Solar Charger Prototype

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Solar Charger Prototype

Function of Capacitors

100 uF capacitor – acts as a storage component. The instantaneous current is as high as 300mA. However, solar panel is only capable of delivering average current of 150mA. This capacitor stores the current and delivers the peak to the circuit, thereby remains the low impedance of the circuit.

10 uF capacitor - When current flows out from the feed back winding, it will flow to the end connected to the base of transistor as it will have to charge up the capacitor (time consumption) if the current flows out the other end. This will eventually ensure the cycle of the circuit to be well-operated.

3 capacitors (2200uF, 2200uF and 4700uF) - to smoothen the high spike voltage as it is  too extreme for a mobile phone battery. They smoothened the amplitude of the high voltage spike and also broaden the rise time of the high spike voltage waveform which absorbs the voltage spikes and make it compatible with charging mobile phone battery.

Extra features

1)      AC adapter – in case of low light condition, users can choose to charge their phones with electricity by switching the single pole double throw(SPDT) switch. However, more emphasis is on the solar charger itself.

2)      NMOS and low current LED – to indicate if users should switch to AC adapter. NMOS will only turn on when the input voltage exceeds the turn-on voltage of NMOS which is about 0.8V. If NMOS is turned on, charging current will pass through the NMOS to the battery and a small amount of current as little as 2mA will light up the LED. . A resistor of 10kΩ is used before the LED to restrict the amount of current going to the LED. This is crucial as the more current flowing to the LED, the less charging current flowing to the battery.

All the components for this circuit are simple and cheap. The battery can be charged either by solar circuit or by AC adapter.

Schematics of the Solar Charger

The uniqueness of this solar charger is that it uses low input voltage as low as 4v to generate high voltage spikes of up to 13.6v. This is due to the principle of electromagnetism and inductance.  Besides that, it has another alternative which is the AC adapter when there is too insufficient sunlight.

Input source	Specification	Values
Solar charger	Input  Voltage	4V(max)
	Input Current	1.6(max)
	Output Voltage	5V(max)
	Output Current	8.48mA(max)
AC adapter (Mobile Charger)	Input Voltage	100-240V
	Input Current	0.15A(max)
	Output Voltage	5V
	Output Current	350mA