Saturday, August 3, 2013

Simple Zero Drop Solar Charger Circuit

The article discusses a simple zero drop or low drop solar charger controller circuit which can be modified in many different ways as per user preference.


A zero drop solar charger is a device which ensures tat the voltage from the solar panel reaches the battery without undergoing any kind of drop either due to resistance or semiconductor interference such as diodes etc in line.

The circuit here uses a mosfet as a switch for ensuring minimum drop of voltage received from the attached solar panel.

Moreover the circuit has a distinct advantage over other forms of zero drop charger designs, it does not unnecessarily load the panel making sure the panel is allowed to operate at it MPPT zone.

Let's understand how these features could be achieved through this novel circuit idea designed by me.

Referring to the proposed zero drop voltage regulator charger circuit diagram we see a rather straightforward configuration consisting of an opamp and a mosfet as the main active ingredients.

Here the opamp is wired as a comparator wherein its non-inverting pin is positioned as the voltage sensor via a voltage divider stage made by R3 and R4.

The inverting pin is as usual rigged as the reference input using R2 and the zener diode.

Assuming the battery to be charged is a 12V battery, the junction between R3 and R4 is calculated such that it produces 14.4V at a certain optimal input voltage level which may be the open circuit voltage of the connected panel.

On applying the solar voltage at the shown input terminals, the mosfet initiates with the help of R1 and allows the entire voltage across its drain lead which finally reaches the R3/R4 junction.

The voltage level is instantly sensed here and if in case it's higher than the set 14.4V, switches ON the opamp output to a high potential.

This action instantly switches OFF the mosfet making sure no further voltage is allowed to reach its drain.

However in the process the voltage now tends to fall below the 14.4V mark across the R3/R4 junction which yet again prompts the opamp output to go low and in turn switch ON the mosfet.

The above switching goes on repeating rapidly which results in a constant 14.4V at the output fed to the battery terminals.

The use of the mosfet ensures an almost zero drop output from the solar panel.

D1/C1 are introduced for maintaining and sustaining a constant supply to the IC supply pins.

Unlike shunt type regulators, here the excess voltage from the solar panel is controlled by switching OFF the panel, which ensures zero loading of the solar panel and allows it to operate at its most efficient conditions, quite like an MPPT situation.

The circuit can be easily upgraded by adding an auto cut off, and an over current limit features.



Parts List

R1,R2 = 10K
R3,R4 = use an online potential divider calculator for fixing the required junction voltage
D2 = 1N4148
C1 = 10uF/50V
C2 = 0.22uF
Z1 = should be much lower than the selected battery over charge level

IC1 = 741
Mosfet = as per the battery AH and the solar voltage.

Adding a current control feature to the above zero drop solar charger circuit

The above circuit looks quite an efficient design however lacks a current control feature.

The diagram below shows how the above circuit can be upgraded with a current control feature by simply adding a BC547 transistor stage across the inverting input of the opamp.

R5 can be any low value resistor such as a 100 ohm.

R6 determines the maximum allowable charging current to the battery which may be set by using the formula:

R(Ohms) = 0.6/I, where I is the optimal charging rate (amps) of the connected battery.


71 comments:

  1. Hi Sir,

    I have a 12V, 130AH battery and a solar panel of 24V 150W.
    How do I calculate R3 and R4 ?? Also please help for the value
    of Z1 and mosfet ratings.

    Thank you in advance.

    Rashid

    ReplyDelete
    Replies
    1. Hi Rashid,

      Use an online voltage divider calculator for determining the values of R3/R4 such that it's junction gives 14.4V at 15V input.

      Set it with a ac/dc power supply in place of the solar panel, means after this anything above 15V will be appropriately controlled as explained in the article.

      Delete
  2. i m tapas
    where i will found solar plates...

    ReplyDelete
  3. Hello sir good day. Sir where I can find solar cell I'm Mumbai, solar panels are redely available at Lamington road electronics market but they are too costly please suggest me name of place or shop where I can find solar cells only. So I can assemble panel in home

    ReplyDelete
    Replies
    1. good day! presently solar panels will be costly no matter from where you buy it.
      I have no idea regarding exact shops who are specialized in the PV field.
      You can try ordering it online from any chinese vendor as they are quite competitive.

      Delete
  4. Thankyou very much sir for your valuable reply.

    ReplyDelete
  5. Sir can we use relay in place of mosfet

    ReplyDelete
    Replies
    1. you can use a BJT (transistor) in place of mosfet, relay will not work.

      Delete
  6. Sir here mosfet is n type of p type?

    ReplyDelete
  7. Sir can you kindly explain me function of r1

    ReplyDelete
    Replies
    1. it's for enabling the mosfet to start conducting, without it the circuit will never initiate when switched ON.

      Delete
  8. Thankyou sir. but what is the function it like voltage divider, current limiter ,voltage drop and load resistor etc

    ReplyDelete
  9. Thankyou very much sir I learn lot of thing from you and still learning. One more help please I understand everything in the circuit about op amp, voltage divider, zener diode, mosfet but I am not under stand about mosfet gate driver resistor. Can you please explain me how it works, why to use and how to calculate.

    ReplyDelete
    Replies
    1. A mosfet requires a voltage across its gate and source in order to conduct, positive for N-channel and negative for P-channel

      here the P-channel acquires a negative potential via the shown resistor for conducting. It can be replaced with a short still the mosfet would work but the positive from the opamp would get shorted to ground getting damaged, that's why the resistor is included specifically.

      When the opamp output goes high it generates a positive potential at the gate and cuts off the negative drive such that the mosfet shuts off and process continues as explained in the article.

      You can refer any online source for knowing how mosfets work in details.

      Delete
  10. And how to calculate it like base resistor of transistor

    ReplyDelete
    Replies
    1. as expressed in the above comment, inclusion or elimination of resistor does not produce any affect in mosfet gate triggering.

      Delete
  11. What is the value of Z1? How do we add the current limit circuit.

    ReplyDelete
    Replies
    1. Z1 can be a 4.7V zener, current limit can be easily included by adding a transistor stage, will try to update it soon.

      Delete
  12. Mr Swags,

    Can you please tell me the values of the resistors, capacitor, zener and diodes i should use to turn a 60V generator to 15V?

    Kindly Appreciated.

    ReplyDelete
    Replies
    1. The zener can be a 6V zener,

      10k for R3, and 10K preset for R4. Adjust R4 until you get exactly 15V at the output.

      Delete
    2. Mr Swags,

      And the mosfet please?

      Delete
    3. Mr Swags,

      Will the IRF9530 mosfet work?

      Delete
  13. Mr Swags,

    Will the IRF9530 mosfet work?

    ReplyDelete
    Replies
    1. If its voltage and current ratings are as per your battery charging rate then it is OK.

      Delete
    2. What happens is that i'm not charging battery but i want a constant 12v output voltage for my circuit from my 70V generator. Is it possible?

      Delete
    3. yes you can use the above circuit for that purpose.

      Delete
  14. Hi Swag,
    pls i would want to use an nmos instead of pmos in the circuit . How could tha be done ?
    Tmx.

    ReplyDelete
    Replies
    1. Hi Kassim,

      You can try swapping the pin2/3 with each other for an nmos at the output.

      Delete
  15. Dear Swagatam Sir,

    I have 150 w Panel with VoC : 21 V and IoC :6.5 in peak conditions and Battery to be charged is 12 V , 100 AH .
    Can you help me in determining values of R3, R4 , Zener Diode No. , and MOSFET No. so that I can procure them .
    Best Regards.
    MANISH VISHWAKARMA
    Hyderabad

    ReplyDelete
  16. Dear Swagatam Sir,

    I have a 150 w solar panel with VoC = 21 V and IoC = 6.7 A ,
    I need to charge 12 v - 100 AH battery
    can you help me in determining values of R3 , R4 , Zener Diode No , Mosfet No . & R6 .
    I can procure them along with the Other material and start this project .
    best regards.

    MANISH

    ReplyDelete
    Replies
    1. Dear <anish,

      You will need a 15amp solar panel for charging a 100AH battery.
      You can use IRf9540 mosfet
      zener can be 6V, 1/2 watt
      R3 = 4.7k
      R4 = 20k

      Delete
  17. Swagatam, good circuit. It seems that you don1t know what mppt cgarging really is. This charger defenently isn`t. For mppt ypu need an inductor and electronics which wont allow PV module voltage to drop below 17.5v +_ 0.5.

    ReplyDelete
    Replies
    1. Thanks Vladimir,

      I have understood MPPT better than anybody else that's why I am trying to prove that it does not have to be all that complex.....and can be implemented by simpler means, although that would come with a few compromises and limitations which are no big deal.

      Please read my other articles about MPPT, you will get an idea regarding my knowledge about it.

      If you have personal queries about MPPT feel free to ask them here.

      Delete
  18. hi Swag
    pin 3(ic 741) calcular:Vbb=((R3+R4)*Vcc)/R3*R4 is valid over charger
    is Z1 valid begin charger

    ReplyDelete
    Replies
    1. Hi Khang,

      I have not yet confirmed this formula so canot say about it.
      In the above diagram Z1 and R3/R4 form a valid overcut configuration

      Delete
    2. Hi Swag
      sorry, formular wrong . but i think circuits not work because mosfet p channel work in negative voltage.pin 4( ic 741) connection 0V(mass) . mosfet cant's work . currents charger very low.I 'm check in actual
      Thank's

      Delete
    3. Hi khang, the 741 will produce negative voltage..... please go through the circuit explanation.

      Delete
  19. Hi Sir
    that is 741 use comparator circuit.741 use dual volte(+vcc and -vcc).you connect pin 4 in 0v .it cant's produce negative voltage.

    ReplyDelete
    Replies
    1. Hi khang,

      here negative refers to zero volt.

      Delete
  20. HI Sir
    I built your circuit design. circuit is limited by the charging line. I choose z1 = 6V, R3 = 3.9k R4 = 10k but the charge under 1A . DC in 10A 20V, 100AH ​​battery.
    Can you guide me
    Thanks

    ReplyDelete
    Replies
    1. Hi khang,
      disconnect pin7 of the IC from the shown position and provide the supply directly from the 20V input but through a 7812 IC and check the response.

      Delete
    2. for a 12V batery the output voltage from the circuit should be set at 14.4v

      Delete
    3. Hi Swaga
      How?formular calcula

      Delete
  21. sir me bhanu actually my problem is I am using here a N-channel mosfet that is IRFZ44N can it be used here...Thank you sir plz help me sir in this....

    ReplyDelete
    Replies
    1. bhanu, an n channel cannot be used in the above design, it'll require many changes for that
      mosfet is not compulsory here, you can use a BJT such as a TIP127 in place of the mosfet

      Delete
  22. sir swagatam good day
    is it possible to add leds to identify solar panel working and to identify the charging status? where shall i put it? thanks again

    ReplyDelete
    Replies
    1. Aureliano, the above charger does not include a cut-off circuit, so indicators cannot be used here.
      you can use an ammeter and put it in series with the battery positive, when it becomes zero would indicate a full battery

      for solar panel working indication you can put an LED across pin6 and ground of the IC via a 10k resistor.

      Delete
  23. Thank you Sir me bhanu.....
    actually TIP 127 is not available but can i use IRF9530 or IRF9540 as i am using 12v 1.3Ah battery for charging...
    Sir one more problem i am facing i know you have told that the BC547 is used here for current control, I just cant' understand how it functions...please sir help me....
    I am not getting a clear description from the note...
    Sir can i use R3 as 10k and R4 as 10 preset as according to comments posted by u...
    Thank you sir.....

    ReplyDelete
    Replies
    1. Bhanu, yes any P-channel mosfet will work here.

      when excess current flows, the base resistor of BC547 develops a triggering voltage for the BC547 which pulls pin2 of the IC to ground, which in turn instantly makes the output of the IC high deactivating the mosfet and switching it off at that instant, the cycle continues keeping the current within the required limit.

      Delete
  24. hi sir
    dc input is mppt
    use dc in trafo is ok?

    ReplyDelete
  25. I need these with input of 20v to 40v with an output of 17.5v @ 40amps. Even if a few are in parallel its okay.

    Efficiency should be greater than 90%

    Kumar
    srestimarketing@gmail.com

    ReplyDelete
    Replies
    1. The above circuit will work for both the inputs.
      use an appropriate preset for R4 for getting the desired output voltage

      Delete
  26. Hello Sir,

    Can I use this circuit for 6V/4.5AH Battery. What will be the changes required? Secondly, can I apply say 9V DC at the input in case no solar power available? Thanks.

    ReplyDelete
    Replies
    1. hello vb,

      no changes would be required, you can use the same circuit.

      Delete
  27. Hi
    Can you please give me some alternatives for IC1 741?
    Thanks

    ReplyDelete
    Replies
    1. you can try IC 301, 318, 709, CA3130, 3140, LF355/356/357, TL071/081 etc

      Delete
  28. Hi Swagatam.
    This looks like a pretty good circuit.
    Thank you both for providing the circuit and answering all those questions.
    I've learned a lot from what might sound like silly questions (but I think they aren't).
    I'd like to interface an ARM microcontroller to my solar panel.
    The microcontroller's job would be to measure the voltage using a resistor voltage divider connected to an ADC pin.
    As the ARM microcontroller runs at voltages below 3.3V, I need to regulate the voltage, but I do not want to use a 7812 and a 7805, because they'd use a lot of power.
    This is why I started to search for better regulators.
    I believe that I could use this as a regulator (and a similar circuit for charging a battery).
    My ARM device would then transmit the voltage whenever it changes (max. once per second) via a wireless connection, so a receiving chip would store the results for graphical display.
    I could also measure the charge currents.

    Without load, my 5W panel gives max. 22.4V; it's intended to be used for charging a 12V battery.
    I'd like to ask how low the regulator circuit can go, because I do not yet have all the components required to create the circuit (still waiting for the LM741 / UA741).
    Would any Mosfet do; eg. the IRF9530 or IRF9540, for a low voltage like 3.3V ?
    (I have a TSM2307 P-channel Mosfet as well, which I would prefer if possible: VDS = -30V max, VGS = +/- 20V max, ID = -3A max, RDS(on) = max. 80...140 mOhm).

    As you write... "should be lower than the selected battery over charge level", I believe that the zener can be anything above my microcontroller's minimum voltage level (for instance 1.8V, as the microcontroller's voltage range is 1.8V to 3.6V) ?

    ReplyDelete
    Replies
    1. Thanks Pacman,

      Your problem can be simply solved by using the following circuit, the above circuit is way too complex considering the small voltage level you intend to control.

      http://homemadecircuitsandschematics.blogspot.in/2012/08/simplest-dc-cell-phone-charger-circuit.html

      Use a 10k resistor instead of the shown 220 ohms, and use a 3.3V zener in place of the existing zener value.

      The output of the circuit then could be directly integrated with your ARM MCU.

      I am sure this will work better and be much easier for you to implement.

      Delete
    2. ..for the TIP122, you can use a 2N2222 or an 8050

      Delete
  29. Hi Swagatam.
    This was exactly what I needed.
    I had some idea that it was possible, I just couldn't spot it. :)
    I have the zener and resistor; and placed an order with the 2N2222 and a SMT version of it in addition.
    The ARM microcontroller (NXP LPC1114) only uses around 9mA, when constantly busy at full speed.
    So it looks like there will be plenty of current left over, even after the RF-chip have been consuming its part. ;)

    You're absolutely a genious and a great teacher!
    I learn a lot from looking at your circuits and trying to follow them.
    I hope that I can return the favour one day. =)
    (I hope I didn't post this twice; my previous attempt was lost; it seems it's a good idea to copy to the clipboard just before pressing "Publish").

    ReplyDelete
    Replies
    1. Thanks Pacman, it's my pleasure!!

      If 9mA is only that you need then may be just a zener diode with a series resistor would simply do the job....but a zener/resistor config would dissipate some unnecessary energy which could be undesirable....

      I have read your other comment will be answering it shortly:-)

      Delete
  30. Hi Swagatam.
    The ARM microcontroller is running fine on the solar panel. =)
    -So I've now started building this circuit for charging my small 2aH/12V Lead-Acid batteries.
    -But I can't seem to find D1. :)
    D1 is not on any of the schematics. (I'll be using the current-regulated version)
    Unfortunately, I don't have the 4.7V zener yet. -But I have a 3.6V, a 3.9V and a 4.3V zener.
    Could I adjust the zener using a 1N4148 in series with it ?

    BTW: I've read that a 'safe' charging current is 7.5% of the total capacity of the battery.
    That would mean for a 2000mAh battery, it would be 2000 / 100 * 7.5 = 150mA.
    I've included the formula, so that others can benefit from it.
    (My 2000mAh battery says it can handle 500mA charging current, though).

    ReplyDelete
    Replies
    1. Thanks Pacman,

      I think the same circuit which you are presently using for your ARM MCU can be applied for charging your battery also.

      Just use a 15V zener and a TIP122 for the transistor in the circuit for the present application, if a 15V zener is not there with you you can put the available zeners in series along with a few 1N4148 diodes for achieving the same.

      The concept discussed in the above article is good but the setting procedures could be quite difficult for a novice, that's why I am not recommending the above design to you.

      As for D1, it was present in the previous slightly different design which I have modified with the existing one, I'll do the required corrections soon in the parts list, thanks for pointing it out.

      Yes 7.5% may be correct but 10% is the recommended value:), so may be you can calculate it as per 10% rate

      Delete
  31. sir, I built this circuit but the output does not requlate to 14.4 volts instead it goes up to 16.5 volts, I tried in so many ways to adjust the circuit but I can not simply get the required voltage as explained in your tutorial.

    ReplyDelete
  32. sir, the output of this circuit is not regulating to , 14.4 volts, it goes up to 16.5volts.

    ReplyDelete
  33. sir, i build this circuit using mosfet IRF9530, problem is output is going as high as 17volts. even i disconnect the gate of mosfet still it is on. i test the mosfet its ok ( switch on when gate goes to 0v and off when gate is +19volts, im wondering what kind of mosfet to use since IRF9540/30 is not functioning correctly with this circuit.

    ReplyDelete
    Replies
    1. Belekoy, if the mosfet is switching ON without the gate connected how do you assume it to be OK? A good mosfet will never switch ON without a gate trigger.

      Anyway for the time being quit mosfet and try using a PNP BJT such as a TIP127, and check the response

      Delete

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