The proposed 48 V automatic battery charger circuit will charge any 48 V battery up to an optimal 56 V full charge level, utilizing very ordinary components. The circuit is highly accurate with its over charge cut off features.
Circuit Description:
As shown in the circuit diagram, the main element in the circuit is the opamp IC 741, which has been arranged as a comparator.
Pin#3 which is the inverting input of the IC is referenced with a fixed voltage of 4.7V through the respective zener/resistor network.
The other input is applied with the sensing voltage which is actually the voltage merged from the supply and the from the battery, in other words the charging voltage which is applied to the battery for charging.
The resistor network at pin#2 along with the preset forms a voltage divider network which is initially adjusted such that the voltage at this pin stays below the voltage level at pin3, which is the reference voltage set at 4.7v by the zener diode.
The preset is set in such a way that the voltage at pin#2 rises above the 4.7 mark as soon as the battery voltage rises above 50V or the fill charge threshold level of the battery.
The moment this happens, the output of the opamp goes low switching OFF the mosfet, and cutting off the voltage to the battery.
Initially as ling as the battery voltage and the over all voltage from the 48V supply remains below the full charge threshold level of the battery, the output of the opamp stays high and the mosfet us kept switched ON.
This allows the voltage to the battery for charging, until the above explained threshold is reached which automatically inhibits the battery from further charging.
The mosfet can be selected as per the AH rating of the battery.
UPDATE: For converting this into a Solar version you can read this article
1) Using Mosfet Cut Of
2) Current Controlled Version of the above Design
NOTE: The above diagrams mistakenly shows 48V as the input, the correct value is 56V. Because the full charge level of a 48 V battery is around 56/57 V.
NOTE: You will have to connect the battery first and then switch ON the input supply, otherwise the mosfet will fail to initiate for the charging process. Make sure the green LED remains illuminated after power switch ON, this will confirm the charging status of the battery.
The above design can be also built using a TIP142 and a red led charging indicator.
Simple 48 V 100 Ah charger Circuit using OP Amp and TIP142
3) Making a Fully Automatic Version
The above circuit can be upgraded into an over charge cut off, as well as low charge restoring battery charger system, for charging 48V batteries.
The modifications enables the circuit to switch OFF the battery charging process at the set over charge threshold and restore back the process when the battery voltage falls below the low threshold value.
The 10k preset must be adjusted to set the full charge level while the 22k preset for detecting the lower threshold of the battery.
NOTE: In the above two circuits, please connect the RED LED in series with the BC546 base. This will prevent the op amp offset voltage from reaching the BC546 base and false triggering.
Simplifying the Design
The above design can be further simplified as shown in the following image. Notice that the input pins of the op amp are swapped in this design, which allowed the elimination of the extra PNP BJT from the circuit.
The above circuit can be also built using PNP BJT instead of a MOSFET, as shown below:
You can also add an current control feature to the above circuit, as shown in the following diagram:
How to Set up the above Circuit:
For setting up procedure, the sample power supply should be connected across the points where the battery is connected, the mosfet does not require any attention initially. DO NOT connect the battery while carrying out this procedure.
Also keep the 22k preset link disconnected initially.
Apply the higher threshold level across the above mentioned points and adjust the 10K preset such that the RED LED just switches ON. Seal the adjusted preset with some glue.
Now reconnect the 22k preset link back into position.
Next, reduce the sample voltage to the lower threshold value and adjust the 22k preset such that now the green LED just lights up, while switching OFF the RED LED.
If you find no response from the circuit try using a 100K preset instead of the 22k preset.
Seal the adjusted preset as above.
The setting up of the circuit is over and done.
Please note that during actual operations, the above circuit will remain functional only as long as a battery stays connected at the shown points, without a battery the circuit will not detect or respond.
Feedback from Mr. Rohit
I have a 50-52v solar panel setup which is charging a 48v 78ah battery. What I want is when my battery is fully charged that is it reaches to 54v the battery charging stops and the supply which is coming from the solar panels is directed to another port from which we can charge any other device connected to the port. This charging should only continue till the battery is above 48v. Once it reaches 48v the battery again starts charging on solar panels and the supply to the other port is stopped.
Hoping you will reply soon.
My Response to the above Circuit Request
You can try the last circuit from the following artcilehttps://www.homemade-circuits.
Regards
hello Sir, I want a 48 volt LIFEPO 4 Battery charger with over charge cut off, can you provide me the circuit diagram, (if possible a fast charging recommendation I need) then I shall be grateful to you, thank you
Hi Bibhuti,
You can try the last circuit from the above article. The input charging current will determine how fast the battery can be charged. Make sure not to exceed it above 75% of the battery Ah value. The resistor Rx value can be set appropriately to adjust the maximum current to the battery.
Thank you Sir, for your quick response on my request,
Yu are welcome Bibhuti!
Hai sir i am sreenivas d, i have small doughs sir 300w inverter 12v dc to 220v ac, incase same inverter ckt, we can reduce turns primary side 12v to 75v what happened sir pls explain to me. can increase. will increase current primary.
Hi Sreenivasulu, It will change the output voltage range of the transformer. You can use the following formula to calculate it:
Vsec / Vprim = Tsec / Tprim.
In this equation, Vsec represents the secondary voltage, Vprim denotes the primary voltage, Tsec is the number of secondary turns, and Tprim represents the number of primary turns.
WILL THESE CKT ASLO WORK AS REVERSE BATTERYPROTECTION FOR P-CHANNEL MOSFET SIMPLIFIED CIRCUIT
For reverse battery protection you can add a diode in series with the drain of the MOSFET
Hello sir, thank you for the very nice circuits and all your follow up help. My question is that I want to build a charging circuit for my 12v (3S1P) lithium ion cell pack. It should have the over charge cut off as in your circuits but also an over discharge cut off for when using the pack. Your insight is appreciated.
And also what can you recommend about cell balancing as I’ve heard it can be important in such battery packs.
Thank you so much Neddan, I can provide you with an auto cut-off and auto restore charger circuit but it won’t have a cell balancing facility in it. I do not have a cell balancing circuit with me yet.
You can try the last circuit or the second last circuit from this article:
https://www.homemade-circuits.com/opamp-low-high-battery-charger/
Thank you very much, I will try out the circuit as for now I only need to use and charge.. balancing can come later on as I improve the circuit.
Sure, no problem. All the best to you.
so i have been doing this project and i wanted to ask is there any other replacement for the ic741
Which op amp is available in your area? You can use that op amp.
OPA548T is what i have available the rest are not rated for 48v
48V op amp is not required, you can use any 12V op amp. The 48V supply is appropriately reduced to 12V by the various resistor networks in the circuit.
I am also a 2nd year electronics student do and the drone is for my project i have the made a schematic system and I just need to add the charger system to it
Sure, you can use the last or the second last circuit from the above article for your application.
I have hybrid drone system and now I am trying to charge the batteries whiles in flight and I wanted to know if this automatic 48v battery charger and cutoff schematic is applicable because it is similar to what I need.
If your battery is a 48V battery then definitely this circuit can be used for your purpose.
I would recommend you this circuit:
https://www.homemade-circuits.com/wp-content/uploads/2022/09/simpel-48-V-batery-charger-circuit.jpg
thank you very much
Hi my name is Ricky I have a blicks electric bike blix and it’s a 48 volt it’s a l i o n battery and I want to make a homemade battery charger for it but I am not electrician not even close to one so can you possibly give me how I would make one out of power cords already
You will need an electronic circuit to build the charger, as explained in the above article. Without proper knowledge it can be difficult for you to proceed.
Hello dear Swagatam,
thank you so much for all the informations. i need a autoturnoff circuit for a 48v Battery that will be connected to a wind turbine ,wich circuits do you recommend me to use ?
i also have a second question if you have an idea : since i want to build a little wind turbine and the output voltage will be variating (depend on rpm ) how can i connect that to a 48v battery ? or in another way : how to keep the output voltage 48v so that the battery can be charged .
thank you verry much for your answers .
best regards
Youness
Hello Youness,
You can try the following circuit for charging your 48 V battery from a wind turbine.
To setup the circuit, feed the AC from the windmill through a 20 amp bridge rectifier across Vin/0V of the circuit, and check the voltage across the output terminals. Adjust the 10K preset until the output stabilizes to 56 V.
In the diagram the Vin wrongly shows 56 V, actually it be can any value up to 100V
https://www.homemade-circuits.com/wp-content/uploads/2022/12/windmill-shunt-regulator-circuit.jpg
The TIP36 will withstand a maximum of 10 amps when attached with a large heatsink.
Thank you sir for your support .
i have a question . since the vertical wind turbine will not provide a stable output voltage depending on wind(for exmple between 10v and 60v ) and the Battery is a 48v Battery . will it work with this circuit that you gave me ?
thank you so much sir for your help
Youness
Hi Youness,
This type of circuit is called shunt regulator. This will keep the supply voltage at 56 V as long as the wind turbine supply is above 56 V…but if it drops below 56 V then the circuit cannot boost it up.
Hallo dear swagatam i appreciate too much. My name is Léon makinde.i’m extremely happy to hear for you.i would need your help please. Im working on a 48volt battery charger.i tested all the components they seem to be good.but the drivers input voltage is zero. Please assist me my email address is :makinde.leon@yahoo.com
Thank you Leon,
Which schematic did you use for your 48 V charger? And please elaborate a little more on “drivers input voltage is zero!
Hello Mr Swagatam,
For circuit 2 current controlled circuit. How can i control the current? As i know, i only can control the voltage from the 10k potentiometer.
Thank you,
Wan
Hello Wan,
The 2nd current controlled circuit is not a tested design so i cannot suggest about the current control feature. I would recommend you to include the current control feature at the input side, with the power supply itself.
Hello Mr Swagatam,
As i tested the current controlled circuit, it is not maintain as constant current Which is 3A as i need. I did use power supply use 3A input it gives a constant current.
The 1st circuit that i test is only for constant voltage. As we know for a battery charger it should be constant current then followed by constant voltage. What’s your comment about this?
Hello Mr.Wan,
Current will depend on the battery consumption and will keep changing as the battery reaches its full charge level.
If you have a constant 3 amp charger then there’s nothing to worry about.
If you are still worried you can use an external current controller between the charger and the power supply. You can use one of the current controller circuits explained in the following article:
2 Best Current Limiter Circuits Explained
We use AC source and convert it using rectifier. Is it possible for me to combine using mosfet cut off charger circuit and mosfet for high current applications? I use the right Rx= 0.6/3 = 0.2Ohm but the current is not constant or maintain. I have tried use the 1st circuit, the characteristics shows for output current is decreasing. Not as we know for their constant current at first then change to constant voltage.
Current will depend on the battery consumption and will keep varying as the battery charges. The constant current can only ensure that the current does not increase above the set limit.
For example if the set limit of the current control circuit is 3 amps then it will ensure the current never inceases beyond 3 amps to the battery. But the current can be lower if the battery consumes lower current, which solely depends on the battery.
Output current surely decrease as the battery reaches full charge level and finally the current will become zero.
Voltage will be constant after the battery is fully charged only if you use a constant voltage regulator power supply.
You can try the following concept for a constant current with auto cut off:
https://www.homemade-circuits.com/wp-content/uploads/2023/01/48V-current-controlled-battery-charger-circuit-with-auto-cut-off.jpg
As I know, after the constant current characteristics, the output current will decrease after the threshold voltage is achieved. Then the battery will charge with a constant voltage. Finally the current will become zero. So by using the concept that you suggest, is it still can be charged with constant current and constant voltage mode with auto cut off system? thank you for your help.
That is correct but that is decided by the battery not by the power supply. The power supply can only limit (restrict) the max voltage and max current to a certain fixed level as determined by the regulator circuit. For example a 12V constant voltage will limit the output volt to 12V and a 5 amp constant current power supply will limit the current to 5 amps. The amount of current and voltage to consumed is solely decided by the battery while charging. The power supply can only ensure that the battery does not pull anything beyond a certain fixed limit so that it remains safe from over voltage or over current..
The circuit suggested by me will restrict the output voltage to a fixed max level as set by the 10K preset and will not allow the voltage to the battery above this limit. Similarly the maximum current will be set by the RX resistor, which will never exceed beyond that limit.
I have tried this circuit, this question is how to set the cut off? I am using the variable resistor to set but doesn’t show any changes. I connected the input and battery, the Led does not light up. I use Rx= 0.2Ohm since i want 3A current. If I connect it, is it charge? The input voltage is set at 56V there is no current flow. Thank you fo your help Mr Swagatam.
Hello Wan,
The setting up procedure for the following circuit is as given below:
https://www.homemade-circuits.com/wp-content/uploads/2023/01/48V-current-controlled-battery-charger-circuit-with-auto-cut-off.jpg
1) Keep the wiper of the 10K preset towards ground.
2) Feed 56 V from the BATTERY SIDE, remember from the battrety side, not from the transistor side….but do not connect any battery during this testing period.
3) You will find the LED glowing brightly.
4) Now, slowly adjust the 10K preset until the LED just shuts off.
5) That’s all the setup is complete.
6) Now, remove the power supply and connect a discharged battery.
7) You will find the red LED illuminating.
8) Now connect the 56V from the transistor side for initiating the charging process.
9) Once the battery is charged to 56V the red LED will shut off indicating that the battery is fully charged.
Hello Mr Swagatam
I have followed all the procedures one by one that you have mentioned but I failed to charge the battery.
Firstly, I have connected 56V supply from the battery side to vary the cut-off voltage. But the LED does not light up and no current flows. As you could see the first circuit you used 4.7V zener diode at pin 6 while this circuit is connected to the led directly. Both transistor used at current constant side is TIP36 right? Instead of using 12V zener diode, may i use 15V zener diode? Why do we feed the input reversely with the first circuit? Is this the way to get the constant current at first and then constant voltage?
Thank you Mr Swagatam for your help. I really appreciate it.
Hello Wan,
The following circuit is a simple op amp comparator circuit and should work 100% without fail, and setting up is also simple.
https://www.homemade-circuits.com/wp-content/uploads/2023/01/48V-current-controlled-battery-charger-circuit-with-auto-cut-off.jpg
If the red is not lighting up in your circuit while adjusting the preset then definitely something’s wrong with the op amp or the connections.
I think your 15V zener might be causing the problem….please try with a 4.7V zener or 6V zener and check the response.
The main PNP transistor on right side can be TIP36 but the current controller PNP transistor can be any small PNP transistor but 100 V rated, such as BD140.
We feed the voltage from the reverse because we want to adjust the preset at 56V. If we feed the voltage from the transistor side then the TIP36 will create problems and not allow correct setting up.
Constant voltage is decided by the automatic 56V op amp cut off which means the voltage can never go beyond 56V, and this is constant voltage.
Constant current is determined by the two PNP transistors and the RX resistor which will never allow the current to go beyond the set value depending on the Rx value..
Hi Mr Swagatam,
Thank you for the previous response.
I have troubleshoot the circuit looks like my IC741 is burned so i have changed it. I have varied the trimmer pot to the certain voltage to be cut off.
Then I connect the Battery to the battery input side, next i connect the power supply to the power supply side then the TIP36 on the left side is on fire/burned. Do you know why this happen?
Is both transistor you used is the same concept with darlington pair?
Hi Wan,
TIP36’s voltage rating is 100V and current is 25 amps so it should not burn at 56V 3 amps or 5 amps.
The two transistors are not connected in Darlington mode, they are in current limiter mode.
How much value did you select for RX?
Did you connect the transistor pins correctly?
If you are having problems with transistors then you should use a relay instead. But relay will require an external 12V source to operate.
Try with the following circuit first:
https://www.homemade-circuits.com/wp-content/uploads/2022/09/simpel-48-V-batery-charger-circuit.jpg
If you succeed then try the other one with current limit.
Hi Wan, also please replace BC546 with BD139 because BC546 can handle only upto 65 V which is very near 56V….we want a higher margin of at least 20 V, so please if possible replace BC546 with BD139
Thank you Mr Swagatam for you reply.
I use Rx 0.2 since I need 3A.
Yes, the transistor pin is connected correctly.
There is a voltage difference before I vary the trimmer pot. After I vary there is no voltage difference.
Why did you use 4.7V and 12V zener diode as reference?
The circuit should be charging the battery without any problem with those suggested components right?
Thank you for your suggestion on the Transistor BC546 used.
Hi Wan,
The 10K preset uses the 4.7V as a reference and cuts off the output as soon as the preset wiper voltage exceeds 4.7V, corresponding to battery 56 V.
If you use 5.6V or 6V or 9V zener then the 10K preset will need to be adjusted accordingly so that it feeds the adjusted battery voltage to the opamp pin#2 which compares it with the reference voltage and cuts off the output at the corresponding 56V.
In this way the op amp uses the preset adjustment to compare with the reference level so that when the battery voltage reaches 56V, it cuts off the output.
Basically when the pin#2 of the op amp increases above the 4.7V reference then the output cuts off. This is adjusted by the 10K preset to happen at a level that corresponds to 56V for the battery.
The maximum range of the 10K preset is between 3V and 17V. So the reference zener voltage must be between these ranges.
The 12V zener is for providing 12V regulated DC supply for the op amp which is a reasonable value for the op amp Vcc
Thank you Mr Swagatam for your explanation.
The circuit should work perfectly right?
Where did you get the 0.6 Reference voltage? For example if we use LM317 the voltage reference is 1.26V so to get the current 1.26V/Current.
I check my Rx is burned so i have change a new one then the circuit is charging the battery.
I want to use Rx=0.2 since i want 3A current. The charging current measured should be 3A after connected to the battery then when it reached the threshold voltage it will decrease.
The temperature at TIP36 increase to 80degree celcius with current 0.8A only and both keep increasing. Is that noral for TIP36?
Hi Wan,
The 0.6 is the optimal base/emitter switch ON voltage level of any BJT. The current limiting transistor associated with TIP36 will switch ON when the current exceeds 3 amp and creates a voltage drop of 0.6V across Rx.
The power of Rx will be
Power = 0.6 x 3 = 1.8 watts, so you can use a 2 watt or 5 watt resistor for Rx.
You must use a large heatsink for TIP36.
And preferably in place of BC546, please use BD139
Hi Mr Swagatam,
I need 3A current, hence 0.6/3=0.2 ohm. I have tested with 0.2ohm, and after an hour it gives me 0.723A constant current. The current increase slowly after 15 mins it started to constant at 0.723A. After 2 hours current start to drop 0.717A but the battery capacity is not at full yet and not achieve it threshold voltage to turn into constant voltage.
I have changed to a bigger heatsink the temperature of TIP36 is maintained around 59 degrees Celcius.
Soon as I receive BD139, I’ll change with BC546.
Thanks for the update Wan,
As I explained you before 3 amp constant current means the current cannot increase above 3 amp. 3 amp is the maximum limit set by the charger circuit.
But now it depends on the battery how much it wants to consume.
3 amp limit does NOT mean the battery will consume 3 amps, NO.
Battery can consume 500 mA, 1 amp, 2 amp, 2.5 amps or anything below 3 amp…. this will depend on the battery.
Battery will reach full charge when 56V is reached and then the op amp will cut off…LED will shut off.
Yes, Mr. Swagatam. So I need to use a smaller resistor to achieve a higher current?
I have tried Rx 1Ohm, thus I got 0.519A. The higher resistance I used, the smaller the charging current.
Do you have any idea how to produce a 3A charging current other than using smaller resistance?
Hi Wan, yes use smaller resistance to achieve higher current and vice versa.
the method shown in the diagram is the only correct way to restrict current.
This current value should be 1/10th of the Ah rating of the battery, if the battery is a lead acid battery.
Hi Mr Swagatam,
What is the use of 10k between TIP36 and BC546. As I changed it to a lower resistor the current increased.
Hi Wan,
the 10K decides and base current for the TIP36 and it also decides how much current the TIP36 can deliver to the battery.
This 10K looks too big actually.
You can reduce it to 470 ohms or 100 ohms and check the results.
I think there is no current flow on the TIP36 for the input side since no heat on the heatsink. The temperature on it is maintained 22 degree celcius. While the other TIP36 that connect to BC546 increase in temperature to 80 degree celcius.
You can decrease the TIP36 base resistor to 470 ohms and check the results.
Hi Mr Swagatam,
I have reduced the resistor for base current TIP36 all looking good.
However, I changed BJT to MOSFET(IRF9530) and it produces better current measurement. Are there any difference of using BJT and MOSFET as i know both can control current and MOSFET for high performance.
By using MOSFET the temperature of it also high so i need to add a fan for better heat dissipation. Do you have any idea to reduce the temperature, what FET should use.
Hi Wan,
MOSFET gates cannot tolerate voltages above 20V, so if you are using a mosfet then make sure to connect a zener diode across its gate and source pin.
The zener diode can be a 12V zener diode with cathode going to the source pin and anode to gate pin.
Also replace the gate resistor with a 10K resistor otherwise the zener will burn.
IRF9530 is a good mosfet, but i think it might be already burned due to the absence of the zener diode.
Hi Mr Swagatam.
TIP36C is good in testing with the temperature of 80-degree celsius at current 2.96A.
However the current keep decreasing and is not constant.
As I know this circuit is only for limiting the current below the maximum charging current that we need.
Do you know how to make it a constant current and constant voltage?
Hi Wan,
I think you are not understanding the working concept.
Constant current means the battery cannot consume current beyond a certain limit. For example if a constant current 5 amp is selected then the battery cannot pull beyond this 5 amp current limit.
But if the battery consumes 4 amps or 3 amp then it can do, we cannot force it to consume 5 amps.
Initially the battery current consumption will be high, but as the battery charges its consumption will keep decreasing until it becomes zero.
For voltage it is the opposite.
Initially the voltage will drop to the battery level, then as the battery charges the voltage will keep increasing until the battery is fully charged.
Is constant current means the current charging remain constant continously until the constant voltage mode is achieved? It also limit from the overcurrent. The best charging method for LI Ion batttery is constant current and constant voltage mode. Firstly the battery is charge with constant current mode continously until almost full it turns to constant voltage mode gradually decrease to provide safety for the battery.
Constant current means current limiting, that’s all. It is the battery which decides how much current it can draw below the current limit.
In constant voltage the battery cannot charge after the full charge level or at the voltage which has been fixed by the power supply, that is why it becomes constant voltage after the full charge level.
For example if the fixed voltage level is 14V, then when the battery voltage reaches 14V it cannot charge anymore so the voltage becomes constant.
Constant voltage and constant current are maximum limits which the power supply allots the battery. Beyond these limits the battery cannot draw the current and voltage.
Constant current constant voltage does not mean that the power will keep varying and FORCING the current and voltage to the battery….never.
It is the battery (load) that decides how much current and voltage it needs to take below the specified limits.
I hope you have understood now.
Thank you for your explanation Mr Swagatam. I get what you said now. Hence the power supply itself we need to control to the maximum limits which allow to the battery.
I need to create the charger for a 48V,8Ah battery. This circuit is the best for the charging circuit as you suggest?
You are welcome Wan, I am glad yu have understood the concept now.
Yes, the suggested circuit is the easiest, safest and the best for charging your battery.
https://www.homemade-circuits.com/wp-content/uploads/2023/01/48V-current-controlled-battery-charger-circuit-with-auto-cut-off.jpg
If your 8 Ah battery is a lead acid battery then make sure to limit the current to 1 amp and set the full charge cut off voltage at 56 V.
For lithium-ion battery the charging current can be around 4 amps
If you don’t want to use the current limiting transistor stage, in that case you can use a power supply which is rated at 1 amp for lead acid, and 4 amps for lithium-ion..
My battery is Lithium-ion. I would like to use the current limiting transistor. Currently, I’m still finding for a suitable resistor for the 3 Amps current limit. When i calculate 0.6/3= 0.2ohm and the current gives only 1.8A with the 0% battery at 44volt. I use 10W resistor for better performance and heat transfer.
May i know your test on this circuit how much current you limit ,does the current limit as you want constant below the limit current, the Rx resistor that you use and does it works for long term.
Thank you very much Mr Swagatam for your help.
Hello Wan,
I did not use a current limiting stage in my circuit instead I used a transformer rated at the specified amount of current. I needed 1 amps, so I used 1 amp transformer for the power supply.
However, a transistor circuit may not be too accurate with its output, so you can try reducing the 0.2 ohm to 0.1 ohm and check whether it delivers a higher current or not.
Also make sure that your input power supply is rated at 3 amp or slightly above 3 amps.
If Rx is a wire wound type resistor then it will work permanently.
The supply I used is AC supply and convert to DC using a bridge rectifier and connect to the circuit that you suggest. Thus, i can’t get the specific Amps for it.
Do you have any suggestions for it?
I highly appreciate your suggestions and explanations.
How did you drop the AC supply voltage to 56V? I strongly recommend using a transformer. You can use a 48V/3amp transformer or a 24-0-0-24V 3 amp transformer and rectify it using a single diode and filter the DC with a 1000uF/100V capacitor. With a 3 amp transformer you won’t require a current limit.
Actually for a 48V lead acid battery the max charging voltage will be 56V, but for Lithium-ion it will be slightly different but will be critical.
I have tested one of the chargers in the market. The voltage increase from 44V(0%) to 55V(100%). The current remains constant at 2.85A at 44V until 54V and starts to decrease after 54V gradually until 55V when the battery has full.
Do you know why the current is constant?
Maybe 2.85 Amp is the maximum current the battery is consuming and the charger is able to supply this much current to the battery. In our previous circuit the transistor is not able to supply 3 amps, maybe due to high base resistor base. You can reduce the base resistor and try again.
…or you can replace TIP36 with TIP147 which is a Darlington transistor with high gain and high current output.
The TIP36C i used is 25A Ic. TIP147 is 10A Ic. I have searched in the online store TIP36C is the highest Collector current.
I used a AC-DC 230Vac-48Vdc supply with 2.08A. The current is not achieve at the maximum rated current and not maintain when charging the battery. I have tested 3 Batteries. Trial and error the resistor at base and Rx. The suitable base resistor to use is around 2-2.5kohm.
Since your maximum current requirement is below 3 amp so 10 amp transistor is quite sufficient, no need of a 25 amp transistor.
I am suggesting TIP147 because it is a Darlington transistor and will be able to transfer current with maximum efficiency.
Also, since your input current is limited to 2.08 amps then no need of the current limiting transistor stage. You can remove it and use 1K resistor for the base resistor of TIP36
Thank you for your suggestion on using TIP147. I will try to do it as well.
I have removed the current limiting stage. My supply is fixed at 48V and 2.08A. I connect with 3k for base resistor TIP36. The initial current measured is 2.23A. The current is decreasing to 1.98 after 15 minutes of charging. The battery I used is Lithium Ion 48V 10Ah.
According to the formula of the transistor base resistor:
Base resistor = (supply voltage – 0.7)hFE / Current
= (56 – 0.7)15 / 3
= 276 ohms
So the base resistor must be rated at around 276 ohms, wattage can be around 2 watts to 5 watts.
For 48V battery the charging supply must be around 55V to 56V.
If you use a TIP147 then the base resistor can be anywhere between 1K and 10K due to the high hFE of the transistor.
Hi Mr Swagatam,
I have used TIP147 as you suggested. I change the base resistor to 1k and the current reading is 2.35A. If I reduce the smaller resistor the current will increase. However, the current is not constant. I have used the supply 56V 2.08A.
https://www.homemade-circuits.com/universal-high-watt-led-current-limiter/
From the above, I can see the graph voltage vs current where the current is constant until the cut off then it gradually decreases.
I have tried using LM317 it is constant but only at a low current.
Hi Wan,
For TIP147, the base resistor should not be decreaesd below 1K, it will not help because 1K is enough to turn ON the transistors with high gain.
As I mentioned before, current consumption will depend on your power supply and the battery consumption, the transistor TIP147 or TIP36 are just a kind of ON/OFF switches, they can only supply the full available current to the battery and then it will depend on battery how much it wants to consume. When the battery is discharged it will consume high current, as it gets charged, the consumption will decrease.
LM317 is also a current limiter only, and will restrict the current to a certain limit depending on the resistor value.
Hello Mr Swagatam,
I would like to create a 48V with 10 Amp battery charger circuit. Is circuit number 1 is suitable for it? I notice that I need to change the mosfet that suit with 48V,10A. What about other components?
Thank you,
Wan
Hello Wan,
The first circuit is fine, but the last circuit is the best one. You can try the last design. You can replace the TIP36 with MJ11033 transistor, and also replace the 22K at pin#3 of the opamp with 10K 1/4 watt.
The transistor datasheet can be seen in the following article:
https://www.homemade-circuits.com/50-amp-transistor-mj11032-mj11033-datasheet-pinout/
Hello Mr Swgatham,
I am planning to use the last CKT which you have posted in this page. My application is for charging the 48V 36AH lithium ion battery pack. Following is my Question.
Is this CKT already tested with actual load? I meant charging the actual battery pack and testing the over charge cut off and under charge switching ? Just to know if there are any observations that to be taken care.
Vijay
Hello Vijay,
The first, third and the last circuits are tested, rest are not tested but I am sure all will work. However, you can build, test and troubleshoot these circuits successfully only if you understand the working and the setting up procedures perfectly.
I would recommend you building the last circuit with an auto cut off feature, however it does not have an auto recharging feature and will not restart automatically once the battery has reached a low state. Nevertheless, this feature can be easily added through a simple feedback network.
Hi Swagatham,
Thanks for the confirmation. I will consider your recommendation. But I am just thinking that, when there is Battery management system integrated with the battery pack, does the battery charger also needs the cut off feature? As BMS normally protects the battery in all aspects, whether this extra protection is required? anyways the protection circuit using opamp is not expensive to build….
Vijay
Hi Vijay,
A battery management does not need an auto cut off because a BMS will have all these features included in it. Yes it is normally designed to protect the battery from all the unsafe aspects of charging.
Hi Swagatham,
Thanks for your feedback.!
Vijay
You are welcome Vijay!