Hacked Gadgets Forum

April 15, 2015

Make a Emergency Phone Charger from a Pencil

at 9:16 pm. Filed under Cool Gadgets, Electronic Hacks


Language Warning on this video by AvE. If some swear words turn you off this video isn’t for you. This is the type of project that could come in handy when you find yourself stuck in the bush with no stores in site. We are shown how to use the resistive properties of the pencil lead to act as a voltage divider and drop the voltage to a save level for phone charging. It would be better to connect it to a 5 volt USB charge cable if one was handy since this will most likely have some voltage protection circuitry built into it, the cable could be cut and stripped with the knife in your back pocket.  That way if you are connected into the USB side of things you could slowly increase the voltage till the phone turns on and starts charging. The only thing to look out for would be the thing you are using as your voltage divider, if it has low resistance it might heat up and burn you. 


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4 Responses to “Make a Emergency Phone Charger from a Pencil”

  1. Mikheil Says:

    This way you should be charging batteries in emergency situation because you are damaging the battery forever especially Li-ion.(source https://youtu.be/A6mKd5_-abk)

    I am not sure about Li-ion batteries but when you are charging regular 1.5V rechargeable batteries with 1.7 Volt the battery Voltage will be 1.7V. So him charging that 3.7v smartphone’s battery with 4.3V will put extra strain not only on battery but on the device also.

    Am I not right?

    Also Why he connected both sides of pencil With positive?

  2. Alan Parekh Says:

    You are correct, many batteries have very special charging characteristics that require complex circuitry to do correctly. He is just showing an example of how to get some lower voltages from a common car battery so you could do something like make an emergency phone call from a dead cell phone. Looks like he is using red wires for lots of stuff but in his overview the right side of the pencil is negative (of the car and cell phone battery).

  3. Ty Tower Says:

    My experience with batteries leads me to conclude that if you connect 4.3V the battery draws it down to its level initially and then creeps up as the battery voltage comes up. Monitoring the battery so its charge does not go above the recommended with LiPo’s seems to be essential.

  4. Ty Tower Says:

    The other consideration is the amount of current flowing into the battery . A high current would damage it irreparable so the resistance of the pencil lead used would be important and how long it flows too. looking at a HB pencil I picked up its total resistance was 100 ohms approx . so say 40% would be 40 ohms . at 12 Volts the current flowing through 40 % of the pencil say 40 ohms would be 300 milliamps which is 10 times more than you should give it on charge

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