The IC LM338 is an outstanding device which can be used for
unlimited number of potential electronic circuit applications. Basically the
main function of this IC is voltage control and can also be wired for
controlling currents through some simple modifications. Battery charger circuit
applications are ideally suited with this IC and we are going to study one
example circuits for making a 12 volt automatic battery charger circuit using
the IC LM338.
Referring to the circuit diagram we see that the entire circuit is
wired around the IC LM301, which forms the control circuit for executing the
trip off actions.
The IC LM338 is configured as the current controller and as
the circuit breaker module. The whole operation can be analyzed trough the
following points:
The IC LM 301 is wired as a comparator with its non
inverting input clamped to a fixed reference point derived from a potential
divider network made from R2 and R3.
The potential acquired from the junction of R3 and R4 is
used for setting the output voltage of the IC LM338 to a level that’s a shade
higher than the required charging voltage, to about 14 volts.
This voltage is fed to the battery under charger via the
resistor R6 which is included here in the form of a current sensor.
The 500 Ohm resistor connected across the input and the
output pins of the IC LM338 makes sure that even after the circuit is
automatically switched OFF, the battery is trickle charged as long as it
remains connected to the circuit output.
The start button is used to initiate the charging process
after a partially discharged battery is connected to the output of the circuit.
R6 may be selected appropriately for acquiring different
charging rates depending upon the battery AH.
Circuit Functioning Details (As Explained By +ElectronLover)
" As soon as the connected battery is charged fully, the potential at the inverting input of the opamp becomes higher than the set voltage at non-inverting input of the IC. This instantly switches the output of the opamp to logic low."
According to me:
V+ = VCC - 74mV
V- = VCC - Icharging x R6
VCC= Voltage on pin 7 of Opamp.
When The battery charges fully Icharging reduces. V- become greater than V+, output of the Opamp goes low, Turning on the PNP and LED.
Also,
R4 gets a ground connection through the diode. R4 becomes parallel to R1 reducing the effective resistance seen from the pin ADJ of LM338 to GND.
Vout(LM338) = 1.2+1.2xReff/(R2+R3), Reff is the Resistance of pin ADJ to GND.
When the Reff reduces the output of LM338 reduces and inhibit charging.
how many amp battery can dis be use 4?
ReplyDelete50AH Max.
Deleteif we want to charge 200AH
ReplyDeleteYou can build the following circuit:
ReplyDeletehttp://homemadecircuitsandschematics.blogspot.in/2011/12/high-current-10-to-20-amp-automatic.html
What was the wattage of the resistors used in the circuit....?
DeleteAll are 1/4 watt except R6 which may be around 1 watt.
Deletehow can i make a 12 volt DC output 7 to 10 amp current, out of 20 volts to 110 volts voltage input? can you help me plz.. tnx!
ReplyDeleteYou will have to incorporate an SMPS circuit for inputs that's more than 50 volts....
Deletepls help how to make power supply charger, i'm using traspormer and 2 diode in5406 the problem is i forgot the diagram for this. pls help me.
DeletePlease refer the following article:
Deletehttp://homemadecircuitsandschematics.blogspot.in/2012/03/how-to-design-power-supply-simplest-to.html
This would work as a solar regulator/charger with the addition of a blocking diode to prevent losing charge at night, correct?
DeleteYes, you are correct.
DeleteHi there I'm Looking all over For a simple diagram for a charging circuit with a variable input from 24 volts to about 80 volts AC to a 12 volt 4 to 6 AH can you please help i looked every where on the internet and so far yours was the closest i could find on what I'm looking for..
ReplyDeleteHi, The above circuit won't be suitable because it cannot tolerate more than 32V at its input, the following circuit looks good, you can try it:
Deletehttp://homemadecircuitsandschematics.blogspot.in/2012/08/simplest-dc-cell-phone-charger-circuit.html
The input can be from 24 to 80V DC.
hi swagatam , can i use 741 instead of lm301
ReplyDeleteif yes then can u tell me the connections
yes, will do....
Deleteif we are using 741 instead of lm301
Deletewhere is the compensation pin(8-pin)
is there any draw backs if neglect that pin connection
thank you
yes due to the presence of the "start switch" a 741 will be difficult to replace the 301.
Deletebut there are other options through which a 741 can be used for getting the same results as above.
Hello sir,
ReplyDeleteCan u please help me on the capacity of the battery should be selected to store a power of 55W(1320Wh).
Helo Rizmy,
Deleteyou may divide 1320 by the voltage to get the rating of the battery.
k sir. thanks alot.
ReplyDeletethen I'm going to store half of this energy to the battery, using a 12V 60Ah battery. So can I use the above circuit to charge a 12V 60Ah battery?.. If not, what r the modifications needed.. please help me on this sir...
Regards!
use LM196 circuit for charging your battery. Refer to the LM196 datasheet you will get the circuit there.
Deletethnk you sir.
ReplyDeleteCan I charge a 12V 60Ah battery using this circuit?... If not what are the modifications needed?. could you please help me on this sir..
Rizmy, The above circuit will not charge a 60 ah battery..... refer to my previous comment.
Deletesorry for the inconvenience sir. I have typed the same message twice mistakenly.
ReplyDeletethanks a lot for your guidance sir. I'll look for it.
thank you!
Sir,
ReplyDeleteCant I use your above circuit with LM196?.
yes it can be replaced but R6 will need to be modified appropriately.
DeleteThank you sir,
ReplyDeleteThen please help me on calculating R6 according to my requirement sir.
How did you arrive in 0.2ohm for the above circuit?.
Hi Rizmy,
DeleteWhat is your battery AH, is it above 100 AH? If it's below 100AH, R6 won't be required.
its obviously not above 100Ah. it's mostly a 60AH one. But sometimes I'll go for a 40AH one. If so is it not required to put a R6 resistor?.
ReplyDeleteThen the above circuit without R6 resistor(S/C) con be used right?..
Are the other components same as like your above circuit sir?. If I need to draw a current nearly 7-8A to charge the battery?.
If any modifications needed please explain me sir.
Regards
then you can use it without R6.....but the input current should not be more than 1/7th of the battery AH.
Deleteyou may refer to the following article to know more regarding the IC specs.
http://homemadecircuitsandschematics.blogspot.in/2013/04/15v-10-amp-adjustable-voltage-regulator.html
thank you sir!
ReplyDeletewhat about the input voltage then?. Is that should be more or equal 18V to charge the battery as you mentioned above?
any voltage above 15V, and below 24V can be used.
DeleteIf i am using a variable input from a turbine generator ranges from 5V to 15V, how should I use that input to charge the battery using this battery charger? what are the modifications needed?. please guide me on this sir.
ReplyDeleteregards!
the above circuit will not boost voltage
DeleteThank you sir!
ReplyDeleteTo use this as a solar charger, a diode at the output is sufficient or any other modifications needed?
According to me that would be enough, but it must be rated appropriately...
Deletewithout R6 means sir is it short circuited or open circuited?.
ReplyDeletethen how the comparator work to swith off the charging?
can you please explain me sir.
regards!
it cannot be open circuited for sure. so then how the comparator works without R6. if shorted always the inverting input voltage will be high and it outputs logic zero, isn't t sir?
ReplyDeleteI was confused sir. please help me on this.
It means, the R6 points should be replaced with a wire link.
Deletethen how lm301A works as a comparator?. according to your explanation above R6 only determines the voltage level of inverting input. so if we remove it how the comparison is done?
ReplyDeletecheck the article now....is it OK now?
DeleteR6 is only for setting the charge current.
"According to me:
ReplyDeleteV+ = VCC - 74mV
V- = VCC - Icharging x R6
VCC= Voltage on pin 7 of Opamp.
When The battery charges fully Icharging reduces. V- become greater than V+, output of the Opamp goes low, Turning on the PNP and LED."
you have mentioned this in your article. According to this R6 is controlling and adjusting the voltage according to the current drawn and making the inverting input high after charging.
Then without R6 how LM301A operates as a comparator?
I dont see any changes in the article sir. Could you please help?
ReplyDeletedon't worry about the article details, it was submitted by some other reader.
Deletepin#2 of the IC detects the battery high level, while pin#3 is fixed with a reference. when pin2 level goes beyond the pin3 level, the circuit latches up and stops any further charging of the battery.