Zero Drop Solar Charger

The article discusses a simple low drop or zero drop solar charger circuit without microcontroller which can be modified in many different ways as per user preference. The circuit does not depend on microcontroller and can be built even by a layman.

What is a Zero Drop Charger

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 shunt the panel making sure the panel is allowed to operate at its highest efficiency zone.

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

How the Circuit Functions

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 zero drop solar charger circuit without microcontroller can be easily upgraded by adding an auto cut off, and an over current limit features.

Circuit Diagram

Simple Zero Drop Solar Charger Circuit without Microcontroller

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

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.

Note: A P-channel mosfet may not work correctly, therefore the mosfet in the above zero drop solar circuits must be replaced with N-channel mosfets as shown in the folowing diagrams. Readers are requested to do the modifications as per the following diagrams.


Simple Zero Drop Solar Charger Circuit without Microcontroller and current controlled


Finalized Solar zero drop battery charger circuit:

As per the suggestion of "jrp4d"the above explained designs needed some serious modifications for operating correctly. I have presented the finalized, corrected working designs for the same through the below shown diagrams:

According to "jrp4d":

Hi - I've been messing about with Mosfets (voltage control circuits) and I don't think either circuit will work except where the line in voltage is only a few volts large than the target battery voltage. For anything where the line in is much more than the battery the mosfet will just conduct because the control circuit can't control it.

In both circuits its the same problem, with P-channel the op-amp cant drive the gate high enough to turn it off (as observed by one post) - it just passes the line voltage straight thru to the battery. In the N channel version the op-amp can't drive the gate low enough because its operating at a higher voltage than the -ve line in side.

Both circuits need a driving device operating at the full line in voltage, controlled by the op-amp

The corrected versions are shown below as per the above suggestion:

Using NPN BJT or N-channel mosfet:

zero drop solar charger circuit without microcontroller

In the above figure the NPN power transistor could be a TIP142, or a IRF540 mosfet .....and please Remove D1 as it's simply not required

Using PNP transistor or P-mosfet


In the above figure, the power transistor could be a TIP147 or a IRF9540 mosfet, the transistor associated with R1 could be a BC557 transistor......and please Remove D1 as it's simply not required.


How to Set up the zero drop solar charger circuit

It's very easy.

  1. Do not connect any supply at the mosfet side.

  2. Replace the battery with a variable power supply input and adjust it to the charging level of the battery which is supposed to be charged.

  3. Now carefully adjust the pin2 preset until the LED just shuts off....flick the preset to and fro and check the LED response it should also blink ON/OFF correspondingly, finally adjust the preset to a point where the LeD just shuts off completely....seal the preset.

  4. Your zero drop solar charger is ready, and set.

You can confirm the above by applying a much higher input voltage at the mosfet side, you'll find the battery side output producing the perfectly regulated voltage level that was previously set by you.

Need Help? Please send your queries through Comments for quick replies! And please Bookmark my site :)


Rashid Ansari said…
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.

i m tapas
where i will found solar plates...
Swagatam said…
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.
Swagatam said…
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.
Swagatam said…
you can use a BJT (transistor) in place of mosfet, relay will not work.
Swagatam said…
it's for enabling the mosfet to start conducting, without it the circuit will never initiate when switched ON.
Swagatam said…
It's mosfet gate drive resistor
Swagatam said…
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.
Swagatam said…
as expressed in the above comment, inclusion or elimination of resistor does not produce any affect in mosfet gate triggering.
Swagatam said…
Z1 can be a 4.7V zener, current limit can be easily included by adding a transistor stage, will try to update it soon.
Swagatam said…
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.
Swagatam said…
If its voltage and current ratings are as per your battery charging rate then it is OK.
Swagatam said…
yes you can use the above circuit for that purpose.
kassimdandago said…
Hi Swag,
pls i would want to use an nmos instead of pmos in the circuit . How could tha be done ?
Swagatam said…
Hi Kassim,

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

Swagatam said…
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
Vladimir Bebek said…
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.
Swagatam said…
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.

khang ly said…
hi Swag
pin 3(ic 741) calcular:Vbb=((R3+R4)*Vcc)/R3*R4 is valid over charger
is Z1 valid begin charger
Swagatam said…
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
khang ly said…
Hi Swag
sorry, formular wrong . but i think circuits not work because mosfet p channel work in negative 4( ic 741) connection 0V(mass) . mosfet cant's work . currents charger very low.I 'm check in actual
Swagatam said…
Hi khang, the 741 will produce negative voltage..... please go through the circuit explanation.
Khang Ly said…
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.
Swagatam said…
Hi khang,

here negative refers to zero volt.
khang ly said…
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
Swagatam said…
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.
Swagatam said…
for a 12V batery the output voltage from the circuit should be set at 14.4v
khang ly said…
Hi Swaga
How?formular calcula
Swagatam said…
it's a standard rule.
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....
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
Swagatam said…
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
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.....
Swagatam said…
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.
Swagatam said…
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.
khang ly said…
hi sir
dc input is mppt
use dc in trafo is ok?
kadimikumar said…
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%

Swagatam said…
The above circuit will work for both the inputs.
use an appropriate preset for R4 for getting the desired output voltage
vb dev said…
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.
Swagatam said…
hello vb,

no changes would be required, you can use the same circuit.
Johan Kotze said…
Can you please give me some alternatives for IC1 741?
Swagatam said…
you can try IC 301, 318, 709, CA3130, 3140, LF355/356/357, TL071/081 etc
PacMan said…
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) ?
Swagatam said…
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.

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.
Swagatam said…
..for the TIP122, you can use a 2N2222 or an 8050
PacMan said…
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").
Swagatam said…
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:-)
PacMan said…
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).
Swagatam said…
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
belekoy tikoy said…
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.
belekoy tikoy said…
sir, the output of this circuit is not regulating to , 14.4 volts, it goes up to 16.5volts.
belekoy tikoy said…
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.
Swagatam said…
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
could you please help to put some LEDs in this circuit to indicate this that battery is charging and one for indicating that it is full?
Swagatam said…
sorry, the above circuit is meant only for regulating the solar panel voltage to the required battery voltage without affecting the solar panel's not designed to cut off at the thresholds.
for N-ch version, what is Z2 voltage value?
Swagatam said…
it can be a 3V, 1/2 watt zener
jithin said…
Sir, How to find the value of Z2 in the modified diagram

Thanking you
Swagatam said…
Jithin, you can use a 3.3v zener diode, it's not critical...
Does current flows from drain to source (in nmos) when solar is off? If yes, Why?
Swagatam said…
That's unlikely and cannot happen in the circuits explained above, however a diode may be introduced in series with the battery (+) to avoid discharge through the circuit resistors....
Renel Allauigan said…
hi sir swagatam,
i have a li-ion battery 12v with 9.8 amp,
can you help me to find the missing value of resistor and z1?
thank you sir...
Swagatam said…
Hi Renel

you can use R2 = 10k

Z1 = 6V

R3/R4 calculation will require the input voltage spec, if you can specify the max input voltage I would calculate it for you.
Mark Ledford said…
awesome job Swagatam i was going to try a buck boost circuit but this is more of what i was looking for i might try one down the road, however
Dear Mr. Swagatam Manjumdar

Thank you very much, I learn lot of thing from your homemade circuit site. I had a wish to assemble a solar charger on my own. Your "Simple zero drop solar charger circuit" made me to assemble it. I did it successfully and made the set up done. The batter charge voltage is 14.5v.

When i connect the variable supply at the solar site for final checking, I shock to monitor the voltage was going more than the set voltage (14.5V) at battery side.

I assembled the IRF540 N channel circuit

1. The LED shut off at 14.5V
2. IRF540 base voltage is 0 or below 1 volt when Green LED shuts off
3. IRF 540 continuous to supply the input voltage to battery side
4. If i increase the solar side voltage above 14.5v I get the same input voltage at battery side ( if input voltage is 20 out put voltage also 20V - the it is not working as constant voltage out put circuit) I feel as a layman the IRF is not block the voltage at the set voltage point.

I did an addition to check the circuit but that also did not work - the addition is a 1k resistor between S and G of the IRF.

Please help me to complete the project successfully.
Thanks and regards,
Benjamin -

Swagatam said…
Thanks Mark, I might have just missed your comment, saw it just now, sorry for the late reply.
Swagatam said…
Dear Rickson, thanks for trying this circuit and discussing your problem here.

Could you please try the same using a BJT? I personally do not like mosfets just because of such unpredictable behavior from these devices.

Please try the same with a TIP122 transistor and let me know how it performs, I am sure it won't disappoint you.

If the issue still persists, I'll see if it can be rectified by adding another buffer transistor stage at the output.
Gadogbe Jerry said…
Thank GOD for your life and you have impacted knowledge into our lives and put food on our table. Now let me ask what is the difference between zero drop charg controller and mppt and their efficiency.
Swagatam said…
It's my pleasure!

a zero drop charger will not drop anything (V or I) between the solar panel and the load, but it's not capable of doing anything beyond this.

MPPT will not drop anything just like the zero drop charger but also make sure that if the load is incompatible with the panel, still it gets the optimal amount of power without loading or distorting the panel output
jrp4d said…
Hi - I've been messing about with Mosfets (voltage control circuits) and I don't think either circuit will work except where the line in voltage is only a few volts large than the target battery voltage. For anything where the line in is much more than the battery the mosfet will just conduct because the control circuit can't control it.

In both circuits its the same problem, with P-channel the op-amp cant drive the gate high enough to turn it off (as observed by one post) - it just passes the line voltage straight thru to the battery. In the N channel version the op-amp can't drive the gate low enough because its operating at a higher voltage than the -ve line in side.

Both circuits need a driving device operating at the full line in voltage, controlled by the op-amp
Swagatam said…
Hi, thanks for the observations and the suggestions.

I agree with you, I'll try to correct the designs soon....
Unknown said…
Hello Majumdar

Let me ask some questions:

In these Finalized circuits, I understand Z2 is a zener 3.3V 1/2 W. Correct?
And what is the value of R1 next to the zener?
Also in the p-mosfet version the value of the resistor at the collector of BC557 is 10K. Correct?
And no need for a resistor of 1K at the gate of IRF9540 as in the n-mosfet? Or is not crucial?

Thank you very much!
Swagatam said…
R1 could be a 10k resistor, for the p-channel version the gate resistor value should be 1k

that's correct no need of the 1K if a N-mosfet is used.
Swagatam said…
for N-mosfet the gate resistor will not be required but for the P-mosfet it will be required, otherwise the BC557 will get damaged...
Evan said…
OK, thank you, so let me summarize to avoid confusion

N-channel mosfet (1st circuit):
Gate resistor=1K needed to avoid damage to BC547
Z2=Zener 3.3v, 1/2 W
Z1 Zener connected to pin 2 of IC 741 (previously it was at pin 3)

P-channel mosfet (2nd circuit):
Gate resistor is NOT needed for BC557
Z2=Zener 3.3v, 1/2 W
Z1 Zener connected to pin 3 of IC 741 (previously it was at pin 2)
Collector Resistance of BC557 to ground = 10K

Please confirm, because I am a bit confused with the circuit names, after your reply....

Thank you
Swagatam said…
for N-channel:

Gate resistor=1K IS NOT NEEDED
Z2=Zener 3.3v, 1/2 W
Z1 Zener connected to pin 2 of IC 741 (previously it was at pin 3)

P-channel mosfet (2nd circuit):
Gate resistor IS NEEDED for safeguarding BC557
Z2=Zener 3.3v, 1/2 W
Z1 Zener connected to pin 3 of IC 741 (previously it was at pin 2)
Collector Resistance of BC557 to ground = 10K

Evan said…
OK thanks,
In this case, the gate resistor 1K needs to be moved to the second circuit (p-channel)
I will try to implement one of them and let you know.

Swagatam said…
In the second last circuit, the 1K from the base of the NPN power transistor can be removed...that's all, nothing needs to be changed beyond this in any of the last two circuits
Unknown said…
for 100W peak solar panel how to design zero drop solar charger and what is main difference MPPT charger & Zero drop solar charger
Chandra Sekhar said…
may i know difference of zero drop solar charger and MPPT
Swagatam said…
zero drop charger will only make sure that no voltage is dropped between the solar panel and the load....MPPT is far more advanced...I have already posted a few MPPT circuits in this blog, you can check them out

for 100 watt it will be the same as explained in the last two designs
Yasir Isnan said…
Hi Swag,
Could you please help me?
I have a problem to developed battery rectifier charger in my motorcylce.
The stator produce the voltage too high, 15v up to 100v by three wire. I'm not sure that it is 3 phase.
I had made the rectifier by 6x6A diode full wave bridge configuration and SCR to shunt the current & voltage.
The output voltage is ok is in 12.7vdc, but all parts become hot after 10 second and hotter as long as after.
Please do you have a good formula and circuit to be applied in my motorcycle?

Thank you verymuch, and it will be great if you cc to my email address at
Best Regards,
Yaosir isnan
Swagatam said…
Hi Yasir, In a shunt configuration the relevant parts can be expected to get severely hot, however these must be appropriately rated and suited for the application in terms of current and voltage in order to execute the function correctly.... an SCR may not be the right candidate, a power BJT looks to be a better choice.

the bridge is OK, however it too should be rated at 10 to 20 amp depending on the current for the alternator. For knowing the current you can connect an ammeter in series with the bridge output and check the max current and then dimension the diodes accordingly, and if possible mount them on heatsinks.

Alternatively you can try employing the following circuit and check the results:

Here T1 will need to be adequately cooled through a heatsink. The "heater" could be a tungsten coil retrieved from a heater coil, or an iron element.
Yasir Isnan said…
Thanks for your advise.
I will improve it..
Unknown said…
after testing the Z2 values I found it works with a 12v zener, I also removed D1 so there is zero voltage dropfrom the panel. Ive tested this configuration and works excelent
Swagatam said…
thank you for updating the info, much appreciated.
Ravipal Singh said…
hi sir,
can i use two or three irf 540 to charge higer voltage and current battries.such as 120 v and 40 amp charging current.thanks
Swagatam said…
Hi Ravipal, I don't think IRF540 is rated at may have to go for some other fet rated above this limit...
Dwines said…
Hi Swagatam, I want to know your opinion with regards to our solar system. Each panel rated 310W, total of 32 Solar Panels and divided into two groups (16 each) and connected to Growatt 4000. I was wondering, the Power output from the solar produces only around 2289W from the LCD Display. if we total all 32 panels with 310W rating that is around 10KW. How come it did not even reach a 3KW output from the growatt display panel? PV voltage output is 275Vdc (both PV1 & PV2)... Please advise...
Swagatam said…
Hi Dwines, It would be difficult for me to judge why the display is not showing the assumed wattage, however the best way to confirm this is by practically checking the voltage and current of each of the panels at a given instant and then comparing it with the display reading, if the display reading shows some other vague reading then it can be considered as incorrect and misleading.
or alternatively you can simply measure the V and I at the junction of the parallel connection and check the actual final wattage delivered at this combined junction for confirming the same...
. Arduino said…
1) Hi Sir may I use TIP31C transistor?
2) I follow (NPN BJT) construct the circuit only the voltage regulator work only I have no idea.
3) There are extra ground connect below BC547?
4)if the solar panel out greater than 14.4v it will turn off the transistor?
. Arduino said…
Hi Sir How do I prove there is not voltage drop ?
Swagatam said…
the max output voltage will show equal to the input voltage from the solar panel
. Arduino said…
why your circuit need to use op amp and zener diode? may I use 3v3 Zener diode?
Swagatam said…
for enabling a reference voltage for the opamp, the value is not critical
allan guillermo said…
hello sir,can i adapt your circuit sir for experimentation sir? thanks ...
allan guillermo said…
hello sir can i adapt your circuit for experimentation sir? i was amazed because it is more efficient as compared to other commercial designs, you're so great sir, instead of an op amp sir what other component can i replace to it?
Swagatam said…
Thank you Allan, surely you can use the design for your requirement, however can you please elaborate why you think it's more efficient, because you are yet to test it practically ?? :)

just a curiosity, that's all

sorry you cannot replace the opamp by anything else since it's the most efficient and straightforward device than anything other option
Mahesh lalya said…
Hi Sir, Mahesh Lalya here last four days back we talk to you regarding DC voltage control digram for wind wheel generator my generator generates 30 volt @ 4.5 amp normal speed and max may be 100 volt you send me circuit diagram using of solar-water-heater-reg circuit not able to read value of some resistors as flows r7/r6/r9/r10/r11 also can I use opamp as 741 with replacements of LM358 and can I use t1 as IRF9540, & T2 as tip147 and T3 as 840. & D1 as blocking diode,. Or email me on maheshlalya@gmail
Com Z's not able to find that link also because website had changed now. Pls replay soon
Swagatam said…
Hi Mahesh, yes the previous comments are lost due to a change in the site platform, I am sorry about that.

please click on the diagram to get an enlarged view of it and you will be able to see the parts clearly.

the IRF9540 is a P-channel mosfet and TIP147 is a PNP device and both of these will not work....because it needs to be N mosfet and NPN BJT as per the circuit's please change them to IRF540 and TIP142

2nos of IC 741 can be used instead of LM358
Mahesh lalya said…
Hi Sir, Thank-you so much for replying,
I made circuit but output 540 burn out after increasing input voltage. but there was wrong wiring connection.
I used Ic lm358 as it is, can I use irf p250n instead of irf 540? I have also connected Ic2 of pin no8 to supply line directly, is it OK? because when input voltage will increase to 100 volt so it may get damaged ics.
There is no voltage on second opamp pin number 7, after turning present of Ic2, and IC1on pin no 5 I am getting 3.5 to 4.5 voltage, currently using 12 and 24 volt DC supply to test circuit, please suggest me what to do?
Swagatam said…
Mahesh, I wil reply it here, but for further discussion please post under the same article which we are discussing:

do not bother about the right side opamp, first make sure the left side opamp operates correctly.

for this apply around 18V input from the solar panel side...then adjust RV1 such that the voltage at the cathode side of D1 becomes can connect an LED in series with the base of T1 to ensure that T1 is shunting the excess voltage to ground.

first do this and make sure no matter how much the input is increased , the cathode side of D1 stays at 14V fixed.

this might make T1 very hot...use a large heatsink while doing this.

I will talk about the other parameters once you finish this....
Andrea Poma said…
HiSwagatam, Cold I use P-channel mosfet to avoid reverse currant in small panels? I have a very simple circuit with 3v/3w solar panel, a 3.2v lifepo4 3A battery and a stepup 0.9v controller usb. But I'm unable after 7h of full sun to charge the battery more then 30%. Do you have any advice apart how stop reverse current? Thanks in advance for your help. Andrea
Swagatam said…
Hi Andrea, yes you can configure a P channel BJT or mosfet with the positive of the panel and prevent reverse discharging of the battery....

alternatively you can also try a schotky diode for the same
Rasanga said…
Hi Mr swargatman.,
I have 50watt solar pannel and 12v/18amp pb- planing to set up these in a place where sun is shining good 6hours.what changes shuold i do in your circuits.
Swagatam said…
Hi Rasanga, you can use any of the last two designs for your applications....make sure your panel produces over 15V at 2 amps rate
Hello Sir, I am thinking about harnessing the excess radioactive frequency in space to be converted into electrical energy but it is too difficult for me to think of a circuit to be used. Can you enlighten me, Sir, if it is possible? I know it is quite a difficult Sir but if it is possible Sir can you help me also Sir in making the circuit Sir THANK YOU SO MUCH...
Swag said…
Hello Allan, did you mean radio waves? I tried to search about radioactive wave but could not find any relevant information, however radio wave certainly is abundantly thrown into the space by the many stars and supernovas and may need a lot of research and investigation to learn about its effective harnessing procedures
Sorry Sir, yes sir its radio frequency, i mean those excess radio frequency signal from transmitting antennas sir, it possible to harness that sir? thank you sir, i appreciate your immediate response sir..
Swag said…
Allan, I don't think that's possible, because Rf from space could be too weak near the surface of the earth, and may be scattered over a wide area, therefore getting a concentrated amount of RF which could do some useful work looks remote to me.
thank you so much Sir, I also have a problem of my Motorcycle's CDI sir, can also ask your help Sir to come up with a circuit to test the condition of my motorcycles CDI Sir thanks...
Swag said…
Hi Allan, you can try the following concept
thank you so much sir..
Swag said…
you are welcome :)

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