Design a circuit to charge mobile phone batteries from solar panel directly during power shortage due to natural catastrophe like flood, cyclone, etc.

Problem Statement:
Design a circuit to charge mobile phone batteries from the solar panels directly during power shortage due to natural catastrophes like floods, cyclones, etc. with some security considerations.

Introduction to the problem.

Power cuts are usually long (typically >48hrs) during natural catastrophes. In such scenarios, the backup power from alternative sources like roof-top solar panels comes into the picture. The power is generated during the daytime to charge the battery to power emergency lighting systems at night. A portion of the power during the daytime can be used for other daily purposes like mobile phone charging. There is no issue with the energy generation and use when it has to power a house of a family. It is easier to keep a check on the family members to make sure that power usage doesn’t exceed the power generation minus main battery charging power. But in a scenario like a hostel, or a high rise-tower residence, where the solar panel energy from a common roof is shared between multiple residents, it is almost impossible to keep a check on individuals to make sure that the power is used judiciously (else the central storage batteries won’t charge up and the power won’t be enough to light the emergency lighting system at night). So, to tackle this problem, the emergency power supply network and main power supply network are often separated making it impossible to misuse the energy meant for charging the emergency battery. But the downside of this is that people can’t even charge their mobile phone and as a result, they are cut off from the outside world once the phone battery is dead. Moreover, the normal chargers can’t be used directly with the solar panels.

So the solution to this problem, I propose is to put an additional chip which could be used to charge the Li-ion battery using solar panel depending upon the level of charge of the main emergency battery. This way, the energy will be used only for charging the mobile phone battery and the emergency power storage system, and not for other heavy load purposes (like running a washing machine).

Design.

  • Designed uses ADP5360CB Evaluation board for demonstration and testing purposes.
  • The Li-ion charging battery is connected between ISOB and GND when then the battery has to be charged separately (Eg. Battery for a flashlight or local intercom battery).
  • The mobile phone charging cable is connected to J7 jack and GND. It utilizes the built-in buck-boost converter to supply a constant voltage to the charger.
  • The buck converter is used to get a reference voltage for comparing the level of charge of the emergency battery. If the level of charge exceeds a set threshold, then the ENCHG pin is set high thus enabling the charging of other external devices.

    Consequently, the Li-ion batteries of mobile phones or other devices are charged only when the main battery meant to power emergency lighting at night is charged to a level beyond the threshold. This way, the excess power generated by the panels- which would have been wasted otherwise because of a separate power network- can be used by the residents for small device charging purposes without worrying the emergency power shortage at night time.
    The chip ADP5360 is especially useful as it draws little quiescent current when not enabled thus helpful during power crisis.
    The circuit diagram of the circuit is shown below.

Circuit Diagram.
AAC_CKT.png



Key Points:

  1. The buck-boost output voltage is set to 5V by adjusting the register values at this address: VOUT_BUCKBST[5:0]
  2. The buck converter output voltage can be adjusted based on the battery and resistive divider output voltage
  3. The other ENABLE pins to power up buck converters are set high.
Conclusion.
This circuit can be programmed using the I2C cable -along with the above-mentioned considerations- and then be deployed for use.

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akshaysethia36
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