voltage is fixed only of 26V, without connect any battery . Is this normal ???.
Thank's in advance.

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November 19, 2012 at 7:10 PM delete

Hi Lklunder,

Yes this is perfect.....once you set the circuit as per the suggestions.... it is done.

Now the only way to test it is by connecting a discharged battery and then wait until it reaches the set 14.3V.... when the LED will light up and the circuit will latch stopping the charging process.

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November 19, 2012 at 7:11 PM delete

Connect battery first and then switch ON the power.....

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November 20, 2012 at 3:10 AM delete

Hi Swagatam, OK.
As you remember, I need a charger for 24V (for two 12V batteries connected on serie)
About this, I have a doubt about the danger of reverse voltage towards the circuit while the charger is off and the batteries are being connected, on this moment there will be 24v from the batteries at the circuit and could be damage it. The last time I remember that the R240 was burned. What's think about this ??..Could be protected with a diode or no is necessary..
Thank's in advance.

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November 20, 2012 at 9:32 AM delete

Hi Lklunder,

yes you will have to put a 6 amp diode after 240 Ohms on the right side just before the battery positive.

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November 28, 2012 at 1:57 AM delete

Hi agaim Swagatam,

Finally I have finished the circuit obtained the following results.

1.- I set the 10K preset until red LED light up at this point the output voltage was 25.2V. (very very poor shine)

2.- I connected two 12V batteries on serie at charger (previously discharged), and then switch ON of the charger; at this moment the charging voltage it was increasing at interval from 24v until 26.2V during 8 hrs approx., the initial current was 700ma and was down until 120ma during the hours. Eight hours. after, the red LED never lit, and the voltage of charge never was stopped..

3.- I proceeded to disconnect the batteries and their voltage was 25.9V. (higher to the setup of output voltage of 25.2V but the red LED never lit).

4.- At first when I connected the LED charge indicator, the output voltage as well as the current began to fall rapidly until 23V; at this voltage the charger no working. When disconnecting this LED was that kept the voltage at 25.2V and could charge the batteries.

5.- Definitely the voltage for red LED is very very limited for lit, it's only 0.5V and no shine, almost invisible, is possible improve this ??.

What do you think about these points ??..The charger still does not work well .Any other adjust or recommendation ??
Thank's in advance.

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November 28, 2012 at 10:15 AM delete

Hi Lklunder,

I have made some changes in the circuit please do them and check, you would understand why these changes have been made, without which the circuit wouldn't work.

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November 30, 2012 at 12:46 AM delete

hi swagatam, i have some doubts on this circuit so, please clear it.
1)will that led glow after the battery is fully charged?
(i'm going to charge 12v/7amps battery with this circuit)
2) is that 10K is 10K POT? which is connected with LM324 positive side?
3)instead of 6V/400mW zener diode can i use a normal diode, if yes which one can i use?
4)there are 14 pins coming out from the IC=LM324, in which pin you have connected the LED's negative side and you have connected two 10K to this IC, please let me know the pin numbers of this IC.
5)can i take the battery's output to the following circuit directly?
http://2.bp.blogspot.com/-LdSSxpTUQck/UGsOLW7G-eI/AAAAAAAAAv8/VuPHboJ0cC8/s1600/40+watt+LED+PWM+Controll+Circuit.png

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November 30, 2012 at 9:53 AM delete

Hi Deepan,

Here are the answers:

LED will glow and cut off supply to the battery when its fully charged.

2) 10K can be a pot or a preset depends on the user what he prefers, a preset is better, though.

3)You may use 4 diodes in series, cathode down, in place of the zener.

4)324 contains 4 opamps, you may use any one of them and connect the pins as per the diagram.

5)Yes you can connect the battery directly to the link circuit.

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November 30, 2012 at 8:40 PM delete

hi swagatam, today purchased this circuits parts but some parts are not available in my locale store so please advice me about that.
1)LM338 is not available
2)240 ohms is not available
3)INSTEAD OF 1N4148 I BOUGHT PH4148 OF ZENER Diode, is it ok?

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December 1, 2012 at 5:29 PM delete

Hi Deepan,

No I am sorry everything has to be exactly as in the diagram.

P4148 will do for 1N4148

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December 7, 2012 at 9:19 PM delete

Hello Swagatam!
Whats the power rating of the resistors in watts
plain and variable?
will 0.15w rated ones do it?
thanks

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Anonymous
December 7, 2012 at 10:18 PM delete

Hai,
where is 470k resistor mentioned in text?

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December 8, 2012 at 9:16 AM delete

Hello Opauszky,

All are 1/4w rated, however you may use 0.15W types....will work without issues.

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December 8, 2012 at 9:33 AM delete

Hi,

It was removed afterwards and replaced with 1N4148 diode and 1K series resistor across the output ans preset pin of the opamp.

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Anonymous
December 10, 2012 at 6:17 AM delete

hello master
Can I replace a 741 ic in place of LM324 without changing other parts??

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December 10, 2012 at 9:42 AM delete

IC 741 will not tolerate anything above 20 volts so IC 324 has been used here.

For 12V batteries you may use a 741 IC.

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December 15, 2012 at 4:23 PM delete

Hi again Mr Swagatam,
With the last changes on the circuit, now works fine, now I have a 24v automatic charger from a recycled line adapter, thanks for all your help and patient.
Thank's again.

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December 15, 2012 at 6:22 PM delete

Congrats! Mr Lklunder, you are welcome...

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Anonymous
December 18, 2012 at 6:01 PM delete

A component connected at pin Vout of LM388 (value as 240) is a combination of two or three resistors. Am I correct??

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December 18, 2012 at 9:39 PM delete

it can be a single resistor or adjusted using more than one appropriately selected resistors, through series or parallel connections.

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Joel
December 19, 2012 at 5:41 AM delete

I've just put together a prototype of this using the same components as you specify. I am attempting to set it up to charge a 12v SLA.

I hooked up a battery that is fairly well charged and turned on the charger, then checked voltage at battery terminals (it was up around 16.4 volts) so I shut it down and decided to check with you.

I'm guessing that the 4.7k trimmer is not set quite right? I wasn't sure exactly how to adjust it, so I just measured 4.7k ohms before I put it into the circuit. I'm supplying the 338 with 30vdc.

What I'm wondering is the procedure to adjust the output voltage of the 338 chip. Reading through all your replies I believe I understand the procedure for adjusting the 10k pot for the op-amp, just wasn't sure if I got the other correct.

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Anonymous
December 19, 2012 at 6:00 AM delete

Can you draw here a low battery indicator using the unused part of this LM324? so we can incorporate it with the circuit. please..

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December 19, 2012 at 10:13 AM delete

If you are charging a 12V battery then it's recommended not to use an input supply of more than 24V, this is also required to keep the ICs well away from their threshold tolerable voltage limits.

The adjustments are very simple.

The charging voltage which is the output voltage of the IC LM338 is set by adjusting the 4k7 preset. Use a digital meter while doing this.

This must be done without connecting a battery.

For a 12V battery it should be set to about 14.3V.

Next the 10K preset should be adjusted such that at the above voltage the LED just comes ON. This must be done by keeping the feedback loop at pin#4 of IC324 disconnected. Once the LED just lights up, the feedback 1K/1N4148 loop may be reconnected.

The adjustments are over.

Switch off the circuit.

Connect a discharged battery to the shown points......and now switch ON power, the battery will start charging and will get disconnected as per the settings discussed above.....

The input current should be 1/10 or 1/5 of the battery AH

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December 19, 2012 at 12:56 PM delete

It can be done through a simpler way, just add a 220K variable resistor in series with the 1K resistor at pin#4. This can be adjusted for fixing the low voltage restoration point.

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ody
December 19, 2012 at 5:05 PM delete

Swagatam i'm a filifino sir thanks for your circuit very useful.i ask also can i use to solar panel directly and can be use as automatic charge the battery and reach the voltage and stop the charge get from solar panel and not backing voltage from battery to solar and also can i use this for substitute to solar charging control, thanks much for the answers.. Godbless

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December 19, 2012 at 5:43 PM delete

Ody you are welcome....yes this circuit can be effectively used with a solar panel for controlling and charging a battery.

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December 20, 2012 at 2:39 PM delete

dear swagatam, instead of 6V/400mW i bought PH C5V6 ZENER DIODE, IS IT OK??

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December 22, 2012 at 10:41 PM delete

OK, I have some 7ah 12v batteries and with the charger operating, the current on the secondary of my transformer is about 1.2 amps...which I assume would be about right. Unfortunately, it's not rated for that kind of load.

So, what I'm wondering (please forgive me if it's a silly question) is if there would be a way to incorporate some form of current limitation into the circuit in order to be able to reduce the size of the transformer. (Space being the main consideration in my project)

Oh, and thank you for your ongoing participation in these conversations!

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December 23, 2012 at 2:47 PM delete

Hi again Mr Swagatam,
I have a question about your suggestion of add a low voltage restoration point to the charger.
How it works ??.....It's posible use it for monitoring one battery which after that was charged, and while the battery continues connected to the charger and unused loses some charge and when this happen the charger may start a new charging cycle (type flotation charge) ???.
I would like add this functionality to the charger ...It's possible ???
Thank's in advance.

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December 23, 2012 at 3:24 PM delete

Thanks!

First it will be important to know how many batteries you have got and how do you want them to be connected, in series or parallel for charging them??

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December 23, 2012 at 3:26 PM delete

Hi Mr.Lklunder,

yes the circuit will automatically sense the low voltage mark and restart the charging process.

The feedback resistor needs to be adjusted correctly for this to happen.

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December 23, 2012 at 10:01 PM delete

Oh sorry, I have 4 batteries but I'm only trying to charge one at a time. I'm going to build 4 copies of this circuit and incorporate each one into a battery powered led lamp. After starting this project I saw you have several other designs for this type of project, but since I already started with this one, I was hoping to get it to work.

So to summarize, one 12v 7ah battery. Charging time is not really a concern. Transformer is 120v .14a primary-24v 10va secondary.

And one other thing I just wanted to double check with you. For adjusting the 10k pot for the lm324, I need to disconnect one end of the 1n4148/1K feedback loop, then adjust till the led just turns on, then reconnect the feedback loop is that right?? I'm guessing I have missed a short or made a mistake somewhere, because I have smoked a few 324's during this step.

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December 24, 2012 at 4:10 AM delete

OK, can I use a mini trimpot 220K ??.
I guess that the 1K resistor goes connected to pin4, then to the trimpot 220K, and the other pin of the trimpot goes to ground .......is this correct ???
Thanks

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December 24, 2012 at 2:03 PM delete

Your transformer secondary current should not be more than about AH/5 of the battery.

After rectification if the voltage exceeds 32V, your IC will fry, also with wrong supply polarity.

Yes the setting up procedure that you've mentioned is correct.

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December 24, 2012 at 2:20 PM delete

Yes it can be used....use the center and any of the other pins and connect the pins in series anywhere in the loop.

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December 24, 2012 at 4:38 PM delete

OK, so, it's correct connect the 220k and 1k resistor between pin4 and ground ???.
What is the point of adjustment of the 220k ???
Thanks

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December 24, 2012 at 7:39 PM delete

Disconnect the 1K from the output of the IC,

connect the center pin of the preset to the output.

Next connect any one of the other pin of the preset to the disconnected of 1K.

Leave the other end of the preset free (unconnected)

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December 24, 2012 at 10:19 PM delete

That is about what the secondary current is, but what I'm wondering is, if there's a way to clamp the current at a lower value. Or in other words, is it possible to control the current regardless of size of battery.

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December 25, 2012 at 9:48 AM delete

current will never damage the circuit as long as voltage stays within the tolerable limits of the devices.

Anyway you may refer the last circuit in the following article, the resistor provided at the emitter of the transistor controls the current to the desired limits.

http://homemadecircuitsandschematics.blogspot.in/2012/07/making-simple-smart-automatic-battery.html

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December 27, 2012 at 7:23 AM delete

hye swagatam.
can you please tell me the specification of the lead acid battery?because there'll be 12v with different current when i was searcing for them at the store.can you tell me 12v with what range of current should i buy so that it'll make the circuit works?

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December 27, 2012 at 8:37 AM delete

Hi, Afiq,

The shown circuit will not support batteries above 50 AH, so anything below 50 ah can be charged on this. The input current needs to be 5 times less than the connected battery AH rating.

Regards.

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December 29, 2012 at 8:57 PM delete

OK, I added the current limiting resistor and that worked like a charm. I wanted to get the load on the input transformer under .4 amps so I put in a 2.2Ohm 5watt resistor (closest they had to 2ohm) per the .6/current calculation and 14.2x.3=4.26 for wattage. Thanks bigtime for your help there.

Now last night when I put it into action, it seemed to be working perfectly, nothing got too hot and the battery was charging nicely. It wasn't fully charged before I went to bed, so I decided to unplug it just in case while I slept,I disconnected transformer and battery. This morning I plugged it back in and was intending to monitor the rest of the charge cycle.

I plugged it in, and while I was checking the voltage at the battery terminals with a DMM something on the board smoked. I disconnected the opamp siide of the circuit again and the regulator is still reading 14.2v output, but when I connect the rest of the circuit and check voltage at battery, I'm seeing around 15.5 volts. I can't see where the smoke came from, but I'm assuming I've burnt the 324 again, even though there is no outward sign of damage.

So, what I'm wondering is what could be causing this? Could connecting the meter to check voltage at the battery be the culprit? This time I used a 16v source, so I'm pretty sure there is no way the voltage across the 324 power inputs could have exceeded the 32v max. And after re-checking the 338 output and finding it correct, I'm assuming the higher voltage is perhaps due to the source backfeeding through the 324 due to some internal damage.

It will be several days before I get the next shipment of 324's in, luckily they are only about 40 cents apiece, heh. So, until then I can't do much further testing. I'm just curious to get your thoughts on what might be happening here.

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December 30, 2012 at 9:23 AM delete

At 16V nothing should go in smoke because the range is well under the tolerable limits of the devices, so it's very difficult to asses the fault without practically checking it.

Checking the battery voltage can never cause anything to burn, so it has no connection with the fault.

Is the IC supply pin of 324 connected at the output of IC338 or directly to the 16V supply? It should be connected to the output of 338.

Are you using a relay at the output? how did you wire the relay contacts with the battery, because 15.5V is weird and cannot happen if it's fed with 14.2V, from where is the excess voltage generating??



Probably the answers to the above questions would help you to trace out the fault.



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December 30, 2012 at 11:33 PM delete

I was using the schematic as shown above(How to Build an Automatic 6 volt, 12 volt, 24 volt Lead Acid Battery Charger Circuit / http://homemadecircuitsandschematics.blogspot.com/2012/02/how-to-build-automatic-6-volt-12-volt.html)but with the addition of the power resistor inserted into the ground between the 104 50v capacitor and the transistor emitter (which limited the current on my transformer secondary nicely so it's operating within it's rated output). So yes, the Vcc to the 324 was fed with the dc source, but I can change that easily. And no, I have no relay on the output since there is no relay in the circuit per that drawing that I could see.

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December 31, 2012 at 10:03 AM delete

OK if you re using the above circuit then it has to be exactly as shown in the diagrm, the supply to the Vdd and to the reference pin cannot be taken from the output of 338 that would cause the operations to malfunction.....so now the mystery still remains unsolved because everything's right in the above circuit.

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December 31, 2012 at 12:48 PM delete

Hmm, I'm almost stumped. Is there any possibility that the transformer inrush could be playing a part in this? I'm really just making wild guesses at this point. This is the specific chip I have in there:

http://www.mouser.com/ProductDetail/Texas-Instruments/LM324N/?qs=sGAEpiMZZMtCHixnSjNA6Araa3jp4DVB37ZJv3RooEc%3d

Best I can tell from the data sheet it is what you had in mind, 32v max. The power section I have built includes a transformer with 16v ac secondary which I have running through a 4amp bridge rectifier to supply the above circuit. I don't know if it's likely, but at the moment the transformer is energized might there be a spike that could damage the chip after repeated on/off cycles?

It's probably something very simple, I'd love to bring the card by your shop to look at, but alas Mumbai is a bit of a long trip from Indiana, haha.

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December 31, 2012 at 3:12 PM delete

Transformer power suppllies are normally very gentle, so I don't think a surge could have caused the frying of the IC, moreover 16V is far below the rated spec of the IC.

The image shows an SMD type IC, such ICs are difficult to solder on general purpose boards and requires skillfull hands for fixing them correctly, I am doubting a short or a drysolder across the pins, may be....just a guess though.

I would suggest you to use an ordinary type of IC,as shown here:

http://www.gophoto.it/view.php?i=http://i00.i.aliimg.com/wsphoto/v0/499138876/25-pcs-LM324N-LM324-Low-Power-Quad-font-b-Op-b-font-font-b-Amp-b.jpg_250x250.jpg#.UOFb-eTR3To

Yeah...Indiana is too far away, no chance of a practical assessment haha..

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January 3, 2013 at 11:02 AM delete

Ok, I got some more 324 chips and so far they seem to be performing well. They are through hole, not SMD, the webpage just had the wrong picture.

If you don't mind could you just go over the 10k pot adjustment for the above circuit (6,12,24v automatic, no relay)one more time in detail, becuase something is not going right for me there. With the feedback loop disconnected, there is a point where the LED is just barely on, but at that point with the circuit completed and battery slightly discharged and connected to the charger board, the LED comes on as soon as I plug it in and the regulator shuts down. During the adjustment, the LED never really just turns on to full bright, in fact I can turn the pot almost it's full range without that happening. It acts more like a dimmer, just gradually getting brighter as I adjust it.

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January 3, 2013 at 2:42 PM delete

I assume you have connected the zener resistor 10K upper end and pin#4 to the positive source that's connected to the input of 338, this is very important otherwise the circuit just won't function.

The 10K preset should be set without connecting a battery.

First adjust the 338 output to the required battery full charge level, and then set 10K such that the LED just comes ON brightly at this voltage.

After this switch off the supply, connect the discharged battery and switch ON the supply back.

The transformer rating should be much lower than the battery AH so that the 338 output voltage drops in response to the connected batteries discharged state.

Now as the battery charges up, the IC324 waits until the full charge level is reached when the intended functions happen, that is the o/p of 324 toggles, switching off the lm338 output and subsequently the charging voltage to the battery......the LED illuminates brightly.

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January 3, 2013 at 3:10 PM delete

hi swagatam, WISH YOU HAPPY NEW YEAR

in my local, some electrical parts are not available, so can you buy it and send it to me by postal or by courier, i'll pay for it.
i need the following parts for making several circuits(from this blog).
1)680pF:2No
2)R1 10ohms/2watt :25No
3)IC1 TIP122: 2No
4)IC2 LM338: 2No
5)104 disc: 3No
6)0.1uF: 3NO
7)0.01uF: 3No
8)R2 240ohms :4No
9)common board: 2No (in low cost)
10)4k7 pot :2 No
11)LDR : 5No

and this is my address.
deepanbabu,
1/39 pillaiyar kovil street,
vengattapuram,
elur,
gobi,
erode(dt)tamilnadu-638506.

thank you in advance,
deepanbabu.

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January 4, 2013 at 9:26 AM delete

Hi Deepan,

Wish you a Happy New Year, too!

Providing small quantities of parts will be difficult for me, and moreover it will be too expensive for you....the actual cost of the above parts may be around Rs.400/- but the forwarding cost will be around Rs.500/-

So it isn't a feasible idea.

Regards.

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January 9, 2013 at 9:16 PM delete

hi swagatam
where is your office i would like to meet you personally
i stay in mumbai-kandiwali
my contact number is 9821448049
please do call me

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January 10, 2013 at 12:25 PM delete

Hi Rakesh,

Please interact with me through my email ID, I would be more comfortable:

homemadecircuits@gmail.com

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January 26, 2013 at 3:56 PM delete

How would i interface a dry cell battery charger ckt. with this ckt.

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January 27, 2013 at 2:38 PM delete

This circuit is for charging chargeable batteries only...cannot be used for dry cells, which is not recommended anyway.

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Anonymous
February 7, 2013 at 6:17 PM delete

Swagatam,

The schematic still indicates a 470K resistor in series with the base of the transistor (output of op amp through a LED). Is this correct?

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Anonymous
February 7, 2013 at 7:20 PM delete

Swagatam,

Please ignore my earlier question regarding the 470K resistor. 50 milliseconds after I hit "return," I realized the base resistor is 4.7K. Thanks.

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Anonymous
February 10, 2013 at 1:02 PM delete

Hi Swagatam

I was trying your circuit above but it seems that i can't make it to work properly. The output voltage that i'm getting from the diode 1n5408 is limited to 5-7v only and i can't get a higher value. I am using a 3Amps 12-0-12 transformer. hope you can help me, i really need this for my project. thanks in advance.

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February 10, 2013 at 9:42 PM delete

Please use a 10K preset in place of 4K7 for adjusting the LM338 output voltage.

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reg
February 15, 2013 at 5:55 PM delete

hello sir.. im just confused with the voltage going to the non-inverting part of the comparator.
why is it connected to the Vout of the 338 regulator and not on the + battery?

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reg
February 15, 2013 at 6:17 PM delete

hello sir.. im just curious what will happen if i change the connection of 10K preset connected on the anode of 1N5408 and move it to the cathode part?
thanks in advance...

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February 15, 2013 at 9:19 PM delete

Hello Reg, you are right, ideally it should connected at the positive of the battery but it won't matter much with the shown connection, just the preset will need to be set at 0.6 V higher, meaning at 15V instead of 14.4V.

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February 15, 2013 at 9:21 PM delete

will do, in fact you can even connect the inverting 10K upper terminal and pin#4 of the IC to this point.....

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reg
February 15, 2013 at 10:12 PM delete

another question sir,
if i connect the 10K upper terminal to the positive part of the battery what voltage will it detect,will it be the voltage from the battery or will it be from Vout of 338

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February 16, 2013 at 2:32 PM delete

It will anyway detect the battery voltage....

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Anonymous
April 15, 2013 at 12:46 PM delete

Sir, to charge the battery needs power battery input or can i use AC transformers to create input power 15-24 volts? if ever what components can i change? thanks in advance!

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April 16, 2013 at 5:25 PM delete

yes it may be used, include rectifier and capacitor section with it ....

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April 16, 2013 at 6:36 PM delete

Thanks a lot for your effort and congratulate, I hope much more to come out day by day, I also have a query regarding this "Automatic 6 volt, 12 volt, 24 volt Lead Acid Battery Charger" Circuit, I'm using 2 x 12v/7Ah SMF Batteries in series to get 24 volts, I want to use your circuit as a charger, can I substitute LM338 with LM317 with proper Heat Sink, I don't need to boost charge the batteries and so no heavy current will flow through regulator IC, I think LM338 will be the wastage of resources an money for such a little charging current, please suggest. also can you suggest the modifications so that current for charging the batteries can be controlled for better life of the batteries, as you have already included the over charge protection and cut-off in your circuit but can you please provide the add-on circuit for "Over Discharge Protection" or "Low Voltage Cut-Off" to have more functionality from this circuit, another query is regarding the Op-Amp LM324 is used as Voltage Comparator in this circuit, would you suggest using LM339 instead of LM324 because it is meant for comparator use only.....please suggest....please email me on my address also if possible...shishirbhatnagar@gmail.com....thanks

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April 18, 2013 at 12:40 PM delete

You are welcome Shishir!

yes definitely LM317 can be replaced here, since the required current is less than 1.5amps.

LM339 would also do, however I would suggest Lm324 because it has better overall spec ratings.

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Anonymous
May 23, 2013 at 7:16 PM delete

Hi Sir Would you kindly Post the circuitry for 12 volt automobile Rectifier regulator unit for two wheeler motorcycle like hero honda splendor, etc

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May 23, 2013 at 9:14 PM delete

you can try out this circuit:

http://homemadecircuitsandschematics.blogspot.in/2013/04/12v-5-amp-fixed-voltage-regulator-ic.html

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May 30, 2013 at 4:03 AM delete

I found a similar circuit using a LM338 with a LM741 that switches off the regulator with a 2N2219 transistor.

The first thing I noticed was that there was no diode on the output of the LM338. That allows battery current to go through the 240 ohm resistor when the transistor turns on.

In your circuit above the diode goes to the battery only, but it also isolates the comparator from the battery voltage and only allows it to read whatever is on the regulator output, which may have been turned off. The comparator needs to read that battery voltage to function correctly!

Now if you move the diode to the output of the regulator and allow the battery voltage to go to the comparator you may find that you don't need the comparator at all. When the battery voltage goes as high or higher than the regulator output voltage, the diode is reverse biased and shuts off current to the battery on its own.

I found this out when I started my car and the alternator voltage shut off the regulator current from a solar cell. The comparator never turned it off as I set that higher than 14 volts to see what would happen.

So all we have to do is set the regulator voltage to the voltage that the battery should reach when it is fully charged. Use the comparator to indicate the voltage status and set it accordingly. Your hysteresis feedback resistor needs to be on the pin side of the comparator also. Use larger resistor values for a better voltage trip spread.

With a 741 I used 2M and 47K on the pot to allow a half volt drop before the comparator went low. That is better than using a 100 mf capacitor like you used in the other circuit too. It also allows the red LED to be placed straight from the comparator output to ground through a 680 ohm resistor.

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May 30, 2013 at 9:18 AM delete

Thanks for the observations!

Here the position of the diode doesn't matter because the above circuit is a "one shot" kind of design meaning the whole circuit would get latched once the battery voltage reaches the full charge threshold.

Even with the shown position of the diode the output voltage from the source would drop appropriately in response to the connected discharged battery lower potential, provided the input current is rated at 1/10th or at least at 1/5th of the battery AH.

A battery can never attain higher voltage than the source voltage, it would tend to show the full charge level but it's only because the source voltage keeps pushing the charge into it.....which can be dangerous for the battery if it's not switched OFF in time....that's why it becomes imperative to use automatic chargers.

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May 30, 2013 at 10:44 AM delete

How is it latched? It might be oscillating. When the regulator is shut off, the only voltage on the comparator input is whatever the regulator gives it. That would make the comparator switch low and turn it back on, no? Why not read the battery voltage directly?

The diode in that position only keeps the battery from draining through the cutoff transistor. That's fine but why not read the actual battery voltage directly?

Also if the hysteresis is set up correctly then you don't need the LED in series on the base to allow the transistor to turn off properly.

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May 30, 2013 at 11:29 AM delete

when the battery gets fully charged, voltage at pin#3 would become higher than pin#2 which would prompt the output to go high, this high would reach pin#3 via the 1N4148 diode latching it up immediately into a permanent high position.

Since the supply to pin#4 of the IC is taken from outside, it would remain operative even after the output from LM338 gets inhibited.

you can check it practically, you would find that the position of the diode is not critical here, though technically it should be placed just after the 240 ohms resistor.

The LED has no relation to hysteresis, it's just for indication purpose....it's a one shot latch up circuit so hysteresis may be an irrelevant issue here.

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May 30, 2013 at 12:46 PM delete

OK, so the 1K feedback latches the comparator output. I was reading your description and it mentions a 470K resistor twice, but it was nowhere to be found.

My friend suspected that the LM741 needed hysteresis to keep it from oscillating in the other circuit where a 100 uf capacitor was on the output.. He then reasoned that the LED was in series because the output voltage was too high to allow it to shut the transistor completely off. Why not just run run the LED separately?

I see what you mean about the battery voltage dropping rapidly after cutoff. It does that after the alternator charges it too. Latching it is a good idea! I've never seen a diode on a comparator like that.

I tried your other circuit with a solar panel. Setting the regulator to 13.3 volts still gave the same 140 ma current as when it sent the full 18 volts directly. The battery charged slowly, but it never made it close to 13 volts unless I ran the engine. What would you set the comparator voltage to so that it doesn't overcharge it?

Thanks for your quick response!

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May 30, 2013 at 2:41 PM delete

the feedback network has been specifically introduced for eiminating the hysteresis issue, if we remove the 1K/1N4148 network, the circuit would start oscillating.

the diode provides better isolation, although the circuit would still work without it.

I guess the solar design includes a current control feature, you may have to calculate the relevant resistor values appropriately for generating more current at the output.

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May 30, 2013 at 3:46 PM delete

On the 104, 50V capacitor: 104 = 10,000 picofarads

mFd,uFd,nFd,pFd
.000.000.010,000 = .01 uf

I'm going to see how it works both ways. It depends on how fast it hits that bottom threshold voltage.

The solar cell really does not need regulating. The battery voltage never gets to 13 volts. I just use it as a second power supply for circuit tests. Normally I just run it through a Shottkey diode. I hope to use one of these circuits for charging tools without a shutoff relay.

Thanks!

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June 3, 2013 at 6:52 PM delete

Hi dear.Your circuit and explaination is great. It really helps me a lot. Thank you, friend.

But I’m quite new on this electronics field and still have some question to ask.

1) You said the inverting input of the IC 324 is clamped at a fixed reference voltage of 6 via a 10K resistor, is the voltage value =6V because of the zener diode?

2) If yes, the IC 324 only become saturated (output become high) when inverting (-ve) and non-inverting(+ve) value are different. The non-inverting(+ve) pin is connected with 10k potentiometer/variable resistor, and that potentiometer is connected with positive terminal of battery, as well as their negative terminal. I just wonder how could the voltage value that come to the non-inverting(+ve) pin could change while the battery is fully charged? Can you explain that?

3) The last one, how could the high output of IC 324 that connect to base of the BC547 transistor can switches off the IC LM 338? Is switch of LM 338 means the whole circuit is switched off?

Sorry for asking too many questions. Thank you again

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June 4, 2013 at 3:39 PM delete

Hi Hazwan,

1)yes the camping voltage is determined by the zenr value.
2)The output of any opamp would go high (saturated) when the non-inverting input gets a higher potential than the inverting input and vice versa.
3)As the battery voltage rises, the center pin of the preset is also subjected with a proportional rise in potential which ultimately crosses the set limit in response to battery full charge level, this results in the output going high.

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June 18, 2013 at 9:26 PM delete

i do not found LM 338 and 2N2219 transistor so which components i should have to used in absence of them?????

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June 20, 2013 at 9:11 AM delete

LM338 has no replacement, use BC547 for the transister

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Anonymous
June 20, 2013 at 9:32 PM delete

Hello Swagatam,
First of all, I want to thank you for all the effort you put in your designs and in answering all our questions.

Now, after looking through the comments and with the help of the scheme I finally have this circuit working. I am using a 19v laptop power supply. Following your instructions I set the 4k7 pot so as to have 14.3v at the output of the lm338. After that I disconnected the 1n4148 loop of the lm324 and set the 10k pot for the red led to barely light up.

My problem is that when I reconnect everything and turn the power on I don't get 14.3v at the ouput, I get less, like 13.5v at the most.

So I have a couple of questions.

1. First of all, how can I calculate the treshold voltage in advance?
2. Why, after connecting the second stage of the circuit (the one with the lm324), I don't get the full 14.3v that the lm338 was providing before?

One thing that may be responsible for this difference is that my zener diode is 6.3v and so I have 6.25v or so at the inverting input of the lm324. Should I just set the 4k7 pot so I get full 14.3v at the lm338 with all the circuit assembled and no battery connected?

If you need any other info just ask me please.
Thank again for everything,
Miguel

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June 21, 2013 at 11:27 AM delete

Helo Migue,

Thank you very much!

You can eliminate the issue by doing the following couple of things:

replace the 4k7 preset with a fixed 2.5K resister and connect a 10uF/25V capacitor across the junction of 1K/1n4148 and ground.

Hopefully these two mods will help to produce the desired results accurately.

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Anonymous
June 21, 2013 at 2:58 PM delete

Hello again Swagatam,
I will try your modifications asap (now I'm at work). Btw, what is the capacitor for?

Moreover, I've been giving it some thinking and looking at the diagram I thought of a plausible explanation for this behaviour: if I have the complete circuit assembled and there is no battery connected, the voltage at the non-inverted input will be higher than that of the inverted input (since there is no battery to lower the output voltage). Then the lm324 will go high and the bc547 will start conducting and therefore adjusting the lm338 (if adj is shorted to ground the lm338 shuts off?).

So with the complete circuit on and no battery one sees the upper voltage threshold -the one at which the charger will stop- and though it cannot be measured, when the battery is connected the lm338 output will be the one set with the 4k7 pot, but lowered to the actual battery voltage.

Is this correct? Please correct me if I am wrong. I want to understand the insides of this circuit rather than just build it.

Miguel

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June 22, 2013 at 10:26 AM delete

Hello Miguel,

Yes that's why the 1N4148 link needs to be removed while setting up the circuit, and I have recommended somewhere in the article to switch ON the charger only once the battery is connected.

Without any battery connected, the opamp would respond with a high output, switching ON the transistor and the LED. This would result in a complete switch OFF of the LM338 output, meaning when the LED's ON the output of LM338 would show a zero voltage. This is how it should work.

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Anonymous
June 26, 2013 at 8:57 PM delete

Hello mate,

Wonder if there is a schematic in your collection that does the following:

Monitors a 24V bank (therefore a range of >18 to <30 volts) and cuts off at low levels (i.e 22V). Maybe it could also do a high voltage cut off, but not necessary for my application.

No external power supply would be much preferred.

Thank you in advance,
Pete

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June 27, 2013 at 12:26 PM delete

Hello Pete,

you can try the last circuit provided in the following article, you will need to replace the 741 with a single IC LM324 opamp (there are 4 inside it, use any one of them......adjust the 10K preset such that the relay just deactivates at the preferred lower threshold. While doing this setting keep the 47K feedback link disconnected, restore the connection once the setting is complete.

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

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Anonymous
June 27, 2013 at 5:54 PM delete

Thanks for the fast assistance! I think this is exactly what I need.

Just a small clarification, can it also be adjusted for an upper threshold with the circuit as it is?

Thanks again!

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June 28, 2013 at 10:35 AM delete

Yes it will do, I have modified the design appropriately and now it will respond to both the levels of the battery while charging and discharging.

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Anonymous
July 8, 2013 at 9:46 PM delete

hello swagatam, is there any process to utilse this circuit for a 48v system. i go thru your post on 48v charger.which did'nt work for full-battery disconnect. how about adding some mosfets and schottkey diodes into this circuit?

regards
james

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July 9, 2013 at 10:16 AM delete

Hello James,

the 48V circuit is perfect and will cut off for both under/over voltage conditions, you will need to set i properly as per the instructions.

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Anonymous
August 1, 2013 at 3:22 PM delete

Hello Swagatam Majumdar,

Can I use yours' (this) circuit for charging SUNCA RB640CS 6V 4.5A rechargeable Lead Acid battery from 220 V line voltage with 9V 1.5A Transformer in the input section.

Regards
Dipu.

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August 1, 2013 at 8:18 PM delete

Hello Dipu,

You can use this circuit but even a better option is shown in the following link:

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

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Anonymous
October 4, 2013 at 7:02 AM delete

Hi!
sir may ask for your help about our Project which is an automatic battery charger....MAy we ask if what are the IC's that we are going to used..thanks hope for your Feedback..

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Anonymous
October 19, 2013 at 12:16 AM delete

Hi,Swagatam :
I have a little knowledge in electronics and trying to repair an Old 24 Volts battery charger 20A,and looking in the web I

found this web page of how to build batteries charger.

A friend of mine that repairs CB radios check the charger and told me that

everything is OK(the timer, the diodes,the capacitor)and found that the transformer

is bad (it's a big transformer) and have no information sticker on it.
I know it's 120V AC primary and dont know the secondary amount output.

Also know it's a center tap transformer and the center tap cable goes out of the

charger to the Negative post of the 24V battery bank.

And each one of the other two live wires goes to a diode each one that's mounted in

a non grounded plate and from there goes a cable that goes to the Positive of the

battery bank.
Also the transformer output side have two little cables that goes to a capacitor.

My friend told me to buy a 120AC primary/24AC secondary center tap transformer to

repair it.
Is this is the correct output for this charger??
I see the pictures of the center tap transformer and they have only 3 cables on the

secondary (the center tap ground cable and the two live wires).
my question is how to connect the capacitor ???
Can someone explain to me??
Help is apreciated and Thanks You In Advance for your help...
Att Carlos

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October 20, 2013 at 11:19 AM delete

Hi Carlos,

From your explanation it looks like a center tap bridge rectifier configuration that's employed with your trafo.

For confirming the trafo simply switch ON power and measure the voltages across the three taps by keeping one prod at the center and the oother to the outer taps, you should get a reading of 24V AC across them.

No voltage or voltage only across one tap will ensure a faulty trafo.

Remember to keep your meter on AC volt range while doing the above.

The capacitors may be connected by joining their negatives together and connecting the joint to the center tap, and the remaining two positives to the other two taps of the trafo.

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October 20, 2013 at 11:22 AM delete

....correction, the cap positive must be connected to the common joint of the two diodes, and the negative to the center tap.

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Anonymous
October 20, 2013 at 7:35 PM delete

Hi Swagatam:
Thanks you for your Help and fast reply.
My friend measure the output of the transformer between all the wires and it reads 1 ac volt,for that reason he told me the transformer is bad..
Also measures the output cables that goes to the battery bank and also measures 1 volt DC.
i will check the capacitor to verify which of the two connectors is the positive one.
The Capacitor info is:
AEROVOX 250P440 4M
4UF 440V 50/60HZ 70C
SH9848 W.O. 3178 M3448

PROTECTED A 10000 AFC
SUPERMET 1238 NO PCB'S
ASSEMBLED IN MEXICO
Thanks You Again and we will be in touch

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October 21, 2013 at 10:24 AM delete

Hi Carlos,

Cap value is 4uF/440V??

are you sure your trafo output is 24V, because for 24V output a 440V cap will never be used.

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Anonymous
December 12, 2013 at 12:59 PM delete

Hi Swagatam,
I have some doubt on the circuit, If I use 24V battery, what voltage of the zener diode suppose to use ?

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Nicholas
December 12, 2013 at 1:55 PM delete

Hi Swagatam,

For 12V Battery
Q1. If input voltage of 14V to charge a 12V battery, why select 6V zener diode as reference. Can explain the principle and how the circuit work ?

Q2. Vin=15V, Vout=14V by adjusting R2=4k7 (potentialmeter)
What is tripping voltage (How many volt ?) at which the circuit should cut off by adjusting the 10k potentialmeter ?

For 24V Battery
Q1. Vin=30V, Vout=28V by adjusting R2=4k7 (potentialmeter)
What is tripping voltage (How many volt ?) at which the circuit should cut off by adjusting the 10k potentialmeter ?

Thanks....

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December 12, 2013 at 8:05 PM delete

Hi Nicholas,

zener voltages are not critical, you can use any value below the battery voltage rating, because the trip point is ultimately set with respect to the zener voltage.
for 12V batt full charge tripping voltage is 14.3V
for 24V, it's the double of the above = 28.6V

so the preset should be adjusted by supplying the above mentioned upper thresholds and the preset setting should be sealed with some glue.

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Anonymous
December 15, 2013 at 3:03 AM delete

hello swagatnam i could not found 324 in store and library.could i replace it with lm741? if yes plz guide me the pin connections. thanks

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December 15, 2013 at 9:48 PM delete

741 will work, but it's pin#7 should not be supplied above 19V.

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Anonymous
December 16, 2013 at 4:31 PM delete

i test it on multisim using lm741 instead of 324, it was not working. suggest me what i should do? i used 317 instead of 338, this section was working. i am using it for 12v battery

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December 17, 2013 at 11:26 AM delete

The above circuit will surely work with IC741 and 317, i have no idea why it's not showing in multisim.

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January 14, 2014 at 5:21 PM delete

i have a 12v 7.2Ah SMF Battery, so i want to good automatic charger for this battery. Above circuit diagram can work for this ?
Is this above diagram can prevent battery from Discharge when circuit not in use..
I think there must we a relay for protecting the battery or auto cut- off..
pls reply.. because i want good charger for my battery and fully automatic.. plz help..

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January 15, 2014 at 11:14 AM delete

try the first circuit from the following link:

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

Use a 15V or higher input and adjust the 317 pot for getting a 14V output across the battery

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January 19, 2014 at 9:28 AM delete

Hi Swagatam

I cannot see any circuit in this article !!!
Would you please update the diagram.

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January 19, 2014 at 6:26 PM delete

Hi Abu-Hafss,
It is there, I can see it clearly, please refresh the page a few times may be.

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January 22, 2014 at 2:35 PM delete

i can use it even my suply is 20v but low of amps. like 1-2A?

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