Cell Phone Charger


Who We Are:
On the farthest left, we have Erika, a third year Physics major from Elk Grove, CA.
In the middle is Jojo, a third year General Engineering major from Anchorage, AK.
To the right we have Kaitlyn, a fourth year Anthropology and Geography major concentrating in International Development from Oakland, CA.

Mission Statement: We want to create a Cell Phone Charger operated by diodes that will be getting energy from the Solar Cook Pot project. We are investigating how to make this affordable and effective.

Currently, we are working on researching diodes, solar panels, and how other solar powered batteries work so that we can figure out how to design ours.

Who We Are Working With: Kuyere
From Kuyere: “Kuyere! (Kuyere.com) is a social enterprise dedicated to the development of a solar system production and distribution network in Africa that can accelerate rural African poverty reduction. The enterprise began work in Malawi in early 2015, when it conducted a pilot project of a preliminary system design for over 100 households in Sept/Oct of that year.”

Who We Are Working For: Families like the Solijala family, in Malawi.


Chapasuka and Fenita Solijala live in in the village of Lilongwe, in rural Malawi. They live with their six children and four grandchildren in a 1 bedroom house. Chapasuka is a farmer and Fenita sells agricultural produce.

Our family’s stove.
A family’s stove in Malawi depends on income and access to clean fuels. The poorest, who are often in rural areas, use open charcoal or animal dung fires to heat a traditional or side-feed stove. Those with higher incomes use clean burning fuels like gas or electricity. The richest homes have integrated stoves and ovens that are safe, fan powered and have ready access to fuel.

At night, the poorest homes have no light or any reliable light source, restricting how productive the family can be. Low to middle income homes use bare light bulbs to illuminate the home.


Most families in the World are connected by mobile phones, but phone functions vary according to income group. For the poorest families, mobile phones are usually for sending SMS messages. Middle income families sometimes have touch screen smartphones for sending images, videos and can be connected to internet services like online banking.

GapMinder Graphs

Decision Matrix

Whats Going on in Shop

Taking Apart a iPhone charger:
The first task that we did was taking a part an iPhone charger to see the different types of wires that are inside. We discovered the positive and negative end of the wire. In between those two wires was a wire that transfers information between the iPhone and a computer (so transferring photos, etc). We disconnected the signal wire to just get the positive and negative end of the wires.

Taking Apart a Solar Panel Phone Charger:
We ordered a solar panel phone charge to get an idea of what is going on in the circuit. In the end we just took the solar panel to create our own phone charger.

Solar Panel
We took the solar panel and measured the voltage that comes out of it when it is in the sun. The voltage varies depending on the angle and the amount of sunlight there is. From there measured the voltage of the solar panel to be 6.12 Volts. This voltage is a little too high for us. The voltage needed to charge a phone is 5 Volts–anything higher could destroy the phone. So in order to decrease this voltage we implemented a string of diodes.

Didoes are useful to reducing the solar panel voltage because it creates a voltage drop of about 0.6 Volts per diode. We started out with a string of 10 diodes and connected to the solar panel to reduce the voltage. We noticed that that with 10 diodes the voltage was still a little too high. We eventually kept taking off more and more diodes until there 6 diodes and we had a voltage around 4.6. (see chart below)

Number of Diodes Voltage (V)
10 6.1
9 5.9
8 5.8
7 5.4
6 4.6

What we are currently working on:
So far we are working with a solar panel that was soldered together with 6 diodes, connected to the ends of an iPhone charging port. We decided to choose 6 diodes with a voltage of 4.6 to be on the safe side. Unfortunately this was not enough to charge our phone.

solar panel phone charger

What We are Doing (5/13/18):
In hopes of getting our solar panel phone charger to actually work, we are going to add another diode to it, to make it a total of 7 diodes. This will get us to around 5.4 V, which is a little over the 5 volts needed to charge the phone.

We are also looking into changing from a smart phone charging system to an older phone charging system. It has also been noticed that the people in Malawi use older cell phones, so now we just need to get one to experiement with and try charging!

The end goal is to eventually add this charging system to the cooking pot group. We would use the diodes that they are using to heat their cooking pot, to connect to a phone charger.

Kaitlyn, waiting for the solder gun to heat up to solder diodes together

sppc me

Erika, holding a string of diodes that were soldered together.

Final Update:
We connected USB ports to the solar panel and tried to charge an iPhone and an Adroid, but it wasn’t working. Then we discovered that the outer positive negative wires weren’t the only ones trasmitting charge and the inner two signal wires that tranmit data also were transmitting a charge. We created a voltage divider by putting two 100k ohm resistors in series and incorporated the signal wires of the USB. Once we did this, we were able to charge an iPhone or an Android.
IMG_5988 (1).jpeg
Here is a picture of USB port with two 100k ohm resistors in series soldered onto it.

IMG_5989 (2).jpeg
Here we have an android that is charging from a voltage source! However, we gave it 6 volts, which we discovered was too high when there was a pop sound and then the android would not charge.

Here is our final result! The iPhone is charging from the solar panel using the USB port with two 100k ohm resistors in series! It only charges the iPhone at a certain voltage, which is tricky when using diodes and the variance of light on the solar panel. At open circuit, the solar panel was 5.93 volts when it was in full sunlight. We had to partially cover the solar panel in order to get our desired voltage, which was at 3.9 volts.