In this post I have explained a 48V solar battery charger circuit with high, low cut-off feature. The thresholds are adjustable through individual presets. The idea was requested by Mr. Deepak.
Technical Specifications
Hi Swagatam,
Thank you for UPS relay circuit.
I am trying to build it very soon. I will update you the result once i am done with that.
Next, i am very keen to build a Solar charge controller circuit for following requirement.
1. Battery shall be of 48 V (lead acid or maintenance free) with capacity go up to 48V X 600 AH.
2. Load to battery may be up to 1500 W (30 Amp at 48V)
3. Solar PV cell in series/parallel configuration producing voltage up to 60V and 40 Amps
The controller circuit is expected to perform as follows.
1. Cut off solar supply to battery when its voltage reaches approx 56V and maintain appropriate hysteresis to avoid frequent switching of power MOSFET. So the solar supply to battery would resume again only when the battery voltage reaches approx 48 V.
2. Low voltage disconnect of load from batter supply when battery reaches around 45 V and maintain appropriate hysteresis to avoid frequent power ON/OFF of load.
I will be grateful if you could help me building this circuit.
Thanking you.
Best regards,
Deepak
Circuit Operation
The proposed 48V solar battery charger circuit with high/low cut off feature can be witnessed in the following diagram.
The functioning of the circuit may be understood with the following points:
The IC 741 is configured as a comparator and is appropriately stabilized from the high 48V input using zener diodes and potential divider networks across its supply and input pins.
As requested, the input voltage which may be in excess of 50v is acquired from a solar panel and applied to the circuit.
The 10k preset is adjusted such that the power mosfet cuts off when the connected battery reaches the full charge level.
The 22k preset is the hysteresis control for the circuit and also serves as the lower threshold adjustment preset.
It should adjusted such the the MOSFET just initiates and switches ON at the preferred low battery voltage threshold.
Once the discussed set up is implemented and power switched ON, the discharge level of the battery drags the supply to around 48V forcing pin2 of the IC to go below pin3 potential.
This prompts the IC output pin6 to go high initiating the MOSFET connected in series with the ground rail so that the battery becomes integrated with the solar panel supply.
The above also switches ON the BJT BC546 which in turn makes sure that the associated MOSFET and the load remains switched OFF.
As soon as the battery attains the full charge level, pin2 is pulled higher than pin3 rendering the output to a logic low.
This instantly switches OFF the ground rail MOSFET and the BJT enforcing two things: cutting off supply to the battery and switching ON the load MOSFET such that the load now gets access to the supply voltages from the panel as well as the battery.
The feedback hysteresis network formed by the 22k preset and the series 10k resistors ensures that the above action locks ON until the battery voltage reaches below the predetermined lower threshold.
Circuit Diagram
Diagram
Feedback from Mr. Deepak
Hi Swagatam,
Thanks for Solar charge controller circuit.
The circuit appears to be little different than what i had requested. Let me reiterate the requirement again.
1. Solar panel should continue charging battery not beyond 56 V.
2. In the event of battery discharge, the charging process should resume again only when it reaches 48V. In other words hysteresis should be maintained.
3. Battery should continue supplying power to load when battery voltage remains in between 42 - 56V.
When battery voltage reaches 42V (due to battery discharge) the load should be disconnected from battery supply.
Once the load is disconnected, it should remain disconnected till the battery voltage reaches minimum 48 V during charging process.
Please confirm if the circuit works as above.
Implementing Window Comparator
The above 48V solar battery charger circuit with high, low cut-off may be modified with these specifications by introducing a window comparator stage, as shown at the extreme left of the circuit below.
Here the opamps are replaced by three op amps from the IC LM324.
The window comparator is made by two of the 4 opamps inside the LM324.
A1 preset is set such that its output becomes high at the lower threshold level of 42V.
The 100k preset is for adjusting the hysteresis level so that the situation gets latched until 48V is reached.
Similarly A2 preset is set to make the relevant output go high at the higher threshold of 56V.
At voltages between these "windows", the BC546 remains shut off allowing the associated mosfet to conduct and feed the load with the required supply from the battery.
Once the thresholds are crossed, the BC546 is forced to conduct by the relevant opamp shutting down the mosfet and the load.
The A3 stage could also be replaced with an identical window comparator as discussed above for controlling the charging of the battery by setting up the presets appropriately, this would allow using all the four opamps from the IC LM324 and also make the operations much accurate and sophisticated.
Adding a Buzzer Indicator Stage
Another version of a 48V automatic battery charger cricuit using a buzzer indicator can be studied below:
The idea was requested by Nadia, please refer to the discussion between Nadia and me in the comment section for more info regarding the design
The transistor are incorrectly shown as BC547, which must be replaced with BC546 for preventing circuit malfunction and damage
How to Set up the above 48V Battery charger circuit with buzzer
Do not connect the charging voltage from the right side.
Keep the 10k preset slider arm towards ground initially.
Connect a DC input using a DC variable power supply from the Battery side on the LEFT of the circuit.
Adjust this voltage to the required potential at which the buzzer needs to get activated....as per the request it should be at around 46V
Now adjust the lower 10k preset very slowly and carefully until the buzzer just activates and starts buzzing.
Seal this preset with glue.
Now increase the input voltage to the desired high cut off level.... which is 48V as per the request here.
Next, adjust the upper 10k preset very slowly and carefully until the relay just clicks. When this happens the buzzer should shut off.
The 48V solar battery charger circuit with high, low cut-off is now set, however the value of the 100k resistor which can be seen connected between the input/output pins of the upper opamp actually decides at what lower threshold the relay must deactivate again, and switch ON the buzzer.
It's been arbitrarily fixed, you may have to adjust the 100k value so that the relay toggles only at around 46V...it may be confirmed with some trial and error
48V automatic solar battery charger using relay
The operations involved with the first diagram above gets much simplified if a relay stage used instead of BJTs, and mosfets.
As can be seen in the above updated diagram, the relay stage is in the form of two 24V relays in series, wherein the coils are joined in series while the contacts are joined in parallel.
The sensing circuit is applied with a proportionately scaled down voltage through an emitter follower voltage divider circuit using the indicated BC546 stage for the intended battery level detection and cut-offs
The following diagram shows an extremely simple 48 V solar charger system which allows the load to access the solar panel power during day time when there's optimal sunshine, and features an automatic switch over to battery mode during night when the solar voltage is unavailable:
The emitter follower TIP142 ensures that the battery is never allowed to get overcharged above 55V.
Questions & Answers
Thanks for your reply regarding R1, can u mention the resistance power( 1W or !/2 W)
R1 Wattage = (55 – 48) * Max charging current limit
What is the value of R1 resistance?
R1 in the last circuit is approximately:
R1 = 55 – 48 / Max charging current limit
hi.
I would like to know if you can adapt the first design to accommodate a 36v battery bank. with high cutoff at 41vdc and charge at 36vdc the same 50vdc to 55vdc solar input
Hey, I would rather recommend you to try the LAST circuit from the following article. This will allow you to charge your 36V battery perfectly from solar panel:
https://www.homemade-circuits.com/make-this-48v-automatic-battery-charger/
Thank you. i will give it a test as soon as the part arrive
Sure, no problem, let me know if you have any issues with the circuit…
I have made a 72v dc transformer which I want to fully make automatic to charge my 72v motorcycle battery from home using 240v ac.
Secondly I’m also connecting 3 24v solar panels each with open circuit voltage of 44.44v in series to also charge in the rural areas of my travels. In both cases I need an automatic cutoff once the battery is fully charged.
You can try the last circuit from the following article:
https://www.homemade-circuits.com/make-this-48v-automatic-battery-charger/
Let me know if you have any further questions…
Sir Naveen again! Sir Now I have a 1.2v battery with 1100mAh is it ok now sir, and I have replaced 3v zener with 1N4148 diode, should I have make any further changes sir! also how long it will take to charge sir ?
thanking you!
Naveen, I just forgot that 1.2V or 1.5V cannot be used to operate the op-amp, so it won’t work.
Instead you can try the following concepts for your battery:
https://www.homemade-circuits.com/simple-ni-cd-battery-charger-circuit/
Sir can i Give a 1.5v rechargable battery in the place of 3.7v, so that it charges faster?
With reference to the following circuit, you can use a 1.5V cell, but then make sure to replace the 3V zener diode with a 1N4148 diode, cathode being towards the ground side.:
Sir Naveen Again! Sir my solar panel has 0.48A as output current is it ok to charge a 2000mAh 3.7v battery and sir if I want to demonstrate the circuit how do I do it by charging and discharging the battery like what load can i use and how? thanking you sir
Hi Naveen, you can use 0.48A to charge a 2000mAh Li-ion battery but it might take 4 to 5 hours to charge it fully…
You can connect a volt meter across the battery to check its voltage, once it reaches 4.1V then you can assume it to be fully charged.
You can connect a 1 watt LED across it to discharge it.
Make sure to use a heatsink for the LED and connect a 3 ohm 1 watt resistor in series with the LED..
Naveen again sir! Thankyou swagatam sir really thankyou! I will notify you once I finish the circuit
No problem Naveen,
For the following circuit, you must set it up in the following manner:
1) Do not connect any battery initially.
2) Keep the 10k preset wiper towards fully ground.
3) Connect a precise 4.1V DC input from the Battery points of the circuit.
4) You will find the LED lighting up.
5) Now, slowly adjust the 10k preset until the LED just shuts off.
That’s all….you circuit is all set…
Sir Naveen Again! 18v solar panel seems to be too much expensive instead can i use 3.7v battery with 2000mah Li-ion cell. and I have 6v solar panel in hands! can i contact you personally Sir?. Thanking you
Thanks Naveen,
For charging a 3.7V 2000 mAh cell, the 6V panel must be rated at at least 1 amp current, then you can use the following circuit:
I think discussing through comments is good because it helps other users also to learn from our discussions…
Hello Sir!
in this circuit What modifications I have to make if I use 12v battery and 6v solar panel and please update me with a modified circuit kindly. I request you to please explain me about the Procedure to connect and working it would be grateful If I am being helped thanking You sir!
Hello Naveen,
A 6V solar panel cannot be used directly to charge a 12V battery, so please change the solar panel to 18V solar panel, and then I will tell you how to modify the previous circuit…
Hello I Have Choosed THis as an mini project in my college. PLease tell me which ciruitit works and help me in what to do!
All the above circuits will work if built correctly, however the following one is the easiest one to build and implement:
Just make sure to reduce the resistor between the collector of the BC546 and the base of TIP36 appropriately in accordance with the current requirement of the battery.
Hi Swagatam, thank you for the above. Is the above also compatible with Lithium battery packs? Can you suggest what changes to be made to the above for 60 V and 72 V battery packs (Lead Acid and Lithium)?
Hi Rajan,
Yes the above designs can be used for charging Li-ion battery after appropriate settings, however i would recommend you the LAST circuit from the following article:
https://www.homemade-circuits.com/make-this-48v-automatic-battery-charger/
This circuit is easy to configure and very safe for charging all types of batteries.
Thank you for the reply. I will check it out. Just wanted to know what modifications to be made to charge 60 and 72 v battery packs?
You can use the same design which was suggested by me in the previous comment, with the following modifications:
Replace BC546 with TIP122
Adjust the TIP36 base resistor and Rx current limiting resistor as per the required charging rate for your battery.
Just curious to know, in your introduction you say you area manufacturer. So do you manufacture PCBs? If yes, I would like to discuss some business opportunities with you. If no, can you share info about some PCB manufacturer who can print boards in a small quantities?
No, I don’t manufacture PCBs, I had the contact numbers of a few PCB manufacturer in Mumbai long back about 10 years ago, but I seem to have lost them, and don’t have them now.
Nevertheless you can easily search online and you should be able to find plenty of PCB manufacturers who will do the job for you.
Sir I have brought Some of its Component, I have put 12v Battery instead of 48 and 6v solar ponal instead of 56v and please tell what are the modifications that i have to make in order to make the circuit working properly and as a kind request can i Contact you personaly !
Thanks, I found one.
Very many thanks, I will try it out.
Thank you, Sir. If I want to build it with a 20V solar panel and a 12V battery, what should I change in the circuit?
Hi Aulia, you can try the last circuit, with the following modifications:
Remove R1, replace the zener with a 15V zener.
Hi Mr.Swagatam, If I want to create a cut-off system for a 12V lead-acid battery with a PV output voltage of 13-20V, which circuit should I use?
Hi Aulia, I would suggest you to try the LAST circuit from the following article.
https://www.homemade-circuits.com/opamp-low-high-battery-charger/
Thank you, Sir. Is the 54V zener diode replaced with a lower voltage zener diode?
No problem Aulia,
That’s correct, you will have to replace the 56V zener diode with a 15V zener for your 12V battery. Also, the 4k7 or the 4.7K resistor does not need to be a 5 watt resistor, it can be a 1/4 watt resistor.
Oke Thank you Mr. Swagatam
No problem Aulia!
thank you very much for your help and see you next schematic
thank you for answering me.if I use a battery 12 volts will be the same
For a 12V battery the circuit can be exactly as shown in the previous link. However, the 270R must be replaced with a 1N4007 diode.
this schematic what part changes for solar panel 50volt
makingcircuits.com/wp-content/uploads/2017/04/SolarBatteryCharger.gif
Use transistor BD139, relay = 48V relay, battery = 48V, replace 270R with a 1N4007 diode.
Hi,
I want a 48 volt battery low voltage alarm circuit which output operate a 12 voltage relay when battery gets below 42 voltage.
Can you suggest me a circuit diagram like this comparator circuit.
Hi,
you can try the following design:
That’s great Sanjaya, glad it is working good.
The maximum input DC to a 48V battery should not be more than 58 V. So you can adjust the solar panel output to 58V DC.
Hello sir swagatam,help me out with a circuit that has both trickle charger and a float charge for charging 4 numbers of 12v/200ah which is equal to 48v. Inshort,i need a charger that can charge this batteries to full charge without overcharging and at the same time maintain the charge in the batteries. I would like a charger that once i connect on power,no unplugging. Let it be self regulating
Hello Evans, you can try the first circuit from the following article. You can connect a 1K 2 watt resistor between the drain/source of the mosfet, this will take care of the float charging or the trickle charging.
https://www.homemade-circuits.com/make-this-48v-automatic-battery-charger/
Hi Swagatam,
Just thought of a cool name for your company if you ever planning one (like Adafruit or Raspberri Pi) – SWAGTronics.
Anyway, the atmega integration is me being overly enthusiastic.
I have a few questions regarding all of these SLA battery charger designs. Have you considered trickle and float charging the batteries because linear charging is going to reduce the battery life time by few years.
Thanks so much Don,
that indeed looks a cool name for my website company. I am worried somebody else might steal this name quickly.
Regarding your question, so far I haven’t included trickle charging or float charging in battery charger diagrams, since these can be easily added to any existing auto cut off battery charger circuit simply through a bypass resistor. The resistor should be added across the cut-off relay so that the current starts flowing through the resistor to the battery once the relay is cut off. This resistor must be calculated such that the current through it just manages to prevent self discharge of the battery while it is idle and disconnected from the charger.
Thanks Swagatam, cheers for that!
Hi Swagatam,
I came across your designs and they are really cool. Thanks for sharing your knowledge for free with the world. Such people are rare these days.
I’m looking for a multi output 48v lead acid charger/DC ups. Outputs being 48v (2A least),12v (15A), and 5v (8A). I understand placing buck converters at 48v load for each output will work as well. But will it be efficient? I’m also interested in adding a coulomb counter for the battery, with a digital display to show input voltage (230v) and all the outputs in an 1136oled display. We might have to work this through using a atmega integrated into the circuit at one point. I’d be greatful if you can integrate all these into one circuit if possible. Let me know if time permits.
Thank you Don, I truly appreciate for kind feedback!
yes buck converters will be efficient. If you don’t want to use buck converter then you can use a transformer with the respective voltage taps and individual regulators.
My microcontroller knowledge is not good, so it can be difficult for me to design an Atmega based circuit.
Hi Sir,
Want to ask question about the circuit under the section “Implementing Window Comparator”, about the 2 LEDs at the right hand side. Because when I think about the operation of the circuit, I suppose now battery voltage is below 56V, let say 55V, the op-amp A3 should output 12V, then both green and red LED ON. Or now battery voltage is 56V, the op-amp A3 output 0V, then both LEDs OFF.
So both LEDs will ON or OFF at the same time. Am I wrong, because want to know about what the 2 LEDs want to indicate.
Thank you very much.
Hi Tommy, no both the LEDs can never be ON. Because when suppose the op amp A3 output is high, it will make the junction of the two LEds high, so the upper LED cannot light up, because now both cathode and anode of the upper lED is high. But the lower LED will light up because its anode is now high, and the cathode is grounded.
Similarly when the A3 output is low, the lower LED will not be able to light up because now both its terminals are at low, but the upper LED will light up because its anode is connected to the positive line, and the A3 side cathode is low.
However, the LED which is supposed to be completely switched OFF may show little illumination due to a leakage voltage from the op amp output, to prevent this you can add a 1N4148 diode in series with each LED
Dear, Swagatam, I have installed a 12 volt emergency lighting system from the 40 Amp lead acid group using your ideas. It works great. First of all, I want to start off by thanking you. I like your diagram above, which cuts in -low/high-voltage. How can I use this circuit in 12 Volt 6o Ampere batteries? I would appreciate if you let me know how to make a change. Greetings and my regards. Mehmet Ovacikli
Thank you Dear Mehmet, I am glad my circuits are working for you!
I have an exclusive article on high low battery charger circuit, which you can read in the following link:
https://www.homemade-circuits.com/opamp-low-high-battery-charger/
You can use one of these concepts for building your battery charger.
You can also try the following concept;
https://www.homemade-circuits.com/regulated-car-battery-charger-circuit-for-garage-mechanics/
Hello, has access to several 48V Lithium batteries. Old electric car batteries.
12 cells with 4 temp sensors mounted, and BMS cards.
Unfortunately, it is not possible to use existing BMS cards as it is not known how to communicate with them. (Maybe someone has solved the problem, battery packs come from a BMW i3). My problem is how to find a solution when BMS cards are necessary.
Since I have access to several packages, it would be good to have a solution where several packages can be connected in parallel for greater effect.
These battery packs should, if possible, be used in a solar and wind solution.
Hello, A BMS basically comes with a few crucial features:
1) Constant voltage, and Constant Current
2) Auto full charge cut off
3)Temperature compensation
4) Trickle charging or float charging, for lead acid batteries.
5) Prevent self discharge
All these could be easily designed using discrete components, like ICs and transistors.
Hi Swagatam,
Do you have any designs at hand for a 48v lead acid battery balancer? This would be used in solar systems so need not think of power being wasted.
Thanks in advance and helping us all here.
Hi Joe, I do not have a balancer circuit at this moment, but you can try one of the circuits available online, such as this:
https://www.mouser.in/datasheet/2/609/3305fb-1271443.pdf
I have to design a battery charger to charge 48V lead acid battery from solar. Actually i have to design this for my final year project (Solar Electric Car) while considering state of charge (SOC) and depth of discharge (DOD).
Then which circuit is best in my case.
I hope you will help me.
Thanks in Advance
If you are referring to a circuit that would indicate the DoD of the battery, then I don’t I have the circuit with me at the moment. If the battery voltage corresponds to the DoD, then probably a voltmeter can be used to translate the discharge voltage to DoD.
Here’s one design that you can try modifying for your requirement:
Precise Battery Capacity Tester Circuit – Backup Time Tester
If i do not consider DoD then which circuit would be best ?
It will depend on the required specifications. Your battery can be charged by simply connecting a low current 56V source to it, without any issues, and it can be also charged with many facilities such constant current, constant voltage auto cut off, float charge etc. if faster charging and guaranteed safety is intended.
You can read the following article for detailed info:
Lead Acid Battery Charger Circuits
Thank you
Sr good evening please i see 12v 24v 6 60v battery charger control board charger power supply circuit diagram, how does it work.
Hi, please show the schematic
Yes this will be cool, when I saw 48 volts I was not thinking I could use it on 3 volt system, but changing some zener and resistors should get me where I want to be. Will spend the day pondering over the changes and tackle this project head on. Now with this virus, I can’t get spares or import what I need so I have to build , like the good old days. – much appreciated.
You are welcome Leium!
Thanks, have printed the circuit and will see if I can use it. I also needed the charger to operate between 2.4 volts disconnect load and 3.6 volts disconnect solar charger. Have see some with relays but would rather use FET or alike. Thanks again, your busy man, Swagatam.
You are welcome Leium, i wish you all the best with the project.
Hi Swagatam – your’e are a busy designer, I have been looking at your designs and would like you to point me to one that will help me with….
I want to charge two LiFePo4 batteries is series ( max 7V) with 8 – 12 volt in put from solar panel, should have prog resister for current and adjustable out put voltage and cutoff for over voltage.
I will be using a step down from 7 v to 5 v for remote use.
No problem Leium, although there are plenty of designs which could be effectively aplied for your requiremenet, I would recomend you to try the first circuit from the following article, and check if that works:
https://www.homemade-circuits.com/battery-current-indicator-circuit/
let me know if you any any further help!
Swagatam, what changes would I need to make to set the auto on off circuit to 120v nominal battery voltage ? Would the resistor values have to go up or just the wattage rating for resistors loaded by zener diodes . I’m looking at a 120v nominal lead acid pack being charged Via solar panels with a peak efficiency voltage around 36v @ 8 amps thinking 4 panels in series for 144v nominal and around 170v peak.
Adam, this circuit may not be applicable for 120 V battery, instead you can try the following concepts:
https://www.homemade-circuits.com/high-voltage-360v-battery-charger/
https://www.homemade-circuits.com/220v-lithium-ion-battery-bank-charger/
Hi Swagatam,
I need a circuit diagram of 48V, 160Ah Li-ion Battery from 230VAC input. Kindly help
Hi Sujit, you can try the 3rd circuit from top, from this article
https://www.homemade-circuits.com/make-this-48v-automatic-battery-charger/
for 100 amp you will have replace the mosfet with a 150 amp mosfet
Hello friend,
I am Kamlesh Jain, we had already discussed few circuit in past, today once again i need favor from you, few month ago, i bought self balancing scooter (Hover-board) for my son, and due to high voltage fluctuation in our area, the charger of the scooter dead, the charger output is 42v 2a. I want to make the same for charging scooter. please help me to build one. Better if you help me to build transformer less because i do not want to build bulky with transformer, i hope you will help me again. Thank you.
Hello friend, I think you can try the following design, but the trafo winding is critical, a little inaccuracy can result in the transistor blowing:
https://www.homemade-circuits.com/32-v-3-amp-smps-led-driver-circuit/
you can modify the 32V to 42V by adjusting the feedback components
Hello Swagatam, thank you for the “48V Solar Battery Charger Circuit with High/Low Cut-off” and I am going to try it out. Only one thing I am much more conservative about the “lower” limit voltage level when the load must be cut-off i.e. it must be when the battery voltage drops to 50 volts and not 42 volts on the battery. Can this be adjusted via the 220K ohm pot ? or can this be made permanently into a fixed value resistor ? Please may you advise as I am not planning to change its value.
Hello Dhoods, yes you can use A fixed resistor across the pin6 and pin2 (low cut off) but this will need to be selected by some trial and error method.
I have changed the diagram a little to make it easier to construct and understand.
Hello sir,
You are doing a wonderful working by helping thousands.
I am Deepak Patel. Can you please help us by providing a circuit dig. of 48V fast charger for charging a set of four batteries of 12V (120Ah) each. Circuit should also display the status of battery also (if possible).
Thank you
Waiting for your reply.
Hello Deepak, you can try the following concept:
https://www.homemade-circuits.com/fast-battery-charger-circuit/
For converting it into 48V please add 22K resistor in series with all the preset positive side, and 10K for the zener resistor.
Also join the supply pin through a 10K resistor to the 48V line, and add a 15V zener across the supply pin and ground of the IC (Vcc and Vss).
Change all the relays with 48V relay.
For LED indication add LEDs in series with the transistor base resistor of all the op amps. The base resistor should be 10K
How to reples 48v contactor to 12v
you will need a separate 12V supply for the relay
Sir I again request u to please help me in making this 48 volt current controller . I have 48 v solar system in my house with 3.6 kw inverter and 150 ah x 4 batteries.
Will thanks a lot.
Labh, you can try the second diagram from the following article
https://www.homemade-circuits.com/make-this-48v-automatic-battery-charger/
Rx = 0.6 / 60 = 0.01 ohms, wattage = 36 watt or 50 watt will be good.
Dear Swagatam,
I want to use 48V automatic solar battery charger using relay circuit.
But I need to charge 4 x 50A battery with constant 3 Ampere.
How can we add current limit to this circuit.
Best regards,
Kaya
Hi Yilkaya,
for getting a current control feature, you can upgrade the circuit as per the last concept from the following article
https://www.homemade-circuits.com/make-this-48v-automatic-battery-charger/