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HOME MOBILE Technical Tips


The circuit is a high efficiency charger, it is useful for charging 6 to 12V batteries using small number of solar cells. The solar cells can be connected in series or parallel to generate 1 to 12V , cells voltage has to be lower than battery voltage. When the mosfet is on it charges the coil with energy from the solar cells, and when the mosfet is off that energy is discharged into the battery.

Circuit Description
See also Technical Tips

The 6 inverters CMOS are used as a free running oscillator. The MOSFET charges the coil when it's on, and when it's off the coil dumps its charge via the diode into the battery.

BS170 can be replaced by equivalent MOSFET.

The MOSFET and the diode are capable of charge currents up to 50mA, for higher currents they can be replaced by higher current components.


Comments and questions

Copy the number from the picture It stops net-robots from adding comments.

21.11.2017 - 12:59
Name: Suresh
Comment: I need some details about 30 watt solar panel and which type of batteries can choose for solar panel. My mail id is gopavarapuvenkatasuresh@gmail.com

17.02.2016 - 11:25
Name: Moty
Comment: Hi Seed. There are many discussions on this subject in this forum, you'll be able to get help there. http://www.edaboard.com/forum.php

16.02.2016 - 16:12
Name: seed
Comment: I need soalr 12V 5W to 220V

20.11.2015 - 22:17
Name: David
Comment: interesting projects I love electronics

05.07.2015 - 23:25
Comment: GOOD

31.12.2012 - 19:54
Name: Moty
Comment: Hi Helal, For 12V battery charged at 20 mA you can use the circuit in the project with no changes.

31.12.2012 - 12:41
Name: helal
Comment: ineed 20 am 12v SOLAR BATTERY CHARGER

Name: Nick Mercury
Comment: What efficiency would you expect from this circuit? I need a 3.3 to 3.6V battery voltage (which chemical type battery would work best). I've sourced some cheap 3.6V 0.2W cells from ebay. I want to run a trial for a few months to see how it goes. Thanks Nick

Name: Moty
Comment: Hi Nick The efficiency of the charger is about 90% when the charge current is 50mA. You can use either NiCad or NiMH cells. You will find that solar cells give the full output on a bright sunny day and on cloudy day the output drops to about 5%. The efficiency of converting sun energy to electrical energy by solar cells is about 0.1%. The cmos 4049B will work at supply voltage of 3.3v but you will need to replace the mosfet with one that has a lower threshold gate voltage, i.e. RFD14N05 Hope you get the results you want.

Name: Santhosh
Comment: Hi I have a 2V 80mA solar cell and I need to charge a 7.2V 1200mAH Ni-Mh battery pack.Do I need to make any changes to this circuit.

Name: Moty
Comment: Hi Santhosh, You don't need to make any changes to this circuit for your application. When the cells source 80mA the charge current will be about 20mA.

Comment: Can I use 220uH inductor instead of 100uH

Comment: Can I use 220uH inductor instead of 100uH

Comment: Can I use 220uH inductor instead of 100uH

Name: Moty
Comment: Hi Santosh, You can either put 2 coils of 220 in parallel to get 110uH, or change the 100K resistor to 220K to adopt the frequency to the coil.