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Homemade Solar MPPT Circuit – Poor Man’s Maximum Power Point Tracker

Homemade Solar MPPT Circuit – Poor Man’s Maximum Power Point Tracker

MPPT stands for maximum power point tracker, which is an electronic system designed for optimizing the varying power output from a solar panel module such that the connected battery exploits the maximum available power from the solar panel.



Introduction

NOTE: The discussed MPPT circuits in this post do not employ the conventional control methods like "Perturb and observe", "Incremental conductance, "Current sweep", "Constant voltage"......etc etc...Rather here we concentrate and try implementing a couple of basic things:

1) To make sure that the input "wattage" from the solar panel is always equal to the output "wattage" reaching the load.

2) The "knee voltage" is never disturbed by the load and the panel's MPPT zone is efficiently maintained.

What's Knee Voltage and Current of a Panel:

Put simply, the knee voltage is the "open circuit voltage" level of the panel, while the knee current is the "short circuit current" measure of the panel at any given instant.

If the above two are maintained as far as possible, the load could be assumed to be getting the MPPT power throughout its operation.

Before we Delve into the Proposed Designs, let's first get acquainted with some of the basic facts regarding solar battery charging

We know that the output from a solar panel is directly proportional to the degree of the incident sunlight, and also the ambient temperature. When the sun  rays are perpendicular to the solar panel, it generates the maximum amount of voltage, and deteriorates as the angle shifts away from 90 degrees  The atmospheric temperature around the panel also affects the efficiency of the panel, which falls with increase in the temperature.

Therefore we may conclude that when the sun rays are near to 90 degrees over the panel and when the temperature is around 30 degrees, the efficiency of the panel is toward maximum, the rate decreases as the above two parameters drift away from their rated values.

The above voltage is generally used for charging a battery, a lead acid battery, which in turn is used for operating an inverter. However just as the solar panel has its own operating criteria, the battery too is no less and offers some strict conditions for getting optimally charged.

The conditions are, the battery must be charged at relatively higher current initially which must be gradually decreased to almost zero when the battery attains a voltage 15% higher than its normal rating.

Assuming a fully discharged 12V battery, with a voltage anywhere around 11.5V, may be charged at around C/2 rate initially (C=AH of the battery), this will stat filling the battery relatively quickly and will pull its voltage to may be around 13V within a couple of hours.

At this point the current should be automatically reduced to say C/5 rate, this will again help to keep the fast charging pace without damaging the battery and raise its voltage to around 13.5V within the next 1 hour.

Following the above steps, now the current may be further reduced to C/10 rate which makes sure the charging rate and the pace does not slow down.

Finally when the battery voltage reaches around 14.3V, the process may be reduced to a C/50 rate which almost stops the charging process yet restricts the charge from falling to lower levels.

The entire process charges a deep discharged battery within a span of 6 hours without affecting the life of the battery.

An MPPT is employed exactly for ensuring that the above procedure is extracted optimally from a particular solar panel.

A solar panel may be unable to provide high current outputs but it definitely is able to provide with higher voltages.

The trick would be to convert the higher voltage levels to higher current levels through appropriate optimization of the solar panel output.

Now since the conversions of a higher voltage to higher current and vice versa can be implemented only through buck boost converters, an innovative method (although a bit bulky) would be to use a variable inductor circuit wherein the inductor would have many switchable taps, these taps may be toggled by a switching circuit in response to the varying sunlight so that the output to the load always remains constant regardless of the sun sunshine.

The concept may be understood by referring to the following diagram:

Circuit Diagram

homemade MPPT circuit with tapped transformer

 

 Using LM3915 as the Main Processor IC

The main processor in the above diagram is the IC LM3915 which switches its output pinout sequentially from the top to the bottom in response to the diminishing sun light

These outputs can be seen configured with switching power transistors which are in turn connected with the various taps of a ferrite single long inductor coil.

The lower most end of the inductor can be seen attached with a NPN power transistor which is switched at around 100kHz frequency from an externally configured oscillator circuit.

The power transistors connected with the outputs of the IC switch in response to the sequencing IC outputs, connecting the appropriate taps of the inductor with the panel voltage and the 100kHz frequency.

This inductor turns are appropriately calculated such that its various taps become compatible with the panel voltage as these are switched by the IC output driver stages.

Thus the proceedings make sure that while the sun intensity and the voltage drops, it's appropriately linked with the relevant tap of the inductor maintaining almost a constant voltage across all the given taps, as per their calculated ratings.

Let's understand the functioning with the help of the following scenario:

Suppose the coil is selected to be compatible with a 30V solar panel, therefore at peak sunshine let's assume that the upper most power transistor is switched ON by the IC which subjects the entire coil to oscillate, this allows the entire 30V to be available across the extreme ends of the coil.

Now suppose the sunlight drops by 3V and reduces its output to 27V, this is quickly sensed by the IC such that the first transistor from the top now switches OFF and the second transistor in the sequence switches ON.

The above action selects the second tap (27V tap) of the inductor from top executing a matching inductor tap to voltage response making sure that the coil oscillates optimally with the reduced voltage...similarly, now as the sunlight voltage drops further the respective transistors "shake hands" with the relevant inductor taps ensuring a perfect matching and efficient switching of the inductor, corresponding to the available solar voltages.

Due to the above matched response between the solar panel and the switching buck/boost inductor...the tap voltages over the relevant points can be assumed to maintain a constant voltage through out the day regardless of the sunlight situation....

For example suppose if the inductor is designed to produce 30V at the topmost tap followed by 27V, 24V, 21V, 18V, 15V, 12V, 9V, 6V, 3V, 0V across the subsequent taps, then all these voltages could be assumed to be constant over these taps regardless of the sunlight levels.

Also please remember that these voltage can be altered as per user specs for achieving higher or lower voltages than the panel voltage.

The above circuit can also be configured in the flyback topoogy as shown below:

simple flyback MPPT design

In both the above configurations, the output is supposed to remain constant and stable in terms of voltage and wattage regardless of the solar output.

Using I/V Tracking Method

The following circuit concept ensures that the MPPT level of the panel is never disturbed drastically by the load.

The circuit tracks the MPPT "knee" level of the panel and makes sure that the load is not allowed to consume anything more which might cause a dropping in this knee level of the panel.

Let's learn how this can can done using a simple single opamp I/V tracking circuit.

Please note that the designs which are without a buck converter will never be able to optimize the excess voltage into equivalent current for the load, and might fail in this regard, which is considered as the crucial feature of any MPPT design.

A very simple yet effective MPPT type device can be made by employing a LM338 IC and an opamps.

In this concept which is designed by me, the opamp is configured in such a way that it keeps recording the instantaneous MPP data of the panel and compares it with the instantaneous load consumption, and if it finds the load consumption exceeding this stored data, it cuts off the load...

 

simple MPPT knee voltage tracker and self adjust
The IC 741 stage is the solar tracker section and forms the heart of the entire design.

The solar panel voltage is fed to the inverting pin2 of the IC, while the the same is applied to the non-inverting pin3 with a drop of around 2 V using three 1N4148 diodes in series.

The above situation consistently keeps the pin3 of the IC a shade lower than pin2 ensuring a zero voltage across the output pin6 of the IC.

However in an event of an inefficient overload, such as a mismatched battery or a high current battery, the solar panel voltage tends to get pulled down by the load, when this happens pin2 voltage also begins dropping, however due to the presence of the 10uF capacitor at pin3, the potential stays solid and does not respond to the above drop.

When the above situation is triggered, instantly causes pin3 to go high than pin2, which in turn toggles pin6 high, switching ON the BJT BC547.

BC547 now immediately disables LM338 cutting off the voltage to the battery, the cycle keeps switching at a rapid pace depending upon the IC's rated speed.

The above operations make sure that the solar panel voltage never drops or gets pulled down by the load, maintaining an MPPT like condition throughout.

Since a linear IC LM338 is used, the circuit could be yet again a bit inefficient....the remedy is to replace the LM338 stage with a buck converter...that would make the design extremely versatile and comparable to a true MPPT.

Below shown is an MPPT circuit using a buck converter topology, now the design makes a lot of sense and looks much closer to a true MPPT

MPPT with tracker and self optimizing buck power supply

48V MPPT Circuit

The above simple MPPT circuits can be also modified for implementing high voltage battery charging, such as the following 48V battery MPPT charger circuit.

60V to 24V MPPT tracker design

The ideas are all exclusively developed by me.

SHARING IS CARING!


About the Author

I am an electronic engineer (dipIETE ), hobbyist, inventor, schematic/PCB designer, manufacturer. I am also the founder of the website: https://www.homemade-circuits.com/, where I love sharing my innovative circuit ideas and tutorials. If you have any circuit related query, you may interact through comments, I'll be most happy to help!



107 thoughts on “Homemade Solar MPPT Circuit – Poor Man’s Maximum Power Point Tracker”

  1. Howdy, Friend! Interested to Learn Circuit Designing? Let's Start Discussing below!

  2. good day Eng Swag,
    please do you have any solar mppt circuit diagram that can output upto 300vdc with input between 200-300vdc?
    thanks

  4. Hello sir,please may explain a difficulty and ask a question based on it.based on the first and second diagrams.that is the buck/boost configuration.I checked online for awg wire current and frequency rating and found that the thickest wire to operate at 100khz with 100% skin depth is awg26.but this wire is able to carry only 0.361amp .so to get 5amps we will need to wound 15 wires together,meaning one will deal with 30 wires at each tap. The question is”can the circuit be operated at a lower frequency”? Say 8-40khz. Which will allow the use of awg15-22. Reducing wire to 1-5

    • Hi Shedrach, It seems you might have missed something, your analysis might be wrong. frequency is related with number of turns, not with wire AWG or thickness. However number of turns is related to current, more turn numbers allow less current and vice versa.

      at higher frequencies the turns number decreases proportionately and vice versa, therefore at higher frequencies number of turns become less allowing smaller inductors to be used.

      you can use any transformer by suitably matching the frequency specs, but lower frequency will mean incorporating bigger transformers and bulkier installation.

        • you can find the wire thickness required for 5 amp at 100kHz, then use stranded wire for that thickness to make things easier and efficient, for example if the required thickness is 14 AWG, we can use stranded 14 AWG wire and effectively minimize the volume of the transformer

  14. Hello sir!
    i am a student of B.tech electrical. i am working on my final year project. Sir i want to make an MPPT Charge controller of rating 200 watt panel. kindly sir guide me how can i make this without using the microcontroller. some suitable circuit diagram. plzzz sir.i have seen many articles of mppt of yours. butt i am confused. suggest me the best suitable diagram of my rating. your help will be highly appreciated.

  16. Hi.Sir Swagatam Majumdar.Sir we are working on Perturb and observe method.Can u provide me with a working dc-dc converter circuit diagram.Range having input 8-20 volts and output range 9-22.thanks

    • Hi Mohammed, I have not yet researched this concept, if possible I'll do it and try to design a suitable circuit with this concept.

  20. I have 200 watts solar panel and i want to build mppt solar charge controller, please send me circuit diagram and component list.

  22. Another quick question please. In the schematic for the 48v version, isn't the 78L12 receiving excessive voltage from the 60V solar panel?

    • yes you are right, a 78XX will not work here, you can replace it with the common collector stage as shown in the second last circuit above…using the BC547 and its base zener diode/resistor design

  24. Dear Swagatam,

    Thank you for providing such brilliant guidance. I am designing a 48v charge controller to hook up with the 200 AH battery bank. The panels array is rated approx. 2000 watts. The batteries are attached to a 3kw ups. This arrangement mainly runs a air conditioner (1200 watts) in summers. Therefore the amps flowing through the system are a lot (2kw@48v). I had a charge controller of 50 amps which is now broken and it costs around 150 usd. I don't plan on buying a new one. Instead I'm going to use your circuits with some modifications like mechanical on/off switches and additional transistor stages to pass all that power. Or perhaps replace the transistors with heavy duty triacs or even high amp car relays in parallel. My question is if I will be able to drive many transistors from the pin 6 of the 741 ic. Is there a circuit simulation software I can use first? Like a spice variant which has IC packages like 741 and 555 that I can employ to test the whole thing? Sorry for so many questions but sensing that you are a noble person who likes to help others I thank you in anticipation for your guidance. Stay blessed.

    • Thank you dear Mooney,

      Actually I have never used a simulator in my life because I simply never needed these artificial means, I normally do the simulation in my mind much reliably…so I am afraid I have no idea about these things.

      By the way if you say I could design the system for you, if you can specify the exact features that you would want the charger to include.

      If you are interested to go for a simpler option here's one very simple circuit which will start charging your batteries as soon as you hook it up with the panels.

      https://homemade-circuits.com/2015/03/100-amp-variable-voltage-power-supply.html

    • I feel extremely grateful to read that you are willing to take the time to help me. And that you have replied so quickly. Thanks bro.

      The 100 amp variable voltage power supply design that you have linked is simply amazing and new to me. I can't appreciate the idea enough. However that one is missing automatic feature of a cut off to end charging when battery voltage drops below a certain lower limit like 50 volts or so. 50 is lower than the standing voltage of the batteries and it'll mean that the UPS is loaded and drawing power from them. The potentiometer in the circuit seems useful to have and I hope to use it in order to raise the voltage going to the batteries manually, only once a month, and give them an equalizing charge.

    • The problem with transistors and linear regulation is waste of a lot of power. I don't want that bro. What I need is mosfets switching by pwm signal and not wasting power. Op amps can control the switching. If you google "the back shed mppt circuit" you will find what I have explained. Bro I need your kind consideration upon that one, please. Its gorgeous and succinct.

    • It is, and I hate to whine to you but it uses a P channel mosfet. Being rare (for some reason), P channel power mosfets are expensive over here, like a dollar for one. Then, I am located far away living on a farm in remote Punjab. I have plenty of n channel mosfets and transistors though and the usual items like 555's, 324's, 741s, and a whole lot of scrap including transformers from local made UPS units.

      The other concern I have is that internet searches bring forth the advanced concepts like H bridge and full bridge mosfets driven by the latest ICs which I do not have. I could try and hunt for 3524 or other PWM and FET driving ICs. But the coolest idea of a 555 based PWM driving mosfets and "chopping" the power coming down from the solar panels and tailoring it to my need seems most feasible to me for now.

      I have made simulations of all the circuits you have developed, all of them, however they don't simulate very well because the applet I'm using, developed by Paul Falstad, does not have a PV input. Otherwise the circuit you have shown here is quite good being simple. Secondly the PV array is 2 kilo watts of power. And I'm not sure how to add mosfets to share the power. To be honest, Mosfets are sophisticated things with a lot of "nakhra" to take care of in their design, as you know.

      I could use a small army of D1047 NPN transistors instead if need be (I have plenty of these from scrap), driven by a 555 based PWM and a 741 or two as comparators, sensing and controlling the voltage limits as long as the circuit doesn't let them go linear to waste the power being conducted down. But I am a newbie so I'm not so confident in designing it. I also have a box full of IRFP150N n cannel mosfets.

      Bro you agreed to help me. Perhaps you could take the time to design such a thing for me? Pretty please. My wife and children are visiting their parents and I want to get the solar power up and running by the time they return which is a week from now. And with all the frequent rains I don't have much outdoor farming work to do anyway. What do you say dear bro? 🙂

    • Thanks bro, for the nice explanation, I'll try to design and publish the required circuit, specific to your application. It may take some time though, since it would be quite an elaborate article and might take a lot of thinking…..

      cheers!.

    • Okay thank you Swagatam, I'll be looking forward to it. In the mean time, I think I am going to build the circuit on this page and instead of a transistor I'm going to use a bunch of car relays driven by the 741. I hope the IC will not be switching them too much because I do not want the inductive kickback spikes from fast switching relays to damage the UPS. Am going to start building this ASAP. I intended to send you report and photos of any build designed by you so I will send you photos of it, hopefully.

    • Brother forgive me but kindly do me this one favor only, modify the 48 volt circuit on this very page only to handle 2 kilo watts of power. The more I read about drive requirements for transistors and mosfets the more I feel ignorant about them. You're the guru so please guru ustad take the time to make this small modification. I will acquire the PNP transistors and everything else. This one here, aptly named Poor man's mppt is the best of them all when it comes to simplicity and efficiency.

    • Sure Bro! I am always ready to help! However the above circuits were built on an mistaken assumption…so it wouldn't be a good idea to try these circuits won't simulate an MPpT, In my previous comment I suggested you an alternative circuit I would recommend you to try that instead of the above.

      Or you can also try the earlier link that I had referred using IC 555 IC.

      I would be updating the article soon with a correct version so that the circuits works more like an MPpT.

    • Still waiting for the update. Bro Majumdar its not so necessary to make it mppt. It just needs to be efficient. Its meant for poor people any way. A full bridge buck converter that can handle the amps and its limits governed by a few ICs may as well do the trick.

  26. can I use this circut direct connect to load?
    means the input of the circut connect to the output of the solar and the output of circut connect to 12v dc fan.
    can this can work good?

  28. if all the component connect same like the above circut but If dont use 10k preset with this circut what would be the result?
    can work fine or not?

  32. HI, instead of using solar panels, can i use external power source/supply with appropriate voltage to charge battery?

  34. I have 150w panel round about 30 to 35v can I use this circut
    and how much time they full fill bettery(50ah).thanks

    • yes you can connect it.
      it will be difficult to predict the battery charging time because it could depend on many external factors.

    • Ajith, did you set the circuit as directed in the article.

      connect an LED in series with the emitter of the transistor, and switch ON the 35V input

      next, without connecting any battery first adjust the preset such that the voltage at pin2 is 12V,

      without any load this LED should stay switched OFF.

      Now short the output terminals, LEd should light up now.

      confirm the above and let me know.

    • Hi Ajith, you can try the last circuit which is the simplest one, make sure to add a 6V zener in series with the base of the transistor.

      connect the panels in parallel.

  50. your designed circuit is not a true MPPT circuit, as expressed by JD Bakker. You fault him, but your headline is for an MPPT controller, which the circuit is not. As we say in America, that's false advertising.

    Rather than just criticize, I will point you to a solution. Review the simple MPPT controller based on the Linear Technology LT3652. Quite an easy circuit to construct, actually MUCH easier than yours. Maybe instead of getting defensive, you should look for a true solution. You could also provide instructions to help enhance output capacity (charge current).

  52. sir gud day,
    thank you for your informative and helpful blog.
    my some question is:
    1.in R1,2,3 0.7ohms, how many watts i apply if my battery is 12v 40AH and my solar panel is 50w, 12v-20v. pls.. give me exact value of the resistor 1,2,3.
    2.IC324 is it also LM324 if i buy in elect. store.
    3.all 4 presets 10k parts under ic324 is it automatically set already or i manually configuring the value to set the right output, if manually do, will you mind how to set this in correct value.
    Hope you appreciated me. Thanks very much!

    • The above circuit procedures could be quite complicated for anyone who may new in the field, it's for the experts….I'll try to update the article soon with an identical design but using lesser number of components and hassle free setting procedures….so please keep in touch until then

  60. i made the circuit,but my solar panel is giving 10 volts without mppt but when the mppt is connected only 6 volts is measured. I measured this 6v by taking away the battery and connected a multimeter in place of battery it showed 6 volts. how can maximum power can be obtained with reduced voltage.
    i connected 3 w 9v solar pannel and 12v 1.3AH battery
    and the red led is always glowing even when the battery is dischearging

    • how can you charge a 12V batt with a 9v input?????

      you will need a 18v panel for a 12v batt and the above circuit.

      also replace the 4k7 pot under LM38 with a 10k pot for getting a 15V adjustable range

  70. In the circuit one transistor base is connected to 100 ohms and after that an a connection with big dot is left freely what to connect there?

  72. hi!
    thanks a lot in helping me in completing the dual axis solar tracker it's working perfectly
    my next step is to connect the solar panel of dual axis solar tracker to this simple mppt circuit
    is this idea good
    Here in the circuit A3 and A4 are the other 1/2 of IC 324 then in circuit A3 is +v and ground connection are these connections pin 4 and 11 in IC 324?

  74. hi i am planning to connect this mppt circuit io dual axis solar tracker.
    1) if my solar pannel rating is 50w what must be the R1,R2,R3 values
    2) Are the relays in this circuit are 12v 8 pin relay
    3)In the circuit an arrow pointing 10k resistor, is this resistor variable 10k resistor
    4) in the circuit the connecting wires are disconnected in some places how the wires connected there

    • 1) resistor values will depend on the battery AH rating.
      2)relays are 12v 5 pin, spdt
      3)those are presets or trimpots
      4) the gap indicates that the overlapping wires are not connected in anyway.

  76. Hi. Great site.
    I agree with the mppt concept. We live completely of grid. We have 8 x 240w 24v solar panels connected with 4 x 40a 24v pwm controllers to batteries and a 3kw wind turbine. Power to the house is done via 3kw pure sine wave inverter. My idea is to connect a simple mppt circuit infront of my pwm controllers. Do you think this will enhance the solar panels charge rate, more important in early mornings and late afternoons.
    If so can you please help with a simple design for 24v 40a mppt circuit than can installed in front of my pwm controllers.
    Thanks
    If so

    • Hi, Thanks!

      It will depend on how the PWM controllers are configured.
      I am assuming the connected batteries to be rated at 12V and the PWM controllers generating the required 14V for charging these batteries.
      If this is so, then I think the PWM controllers would itself be quite efficient in optimizing the solar panel current, and external MPpTs wouldn't be required.

    • Hi
      No sorry we have 24V battery bank. The PWM's are charging at 28.8V. My solar panels open V are +- 40V, I think it would be better to install a dc – dc converter in front of the PWM controller to change the higher volts low amp to lower volt higher amp. Can a converter be made with high current +-40A.
      Thanks

  80. I don't blame you for this comment because may be you yourself are much ill informed about electronics and might have failed to understand the above circuit details.

    The above mppt cannot be considered a real mppt only because it doesn't employ I/V curve tracking but that doesn't take away its credit of being extremely efficient than the ordinary solar chargers that you are referring to.

    How much do school students know about electronics and how much experience do they have this such field? I have seen experienced hobbyists consulting me for days and multiple failures until finally I make them succeed in making a particular project.

    If your students couldn't make this simple looking solar optimizer then imagine what they would do with an actual mppt.

    People appreciate me for providing alternate innovations, concepts, inventions that are easier and much effective.

    It's unfortunate that there are folks who like to break their frustrations on creative helping engineers like me who are very rare online.

    If you are unable to understand a concept you better quit instead of criticizing it due to your own inefficiency.

  82. Then it may be fairest to be honest about that.

    NONE of the circuits that you label as such, are actually MPPTs, as none of them will transfer maximum power to their load (the battery). If you want a cheap and easy way to non-MPPT charge a battery, you could suffice with a diode between solar panel and battery, perhaps with a relay or MOSFET to turn of charging once the battery is full. This will work better than any of the designs you've posted.

    Misinformation is worse than no information at all. Two project teams at my school have attempted to use your designs as a basis for their MPPT, only to lose valuable time and resources before finding they don't work as advertised.They now risk failing their course, as we don't give them a passing grade if they can't demonstrate MPPT functionality. (They have learned a valuable lesson — don't just trust any information you find on the Internet…)

  84. hi sir,how are you?actually i want to know i am already using a pwm based solar charger with my inverter.but want to use MPPT.can you publish a cicuit which can handle 24v 30 amp. thanks

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