Solar Charger using Transistors

The post details a simple solar charger circuit with automatic cut-off using transistors only. The idea was requested by Mr. Mubarak Idris.

Technical Specifications


Please sir can you make me a 12v, 28.8AH lithium ion battery,automatic charge controller using solar panel as a supply, which is 17v at 4.5A at max sun light please sir it's urgent thanks in advance, and the charge controller should be able to have over charge protection and low battery cut off and please sir the circuit should be simple to do for beginner without ic or micro controller, please sir the circuit should use relay or bjt transistors as a switch and zener for voltage reference thanks sir hope to hear from you soon! and sorry to say that I am a student.thanks sir!

 The Design





PCB Design


Transistor solar battery charger PCB Design

Referring to the above simple solar charger circuit using transistors, the automatic cut off for the full charge charge level and the lower level is done through a couple of BJTs configured as comparators.

Recall the earlier low battery indicator circuit using transistors, where the low battery level was indicated using just two transistors and a few other passive components.

Here we employ an identical design for the sensing of the battery levels and for enforcing the required switching of the battery across the solar panel and the connected load.

Let's assume initially we have a partially discharged battery which causes the first BC547 from left to stop conducting (this is set by adjusting the base preset to this threshold limit), and allows the next BC547 to conduct.

When this BC547 conducts it enable the TIP127 to switch ON, which in turn allows the solar panel voltage to reach the battery and begin charging it.

The above situation conversely keeps the TIP122 switched OFF so that the load is unable to operate.

As the battery begins getting charged, the voltage across the supply rails also begin rising until a point where the left side BC547 is just able to conduct, causing the right side BC547 to stop conducting any further.

As soon as this happens, the TIP127 is inhibited from the negative base signals and it gradually stops conducting such that the battery gradually gets cut off from the solar panel voltage.

However, the above situation permits the TIP122 to slowly receive a base biasing trigger and it begins conducting....which ensures that the load now is able to get the required supply for its operations.

The above explained solar charger circuit using transistors and with auto cut-offs can be used for any small scale solar controller applications such as for charging cellphone batteries or other forms of Li-ion batteries safely.

For getting a Regulated Charging Supply


The following design shows how to convert or upgrade the above circuit diagram into a regulated charger, so that the battery is supplied with a fixed and a stabilized output regardless of a rising voltage from the solar panel.



Need Help? Please send your queries through Comments for quick replies!




Comments

King Dedon said…
Pls sir, can u guide me, I need an auto-cut off 96volts/40amps car battery charger to be able to charge my 96vols/400amps car battery for my new inverter, tnx a lot in advance!
Swagatam said…
King, I have already answered to this comment in the other post
Gajendra Mishra said…
How can set this circuit for lithium ion 11.1v 10Ah battery
Swagatam said…
what is the low voltage threshold for your battery??
Gajendra Mishra said…
Rated voltage is 11.1v
Low side 8.5v
High side 12.6v
Swagatam said…
you will need to apply 9V across the battery points from a DC power supply without connecting any battery, and adjust the 47K preset such that the LED just begins to light up....that's all. your circuit is set.
Swagatam said…
sorry don't apply 9V, apply around 10V.
manjunath said…
sir i need very simple solar BATTERY CHARGER ( AAA 1.2v 800mah recharagabl two batteries ) the solar pannel is small that i don"t know how to test it with multimeter and it mesures 4intch * 3 intch . i want to use battery to bluetooth mouce . or can i make simple charger with my CPU 'S UsB POINT thank you sir.
Swagatam said…
Manjunath, you can check it with your DMM at DC 12V range and then connecting the prods across the solar panel....this will tell you the voltage of the SP when positioned in sunlight....similarly test the current by only changing the DMM range to 1 amp or 2 amp DC range, without changing the panel connections.
OllyW said…
Brilliant design! Thank you so much for sharing - I'm gradually getting my head around how it works :). Can I ask what is the function of the red coloured diode in the diagram? Is this an L.E.D.?
OllyW said…
If the battery voltage falls causing the TIP127 to switch on, what would happen if there was no sunlight? Would this cause the remaining charge in the battery to discharge through the solar panel? Would we need a diode on the solar panel to stop this reverse current flow? Thanks for your help!
Swagatam said…
I am glad you liked it!

the red part is an LED and it indicates the charging status of the battery....ON indicates battery is charging
Swagatam said…
under no sunlight the battery would slowly discharge via the preset and the associated resistor...a rectifier diode could be connected between the 10K resistor and the battery positive....this will not affect the battery charge sensing ability of the circuit
OllyW said…
Ah - that makes sense, thanks! I am planning to incorporate your 'Simplest Automatic LED Solar Light Circuit' with this charging regulator circuit... The only difference is that I will be using a 12V rechargeable battery which drives a 0.2A 12V computer fan, rather than LEDs. I'm guessing that should be fairly straight forward to do...
Thanks again - it's great to dust off my electronics high school education!
OllyW said…
Brilliant - thanks!
Swagatam said…
You are most welcome please go ahead!!
manjunath said…
sir, i had checked solar panel in sun light it shows dc volts 4.41 and in amps 95.5 . so please help me to make solar charger for 2 rechargeble 1.2v 800mah batteries with the above solar panel thanks a lot.
manjunath said…
sir Solar panel tested with DMM volts range is 20 result = 4.41
and amps range is 200m result = 95.5 . for this panel i need circuit sir thank you.
Swagatam said…
Manjunath, you can use the circuit which is shown above, it's the simplest one and is suitable for low voltage charging applications.

you can remove the TIP122 and the associated parts to make the design even simpler, as these are not essential for your need.
Osere Tobi said…
Hello sir, can you help me design a very small circuit of charge Controller for power bank and also a perfect recommendation of solar panel and battery to be used... Thanks
Please I am a novice in the field of practical Electronics. Can you guide me on possible start-off steps? Thanks in anticipation
Swagatam said…
hello osere, I can surely suggest, but first you will have provide the power bank specifications so that I can calculate the parameters correctly.
Swagatam said…
Please feel free to put forth your specific queries, I'll try to help you out
OllyW said…
Hi again Swagatam! Please could you explain how the zener diode modification provides a regulated fixed voltage supply? Many thanks :)
OllyW said…
Here is the modification I have made so that a fan (load) only comes on at night, but which hopefully allows the solar cell to charge the battery in the day - if the battery needs it. Does the modification look like it would work? Thanks again for your time :). https://drive.google.com/open?id=0B_b88oA4THJgb3o2NTBxM0p1M1U
Osere Tobi said…
I want the power bank to charge for about like 8 hours but I don't know maybe I can use 6V solar panel, please explain better to me with a perfect recommendation circuit that you think with be suitable for the project please
Swagatam said…
Hi Ollyw, the zener is connected to an emitter follower configuration of TIP127, meaning the transistor emitter is now connected to the battery side and collector to the panel side....this configuration makes sure that the voltage never exceeds the zener value for the battery. You can research "emitter follower" or "common collector" transistor for more info on this.

However there seems to be a mistake in my second diagram, the TIP127 should be now at the negative line of the supply, not positive line....I'll correct it soon.

Your suggested diagram is OK, it will work
Swagatam said…
Tell me the power bank's battery voltage and AH specifications.
OllyW said…
Thank you Swagatam. I'll look up the 'emitter follower' configuration and see if I can get my head around how it works - much appreciated!
Best regards,
Olly
manjunath said…
sir should i use the very first circuit or the last one circuit THAT mentioned under name (The TIP127 configuration in the above design looks incorrect, the correct version should be as indicated in the following diagram:) and PLEASE HELP ME REGUARDING TIP122 and TIP127. AS TIP122 FROM left of printed side IS BASE,COLLECTER,EMMITTER simenteniously. was TIP127 same as TIP122 OR that should connect reverce thank you
Swagatam said…
Manjunath if you want a regulated supply for the battery then you can try the last circuit otherwise the first one will do.

TIP122 and TIP127 pin assignments are exactly identical....the difference with their polarity, TIP122 and is NPN and the TIP127 is PNP.
Swagatam said…
you are most welcome!
Osere Tobi said…
The power bank battery Voltage is 1.2v and 1900a
manjunath said…
SIR WAS TIP122 AND TIP127 CONNECTIONS ARE RIGHT PLEASE GUIDE ME THANKS A LOT

https://photos.google.com/share/AF1QipMzAdd9gtRiPLW9pE88oJD8PrqgD_H9Y3WDr1csYM7tGgEn8NwqeiK5iDUk3No-SQ?key=SkFzUVIwUUF6ZDJFajRoWjQ1Vm5iTW5kNmUxcV9n
Swagatam said…
you can use a 6V panel, and charge the cell using the following circuit

https://homemade-circuits.com/2012/08/simplest-dc-cell-phone-charger-circuit.html

use 1K for the resistor and instead of the zener use 3nos 1N4148 diodes back to back between base of transistor and ground (cathode to ground)
Swagatam said…
yes the connections are correct!
manjunath said…
SIR SORRY TO DISTURB YOU. PLEASE GO THROUGH BELOW LINK THAT I SENT ABOUT CONNECTION OF " TIP122 AND TIP127 " WHEATHER THEY ARE CONNECTED CORRECTELY OR IF PLEASE GUID ME THANKS LINK IS BELOW
https://photos.google.com/share/AF1QipMzAdd9gtRiPLW9pE88oJD8PrqgD_H9Y3WDr1csYM7tGgEn8NwqeiK5iDUk3No-SQ?key=SkFzUVIwUUF6ZDJFajRoWjQ1Vm5iTW5kNmUxcV9n
Swagatam said…
Manjunath, I have already answered you above. It's cortrect
manjunath said…
Thank you guruji
manjunath said…
SIR what is the result if load was not connected , mean does battery charges even if load disconnected. and switchs off after fully charged ,
- Can we make any indication for fully charged battery ( does "RED LED" off when battery fully charged . as it glows while charging)
- how to connect rectifier diode(which diode) with battery positive and 10k resistor
Swagatam said…
manjunath, red LED indicates battery is charging, when it shuts off indicates battery's full.

The load has no connection with charging of battery, the battery will charge and cut off regardless of the load.


refer to the last circuit for the diode connection, use a 1N4007 or a 1N5408 as per the batt/load specs.
Manish Gupta said…
sir where are use ground in this circuit
Manish Gupta said…
sir, how to slove the circuit
Swagatam said…
Manish, the line which is connected with the TIP122 emitter is the ground....the negative line.
Manish Gupta said…
sir, what is effect if zener are not use and how to slove the circuit.
sir,47K resistance how to connected the base of the transistor.
Manish Gupta said…
sir, 47K resistance how to connected the base of transistor.
Swagatam said…
Manish, you'll have to learn everything from the beginning, regarding how the various parts work and how they need to be connected in electronic circuits.
begin with transistors, I have many related tutorials which you can find in this website and learn through them...please use the search box to find the relevant topics
Manish Gupta said…
sir, I want to simulate this circuit in some software please suggest me which software to use.
Swagatam said…
Manish, I have never used or relied on simulators, so can't suggest much about them...
manjunath said…
sir how to adjust base preset to threshold limit. should i rotate 47k preset until the load light glow. or until the charging red led glow
manjunath said…
"GURUPOORNIMA" ke din "GURU" ko pranaam
Swagatam said…
thank you Manjunath!!
OllyW said…
Hi again Swagatam. Please could you explain the advantage of using the zener diode circuit (regulated voltage) compared to the first circuit? I'm using 10 x 1.2V AA cells as the rechargeable 12V power supply and although I would like them to last as long as possible, I'm also just trying to keep things as simple as possible :). Thank you!
Swagatam said…
Hi Ollyw, the zener version ensures a regulated constant voltage for the battery
Swagatam said…
the zener option is not crucial...the first circuit is much better according to me
manjunath said…
Sir can charge 12v 7.2AH battery with this above design. Thank you
manjunath said…
SIR, WAHT IS THE PROMINENCE OF 47K PRESET IN THIS CIRCUIT.AND HOW SHOULD I ADJUST THE 47K PRESET AND HOW THE LOAD REACTS WHILE CHARGING THUS THE LOAD ACTIVATE IF BATTERY FULLY CHARGED AND SHUTT OFF AFTER DISCHARGED.
SORRY FOR MY QUESTIONS LIKE THIS AND
THANK YOU FOR YOUR COOLEST ANSWERS.
Swagatam said…
Manjunath, the 47k is for setting the charging initialization threshold. It must be set such that at the preferred lower threshold the LED just begins glowing, so that the charging could be initiated by the TIP127.

Load will activate only when the LEd is fully shut-off and vice versa.
Yohana Tijala said…
hello sir long time how are you doing?,thanks for this design
Yohana Tijala said…
sir what is the meaning of TIPS 122?
shrirang dhapre said…
Hi sir, I am a student of engineering. I want to make turbo mobile battery charger, so can you plzz help for making this project. Because I don't no the exact design of this. And I want to make it with very easy way without using microcontroller. Sir plzz help me.
shrirang dhapre said…
Hello sir, I am a student of engineering. I need your help. I want to make turbo android mobile battery charger without using any microcontroller. But I don't have that much knowledge to make the design of this project. But i want to make this charger. So sir plzz help me. Plzzz. Thank you.
Swagatam said…
you are welcome!
Swagatam said…
Hello shrirang, presently I do not have a turbo mobile charger circuit but if I find one I'll surely let you know...

Long back I made using a 555 PwM circuit and it worked but made the cellphone quite warm...
shrirang dhapre said…
Ok sir no problem. But plzz try as early as possible. Thank you
Swagatam said…
Shrirang, Actually I already have the design in my website, you can find it below:

https://homemade-circuits.com/2012/01/how-to-build-simple-pwm-controlled-dc.html
Swagatam said…
Thank you dear Chandan,

Actually I already have a few solar panel changeover designs posted in this website, but the mentioned features are not present together in one design rather separately in different posts.

I'll try to update this universal changeover circuit as a new article soon. But it could take a little time, since I have a couple of previous assignments which I'll publish first and then this one..please stay tuned.
Swagatam said…
Dr. Chandan, I have published it here

https://homemade-circuits.com/2016/11/10kva-solar-grid-inverter-changeover.html
Haroon Haroon said…
Salam sir can i use 2n3055
Swagatam said…
Salam, where do you want to use 2n3055??
Mohit said…
whats the wattage of resistors in circuit? thanks
Himachal Guide said…
i have a solar light 9 w-12v in which two wires are for solar panel and 2 wires for battery and load. Problem is it doesn't have overcharge protection.
So can we put this circuit with battery and charge with those two wires comming from Led light. (14 v).
Means can we put this circuit like BMS?
Swagatam said…
Not the above, you can try the following circuit

https://homemade-circuits.com/2012/08/make-this-48v-automatic-battery-charger.html

you can remove the 22k resistors and the 15V zener, and replace the mosfet with TI122
Swagatam said…
...use the first circuit
Himachal Guide said…
1) there are 3 circuits, you mean very first design to follow.
2) and IC741 to be replaced with TIP122?
Himachal Guide said…
ok i understand 22k resistors and 15v zener to be relaced with mosfet TIP122
Swagatam said…
the first one.

replace the mosfet with TIP122 transistor.....not the IC
Swagatam said…
NO!!

remove the 22K resistors and the 15V zener completely.

and remove the mosfet also...and use a TIP122 in its place.
Himachal Guide said…
ok thank you very much
Nagendra Varma said…
Please sir, can u guide me, I need to be able to charge a 12vols/5amps battery, thanks a lot in advance!
Swagatam said…
Nagendra, you can use any LM338 IC based design for that...there are many published in this site
Erkan Karabulut said…
Hello Swagatam Majumdar,

Firstly, thank you for this great job. I couldn't understand something. If we have partially discharged battery, it causes to stop first bc547 stop and the next one conduct. How it is happening exactly?
Swagatam said…
Thanks Ekran,

when the left BC547 is not conducting, the current from its collector 10K is able to pass through the LED and reach the other BC547 transistor.

but when the left BC547 transistor is conducting its collector current is getting grounded through its collector/emitter leads and so the next BC547 transistor is not able to conduct.
Swagatam said…
Hi, you can try the second concept from the following article:

https://homemade-circuits.com/2015/11/make-this-power-bank-circuit-using-37v.html
Swagatam said…
current control feature is not included in this diagram for the sake of simplicity....to ensure current controlled charging you can choose a solar panel that may be rated with the correct required amount of current, as per the battery specs
Swagatam said…
yes, surely you can do that!
Jane said…
Hello Swagatam

I am very impressed with this site, having just found it. Do you do all this work helping us voluntarily? :)
We are doing a project where we have to power a waterpump (load) through a battery and solar cell. We want to be able to charge the battery and power the load at the same time, and have been instructed to do this through PWM control of transistors. Is that what this is? We looked up the transistor that was shown and its code showed it to be a MOSFET type (and not BJT as the diagram suggests). Will this cause any difference?
Would we be able to use some version of the system you have put up here to control the varying current that comes from a solar cell?

Our prior classes the last two months haven't been very thorough, so I'm still trying to understand everything :)
I write also just to see if you are still answering questions here :)

Kind regards
Jane
Swag said…
Hello Jane, I am happy you liked my site :)

The circuit shown above is a transistor based simple yet reliable solar charger, but it is not a PWM, and it does not use mosfets.

By solar cell do you mean solar panel? I think it has to be a solar panel, because solar cells are generally smaller in size and won't be able to drive a pump

If you can provide all the technical details of the solar panel and battery and the pump, I may surely try to help you with a suitable circuit design.
Jane said…
Hello Swagatam

Thank you for replying back in october and sorry I didn't respond. I wanted to do most of the work outselves and didn't figure out which questions to pose you.
We have finished a setup to control our solar panel, pump and battery, and I was wondering if it was possible for you to take a look and provide comments? I am aware that it is quite basic, but any comments would be appreciated whether they are complex additions or not.
Is there any way I can send/show it to you though the website?

Regards
Jane
Swag said…
Hello Jane,

You can send the details to my email ID, I'll look into it and try to solve it through a relevant schematic, if it is possible for me.

email: homemadecircuits

@gmail.com
ABBA said…
hello Swagatam
in the aboand the low cut-off setup but i can't understand the over-voltage cutt-off.
for example in if we set low cut-off 3V it means at three volt the first transistor at left will go off. battery will begin charging.Does that means that the moment the battery reaches just above the 3V threshold the indicator will go off. if you don't mind could you pls explain the setup of the over-voltage cutoff part. thanks
Swag said…
Hello Abba, yes you are right, but since it is a two BJT circuit the hysteresis level will be slightly higher, meaning the high voltage will be not immediately after 3V but may be after about 0.5V, so at 3.5V the first transistor will begin conducting, it is kind of slow fading rise and fading fall transitions and will cause the cut offs in a slow "choking" manner, not by sharp ON/OFF
ABBA said…
so can this can allow us to charge our battery upto 70 to 80% ?
Swag said…
yes surely, why not?
Kabiru Ali said…
sir, can I use this circuit to charge 50/60Ah battery?
Swag said…
It may be possible if the transistors are upgraded accordingly, TIP122 can upgraded to TIP142, and TIP127 with a TIP147

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