Not very many items we I’m out on the trail take batteries but a few do. My headlamp, Spot, Cell Phone, and our MP3 players all are battery powered. The headlamps and Spot both take AAA batteries and the spot has to have Energizer Lithium batteries and only last about a week. Our plan is to have 3 new AAA batteries in each drop to swap out in the spot once they go dead. Our headlamps we are not too worried about as we wont be using them much and they will probably last 3-4 months on a set of batteries with the amount we will be using them. By the time we need to replace the batteries in our headlamps we will have some spare AAA from the drop boxes that we don’t need in the Spot. The big worry is our MP3 players! Both our MP3 players and the cell phone we will be caring charge off a computers USB port. The cell phone is nothing more then a prepaid Verizon phone.
From the research I have done its the best deal for the money as far as prepaid phones go and the LG Accolade charges from a USB cable. I specifically choose this phone for that reason. Our MP3 Players are the Sandisk Sansa Clip which are great as they are supper light, inexpensive, charge from a USB port, and have a memory card slot. Ours have 4GB of internal memory and we have 16GB cards for them. The nice thing about a smaller non color MP3 player is that they take less battery power which means the battery charges faster. The battery in the Sandisk Clip is only 3.7V 290mAh when you compare that to the 3.7V 2700mAh battery in an Iphone you can see how much faster it would charge from solar. I think that will be plenty of music for the trail.
Ok, to get to the point. Yes you can make a home made USB charger. A USB port is a standardized device among all computers and electronics. The USB standard is 5V and 100mA. The standard allows for a minimal voltage of 4.75V and a max of 5.25 V which means as long as you have a solar panel that puts out a voltage in this range and at least 100mA you can make a USB charger. Do keep in mind some devices do not follow the USB standard. I know that some Apple products such as the Iphone 3G charge at a higher rate then 100mA. this is possible as the port on a computer actually has 500mA of power available as the standard allows up to 5 devices plugged into a single port without additional power provided.
What I recommend its to purchase a solar cell that puts out 6V and at least 120-200mA. I recommend purchasing a 6V 200mA solar panel. The reason why I say to purchase a 6V A 6V 200mA solar cell which depending on the cell is only 109mm x 84mm in size.
Now to get started making your USB solar charger you will need the following items.
- a 5V solar cell (you can purchase these off Ebay from China for about $8, search Ebay for “6V solar cell”)
- Schottky Diode 5819 (you can find solar cells that will come with a Diode on Ebay or purchase from mouser.com part number 625-1N5819-E3 for $0.58)
- 5 Volt voltage regulator model 7805
- A USB cable. You can simply cut a car charger cable or a normal cable. One of our devices uses a mini USB and the other uses a micro USB so we choose to use a female USB plug so we can plug any USB cable in we want.
How to wire solar panels
Check out the images below to see how to combine multiple solar cells to achieve more voltage or more amperage.
So the main concept is to wire the solar panel to the 5V voltage regulator inline with the Diode to a USB port. This is a basic easy to make charger. I will go into more details in Part2 once I get my solar cells and make the charger.