Home-made solar charger for cell phones with MPPT

electronic projects

At first - two reasons for building special solar charger controller with function "maximum power point tracker" for work with solar panel.

People, who use mobile phone and other devices in outdoor conditions, without power nets (tourists, camping, etc.),often take with problem for charge batteries of this devices. Very popular solution is using solar panels as power source. In summer time this is good solution, but for fully using potential of this panels you need for controller, what can matched load of output solar panel with input of your device. When solar panel work with maximum power point tracker, you can have 25-40% added energy. It's because solar panel have current source output behavioral. For example: solar panel has 6.5v output voltage and 0.15A output current (1W output power). In case direct connection to mobile charge input: as usual battery of phone have 3.6v voltage and this voltage will be on output of solar panel, therefore we will take 3.6Vx0.15A=0.54W from panel. In case of use maximum power point tracker (MPPT), we will have 1W*0.8=0.8W, where 0.8 is efficiency of circuit. In this case we will have 1.5 shorter time of charge (usually cell phones have 800-950 mAh accumulator, because it can be 4 hours instead 6 hours in outdoor conditions, 220mA charger current instead 150mA) or 1.5 smaller solar panel (you can choose for yourself). You must be borne in mind this example is demonstration only, because low level of charge current for start charge phone is 270-300mA (for Nokia), charge controller of phone check it before starting charge. Possibility have bigger current then in direct connection solar panel for start charge process is auxiliary reason too.
Second reason is that fact that sun shines not always. In this situation is good if you have full charged accumulator. And very good situation when you can charge this accumulator by same solar panel. Of course, you need in control of charge of this battery. When I live in camp I use 6V 4Ah SLA accumulator (It's enough for 3-4 times full charge phone). It weight near 0.8-1 kg, because in hiking use this accumulator isn't clever, it's for camp only. Of course, you can use lighter Lithium battery, after change program of controller.
My solution of this problem is using of solar panel with controller, that to be able take maximal power from solar panel, control process of charge of accumulator 6V or 12V (built detection function) and have source current 350mA, max 5.6V for charge of mobile devices.

There is circuit and board design of portable solar charger:

solar charger circuit.pdf
solar charger board.pdf
solar charger parts TOP.pdf
solar charger parts BOTTOM.pdf

Foto board

program code for charger controller
theory explanation

Design description:

Design have 2 independent bloks:
1. Controller solar panel and charger sla-accumulator (ATmega8).
2. Current source 350mA with limited output voltage 5.6V (MC34063).

Controller include simple buck converter circuit (Q1B, D24,L1), 2 voltage feedback and feedback of peak of current.
Voltage feedback: difference voltage between voltage measure channels (inputs ADC1 and ADC2 of mega8 controller) give information about voltage level of accumulator. Under this info we can make solution about type of accumulator (6/12V) or work without accumulator and level of accumulator charge .
Feedback of peak of current: input ADC0, peak detector D15,R4,C10, current shunt R2. Info about peak of current is needed for maximum power point tracker work. When we have so width of pulse of PWM chopper that we have stay in maximum peak of current position it means that we take maximum power from solar panel. Attention - I tell about max peak of current during PWM period, not for average level of current. Average level of current can be easy filtered from voltage signal of current shunt over simple RC chain, but this isn't useable info for MMPT work.
Current source is almost recommended design from datasheet of MC34063. Only small change in part of connecting output transistor, in this variant will be more efficiency of conversion, because will be drop down voltage on collector-emitter 0.2-0.3V instead 1.3-1.5V in datasheet design.
Solar panel: 18V, 0.11A, 1.9W for normal exposition (1000W/m2), dimension 20x30 cm. I constructed panel from 24 photovoltaic cells of YH40*40-4A/B40-M_1203. There are 3 parallel threads, every 8 series pieces. Thread connected over Schottky diodes 1n5819. Every element have 1n4148 diode in counter-parallel connection. With this feature give better work in condition of partly shadowed (tree branches, grass). I glue these elements to bit of textile, because I can transport this panel coiled in small roll.
Be careful, for 3 season use of the cells have strong degradation. These cells are defective. I will not use this photovoltaic cells in new panels.


Attention! Wrong work device can damage connected mobile phone, because you must carefully check charger before use it. You must know that you make this device for your own risk only. I give you recommendations for check charger device, but I can't give you any warranty. If you don't have enough skills and experience better if you will not make this work.

adjustment tips

few tips for using

In case you have question about this device you can ask it here:


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