This circuit is capable of providing as high as 25 Amps of current at any specified voltage between 1.25 V to 30V as per the adjustment of the given pot. The current is constant irrespective of the voltage settings. The circuit can be used for charging batteries in range of 50 to 200 AH.
How the Circuit Works
The figure below shows a straightforward design of a 25 amp solar battery charger power supply circuit which would generate a constant 25 amps of current from any source which is able to generate currents in excess of 25 amps and at 32 volts maximum.
We know that the IC LM338 is specified with a maximum of 5 amp current, the IC restricts anything above this limit.
By connecting 5 of these ICs in parallel it thus becomes possible to generate a current output of about 25 amps. The great thing about using these ICs is that, these devices are internally protected from thermal runaway situations and short circuit or overload conditions.
It means the present circuit automatically becomes safe from such adverse parameters and thus becomes completely indestructible given the input is not exceeded above 32 volts.
However the ICs cannot be directly connected in parallel, because that would cause a difference in the voltages at the output from each of the ICs which in turn would cause an imbalance between the IC dissipation, this wouldn't be good for the overall functioning of the circuit.
Therefore the additional components in the form of the opamp and the transistor have been included in the circuit which controls and maintains a constant voltage output from all the ICs keeping the situation well under control.
yesir irfan says
Hi
I want to know it will be work on atransformer or a solar panel or both
Swagatam says
it will work with all types DC inputs
shivu ns says
pls send the 1a , 5a and 10a charger circuit for solar panels. i have tried with so many circuit but i am not getting exact output from that please send detailed circuit for solar charger with charging, battery low and battery full indications
Swagatam says
you can try the following circuit:
https://homemade-circuits.com/2012/04/how-to-make-solar-battery-charger.html
use LM317 for amp…LM338 for 5 amp and LM396 for 10amp.
use a 18v panel and a 12V battery with the panel…
mexzony says
Hello Sir,
Sometimes the electricity can be unstable at times. But will need stable voltage to charge batteries so is it possible to have constant voltage and at the same time have a desirable constant current range depending on how many batteries I want to charge.
Basically if i have 3 (12v)batteries and I want to charge just one of them, I want to be able to selext the charging current and voltage. Then if I want to charge two batteries connected in series to give 24v then I want to selxt charge current and voltage too.
Kind of like a flexible charger.
I don't mind how many IC I have to buy but is IR doable.
Swagatam says
Hello Michael,
yes it's possible, you can follow the instructions as given in the following articles in order to altyer the specs as per your specific needs:
https://homemade-circuits.com/2015/07/designing-customized-battery-charger.html
https://homemade-circuits.com/2015/07/designing-customized-battery-charger_13.html
Gopal Chauhan says
Hi Swagatam,
Thanks. Can i use 2-3panels in parallel with this circuit to get 16-24 amp. Or can i add the fourth one too for getting close to 32 amp peak and generally around 20-28 during most day.
Regards
Gopal
Swagatam says
Hi Gopal, yes that surely is possible, you may go ahead with it.
Mark Wright says
What is the power rating of resistors?
0.1ohm @ 5Watts?
the rest of the resistors @ 0.5 Watts?
Swagatam says
yes, will do.
Gopal Chauhan says
Hi Swagatham,
I want to use the above circuit, however the Solar panels have rated voltage as 30.04 and are generally recording about 31-32.5 Volts/8 Amp when placed in Sun, will I be able to use this circuit for charging 150AH batteries.
Gopal
Swagatam says
Hi Gopal,
The above circuit will be able to handle upto 25amps, so according to me you can use it for charging a 150AH battery easily with the mentioned solar panel, but 8amps won't be sufficient and make the process very slow
sultan says
i hav implemented the abov circuit and powered it with 20v/5.5amp solar panel
but the 338 chips got very hot and the comparator also burned out ,even with such low rated panel ??
also for avg solar panel voltage of 18v at input ,i couldnt set 14 v at output( battery terminals). plz tell me where iam wrong???
Swagatam says
this circuit is taken from the datasheet of LM338 IC, so it cannot be wrong.
did you measure the voltage from the panel before connecting it to the above circuit??
the ic will burn at anything above 20V, IC338 will become hot if the load draws more than 5 amps.
you can also try the circuit given in this article:
https://homemade-circuits.com/2012/11/high-current-transistor-tip36-datasheet.html
sultan says
plz tell hw can i use auto cutoff in this very circuit
Swagatam says
You may try the last circuit in this article:
https://homemade-circuits.com/2011/12/how-to-make-simple-low-battery-voltage.html
sultan says
can u give me a circuit which auto cutoff once battery reaches desired voltage
sultan says
kindly tell me if the charging will stop once battery reaches full cahrge
Swagatam says
No there's no auto cut off in this circuit.
sultan says
will this circuit stop charging once battery reaches full charge
sultan says
plz tell substitute for lm308 ,,, can i use 741 ?
Swagatam says
yes…you may use it.
Swagatam says
you can also try the last circuit that's given in this link:
https://homemade-circuits.com/2012/11/high-current-transistor-tip36-datasheet.html
sultan says
what is the input range of this circuit if iwa nt output between 12 to 14v at 5 amps
Swagatam says
input range is max 30 volts.
the 1.5k preset may be adjusted for getting the required output voltage
sultan says
if i want output between 12 and 14v what would be the min input voltage required for the circuit
and can i use 741 instead of lm308