Cellphone Charger Using Bike Battery

This is the simple and easy way to tap current from a Motor Bike battery to charge the Mobile Phone. Most of the Mobile Phone battery pack has three 1.2 volt cells making the voltage to 3.6 volts. For fast charging of the battery pack, each cell requires more than 1.2 volts and sufficient current. This circuit can deliver 5 volts at 300 mA to charge the battery quickly. The circuit is Voltage and Current regulated and with Polarity and Surge protection components.

Mobile Charger using Bike Battery Circuit Schematic

The circuit uses a Positive Voltage regulator IC 7805 to give 5 volt regulated output. The components around IC1 are meant for protecting the IC so as to give smooth output power. Zener diode ZD act as the Input Surge protecting diode. It provides 7.2 volts to the input of the regulator IC from the 12 volt bike battery. Diode D1 is the Output Surge and Input Short protecting diode.

When a surge voltage exceeding maximum voltage rating of the regulator is applied to the input or when a voltage in excess of the input voltage is applied to the output, the regulator will be destroyed. If the input terminal shorts with the ground, the output voltage increases above the input voltage(ground potential)and the charge in the capacitor connected to the output flows into the input side which is also fatal to the regulator. Both these situations can be avoided by using the Zener at the input and the diode D1 across the regulator. Capacitor C1 and C2 provide stability to the regulator and these should be soldered close to the legs of the regulator. Capacitor C3 act as a buffer to give constant voltage in the output.
7805 Datasheet

7805 IC can tolerate maximum 35 volts and its current rating is 1 Amps maximum. Resistor R1 restricts the charging current to around 330 mA as per the Ohms law. Even if the current is low, charging process will not be affected. Slow charging with 80 to 100 mA current is generally advised. But in case of an emergency, quick charging can be done with high current

Assemble the circuit on a Perfboard and enclose in a small case that can be fitted near the Bike battery. Use suitable pins to connect with the Mobile phone. Charging current can be tapped from the battery using Alligator Clips. Before using the circuit, double check the connections especially the polarity of connectors and measure output voltage and current using a Digital Multi Meter. The same circuit can be used for charging Mobile battery from 12 volt Car battery or from a 12 volt Solar panel.

IC 7805 Pin connection and Alligator Clips


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  • rahul

    dear sir i had tried with your given circuit and i am getting 5 volt o/p also. but still my 2600mah battery is not charging,it show charger is connected but instead of charging it start discharging the battery.pls help to rectify the problem.


    Ic heating so.what is solution

  • shekar

    I want all electronic components where I get? any online in AP

  • ananth

    When I connect ic 7805 in my bike while connect my mobile phone the ic gets heat the charge connect&disconnect continuously comes pls give me any idea

  • I need help


    I need to know that is that any way i can get a output of around 5v and 1~2A from a 12vDc 0.5A battery?

    If yes then some idea how it can be done?

    Thanks in àdvance.

  • neel

    I want to use another signal to reclose the circuit.
    In a simple manner the circuit will be operate remotely in which it can be open or close by two different signals.
    If it is possible then plz give your mail id or another contact details.

  • C.Mitra

    There is no such single component which can behave in the manner that you want. It seems what you need is a relay which is normally closed, but on applying a voltage to the associated circuit, it opens. But you want it to remain open even after the signal is removed. But then how do you want it to close again? Does it need to be closed under certain conditions? Please clarify.

  • C.Mitra

    Hi Neel
    I don’t know what you mean by ” i want to make a circuit which can open circuit”. A circuit which can open a circuit? What circuit do you want to open? Please write your requirements in clear understandable English.

    • neel

      Plz suggest any component which can use as a switching device.
      Basic requirement is the component can work as closed switch in normal conditions, and it can be open by a single electric signal and will remain open even after signal is disconnected.

  • neel

    Sir i want to make a circuit which can open circuit by a single external signal. And will remains open even after when external signal is disconnected. Please give me suggestions which dc component can work as that.
    Circuit should remains close in normal conditions.

  • neel

    Dear sir,
    Yes it gets hot while connected but not so much hot.

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